Citation

Besides poaching and habitat loss, infectious diseases can also contribute significantly towards the decline of threatened wildlife species. This is the case in Ta National Park (TNP) in Ivory Coast, where anthrax, caused by Bacillus cereus biovar anthracis (Bcbva), is a major contributing factor to the mortality of chimpanzees living there. Vaccination is an option to reduce the risk of contracting anthrax. However, the unique living conditions of wild chimpanzees in a dense tropical rainforest pose a major challenge for systematic vaccination. The use of blowpipes for vaccination had a negative effect on the otherwise neutral behavior of some habituated chimpanzees towards humans. Thus, the aim of this study was to assess whether vaccination by food bait is a possible non-invasive alternative. First, a suitable method for the application of the vaccine by food bait had to be established and the development of diagnostic assays for the detection of anthrax-specific antibodies in urine was necessary in order to be able to pursue a largely non-invasive approach for the planned study. The non-invasive assays were furthermore used to examine the success of the blowpipe vaccinations already carried out and the Bcbva seroprevalence in chimpanzees and sooty mangabeys. ELISA and Western Blot protocols for the detection of anthrax-specific antibodies excreted via urine were developed using human serum and urine samples of anthrax vaccine recipients. For the comparative vaccination study in TNP, two different oral doses of the live spore vaccine Sterne 34F2 were tested in a group of habituated sooty mangabeys. In addition, mangabeys immunized by blowpipe and hand injection served as controls. After oral administration of the vaccine, no immune response was measurable and only two out of ten control animals had detectable antibodies after vaccination. When the vaccination campaign of 36 chimpanzees vaccinated by blowpipe was investigated, no reaction to the vaccine was observed. These observations question the use of Sterne 34F2 in chimpanzees and sooty mangabeys, not only for oral usage, but also fundamentally. Due to the lack of suitable alternative vaccines, there is currently no possibility of using vaccination to protect primates threatened by Bcbva. Another way to reduce the risk of infection is to identify and eliminate sources of infection. Further research is needed to understand the infection cycle and the involvement of possible vectors. One approach is the current investigation of potentially contaminated water and food sources, especially in the vicinity of deceased animals that have succumbed to anthrax. The observed Bcbva seroprevalence was low in chimpanzees and sooty mangabeys. Only one chimpanzee was positive for antibodies against the protective antigen, a protein of the anthrax toxin. All urine samples available for this animal, collected over a period of twelve years, were positive. This suggests long lasting antibody production after Bcbva infection. The extent to which possible repeated non-lethal contact with Bcbva or anthrax toxin components acted as boosters and had a positive effect on detectability could, however, not be determined from the available data. Together with the high Bcbva mortality in TNP, the low seroprevalence indicates that Bcbva infections are mostly lethal. This observation is consistent with earlier studies on the virulence of Bcbva.