Infectious diseases of animals in sub-Saharan Africa: The wildlife/livestock interface

R G BENGIS, R A KOCK, G R THOMSON AND R D BIGALKE

Introduction

The critical need for rural development to support the rapidly growing human population in sub-Saharan Africa is increasing the pressure on wildlife in the region. Poverty and lack of food security are root causes of the massive destruction of habitats and animal populations.^{25, 58, 59, 96} Wilderness areas are being encroached upon and are often perceived by rural communities as legitimate sources of natural resources from which they are unreasonably precluded access for livestock grazing, collection of firewood, thatching grass and other products, and subsistence hunting. On the other hand, the potential of the rich wildlife heritage of the region for sustainable exploitation and therefore economic development is obvious. It is also important for sub-Saharan Africa to preserve the diversity of its fauna and flora, because nowhere else on Earth is there a comparable resource. It is difficult to reconcile these essentially conflicting imperatives.

The growth in the livestock population of Africa is no longer keeping pace with human population increase, and livestock productivity is not improving in most regions to compensate for the increasing needs.⁹⁶ There are a number of reasons for this static livestock economy, the most important being land degradation,¹⁰³ declining livestock production and faltering disease control services.⁹⁶ There is also a decline in wildlife populations, even within many protected areas, with over 60 per cent of all such areas now being relatively depleted of antelopeandlarge bovids.⁴⁸ This resource willnolonger provide the supplementary (and free) food enjoyed by past generations. The concomitant increasing need for landontheonehand,and greater awareness of the intrinsic and economic value of wildlife resources and savannah biodiversity on the other, result in the issues at the interface between livestock and wildlife becoming increasingly acute and politicized.

The presence of diseases that occur in both domestic and wild animals and which may be transmitted from one to the other constitutes one of the constraints on land-use options in sub-Saharan Africa. Although the interface results in some disease transmission and economic loss, it should be appreciated that with the massive decline in available habitats for wild herbivores in most regions of Africa, the extent of this interface is actually shrinking on the macro-scale, yet intensifying in other regions. In addition, amongst the wide variety of wild artiodactylids in Africa, only a few species are epidemiologically important with regards to serious economic livestock diseases. These are African buffalo (Syncerus caffer), warthog (Phacochoerus africanus), bushpig (Potamochoerus, sp.) greater kudu (Tragelaphus strepsiceros), bushbuck (Tragelaphus scriptus), and wildebeest (Connochaetes spp.), which have all been linked to one or more of the following important diseases: rinderpest (RP), foot-and-mouth disease (FMD), African swine fever (ASF), malignant catarrhal fever (MCF), East Coast fever (ECF), bovine petechial fever, and trypanosomosis. These major infectious diseases of livestock and wildlife are comprehensively presented elsewhere in this book.

With this background, the objective of this chapter is to discuss the key wildlife-related issues that impact on disease persistence and control. These include free-ranging wildlife as disease reservoirs, alien diseases introduced with domestic animals, pastoralism and transhumance, the use of fencing, and compliance with animal health requirements, which are necessary to gain access to international markets and trade. In addition, certain current trends in wildlife management, such as the development of game conservancies and transfrontier parks, and the increasingly popular introduction and relocation of wildlife to privately owned game reserves, which may expand or intensify the interface, are also of concern and are discussed.

Historical perspective

Sub-Saharan Africa has a larger number and diversity of indigenous free-ranging wild mammals than any other comparable land mass. This is especially true for ruminants. As a possible consequence, an equally impressive array of pathogenic micro-organisms and macro-parasites, as well as arthropod vectors of certain micro-organisms, have coevolved with their hosts for millennia, which has culminated in evolutionary adaptation and tolerance between host and pathogen or parasite, and the development of endemic stability. Infection is usually ‘silent’ in the definitive wildlife hosts, which serve as reservoirs of specific pathogens. Infection of wildlife species other than the definitive hosts may result in disease, which is generally mild. Infection rates may be high, but clinical expression of disease is generally cryptic in these ‘incidental hosts’.

The evolution of the wildlife/livestock interface in sub-Saharan Africa is inseparably linked with the more recent history of Homo sapiens on this continent. The best examples of the recent history of human migration and interaction with livestock are those which took place in southern Africa; some of these are used here to illustrate certain major factors that have played or continue to play a role at this interface.

The San (Bushmen) were the first modern humans to occupy southern Africa. They were hunter-gatherers,^{19, 97} who left us ample evidence of the distribution and diversity of the resident and migratory wildlife in their numerous rock paintings and engravings. These relatively nomadic and sparsely distributed inhabitants of the sub-continent cultivated no crops and possessed no livestock,⁵⁷ and were therefore unaffected by the animal disease agents that were cycling in the wildlife environment.

The next incursion of humans into the sub-continent were the Khoikhoi (Hottentots), who are now regarded as being closely related to the San.^{19, 57} They migrated from the central interior of Africa to the grazing lands of the coastal regions of the Western and Eastern Cape provinces of South Africa, in particular. They were pastoralists, herding fattailed sheep, cattle and possibly also goats, and were probably the first people to bring livestock into southern Africa.⁴⁵ It is possible that their migratory route, which was mainly south-westerly, was influenced by ‘belts’ of tsetse flies and hence trypanosomosis,⁹⁷ and they must have experienced the presence of other serious livestock diseases, such as theileriosis and heartwater, which were prevalent in the east of the sub-continent. This was later followed by southward migrations of different ethnic, but primarily Bantu, groups and evidence of their presence in southern Africa goes back some 2 000 years.^{45, 66} They had cattle of the Sanga (Nguni) type as well as sheep and goats. There is, however, evidence of a degree of resistance to certain endemic diseases and parasites in cattle, sheep, goats and dogs that have an historic association with Africa, resulting from their exposure to wildlife and their endemic diseases and parasites, over many centuries.^{17, 49, 61} Tick resistance, local trypanotolerance and partial adaptation to certain viral, rickettsial and protozoal diseases were probably the result of natural selection pressures on the livestock of these early migrants.

