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.

KEY WORDS:

• Possum
• Trichosurus vulpecula
• enterovirus
• inoculation
• antibody response
• virus excretion

Acknowledgements

We thank Dr Bryce Buddle for helpful advice and assistance with this project, Wallaceville Small Animal Unit staff for expert husbandry of the possums, and Lilian Morrison for statistical analyses. This work was funded by the Foundation for Research, Science and Technology, New Zealand.