Identification and Prevalence of Phascolarctid Gammaherpesvirus Types 1 and 2 in South Australian Koala Populations

Abstract

To determine Phascolarctid gammaherpesviruses (PhaHV) infection in South Australian koala populations, 80 oropharyngeal swabs from wild-caught and 87 oropharyngeal spleen samples and swabs from euthanased koalas were tested using two specific PCR assays developed to detect PhaHV-1 and PhaHV-2. In wild-caught koalas, active shedding of PhaHV was determined by positive oropharyngeal samples in 72.5% (58/80) of animals, of which 44.8% (26/58) had PhaHV-1, 20.7% (12/58) PhaHV-2 and 34.5% (20/58) both viral subtypes. In the euthanased koalas, systemic infection was determined by positive PCR in spleen samples and found in 72.4% (63/87) of koalas. Active shedding was determined by positive oropharyngeal results and found in 54.0% (47/87) of koalas. Koalas infected and actively shedding PhaHV-1 alone, PhaHV-2 alone or shedding both viral subtypes were 48.9% (23/47), 14.9% (7/47) and 36.2% (17/47), respectively. Only 45.9% (40/87) were not actively shedding, of which 40.0% (16/40) of these had systemic infections. Both wild-caught and euthanased koalas actively shedding PhaHV-2 were significantly more likely to be actively shedding both viral subtypes. Active shedding of PhaHV-2 had a significant negative correlation with BCS in the euthanased cohort, and active shedding of PhaHV-1 had a significant positive relationship with age in both wild-caught and euthanased cohorts.

A novel alphaherpesvirus and concurrent respiratory cryptococcosis in a captive koala (Phascolarctos cinereus)

“…[35][36][37] A recent molecular and serological study of wild koala populations in South Australia showed both PhaHV-1 and PhaHV-2 were highly prevalent, with over 66% of koalas actively shedding the virus, but the koalas studied showed no clinical signs of disease. 47 To our knowledge, this is the first alphaherpesvirus reported in a koala, associated with severe respiratory disease.…”

“…Herpesviruses previously isolated from koalas include two gammaherpesviruses; Phascolarctid gammaherpesvirus 1 (PhaHV‐1) and Phascolarctid gammaherpesvirus 2 (PhaHV‐2) 35–37 . A recent molecular and serological study of wild koala populations in South Australia showed both PhaHV‐1 and PhaHV‐2 were highly prevalent, with over 66% of koalas actively shedding the virus, but the koalas studied showed no clinical signs of disease 47 . To our knowledge, this is the first alphaherpesvirus reported in a koala, associated with severe respiratory disease.…”

“…In Australia, nearly all herpesvirus disease outbreaks or isolated deaths in marsupials have been recorded in captive zoo populations, where animals were held in higher densities than would naturally occur in the wild or were in contact with another species. Many marsupial species have succumbed to herpesvirus infection and death, following stressful events including recent capture from the wild, translocation from another country or facility, reintroduction into a new facility, or after inter‐mixing and contact with a new cohort of marsupials of the same or with a different marsupial species, or following induced immunosuppression after corticosteroid treatment 19–25, 28, 29, 42, 47–49 …”

Development of diagnostic and point of care assays for a gammaherpesvirus infecting koalas

“…Koala retrovirus (KoRV) is another pathogen infecting koalas that has been associated with chlamydial infections and neoplasia [ 6 , 7 ]. Two recently discovered gammaherpesviruses, phascolarctid gammaherpesvirus 1 (PhaHV-1) [ 8 ] and phascolarctid gammaherpesvirus 2 (PhaHV-2) [ 9 ], infect koalas, with research on distribution and prevalence currently limited to South Australian and Victorian koala populations [ 10 , 11 ]. Gammaherpesviruses are one of three subfamilies of double-stranded DNA viruses, Herpesviridae , along with the Alpha - and Betaherpesvirinae .…”

“…These interactions suggest that immune status and co-infections may be playing a role in disease progression in koalas. For precautionary risk management in koala rehabilitation facilities, PhaHV-1 is considered of higher priority due to its association with KoRV, and its association with older koalas suggesting it is horizontally transmitted, while PhaHV-2 may be acquired early in life through mother to offspring transmission [ 10 , 11 ].…”