It was during the colonization of Africa by European nations during the past three-and-a-half centuries that the introduction of imported livestock breeds^{17, 104, 105} unmasked the presence of many African endemic diseases that were silently cycling in the free-ranging wildlife. These diseases caused significant morbidity and mortality in the poorly adapted, immunologically naive European breeds, and had a significant influence on the day-to-day lives and activities of the settlers, due to their deleterious effects on draught, transport and production animals. Furthermore, efforts to ‘upgrade’ the indigenous tribal cattle by cross breeding also probably had negative effects on their disease resistance.

Since the emergence of embryonic government veterinary services in Africa, some ten decades ago, epidemic diseases have received the most attention, and were the most feared because of their devastating effects.

Disease control emphasis was accorded to domestic livestock, which were so important for transport, production and trade in the developing colonies. One factor, which has contributed significantly to the persistence of infectious diseases, is the continued dependence on pastoralism as a livelihood for large numbers of the African peoples. For example, over 50 per cent of the Somali community are involved in, or rely on, pastoral cattle and small stock for their livelihood.^{58, 59} The large-scale movement of animal populations across borders in some regions, in search of pasture⁶⁴ and associated trade, has been the single most important factor in the spread of epidemics such as RP, peste des petits ruminants (PPR), contagious bovine pleuropneumonia (CBPP), and FMD.

The importance of international trade on livestock economics and the impact of disease on this trade must be mentioned. The more developed nations, where much of the trade is centred and a high commercial value for livestock exists, are primarily concerned with food safety and hygiene, whereas food security is the major interest of developing nations.³² This difference has resulted in a greater emphasis being placed on disease eradication and control in some regions, and international regulations and requirements to support these aims have been implemented. As a consequence the developing countries are frequently severely penalized in economic terms through their inability to trade in these more lucrative markets.⁹⁶ In essence, although these poorer nations are highly dependent on livestock for human survival, their livestock is not providing a means of escaping from the poverty trap. This issue has become more prominent with the recent experiences in developed countries of the effects of epidemics of foreign animal diseases such as FMD and ASF on their livestock industries. Recent developments, however, including some associated with the wildlife/livestock interface in Europe and North America, may result in more flexibility in international trade rules.⁵ For example, with regards to bovine tuberculosis, transmissible spongiform encephalopathies,^{65, 76} FMD, and classical swine fever, the current control policies are being hotly debated.

The wildlife/livestock disease interface

Many disease-causing agents that cross-infect wildlife and livestock have been identified on most continents.¹⁴ Some of the more important of these in sub-Saharan Africa, where range and habitats are shared or where close contact is possible, are listed in Table 10.1. This interface may be linear, as along a dividing fence-line; patchy, reflecting habitat preference of a disease host or vector; or diffuse where range and resources are shared. The sympatric sharing of range with wildlife is typified by the pastoral societies in certain African savannah ecosystems.

Disease, livestock, wildlife and rural subsistence Wildlife-maintained diseases that infect livestock

From an international trade point of view, FMD and ASF are probably the most important wildlife-maintained diseases, and present the greatest constraint to rural agricultural development in sub-Saharan Africa.

In the case of FMD, the pivotal role played by the African buffalo as a sylvatic maintenance host was identified in the late 1960s^39–41 and possible maintenance mechanisms of infection have been discussed.^{41, 94, 101} Strict management of the disease around national parks is necessary in some countries, a good example of which is the Kruger National Park in South Africa. This Park is fenced and buffer zones have been created along its South African borders; these.together with vaccination of cattle and regular FMD surveillance and testing of animals in the buffer zones have been relatively effective in containing the disease in the only endemically infected area in that country.

Table 10.1 Diseases of importance at the wildlife/livestock interface

DISEASE AND CAUSATIVE AGENT	TRADITIONAL OR ENDEMIC HOST(S)	MAIN EPIDEMIC HOST(S)
Foot-and-mouth disease Apthovirus	Cattle and African buffalo	Most cloven-hoofed livestock and wildlife
Rinderpest Morbillivirus	Cattle, wild ruminants?	Cattle and most wild African ruminants and suids
African swine fever Asfivirus	Tampans (Ornithodoros) Wild African suids	Domestic pigs
Canine distemper Morbillivirus	Domestic dogs	Domestic dogs and certain wild carnivores
African horse sickness Orbivirus	Zebras and donkeys?	Horses, mules and donkeys
Bluetongue Orbivirus	Certain wild ruminants and cattle?	Cattle, sheep and goats
Rift Valley fever Phlebovirus	Aedine mosquitoes	Sheep, goats, cattle and certain wild ruminants
Malignant catarrhal fever Alcelaphine herpesvirus 1 Ovine herpesvirus 2	Blue and black wildebeest, sheep	Cattle, cervids and certain captive wild bovids
Rabies Lyssa virus 1	Numerous wild canid, felid and viverrid species, domestic dogs	Multiple
Heartwater Ehrlichia (Cowdria) ruminantium	Certain wild ruminants, chelonians and gallinaceous birds	Cattle, sheep, goats and some wild ruminants
Bovine petechial fever Cytoecetes ondiri	Bushbuck	Cattle
Trypanosomosis Various Trypanosoma spp.	Wild bovids, suids, elephant and black rhinoceros	Cattle, horses, pigs, sheep, goats and dogs
Corridor disease African buffalo-derived Theileria parva	African buffalo	Cattle
Anthrax Bacillus anthracis	Soil	Multiple
Bovine tuberculosis Mycobacterium bovis	Cattle	Many wild ruminants, suids, felids and primates
Brucellosis Various species and biotypes of Brucella spp.	Cattle, sheep, goats, pigs and marine mammals	African buffalo, eland and waterbuck

With regards to ASF, the elegant studies by Plowright and co-workers ^82–85 elucidated the maintenance host and virus amplification role of argasid ticks (Ornithodoros spp.) in East Africa. The role played by wild suids in this regard in both East and southern Africa have also been described. ^{83, 99} The situation in West and Central Africa is, however, different as there is no evidence of a wildlife reservoir. The increasing use of virtually free-ranging pigs in subsistence agriculture in the coastal regions of West Africa and recent outbreaks of ASF experienced there have brought this issue once more to the fore.

