Coinfection is an Important Factor in Epidemiological Studies: the First Serosurvey of the Aoudad (Ammotragus Lervia)

Despite being considered an invasive ungulate outside its native range (North Africa), little information exists regarding the role of the aoudad (also called Barbary sheep, Ammotragus lervia) as a pathogen reservoir. Furthermore, in most epidemiological surveys the potential role of coinfections (e.g. a first infection may make the host more immuno-competent or susceptible against a second pathogen) as a risk factor is often neglected. In this study we first performed a serological survey for selected pathogens (Mycobacterium bovis, M. avium subsp. paratuberculosis, Chlamydophila abortus, bovine viral diarrhoea/border disease viruses (BVDV-BDV), Salmonella spp., Brucella melitensis and Toxoplasma gondii) on free (n = 66) and captive (n = 25) aoudad from south-east Spain. Then, by using Akaike's information criterion, we evaluated the importance of coinfection in two statistical models that included the effects of population, age, and sex. Our results show that neither free nor captive aoudad had antibodies against Brucella melitensis, Chlamydophila abortus, or BVDV-BDV. However, compared to other wild ungulates in Spain, aoudads have high prevalence of antibodies against M. bovis (free = 49.5%; captive = 8%), very high prevalence of antibodies against M. avium subsp. paratuberculosis (free = 19.4%; captive = 56%), and intermediate prevalence of antibodies against Salmonella spp. (free = 13.4%; captive = 0%) or T. gondii (free = 1.5%; captive = 24%). Although the additive effects of population and age were included in our set of selected models, coinfection was the most influential factor to detect antibodies response against mycobacterials and salmonella infections. The direction of this influence could be exclusion of disease between tuberculosis and paratuberculosis seroreactor animals, or enhanced susceptibility to disease between tuberculosis and salmonella seroreactor animals. In conclusion, we believe that wildlife managers must pay more attention to the potential risk posed by aoudads as hosts (and probably reservoirs) of paratuberculosis and tuberculosis mycobacterials, while epidemiologists should be more aware of coinfection as an important factor in epidemiological surveys, especially in wildlife populations where multiple infections are common.