Brucellosis in wildlife

Brucellosis in wildlife

J GODFROID

Introduction

Brucella spp. infections have been documented worldwide in a great variety of terrestrial wildlife species and marine mammals. For example, B. abortus or B. suis have been isolated from wild animal species such as bison (Bison bison), elk/wapiti (Cervus elaphus), feral pigs (Sus scrofa), European wild boar (Sus scrofa), European hares (Lepus capensis), foxes (Vulpes vulpes), African buffalo (Syncerus caffer), eland (Taurotragus oryx), waterbuck (Kobus ellipsiprymnus), reindeer (Rangifer tarandus tarandus) and caribou (Rangifer tarandus groenlandicus).12 Brucella melitensis rarely occurs in wildlife but has been reported in Europe in chamois (Rupicapra rupicapra) and ibex (Capra ibex) in the Alps.22, 30 Brucella ovis and B. canis are responsible for epididymitis in domestic sheep and disease in dogs, respectively, and are generally transmitted venereally: these species are seldom reported in wildlife. Brucella neotomae has only been isolated from desert rats (Neostoma lepida) in Utah, USA, and has no known pathogenicity in any other animal species. Neither B. ovis nor B. neotomae is known to cause disease in humans.3

Since the first description of an abortion due to brucellosis in a captive dolphin in California in 1994,19 several reports have described the isolation and characterization of Brucella sp. strains from a wide variety of species of marine mammals such as seals, porpoises, dolphins, and a minke whale (Balaenoptera acutorostrata).8, 26, 27, 44, 53 The overall characteristics of these marine mammal strains are different from those of any of the six currently recognized Brucella spp.7, 8, 9, 39

Wildlife brucellosis is a political issue: the livestock, hunting and game farming industries, and those involved in wildlife conservation and welfare, have conflicting interests. It must be borne in mind that in certain countries where B. abortus has been eradicated in the cattle population, B. melitensis and B. suis have been isolated from cattle; the source of infection being infected sheep62 or feral pigs,11, 20 respectively.

Spillover or sustainable infection of disease

In regions or countries that have officially been declared ‘brucellosis free’ it is particularly the concern of the livestock industry to prevent the reintroduction of the infection into livestock due to the financial implications involved and the need to reinstate pre-movement testing of domestic animals. In this context it is very important to distinguish between a spillover of infection in terrestrial wildlife contracted from domestic animals and a sustainable infection in them.

It should be emphasized that the introduction of an infected individual does not necessarily imply that transmission of the disease to other animals will occur. The probability of brucellosis becoming established and being sustainable in a species will be equal to or less than the probability of infection and in some cases will be close to zero because a combination of factors including host susceptibility (or resistance), infecting dose, contact or repeated contacts with infected animals, and seasonal (calving), managemental and environmental circumstances must be taken into account.29 In this regard, the development of the game farming industry has contributed to the re-emergence of brucellosis as being of international concern for both livestock and wildlife because of the lack of pre-movement screening, an increase in the density of possibly infected game species, the introduction of artificial feeding,50 and the movement of certain wildlife species among wildlife ranges or conservation areas.

In this chapter brucellosis as a sustainable infection in wildlife populations is discussed; infections in wildlife species where anecdotal or circumstantial evidence based on limited serological data exist are not considered. In the latter case the available data suggest that brucellosis is probably only a marginal problem, if at all, and poses little risk either to the species concerned or to livestock.

Brucella abortus infections

As the bovine brucellosis eradication efforts in the European Union, USA and other countries throughout the world progressed, emphasis was placed on the identification of possible reservoirs of B. abortus in wildlife. Occasional seropositive animals in wild ungulates, particularly cervids,50 have been identified in numerous surveys but these infections were considered to be self-limiting or a spillover of the infection from cattle. In 1995, in Italy for example, B. abortus was isolated from 7 of 112 culled chamois but brucellosis did not seem to be present in this species in larger areas of the Western Italian Alps, where bovine brucellosis is absent.23

In countries in which bovine brucellosis has been eradicated or where good progress has been made in its eradication, few sustainable reservoirs of B. abortus in wild species are known to be present. Exceptions to the latter are, however, bison and elk in the American national parks of the Greater Yellowstone area 50 and in the Wood Buffalo National Park, Canada. 57 The African buffalo is also considered to be a reservoir of B. abortus in southern Africa. 43

Brucellosis in bison

Brucellosis is thought to have been transmitted to the bison herds in the American national parks in the Greater...

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