However, at the rural, extensive, communal farming level in sub-Saharan Africa, it is most frequently the vectorborne diseases, such as trypanosomosis, heartwater and theileriosis, that are the greatest disease obstacles to local livestock-based agricultural development and prosperity, although certain viral diseases such as ASF, MCF and FMD also play a role in this respect. It is in this area that conflicts between livestock-dependent communities and wildlife most often arise, as the owners of livestock frequently understand the role that wildlife play in the maintenance of these diseases. An example of this is the role of wildlife in the maintenance of tsetse flies (Glossina spp.) and trypanosomosis, the resultant restricted access of livestock to infected areas being a major constraint on agricultural development. ⁷⁰ Conversely, from a conservation point of view, trypanosomosis is held to be a major factor favouring the survival of many of the remaining wildlife populations and their refuges in Africa.

The important role played by wildebeest (Connochaetes spp.) in the maintenance and seasonal shedding of alcelaphine herpesvirus 1, a cause of MCF in cattle, has been elucidated.^{71, 80, 81} In eastern Africa transmission is most frequent during the wildebeest calving period when pastoral cattle, grazing on shared grassland, come into contact with wildebeest foetal membranes or young calves.⁸⁸ The economic impact of this disease on communities is not well defined but is probably limited given the pastoralists’ knowledge of this disease. As a preventive measure, livestock are kept off pasture shared with calving wildebeest in Maasailand in eastern Africa until late morning by which time the sun (and time) has rendered infected placentas safe. In southern Africa the increase in wildebeest populations associated with game ranching activities has seen a resurgence of MCF and this is not always associated with direct contact with placentas or young wildebeest calves. The actual mechanism of transmission of infection in this latter situation has not yet been determined.⁶

With regards to certain African infectious tick-borne diseases, wildlife may fill the role of tick amplifiers or carriers of the causative agents. African buffalo, eland (Taurotragus oryx), sable antelope (Hippotragus niger)and impala (Aepyceros melampus) are, for example, the preferred hosts for all three stages in the life cycle of brown ear ticks (Rhipicephalus appendiculatus and R. zambeziensis).⁷⁴

Buffalo, eland and sable antelope have also been shown to be long-term carriers of several Theileria spp. parasites, some of which can cause disease in livestock or in certain wildlife hosts. The biology and epidemiology of Corridor disease caused by buffalo-adapted Theileria parva in cattle has been well studied. Infection with this organism, which is ‘silent’ in buffalo, causes high mortality in cattle, making farming of cattle in the presence of infected buffalo and a suitable vector a hazardous undertaking.⁷² Cattle are generally ‘dead-end’ hosts, being unable to infect the tick vectors.

As a further example, giraffe (Giraffa camelopardalis) and black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros, African buffalo and warthog are preferred hosts for adult ticks of the genus Amblyomma, whereas the nymphs and larvae feed on a variety of large and smallmammals, birds and even reptiles.⁷⁹ Several of these hosts, including buffalo, gallinaceous birds and tortoises have been shown to be potential carriers of Ehrlichia (Cowdria) ruminantium, the cause of heartwater in domestic ruminants.⁷⁵

Diseases that may impact on wildlife

It is appropriate that those diseases be considered which may seriously affect wildlife populations directly, or may undermine wildlife management efforts, and ultimately determine the rate of development of the wildlife industry and conservation initiatives in Africa. Diseases that constitute a livestock threat, such as FMD, ASF and theileriosis, are generally managed by the imposition of severe restrictions on wildlife use, translocations and certain management activities.

Foot-and-mouth disease containment measures in several African countries restrict the translocation of wild cloven-hoofed ungulates out of endemically infected areas, thus effectively isolating such populations into ‘conservation islands’. South Africa also relies on delineated ASF and Corridor disease control areas to contain their spread, and legislation is in place, which limits the translocation of their natural wildlife hosts out of these areas.

On the other hand, there are certain diseases, such as RP, anthrax, rabies, bovine tuberculosis and canine distemper, which may have significant direct impacts on the population dynamics of certain wildlife species, on various spatial and temporal scales. Some of the agents causing such diseases appear to be historically alien to sub-Saharan Africa, and were probably introduced onto the African continent with the importation of domesticated animal species. Indigenous African free-ranging mammals (within similar taxonomic groupings to the traditional domesticated maintenance host) have little inherent genetic resistance to these foreign agents. Significant morbidity and mortality may therefore be encountered in wildlife where contact with infected domestic animals occurs.

A striking example of a disease with a devastating impact on populations of wildlife is RP, currently still present in Africa in southern Somalia and southern Sudan. The virus is reputed to have been introduced into Eritrea from India by the Italian army in 1887/88, or by a German military expedition that brought infected cattle from Aden and Bombay to the East African coast.^{42, 44} Much has been written⁶³ on the grave social, political and economic repercussions of the massive cattle mortalities caused by this disease as it spread progressively westwards and southwards. Countless wild artiodactylids also perished, with buffalo, tragelaphids (spiral-horned antelope), wild suids and wildebeest being most severely affected, with only relic populations surviving in some areas.⁹³ The decimation of both cattle and wildlife apparently led to the disappearance of tsetse flies (Glossina spp.) from certain areas, and may have contributed to wildlife distribution anomalies, such as the formation of isolated meta-populations of species such as sable antelope and greater kudu.⁸⁹

An interesting progression with regards to RP in wildlife during the twentieth century has been the recognition of various strains with apparent differing pathogenicity and host preferences. The strains that were most commonly associated with high mortality in cattle have been relatively easy to eradicate, but the apparently milder strains for cattle have persisted. Although mild in cattle, the strain currently circulating in East Africa, characterized as part of the lineage 2 group,⁸ can be highly pathogenic in African buffalo, lesser kudu (Tragelaphus imberbis) and eland, but apparently mild in some other species such as wildebeest and warthog. However, host susceptibility appears not to be consistent, nor in fact is pathogenicity constant with any one strain, species or population of animals, with both temporal and spatial variation occurring. Erratic and low rates of virus shedding occur in cattle. Another complicating factor is the ‘atypical’ virology of some strains with antigenic epitopes poorly detected by standard test systems, which reduces the sensitivity of surveillance protocols.

