EPIDEMIOLOGY
Anthrax is a disease known to humans since ancient times, and the first reports appear in the Bible (Exodus, Chapters 7 to 9), as the characteristics of the fifth and sixth plagues are identifiable with anthrax.
Between the late 19th and early 20th centuries anthrax was one of the infectious diseases identified with major mortality among domestic and wild animals. Probably the most serious incident occurred in 1923 in South Africa, where in one year it killed between 30,000 and 60,000 animals. The disease has lost its importance, now being of more sporadic occurrence in Europe. It is now an uncommon disease in much of Western Europe, Northern America and Australia. One exception is endemic foci in wild fauna in the African national parks(1). In Europe, the major enzootic areas are Greece, Spain, Turkey, Albania, France and Southern Italy (Table 25.1).Herbivores are particularly susceptible to anthrax infection, whereas omnivores and carnivores are moderately resistant but still succumb. Among herbivores, in addition to domestic species including donkeys and mules, wild
Infectious Diseases of Wild Mammals and Birds in Europe, First Edition. Edited by Dolores Gavier-Widen, J. Paul Duff, and Anna Meredith. © 2012 Blackwell Publishing Ltd. Published 2012 by Blackwell Publishing Ltd.
TABLE 25∙1 Anthrax outbreaks in wild animals in the last 15 years in Europe.
| Country | Year | Animal species | Number of outbreaks | Number of deaths |
| Italy | 1998 | Cervus elaphus | 1 | 4 |
| Russia | 1999 | Rangifer tarandus | 1 | 1 |
| Ukraine | 1999 | Rangifer tarandus | 1 | 1 |
| Hungary | 2002 | Capreolus capreolus | 1 | 1 |
| Italy | 2004 | Cervus elaphus | 2 | 8 |
Data from the World Organisation for Animal Health (OIE) and Promed
species are also susceptible — in particular, zebras and species of wild ruminants such as cervids (Odocoileus vir- ginianus, Cervus canadensis, Alces alces, Cervus elaphus, Rangifer tarandus, Capreolus capreolus), gnu (Connochaetes taurinus, Connochaetes gnou), buffalo (Syncerus caffer, Bubalus bubalis, Bison bison), gazelles ( Gazella spp., Eudor- cas spp., Nanger spp.), antelopes (several genera) and kudu (Tragelaphus imberbis, Tragelaphus strepsiceros).
Several anthrax outbreaks that occurred in Southern Italy showed that red deer are highly susceptible to infection with B. anthracis and that the mortality rate in these deer could be even higher than that observed in domestic animals(2). Pigs and scavengers are more resistant to the disease than herbivores, and they must ingest a large number of bacilli bacteria to become infected and develop disease. Generally birds are resistant, but outbreaks have been seen in wild and commercial flocks of ostriches; their body temperature is lower than other avians, and this is considered to be the reason for their susceptibility.Anthrax is not transmitted from infected individuals to healthy animals but by the ingestion of spores dispersed into the environment. Bacillus anthracis is known for its rapid proliferation and dissemination in receptive hosts, but little is known about its ability to grow and reproduce outside the animal. It is clear that in the external environment, where conditions are less favourable to the survival of vegetative forms, B. anthracis spores are one of the most advanced type of resistant life forms known in nature and can persist in soil for many years. Severe outbreaks of anthrax develop mainly during the dry months that follow a prolonged period of rain in the spring. These climatic aspects suggest that water plays an important role in the ecology of the bacterium. Rainwater, having washed the ground surface, tends to stagnate in the lower-lying areas, concentrating spores there. This sequence of events encourages the adhesion and distribution of spores on soil humus, so the chances to infect herbivores increase1-3). It is widely believed that the vegetative forms of B. anthracis sporulate when exposed to oxygen. Under these conditions it is assumed that in an intact carcass, putrefactive processes should destroy virtually all bacteria in a period of time ranging from 48 to 72 hours. However, rarely in nature are carcasses of dead animals left undisturbed by scavengers (Figure 25.1).
Carnivores and scavengers are considered to be less susceptible to the disease than herbivores, and the vegetative cells do not survive transit through their more acidic stomach. However, by scavenging older carcasses containing spores, they may spread viable spores in their faeces. In rural areas, avian scavengers such as ravens (Corvus corax) and vultures can contaminate pastures or small bodies of water far from the original outbreak by spreading spores of anthrax in their faeces. Ticks collected from terminally ill animals have been found to contain B. anthracwl∙4), but they do not seem to play a significant role in the transmission of the disease, as inter- host transference of adult ticks is most unlikely. Laboratory studies have shown that stable flies ( Stomoxys calcitrans) and the mosquitoes Aedes aegypti and A. taeniorhyncus are able to transmit the infection1-5). The role of the tabanid fly (Hae- matobia irritans) in the spread of the disease was confirmed in two old scientific papers1-6’7). Latterly tabanid flies are seen to be of greater importance(8). Although non-biting flies can act as carriers of B. anthracis spores, they generally do not play an important role in the epidemiology of the disease for grazing animals, but are an important source of infection for browsers. Recently it was demonstrated that Musca domestica infected by feeding on anthrax- infected rabbit carcass can eliminate anthrax spores in their faeces and vomitus. It was also observed that anthrax spores were able to germinate and replicate in the gut content of insects, confirming the role of insects in spreading anthrax infection1-9).