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Frequent and seasonally variable sublethal anthrax infections are accompanied by short‐lived immunity in an endemic system
Author(s) -
Cizauskas Carrie A.,
Bellan Steven E.,
Turner Wendy C.,
Vance Russell E.,
Getz Wayne M.
Publication year - 2014
Publication title -
journal of animal ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.134
H-Index - 157
eISSN - 1365-2656
pISSN - 0021-8790
DOI - 10.1111/1365-2656.12207
Subject(s) - bacillus anthracis , biology , anthrax vaccines , context (archaeology) , outbreak , emerging infectious disease , infectious disease (medical specialty) , immunity , immunology , immune system , zoology , virology , disease , immunization , medicine , dna vaccination , paleontology , genetics , pathology , bacteria
Summary Few studies have examined host‐pathogen interactions in wildlife from an immunological perspective, particularly in the context of seasonal and longitudinal dynamics. In addition, though most ecological immunology studies employ serological antibody assays, endpoint titre determination is usually based on subjective criteria and needs to be made more objective. Despite the fact that anthrax is an ancient and emerging zoonotic infectious disease found world‐wide, its natural ecology is not well understood. In particular, little is known about the adaptive immune responses of wild herbivore hosts against B acillus anthracis . Working in the natural anthrax system of Etosha National Park, Namibia, we collected 154 serum samples from plains zebra ( E quus quagga ), 21 from springbok ( A ntidorcas marsupialis ) and 45 from African elephants ( L oxodonta africana ) over 2–3 years, resampling individuals when possible for seasonal and longitudinal comparisons. We used enzyme‐linked immunosorbent assays to measure anti‐anthrax antibody titres and developed three increasingly conservative models to determine endpoint titres with more rigourous, objective mensuration. Between 52 and 87% of zebra, 0–15% of springbok and 3–52% of elephants had measurable anti‐anthrax antibody titres, depending on the model used. While the ability of elephants and springbok to mount anti‐anthrax adaptive immune responses is still equivocal, our results indicate that zebra in ENP often survive sublethal anthrax infections, encounter most B . anthracis in the wet season and can partially booster their immunity to B . anthracis . Thus, rather than being solely a lethal disease, anthrax often occurs as a sublethal infection in some susceptible hosts. Though we found that adaptive immunity to anthrax wanes rapidly, subsequent and frequent sublethal B . anthracis infections cause maturation of anti‐anthrax immunity. By triggering host immune responses, these common sublethal infections may act as immunomodulators and affect population dynamics through indirect immunological and co‐infection effects. In addition, with our three endpoint titre models, we introduce more mensuration rigour into serological antibody assays, even under the often‐restrictive conditions that come with adapting laboratory immunology methods to wild systems. With these methods, we identified significantly more zebras responding immunologically to anthrax than have previous studies using less comprehensive titre analyses.