Experimental infection of possums with macropodid herpesvirus 1

To determine whether macropodid herpesvirus 1 (MaHV-1) could infect brushtail possums (Trichosurus vulpecula) and whether such infection would lead to latency in possums.

Possums (n=9) were instilled with 1.9 x 10(8) TCID50 of MaHV-1 into the conjunctivae and nostrils, while controls (n=3) were administrated with sterile saline. For virus isolation, all possums were swabbed from the conjunctivae and nasal cavities prior to inoculation, and on Days 1, 3, 7, 10 and 14 post-inoculation (p.i.), and then at weekly intervals for up to a further 6 weeks. Sera were collected on Day 0 immediately prior to inoculation and fortnightly thereafter, for the measurement of antibody. Corticosteroids were administrated to 4/9 virus-inoculated possums on Days 36 and 41 p.i. to determine whether latent MaHV-1 infection could be reactivated. Trigeminal ganglia and other tissues were collected at necropsy for viral detection. A nested polymerase chain reaction (PCR) targeting the DNA-dependent DNA polymerase (DNA pol) gene of the herpesviruses using degenerate primers was conducted on DNA samples isolated from the ganglia and livers from the possums, and blind-passaged cell cultures, for viral detection.

A mild conjunctivitis was observed in the majority of the virus-inoculated possums between Days 3 and 21 p.i. Virus was recovered from the conjunctiva and/or nasal swabs from 8/9 virus-inoculated possums on Days 1 and 3 p.i. and from 3/9 on Day 7 p.i., but not following administration of corticosteroids. No virus was recovered from the trigeminal ganglia of the virus inoculated possums and possum DNA samples were negative for viral DNA following nested PCR. All of the virus-inoculated possums produced a virus neutralisation antibody response by Day 28 p.i., and five had a titre >/=512. The sequence of a 133 base pair (bp) segment of the MaHV-1 DNA pol gene was considerably different from that of other published data.

This study demonstrated that MaHV-1 might have established a transient infection at the inoculation sites, and the inoculation of MaHV-1 via intranasal and conjunctival routes could elicit MaHV-1-specific antibody responses in possums. However, systemic and latent infection of MaHV-1 in possums was not demonstrated.