Mortalities associated with toxoplasmosis, histoplasmosis, aspergillosis, and a variety of cutaneous and systemic bacterial infections occurred in a captive population of Bennett's and Dama (Tammar) wallabies. Individuals of both species demonstrated a rough hair coat and poor body condition. The clinical impression was that of an immunosuppressive disorder as seen in retroviral infections and diagnostics were directed toward that etiology.
Leukocytes were isolated from heparinized blood from both wallaby species at the Indiana Animal Disease Diagnostic Laboratory. Using co-cultivation techniques, a virus was isolated and replicated in three cell lines: a low passage of Dama wallaby fetal cells, a scrub wallaby kidney cell line (QK2K) and a potoroo kidney cell line (PTK2). The best growth was demonstrated in the potoroo cells and multiple passages have been made. Infected cultures show marked cytopathic effects (CPE) with the formation of very large syncytia. If allowed to incubate long enough, the entire cell sheet becomes fused into massive syncytia. This type of CPE is similar to that seen in cultures infected with caprine arthritis encephalitis (CAE) virus and ovine progressive pneumonia (OPP) virus, both retroviruses in the genus lentivirus. Reverse transcriptase (RT), an enzyme associated with retroviruses, was evaluated in infected and control potoroo kidney cell cultures. Both magnesium-dependent and manganese-dependent RT activity were detected in the supernatants from infected cultures. The presence of RT activity is consistent with that of a retrovirus, but characterization of the virus to genus based on RT activity is not possible at this point. Viral particles consistent with retrovirus size and ultrastructure have also been observed on EM of leukocyte cultures from individuals of both wallaby species of the affected mob (Michael Worley, personal communication).
An indirect immunofluorescent antibody (IFA) assay was developed using wallaby retrovirus-infected PTK2 cells grown on Teflon matted, ten-well dot slides. Sera from individuals of both species in this retrovirus culture-positive population were tested and found to have antibodies against their virus. An ongoing serosurvey of captive macropods from other facilities has identified five seropositive individuals out of 44 wallabies of mixed species tested. Twenty-six individuals of other macropod species (e.g., tree kangaroo, red kangaroo, etc.) tested negative. Currently, a PCR-based test is being developed to detect the presence of the virus.
In summary, a retrovirus has been isolated from a population of Bennett’s and Dama wallabies which experienced mortalities from opportunistic infections. Further work is needed to characterize the virus to its genus. Additional RT activity studies are warranted. The availability of an IFA and the development of a PCR assay will allow screening of the population to determine prevalence and will permit monitoring to determine if infected animals are at greater risk for acquired immunodeficiency syndromes.