The role of wildlife in the persistence of RP has become of interest in the last decade during the final phases of eradication of the virus, with the identification of strains that appear to spread efficiently even in partially immune populations. This may be the key reason for the persistence of the strain in East Africa despite massive vaccination campaigns on the continent between 1960 and 2000. Free-ranging wildlife and pastoral livestock cattle especially in times of drought, may be a key epidemiological factor. Most evidence, however, is that the wildlife is only acting as an indicator and vector of this disease, which is in fact maintained in cattle populations.

Bovine tuberculosis caused by Mycobacterium bovis is another foreign animal disease that was most probably introduced into Africa with imported dairy and Bos taurus type beef cattle during the colonial era. This disease has now spread to, and become endemic in, several African buffalo populations in South Africa^{10, 15, 28} and Uganda,^{38, 107, 108} aswell as in a Kafue lechwe (Kobus leche kafuensis) population in Zambia.³⁴

It has also been diagnosed in buffalo and wildebeest in the Serengeti National Park ecosystem in Tanzania. ⁶⁹ Buffalo and lechwe have become true maintenance hosts of this disease, and sporadic ‘spill-over’ of infection has been documented in greater kudu,^{13, 51, 102} chacma baboon (Papio ursinus),⁵³ lion (Panthera leo) and cheetah (Acinonyx jubatus),⁵⁶ warthog,^{107, 108} eland, topi (Damaliscus lunatus), giraffe,⁶⁹ leopard (Panthera pardus), common genet (Genetta genetta), spotted hyaena (Crocuta crocuta), bushpig (Potamochoerus larvatus), and honey badger (Mellivora capensis).⁵² The long-term effects of this chronic progressive disease on wildlife host populations at sustained high prevalence rates is unknown, but early indications are that it may negatively affect population structure and dynamics in buffalo⁸⁶ and lion. Bovine tuberculosis is probably one of the most serious wildlife health issues currently confronting conservationists and veterinary regulatory officials in South Africa, Zambia and Uganda, and possibly some other sub-Saharan countries.

Canine distemper is thought to be another foreign animal disease which entered Africa in the post-colonial era and has demonstrated the potential to impact severely on certain wild carnivore populations. Less robust populations of social carnivores, such as wild dog (Lycaon pictus) and Ethiopian wolves (Canis simensis) are especially vulnerable. This disease and rabies are considered to be partially responsible for the demise of the wild dog in the Serengeti ecosystem in Tanzania over the past decade.² Canine distemper has also demonstrated an ability to cross the ‘species barrier’ as severe outbreaks with mortality have been reported in Serengeti lions.⁸⁷

Certain endemic multi-species diseases that occur on most continents may also have severe effects on wildlife in the sub-Saharan region.

Anthrax outbreaks have been documented in wildlife populations with no livestock link in the Etosha National Park in Namibia⁶² and Kruger National Park in South Africa. ^{11, 27, 29, 30} Large-scale outbreaks may cross the interface especially where domesticated and non-domesticated species share range and resources, as has occurred in the Luangwa Valley National Park in Zambia,²⁶ and Serengeti National Park,⁶⁸ and more recently in Mago National Park in Ethiopia, where a die-off of many cattle and more than 1 500 lesser kudu was documented.^{37, 92}

Rabies is another multi-species disease that is endemic in many areas of sub-Saharan Africa, with sporadic epidemic cycles. It has been diagnosed in 33 carnivorous species and 23 herbivorous species, with a regional variation of dominant epidemiological role-players.⁹⁵ In spite of this, by far the largest number of rabies cases reported in the developing world occur in domestic dogs, with ‘spill-over’ into other domestic livestock, humans and wildlife. Rabies and canine distemper are thought to be partially responsible for the demise of the wild dog population in the Serengeti ecosystem³⁵ and is considered a major disease threat to the highly endangered Ethiopian wolf.

In Africa, endemic rabies (caused by both viverrid and canid biotypes) is often associated with certain communal burrow-dwelling species, such as the yellow mongoose (Cynictus penicillata) and the bat-eared fox (Otocyon megalotis), as well as jackals (Canis spp.). Rabies outbreaks in certain host species frequently appear to be density dependent. In a unique documented outbreak of rabies in kudu, where non-bite transmission probably occurred as a result of salivary contamination of browse, more than 10 000 kudu died over a four-year period in Namibia.⁷ Abnormally high population densities of kudu were cited as being a major contributing factor.

Fencing and wildlife 

Several of the diseases associated with wildlife that have major epidemic potential and therefore affect international trade in livestock and their products, are highly contagious viral infections. These diseases may have severe adverse effects on livestock-based export economies. It is particularly in this context that the wildlife/ livestock interaction is critical. The most significant of these diseases are FMD, RP and ASF for which fencing has been a major tool for control by restriction of animal movement. If wildlife carriers or vectors of these diseases are allowed to range freely in contact with livestock, creating a diffuse interface, then there is little possibility that exporters will be able to develop trade in live animals or animal products beyond their immediate region.

In certain countries in southern Africa, where there is a well-developed livestock production industry, the means of preventing the maintenance and spread of these diseases in livestock has been based on the separation of wildlife and livestock by strict land use policies and fencing at the interface. Botswana, for example, has a lucrative trade with Europe based on an early and clear understanding of the epidemiology and control measures necessary for containment of FMD.³¹ As the economics of wildlife enterprises have proved to be more competitive in marginal, often semi-arid areas, than cattle ranching, there has been a transition of land use from livestock to multi-species or exclusive game management systems.²⁴ The fencing was already in place in many of these areas, and only game-proofing upgrades were necessary. Game fences are also popular with commercial wildlife ranchers due to the value of individual wild animals and their need to retain them on their properties. The fencing debate has become more contentious as the ecological impact of fencing has become better appreciated. Fences are frequently criticized because wildlife are precluded from following historically important migration routes, which are necessary for survival in ecologically marginal areas where surface water is scarce and grazing availability is seasonal. Detailed studies of this real or perceived problem are scarce and reports that exist on the environmental effects of fencing in Africa^{78, 91} show that generalizations are unhelpful In the Botswana study some fences were successful in the control of diseases such as FMD and CBPP, and were effective in reducing animal movement. The impact of these fences on wildlife was based on population trends, which did not show a consistent picture across all species, the implication being that some species benefit and others do not.

