Abstract
Anthrax, caused by the bacterium Bacillus anthracis, is a seasonally occurring infectious disease affecting primarily herbivorous wildlife and livestock. The seasonality of anthrax outbreaks varies among locations, making it difficult to develop a single consistent ecological description of this disease. Over 44 years of mortality surveillance, most anthrax cases in Etosha National Park, Namibia are observed in the wet season, although elephants have an anthrax mortality peak in the dry season. Focusing on three host species (plains zebra, Equus quagga; African elephant, Loxodonta africana; and springbok, Antidorcas marsupialis) occupying the endemic anthrax area of Etosha National Park, Namibia, we tested two commonly posited causes of anthrax seasonality in herbivores: increased pathogen exposure due to greater soil contact, and increased host susceptibility due to seasonal nutritional stress. These hypotheses were assessed using fecal sampling and measurement of the percentage of fecal silicates as an index of soil ingestion and fecal nitrogen, phosphorus and crude fiber as nutritional indices. Nutritional quality for all three species was higher in wet than dry seasons. Comparing among wet seasons, nutritional indices showed either a decline in nutrition with increasing rainfall or no significant pattern. All three species had greater soil ingestion in the wet season than the dry season. Higher soil contact during the anthrax peak suggests that anthrax seasonality may in part be due to heightened exposure to B. anthracis in wet seasons, for zebra and springbok. Elephant anthrax deaths do not correspond with the season of increased soil ingestion or grazing, suggesting that other behavioral mechanisms may overshadow foraging‐based risk factors for this species. Nutritional stress is unlikely the primary causative factor in wet season anthrax systems, although nutritional stress sufficient to reduce resistance is difficult to assess non‐invasively in wild herbivores. In contrast, increased soil ingestion may be an important predisposing factor for wet season anthrax outbreaks. Ultimately, the amount of soil ingested and its importance in the transmission of soil‐borne pathogens will vary based on foraging behaviors, intake rates, grassland structure and on the likelihood that foraging areas intersect with pathogen aggregations in the environment.
Highlights
Anthrax outbreaks occur world-wide and are of concern for animal conservation (Leendertz et al 2004, Muoria et al 2007), wildlife management (Clegg et al 2007, Wafula et al 2008), agriculture (Mongoh et al 2008, Durrheim et al 2009, Lewerin et al 2010) and public health (Siamudaala et al 2006)
Anthrax is caused by the bacterium Bacillus anthracis which can infect a wide range of animal species, but mortalities are most commonly observed in herbivorous mammals
This study evaluated two factors thought to influence the timing of anthrax outbreaks, enhanced host susceptibility due to nutritional stress and enhanced host exposure due to soil ingestion
Summary
Anthrax outbreaks occur world-wide and are of concern for animal conservation (Leendertz et al 2004, Muoria et al 2007), wildlife management (Clegg et al 2007, Wafula et al 2008), agriculture (Mongoh et al 2008, Durrheim et al 2009, Lewerin et al 2010) and public health (Siamudaala et al 2006). Anthrax can occur as different forms, depending on the route of infection: cutaneous, pulmonary or gastrointestinal. Because of obvious health and safety concerns, not many anthrax carcasses are necropsied to determine the route of infection. When animals have been necropsied, they have shown signs suggestive of gastrointestinal anthrax (Ebedes 1976, Wafula et al 2008). For the purposes of this study, we assume that transmission occurs via the oral route and that herbivores are contracting gastrointestinal anthrax
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
