Routes of transmission of wobbly possum disease

To determine the routes of transmission of wobbly possum disease (WPD) virus and whether or not these would favour further examination of its potential for biological control of possums.

A standard inoculum, prepared as a tissue suspension from possums which had been infected with WPD, was titrated in vivo. Possums were challenged with this inoculum by the intra-gastric, intra-tracheal and intra-dermal routes. Further possums were challenged with blood by the intra-dermal and intra-peritoneal routes, with urine by the intraperitoneal route and with homogenised mites (Trichosurolaelaps crassipes) by the intra-dermal route. Transmission was investigated between possums in closely-adjacent, individual cages and between possums in a group enclosure.

Possums developed WPD following administration of the standard inoculum by all of the above routes, following administration of blood by the intra-peritoneal and intra-dermal routes, following administration of urine by the intraperitoneal route and following administration of homogenised mites by the intra-dermal route. Individually caged control possums did not contract WPD. All non-inoculated adult possums in the group enclosure and many joeys in direct contact with infected possums contracted WPD.

WPD was efficiently transmitted by close contact. Without such contact transmission did not occur. Infectivity was demonstrated in tissue suspensions, blood, urine and mites. Given the routes by which possums are susceptible to these substances and the need for direct contact, infection may be spread in the wild by several mechanisms, including aggressive encounters in which blood is exchanged, contamination of wounds with urine, ingestion of contaminated food, transfer of mites during den-sharing, and other social encounters. WPD has potential as a biological control agent for possums on the basis that it is readily transmitted between individuals in close contact.