AbstractEpidemiological studies of disease ecology typically ignore the influence of host sex, age, nutritional condition and immunocompetence factors. However, this can lead to shortcomings and incorrect conclusions regarding the mechanisms of pathogen transmission and prevalence in wild animals. In many European countries, European Brown Hare Syndrome Virus (EBHSV) causes a disease lethal to brown hares Lepus europaeus. Associations of EBHSV infection, sex, age, body condition and spleen mass were studied in hares collected, from the prefectures of Chalkidiki and Thessaloniki, Hellas, during the hunting season. Data showed a sex‐biased prevalence with twice as many males infected with EBHSV than females (P = 0.061), indicating a sexual dimorphism in disease exposure or susceptibility. EBHSV infection was not related to hare body condition (P = 0.853). Adults had significantly greater spleen mass than young hares (P = 0.003), indicating past infections. Significantly greater spleen mass was found in hares positive for EBHSV (P = 0.010) and a negative relation was found between spleen mass and body condition (P = 0.038), indicating energy consumption for immune defense investment. The present study is one of the few that examine the relevance of individual risk factors in understanding patterns of viral infections in natural populations of wild animals.