Serology in wildlife: two problems and how to deal with them

Romain Garnier, Raül Ramos, Ana Sanz-Aguilar, Maud Poisbleau, Henri Weimerskirch, Sarah Burthe, Jeremy Tornos, Thierry Boulinier

How can we track infectious diseases in wild animal populations? Serology, the quantification of antibodies present in the blood following exposure to a disease agent, is a tool of primary importance. However, the lack of specific reagents for detecting antibodies in wildlife impairs the ability to interpret serological assays, and the absence of known positive individuals makes determining when a given individual should be considered seropositive challenging. To demonstrate the usefulness of non-specific reagents, we vaccinated four seabird species against Newcastle Disease Virus and measured antibody levels using two different serological assays, one widely available using chicken-specific reagents and another less available but non-species specific. We found high correlations in all four species between the results obtained with both assays. This indicates that the chicken reagent may be used in all four species and the resulting serological measures would be quantitatively accurate.

Quantifying the antibodies is not the only issue: determining the cut-off value above which an individual, called seropositive, is deemed to have been exposed is key. Traditionally this requires the use of known infected samples, which are scarcely available when screening wildlife. We applied a statistical tool that does not require known positive individuals to determine a cut-off value. We demonstrate the applicability of this method first with the ideal dataset of a population of vaccinated Cory’s shearwaters (Calonectris borealis) and second with the real-wildlife case of a population of Indian yellow-nosed albatrosses (Thalassarche carteri) exposed to the Lyme borreliosis agent Borrelia burgdorferi sensu lato. In the ideal case, the cut-off set by our method properly identifies all vaccinated individuals. In the second case, we report that 12 out of 49 individuals (24.5%) were seropositive. The results of this study will help alleviate some of the recurrent issues faced by researchers studying diseases in the wild, and are likely to help serology remain one of the hallmark methods in disease ecology and ecological immunology.

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