In the end the environmental, social and financial costs of some fences may outweigh their benefits but the decision on this will depend on complex analyses, including environmental impact assessments.The recommendations of a study by Scott Wilson in Ngamiland, Botswana,⁹¹ included the removal or realignment of some fences and the endorsement of others as effective and necessary.

There is also the realization amongst ecologists that island communities of wildlife are unlikely to survive intact in the long term.⁷³ In recent years, this has driven some conservationists to think in the direction of complex conservation systems, including transfrontier areas involving communal, private and public lands with corridors along which wildlife can move, and different land uses without necessarily excluding human activities.⁹ This approach is intellectually appealing but highly theoretical, and does not take into account basic humanocentric social and economic realities, and it certainly has no consideration of diseasecontrol implications. Nevertheless, the impact of fencing on migratory populations, such as wildebeest in southern Africa, has provided stark evidence of the deleterious effects certain policies can have on populations.^{58, 59} The debate on appropriate conservation policies in Africa will go on and it is definitely not the intention here to criticize or promote any particular approach, but only to highlight animal disease aspects that need to be considered, whilst assessing risks and impact of policy change.

Decisions made by governments pertaining to livestock health are affected by the present global restrictions on trade as set out in the recommendations of the International Animal Health Code of the Office International des Epizooties (OIE). For certain diseases, this Code does support the concept of zonation of infected and non-infected areas, where appropriate control measures are in place at the interface. Thus, without a fencing policy, commercial livestock industries in unrestricted wildlife areas cannot develop in the conventional sense.

The concept of species compartmentalization is also currently being discussed at the OIE. This concept accepts that if an outbreak of a listed disease (all of the OIE list A, and some list B diseases) occurs in a free-ranging wildlife population, but does not involve domestic livestock, then the reporting country should not necessarily be penalized by agricultural trade restrictions. Some southern African countries have taken a vigorous approach to disease control and viable livestock industries have developed.

In eastern Africa the more laissez-faire attitude remains a constraint to commercial livestock development, and governments are under increasing pressure to seek economic solutions to the increasing poverty.

The issues of land use, disease control and fencing have not been resolved due to conflicting economic interests involving the expanding and lucrative tourism industry. Ecotourism, based on game viewing of free-ranging wildlife and environmental appreciation, certainly provides significant economic benefits to a region, but frequently, only to a small proportion of the community.⁷⁷ Profitable ecotourism and well-marketed environmental appreciation have also made a major contribution to the maintenance of the world heritage of animal life, and indigenous biodiversity. As a result there has been reluctance by governments to tackle the livestock problems, which they believe would impact on the wildlife estate, e.g. through fencing. Ironically it is the very desire to keep the systems open that results in the easy access by livestock to the grazing resources in protected areas, leading not only to intensification of the interface between livestock and wildlife, but also to conflicts between humans and animals, including predation and disease impacts. In practice, with rapidly growing human populations, fencing of wildlife-protected areas is inevitable and beneficial in many aspects. Fences also effectively reduce predation and depredation on livestock and crops of adjoining communities, which are often of a subsistence nature. Some negative ecological effects of fences may have to be accepted in order to maintain viable populations of key African wildlife species.

Transhumance, pastoralism and wildlife

The key constraint to achieving an improved animal health status in much of Africa that would be acceptable to the majority of livestock trading nations, is the current unrestricted trans-boundary movement of people, livestock and wildlife.⁶⁴

The animal health code developed by the OIE,⁷⁶ designed to reduce disease risk and facilitate international trade in livestock and livestock products, has become complex and requires a high level of management and investment in veterinary services. Although this code has greatly enhanced the economic potential of the livestock industry, it has also set recommendations and standards with which many African countries cannot comply. Without the benefits of international trade, the value of the livestock sector to these national economies has not improved and this has deterred the governments concerned from maintaining investment in the industry.⁹⁶ In addition, as pastoralists are often politically marginalized,⁹⁰ there has been little incentive to shift resources in their direction.

In reviewing the wildlife disease impact it is important not to over-emphasize the role of non-domestic artiodactyls because, in pastoral systems, there are frequently adequate populations of free-ranging livestock to enable the maintenance of these infections in the absence of wildlife. Thus, wildlife populations are not always a critical factor, except where they are the only definitive maintenance host for a specific disease. The role of wildlife as reservoirs or vectors of disease are sometimes misunderstood and may be overstated, even among veterinarians.

Many pastoral communities are poorly supported by veterinary services, if at all, so control through vaccination of domestic animals is rarely possible. The issue is whether these free-ranging livestock and wildlife populations can be isolated from commercial ranching to enable a sub-sector of the livestock industry to function and trade. In eastern Africa, for example, without effective movement control, there is little likelihood of FMD ever being controlled (irrespective of wildlife). Nevertheless, wildlife does present a further complicating factor because, even if improved veterinary control such as vaccination were initiated in pastoral livestock, wildlife could still harbour pathogens and so maintain a reservoir of infection.

Pastoralists frequently have extensive ethno-botanical and ethno-veterinary knowledge. They understand many infectious disease processes and often treat animals successfully without sophisticated medicines.^{21, 22, 106} Often simply by the ability to move stock rapidly over long distances, they avoid contact with diseased animals at appropriate times, but this can equally assist in spreading infection. This knowledge-base also exists at the wildlife/ livestock interface, amply demonstrated in the case of MCF⁸⁸ by the response of livestock keepers in avoiding cattle contact with wildebeest particularly during the calving season.

