Lessons learned regarding survival, carrier status, and recurrence of ranavirus (FV3-like virus) after an outbreak in Eastern box turtles (Terrapene carolina carolina) in Maryland, USA

An outbreak of concurrent Frog Virus 3 (FV3)-like virus, Terrapene herpesvirus-1, and Mycoplasma spp. occurred in a group of 27 Eastern box turtles (Terrapene carolina carolina) held in a naturalistic zoo exhibit surrounded by... [ view full abstract ]

An outbreak of concurrent Frog Virus 3 (FV3)-like virus, Terrapene herpesvirus-1, and Mycoplasma spp. occurred in a group of 27 Eastern box turtles (Terrapene carolina carolina) held in a naturalistic zoo exhibit surrounded by native box turtle habitat. The affected turtles demonstrated fibrinonecrotic stomatitis, cloacitis, and blepharoedema with a survival rate of 52% after intensive care with fluid therapy, antibiotics, antifungals, and nutritional support. All turtles that survived the outbreak successfully emerged from brumation and were enlisted in a challenge study to assess survival and shedding after exposure to ranavirus the following summer. Seven turtles were inoculated with the same FV-3 like virus strain with four controls. One of the seven inoculated, and none of the control turtles succumbed. The turtle that died with severe pathologic findings consistent with ranavirus had mild signs during the initial outbreak. The clinical signs observed in the inoculated turtles that survived were mild compared to during the initial outbreak; all were FV3-like virus positive using quantitative PCR on oral swabs and blood, indicating that turtles that are re-exposed to ranavirus will shed the virus in oral secretions. Half of the turtles in both the inoculated and control groups were euthanized and examined histologically. Ranavirus was detected in the spleen of one of the control turtles, indicating persistence of the virus from the initial outbreak. Multiple turtles have been added to the group in the past years without signs of virus resurgence except for one animal that had been in the group for 2 yr, which succumbed and tested FV3-like virus PCR-positive, indicating that turtles continue to shed virus. The origin and transmission of the infections remain unknown, although ongoing monitoring of the box turtles in the surrounding woodland have not indicated signs of ranavirus nor herpesvirus, and only low levels of Mycoplasma spp. exposure.