Oral challenge of brushtail possums (Trichosurus vulpecula) with possum enteroviruses: Clinical observation, antibody response and virus excretion in faeces

Abstract

AIM: To investigate the pathogenesis of two cytopathic enteroviruses, W1 and W6, isolated from possums, to evaluate their potential as vectors for biological management of possums. METHODS: Possums (n=10) were fed 1 x 107 median tissue culture infectious doses (TCID50) of either the W1 strain (Possums 1–5) or W6 strain (Possums 6–10), while controls (n=2, Possums 11 and 12) were fed uninfected cell culture medium. Blood samples were collected from all possums on Days −1, 2, 7, 14, 21 and 34 or 35 post-inoculation (p.i.), and bodyweight and rectal temperatures were measured on the same days. Virusspecific antibodies were determined using virus neutralisation tests (VNTs). Faeces were collected on Days −1, 2, 7, 9, 14, 16, 21, 28 and 34 or 35 p.i., and the presence of W1 and W6 virus in faeces was determined using cell culture and reverse transcriptase-polymerase chain reaction (RT-PCR). Possums were euthanised on Day 34 or 35, and ileal Peyer's patches were collected for detection of virus using RT-PCR. RESULTS: No diarrhoea or significant changes in rectal temperature or loss of bodyweight were observed in virus-inoculated possums during the study period. Virus-neutralising antibodies were detected using VNTs in 2/5 and 3/5 possums exposed to the W1 and W6 strain, respectively. Excretion of virus in faeces was detected in 6/10 virus-inoculated possums, from as early as Day 4 p.i.; virus excretion in faeces was transient in some and persistent in other possums up to the time of euthanasia. The viruses were detected in 3/10 virus-inoculated possums following necropsy, but were not detected using RT-PCR in sera collected on Days 2 and 7, nor in Peyer's patches of virus-inoculated possums collected on Day 34 or 35. CONCLUSIONS: Possum enteroviruses W1 and W6 established an asymptomatic infection in the gastrointestinal tract (GIT) in a proportion of challenged possums. A virus-specific antibody response was elicited in infected possums, which excreted the virus in faeces for up to 35 days p.i. The absence of noticeable adverse effects in enterovirus-infected possums is an advantageous characteristic for candidate vectors on animal welfare grounds.