Attempts to improve the delivery of veterinary services to pastoralists will continue in many countries, and a spin-off may be reduced disease challenge to wildlife. This challenge will, however, remain inherently difficult as delivery of expertise and veterinary vaccines and medicines is logistically problematic and economically non-sustainable unless livestock values and markets improve. Therefore, diseases such as FMD, ASF, and CBPP are likely to persist for the foreseeable future. It is only after zonation of land as practised in southern Africa, which identifies problem populations and regions, and the designation of these as disease control areas, that the resultant strict movement control and reduced contact between wildlife and livestock will improve the situation. It is historically interesting that modern human society has seen the decline of the hunter-gatherer communities and most probably will see the next transition, which will be the disappearance of true pastoralism.^{58, 59}

Wildlife industry and conservation areas

The three categories of land use involving wildlife are essentially:

• national land set aside for conservation of wildlife, habitats and ecosystem processes;
• private land on which a variety of wildlife-based activities are conducted; and
• communal land with a wildlife-use element

Formal nature conservation in Africa is only slightly more than 100 years old. The early conservation initiatives were within national programmes, with land set aside exclusively for nature conservation. In broad perspective, the first 50-odd years was a period of consolidation, during which recreational tourism was only a small consideration and a limited income earner. The second half of the twentieth century saw a rapid growth in the tourism industry in formal conservation areas, which coincided with the development of the first private lodges and private nature reserves. Much of this growth was based on foreign visitors and facilitated by improved travelling opportunities, and in both formal and private sectors, facilities and opportunities for tourists increased sharply towards the close of the century. National and international demands for wildlife conservation still continue but as human population growth continues, with increasing hunger for land, conflict arises. As a result there has been a recent trend towards community-based conservation initiatives.^{9, 43} Biodiversity conservation with the preservation of local livelihoods1 is an example of some of the recent thinking. This thinking has evolved as academics believe that previous attempts at conservation through national parks and protected areas have been ecologically inadequate or unable to contribute significantly to human development needs.

In the private sector, differences in land tenure policies between countries in sub-Saharan Africa and the right of private individuals to own land and wildlife has fundamentally affected the way in which wildlife is valued. In some southern African countries where private ownership of land and wildlife is enabled by the country’s constitution, exploitation of wildlife resources is gaining momentum and becoming a major economic activity. As a result, borders between enterprises involved in ecotourism and farmland, as well as publicly owned wildlife areas and traditional communal areas, are becoming increasingly sharply demarcated.

East Africa is quite different because the land use system is much less developed, there are fewer fences and considerable mixing of people, livestock and wildlife. The main wildlife use is ecotourism, which is based on a complex of public and private conservation areas, as well as subsistence and some commercial hunting.

In West and Central Africa the situation is more complex with, on paper at least, a multitude of parks as well as hunting reserves. However, non-sustainable exploitation has resulted in a massive decline in numbers of wildlife in these conservation areas. The result is that, unless this trend can be reversed in these regions of Africa, the remaining wildlife will be isolated in small meta-populations sequestered in reserves.

The disease problems associated with the varying approaches to wildlife land use are also different. In the more intensively managed systems, e.g. game farms where animals are in pens or small camps, and are fed artificially throughout the year, the production-related diseases, such as foot rot, verminoses, coccidiosis, and nutrition-related problems, are more prevalent. On small game ranches, where ‘free-range’ wildlife are often fed supplementary hay in the dry season and during droughts, a common problem that is encountered is relative overstocking, which results in the so-called sick habitat syndrome.

This is a multifactorial syndrome related to progressive depletion of palatable grasses and browse, bush encroachment, soil erosion, a progressive build-up of ecto- and endoparasites, and stress and tick toxicosis-related immuno-suppression. The net result is a loss of body condition, anaemia, tick-bite abscesses and mortalities that may be associated with normally benign agents. The relative overstocking due to the inability of the game to move out of the area, also favours the spread of density- dependent infectious diseases.

More extensive systems, such as national parks, game reserves and game conservancies, may vary in size and may be fenced or open. The more natural the ecological system, the less likely that a single disease entity will be problematic, since the relationships between hosts and indigenous parasites should be relatively balanced.³³ In these systems it is predominantly cyclical climatic factors and related animal population densities which lead to expression of disease, for example duringandafter severe droughts.Underthese circumstances, with the clumping of large concentrations of herbivores around dwindling resources, and concomitant nutritional and social stress and immuno-suppression, parasite burdens may increase to pathological levels. Viral and bacterial diseases are also frequently associated with these environmental stress factors, e.g. anthrax, epidemic FMD and possibly RP.^{16, 27} However, truly natural ecosystems (defined as having minimal human interference) are now rare, and a natural state in respect of disease ecology is probably the exception.²³

Looking to the future, disease problems at the wildlife/livestock interface are likely to increase and possibly intensify in some regions of sub-Saharan Africa, as many are related to more recent conservation developments, such as the new community-based wildlife initiatives, large-scale translocation of key wildlife species, enlarging conservancies and transfrontier parks.³⁶ With regards to transfrontier conservation areas (TFCAs), it is not the intention here to portray these initiatives in a negative light. From an environmental conservation, biodiversity, heterogeneity and ecotourism point of view, the integration of land across international borders as well as the consolidation of state and privately owned land in joint ventures is justifiable,andmayhave major economic benefits.The message that needs to be conveyed, however, is that all involved parties and role players must approach these initiatives fully aware and forewarned of the potential animal health implications and challenges that may be expected when increasing the geographic range of various pathogens. The possible implications for animal disease control are profound and the potential impact on the economies of the region through loss of life-sustaining livestock and/or trade should be calculated. It is totally predictable that without international boundary barrier fences and with a ‘biological bridge’ formed by contiguous wildlife populations, any infectious disease present in any one of the participating countries or areas will eventually spread throughout the entire conservation area unless containment or control measures are established.

