Barandongo, Z.R. A.C. Dolfi, Y-H. Huang, K. Rysava, S.A. Bruce, P.L. Kamath, H. van Heerden and W.C. Turner. 2023. The persistence of time: the lifespan of Bacillus anthracis spores in environmental reservoirs, Research in Microbiology. https://doi.org/10.1016/j.resmic.2023.104029
Anthrax is a lethal bacterial zoonosis primarily affecting herbivorous wildlife and livestock. Upon host death Bacillus anthracis vegetative cells form spores capable of surviving for years in soil. Anthrax transmission requires host exposure to large spore doses. Thus, conditions that facilitate higher spore concentrations or promote spore survival will increase the probability that a pathogen reservoir infects future hosts. We investigated abiotic and pathogen genomic variation in relation to spore concentrations in soils at 40 plains zebra (Equus quagga) anthrax carcass sites in Namibia. Specifically, how initial spore concentrations and spore survival were affected by seasonality, temperature and rainfall associated with the timing of host mortality, local soil characteristics, and pathogen genomic variation. Zebras dying of anthrax in wet seasons—the peak season for anthrax—had soil spore concentrations 1.36 orders of magnitude higher than those that died in dry seasons. No other variables considered affected spore concentrations, and spore survival rates did not differ among sites. Soils at these pathogen reservoirs remained culture positive for 3.8 – 10.4 years. Future research could evaluate if seasonal patterns in spore concentrations are driven by differences in sporulation success or levels of terminal bacteremia.