Ranavirus is an infectious disease of amphibians, reptiles, and fish caused by viruses from the genus Ranavirus. There are several different species of ranavirus that cause varying levels of disease in affected animals.
Ranavirus is believed to be the cause of several recent massive mortality events in amphibian populations across the globe. With a mortality rate of 90%-100%, the disease has the potential to eliminate entire species if not controlled. Scientists in the United States have identified ranavirus to be associated with mortality in over 25 states in 20 different species of turtles and amphibians. Ranavirus outbreaks can affect multiple species at the same time.
Ranaviruses affect amphibians, reptiles, and fish. In the United States, the USGS National Wildlife Health Center has identified ranaviruses in 16 species of frogs, 1 species of toad, and 6 species of salamanders, including the true frog, the tree frog, and the mole salamander. Ranavirus also severely aects both captive and wild populations of eastern box turtles and true tortoises and has been diagnosed in snakes and lizards. The viruses have been linked to mortality in several species of boney fish, including the pallid sturgeon and the threespine stickleback. Ranaviruses aect these animals at all life stages, though in general, mortality rates are highest if the animal contracts the virus during the larval stage. At this time, ranavirus is not known to affect mammals or humans.
Ranavirus mortality has been identified in North America, South America, Europe, Asia, and Australia. In the United States, confirmed cases have been documented in the northeast, southeast, Midwest, and northwest (see map of United States distribution of ranavirus). There have also been cases in parts of southern Canada.
Transmission of ranavirus occurs through direct contact, ingestion of the virus, ingestion of infected animals, or exposure to infected soil or water sources. Because ranaviruses most severely affect amphibians and reptiles in the larval stage, mortality events tend to be seasonal. In amphibians, mortality events due to ranavirus are most frequently seen in the spring and summer, while in turtles they are most common in the late summer and autumn. Though it is poorly understood at present, ranaviruses are believed to be able to persist in the environment for a period of time and can likely survive for months in water under favorable conditions.
Frequently, the first sign of an outbreak of ranavirus is the sudden onset of illness and death in large numbers of amphibians and/or reptiles over a 1-5 day period. Clinical signs in amphibians include mild to severe hemorrhages in the skin, especially near the base of the hind limbs and the vent opening, lethargy, weak or erratic swimming, buoyancy problems, gasping for air, and mild to severe fluid accumulation under the skin of the abdomen or hind legs. At necropsy, there may be fluid accumulation in the body cavity and hemorrhages on the surfaces of the heart, stomach, and liver. Occasionally, the liver or spleen are affected and ulcers in the skin and palate may be observed. In turtles, clinical signs include weakness, swollen eyelids, discharge from the nose and mouth, ulcers on the feet, and dull white or thick yellow plaque on the tongue, palate, pharynx, and esophagus.
Laboratory examination of diseased tissue and isolation and identification of the ranaviruses is used to confirm diagnosis of this disease.
There is currently no treatment or vaccine for ranavirus.
Since there is no treatment for ranavirus, management is focused on quarantine and sterilization to prevent the spread of the virus to other animals and new environments. Any infected animals should be quarantined to prevent infection of other animals. Water from captive facilities and home aquariums should be disinfected prior to disposal to prevent the virus from spreading into new water sources. All equipment, surfaces, and storage tanks in captive facilities should be disinfected after use. Wildlife biologists, veterinarians, rehabilitators, and anyone else involved in amphibian or reptilian fieldwork should disinfect all equipment and clothes before and after working at a field site.