For example, in the recently created Great Limpopo Transfrontier Park, which incorporates conservation areas in Mozambique (Gaza National Park), South Africa (Kruger National Park) and Zimbabwe (Gonarezhou National Park), and which will eventually constitute one of the largest conservation areas in the world, there are animal disease risks to all three regional participants. Once international barriers have been removed and contiguous wildlife populations have become established, bovine tuberculosis may spread northwards and eastwards from the infected Kruger National Park component, tsetse flies (Glossina morsitans) may recolonize the Kruger Park from the north, rabies may enter this park from the north and north-east, new topotypes of FMD virus from Gonarezhou National Park may enter the other two parks, and cattle-adapted Theileria parva may move southwards and westwards. With this scenario, proactive disease management strategies need to be discussed at high level by participating countries and agencies.

There is also a trend to create larger ecologically sustainable conservation areas (conservancies) by the private sector. In marginal cattle farming areas, well-managed ecotourism based on wildlife is potentially more profitable than livestock farming. Farmers in these areas are increasingly abandoning traditional cattle ranching for commercial wildlife-based activities, pooling their resources by creating jointly owned reserves enclosed by substantial perimeter fences and with internal fences removed.⁴ These conservancies may be very large, and several in South Africa and Zimbabwe exceed 100 000 hectares.⁹⁴ This does not, however, preclude the keeping of wildlife and livestock together, which is often done, but currently accepted ‘wisdom’ has it that productive livestock farming and ecotourism centred on wildlife are incompatible on the same land area as a result of the higher risks of disease and for aesthetic reasons.^{50, 77}

This sentiment is probably true for much of East, Central and West Africa, as well as parts of the eastern lowlands of southern Africa where many of the wildlife-associated livestock diseases are endemic. The development of these large conservancies sometimes conflicts with the policies of developing countries, which place a premium on agricultural and industrial development, and has led to the criticism that wildlife is held in higher regard than people.⁹⁸

These ecotourism-based enterprises generally require a wide diversity of game species and adequate populations of them for easy visitor viewing and frequently necessitate large-scale translocation of wildlife, which in itself may have inherent disease risks. Translocation of any animal is, in fact, the translocation of a ‘biological package’ consisting of the host together with its attendant macro- and micro-parasites. Furthermore, it is important to realize that once released into a free-ranging system, such animals and their attendant parasites are difficult if not impossible to retrieve. Thus strict quarantine, disease-screening, and ecto- and endoparasite control are essential requirements for the responsible translocation of wildlife.¹⁰⁹ Disease hazard identification in founder populations, followed by risk assessment and risk management strategies, form the backbone of regulatory disease control for wildlife translocations on a national and international level. Endemic diseases and parasites in the ecosystem at the destination of translocated animals may also influence the success of these exercises, and should be taken into consideration.

A current major issue is how to enable increasing commercial exploitation of wildlife resources while at the same time ensuring that the local communities do not become dispossessed. It is a difficult balancing act that is being tilted by Africa’s rapidly growing human populations. The Camp Fire Programme in Zimbabwe⁶⁷ and related community based conservation initiatives elsewhere have achieved some limited success in enabling local communities to participate and share in the benefits of ecotourism and commercial hunting. Nevertheless, there is no doubt that more progress on this front needs to be made if the conflicting demands of wildlife conservation, commercial agriculture and deprived rural communities are to be reconciled.⁴⁶

Disease surveillance and control at the interface

The responsibility for disease surveillance generally rests with the veterinary regulatory authorities of a given country, and the surveillance techniques used include passive reporting, farm inspections, problem investigations, abattoir surveys, serological surveys, and dedicated testing for specific disease eradication schemes. Unfortunately, legal frameworks and responsibilities (including financial responsibilities) for wildlife disease surveillance, investigation and reporting are not clearly defined in many African countries and free-ranging pastoral cattle and wildlife do not easily lend themselves to monitoring.

Given the depressed state of veterinary services in many countries in Africa, it is difficult to envisage any systematic collection of surveillance data from livestock in remote areas. The best hope for these areas is community-based approaches to monitoring animal health.⁴⁷ On the wildlife side, a growing interest by wildlife managers in wildlife diseases and their potential impact, is improving information flow and should be integrated into conventional epidemiological reporting systems.

The need to improve the control of animal diseases at the interface is a complex evolving issue. Control strategies will increasingly have to accommodate the conflicting requirements of a variety of land users and interest groups, and adaptive policies coupled to pro-active thinking and appropriate planning are necessary to pre-empt the development of serious animal disease events.¹⁰⁰ Innovative possibilities should be examined. For instance, following the repeated failures to develop an effective ASF vaccine, would it not be more advantageous and appropriate for developing countries that do not export pork to embark on a programme of selection and breeding of pigs that are genetically resistant to ASF in order to address this disease problem in subsistence rural communities? Another innovative strategy is to select or breed wildlife that are free of certain diseases, and to use them for stocking or translocation exercises. The breeding of African buffalo free of FMD, theileriosis, bovine tuberculosis and brucellosis, for example, is becoming an ecological success and a profitable enterprise in southern Africa.¹²

That serious disease events are still occurring is amply demonstrated by the current problems associated with FMD, MCF and bovine tuberculosis control in southern Africa,^{3, 28} and the issues of RP (see above), PPR and ASF in eastern and Central Africa.⁶⁰

When dealing with the threat of certain endemic African diseases, such as FMD, ASF and buffalo-derived theileriosis, the containment option has given best results to date. This is usually effected by means of control zones/areas, gameproof fences, physical barriers, cordons and movement controls which effectively separate the wildlife from domestic livestock, thus preventing contact at the interface, and is characteristic of countries with an advanced land-use policy. It is not an option in regions where pastoralism with free-ranging livestock and subsistence agriculture are the norm.

When dealing with endemic arthropod-borne infections, such as trypanosomosis, African horse sickness (AHS), RVF and bluetongue, containment is less likely to succeed, and vaccination and vector control, where possible, may be included to reduce infection and/or transmission.

