Feline Immunodeficiency Virus (FIV) is a pathogenic lentivirus related to human and simian immunodeficiency viruses (HIV and SIV, respectively), and has been associated with AIDS-like pathologies in domestic cats (Felis catus). Immunosuppression is the signature symptom of infections by FIV, which attacks a broad range of immune cells and can lead to dysregulation of the systemic inflammatory response. However, host responses to infection by immunodeficiency viruses vary broadly; and it is unclear, to what extent this variation is mediated by the environmental circumstances the host is experiencing. Here, we investigated how two key ecological factors –nutrition and exposure to co-infections by a broad range of gastrointestinal and hemoparasites – mediate the effects of FIV infection on immunity of free-ranging African lions. We conducted a structured survey of 110 wild lions living in Kruger National Park, South Africa to collect data on FIV status, body condition, demographic parameters, endocrine indicators of nutrition, and 21 other co-infections, including four viruses, six gastrointestinal parasites, and 11 hemoparasites. We then compared these metrics to, white blood cell differential counts and indicators of host health and inflammation using a path analysis.
Results/Conclusions
Our results indicate that FIV-positive lions indeed had significantly lower levels of white blood cells – particularly lymphocytes and monocytes. More importantly, co-infections by hemoparasites and poor nutritional condition were equally strong drivers of this immunosuppression when compared to FIV infection itself. Disease progression in immunodeficiency virus infections is closely tied to immunosuppression; as such, our findings suggest that variation in host morbidity due to FIV infection may, in part, be explained – and perhaps mitigated – by nutritional factors and co-infections.