With regards to alien/exotic diseases that threaten freeranging wildlife populations, such as RP, canine distemper and bovine tuberculosis, containment and control can best be effected by addressing the disease in the domestic host by mass vaccination and/or test and slaughter respectively. In addition, prevention of contact between infected domestic animals and wildlife is desirable, but unfortunately not always feasible in many countries in sub-Saharan Africa. In these situations, improving the delivery of animal health services (e.g. through vaccination) to domestic livestock sharing ranges with wildlife and/or adjacent to conservation areas would probably be most beneficial if a suitable vaccine is available. Rinderpest control has been based on vaccination and the benefits of eradication are economically significant even without calculating the benefits to wildlife populations. There is the added benefit that resident wild animals may also act as sentinels, providing spatial and temporal (based on age stratification) data to facilitate disease surveillance and identify existing and new foci of infection. Where an alien disease has become established in a conservation area, the situation is serious and control options are limited, and frequently contentious or unpopular.¹⁰ The bovine tuberculosis situation in buffalo in South Africa and Uganda, and lechwe in Zambia are examples.

In general, control of diseases of limited epidemic potential is best addressed at the local level, with the assistance of veterinarians and wildlife experts with detailed knowledge of epidemiological and ecological determinants. For infections capable of causing trans-boundary epidemics, control needs to be co-ordinated at both national and international levels.

While short- and medium-term disease control and longterm eradication goals can be, and have been, attained in domestic livestock using judicious vaccination programmes, vector control and test-and-slaughter policies, these options and techniques are frequently impractical, difficult to execute, and may be culturally or morally unacceptable in free-ranging pastoral livestock and indigenous wildlife populations.

With regard to the multi-species diseases, such as anthrax and rabies, many ecologists will argue that these diseases are also endemic and part of the greater ecosystem, and because they function as natural population regulators, they should not be controlled. However, both these diseases also affect domestic animals, and have significant zoonotic potential. There are now few if any ecosystems that are isolated from humans and domestic animals, and modern societies will no longer accept the impact of disease as natural. This renders the laissez-faire argument redundant. For these reasons, control of anthrax outbreaks in wildlife have been attempted, using various techniques including burning/ burying of carcasses, strategic veld burning, waterhole disinfection and remote vaccination by means of disposable darts or bio-bullets. These attempts have met with varying success. On the other hand, mass vaccination of foxes against rabies in Europe, using oral bait techniques, has been highly effective and successful.²⁰ Central to the reduction of livestock losses and human exposures during anthrax or rabies outbreaks in wildlife, are large-scale public awareness campaigns and mass vaccination of livestock.

In the case of multi-species production systems, where livestock and wildlife are farmed together, certain precautionary measures may reduce the possibility of significant disease events occurring; these include:

• avoiding introduction of certain key wildlife species, which are maintenance hosts or ‘carriers’ of certain indigenous diseases, e.g. FMD, theileriosis, MCF, AHS and ASF; and
• screening all cattle for bovine tuberculosis and brucellosis prior to introduction onto a ranch.

Some positive aspects of such a mixed farming enterprise should also be highlighted; these include:

• the ‘vacuum cleaner’ effect created by the regular dipping of the cattle component in order to reduce environmental tick burdens;
• the reduction of parasitic ova and larvae when ingested by non-patent species; and
• an appropriate combination of cattle and wild ungulatesfor a particular veld-type will ensure that a wider diversity of natural plant species will be consumed, which will optimize the utilization of different strata of thevegetation from ground level to the canopy. This may effectively increase productivity for the ranch.

Conclusion

The long-running conflict between livestock owners and animal health authorities, on one hand, and wildlife conservationists on the other, is largely based on differing attitudes to controlling diseases of livestock associated with wildlife. An attempt is made in this chapter to highlight the key disease issues and to emphasize that these disease problems are frequently bi-directional at the interface. A new dimension currently faced by veterinary regulatory authorities is the spectre of new sylvatic foci of diseases, such as bovine tuberculosis, brucellosis and possibly RP, that threaten to derail national and international eradication schemes which have been implemented and executed with significant success and at great cost.

Conversely, wildlife-based ecotourism in Africa has expanded rapidly over the past few decades, and is the source of much-needed foreign revenue for many African countries. Traditional subsistence farming is still the largest source of dietary sustenance on the continent, and this together with the growth and hunger of historically disadvantaged communities for land, is forcing enterprises and communities with markedly different objectives and land use practices and priorities to operate effectively in close proximity. In sub-Saharan Africa the interface between wildlife and livestock is declining overall as a result of progressive decimation of wild animal populations. Nevertheless, in certain areas there is an intensification of the interface, as shared resources become scarce, and the development of wildlife and livestock enterprises increase the shared use of land. In southern Africa, over recent years, the trend has been contrary to the rest of Africa, with an increase in use of land for wildlife or mixed enterprises.The creation of large wildlife land-holdings (e.g. transfrontier parks and conservancies) accompanied by the introduction of species such as African buffalo, wild suids and wildebeest into certain areas, may have a negative impact on the regional livestock trade as a result of disease risk factors.

With the diversion of finance from natural and animal resource sectors to human welfare, health and education (a trend in Africa over recent decades), the risk of losing control of animal diseases is increasing, and this may compound the issue. The increased use of land for mixed wildlife/ livestock systems in areas previously subdivided by fences may also increase levels of epidemic disease. The question is whether countries can afford to ignore this problem, however ideal and attractive the theories.

If poverty alleviation is a goal and a necessary step to ensure conservation of resources, a pragmatic approach to the economics of land use may in fact be more important to conservation than recreating ‘Eden’. It should also be kept in mind that until relatively recently, many of the developments in wildlife conservation and utilization were initiated and controlled by communities of European origin, and that these may not be sustained with the changing social and political status of countries concerned. Equally, there appears to be an increasing realization among world leaders that globalization is perpetuating the dominance of the developed world and that there is a genuine desire to address the issues of poverty in Africa. This may lead to changes, which will facilitate trade of livestock and their products.

Whatever the attempts at global solutions, the changing land-use patterns in many areas of Africa will require ongoing and focused research to further elucidate the epidemiological determinants of many diseases at the wildlife/ livestock interface, in order to develop innovative control strategies that do not limit land use options of communities or a country’s ability to market animals and animal products profitably.

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