"Ranaviruses are non-zoonotic viruses (i.e. don't infect humans) of the Iridovirus family that mainly affect amphibians, but there are also reports in fishes and turtles. Ranavirus infection was first described in 1966 but not associated with disease until the 1980's, when mass die-offs of frogs were 1st seen. Ranavirus has now been reported on every continent except Africa.
The mode of transmission is via contaminated water. The most common
presentation is an explosive mortality event with death due to
peracute systemic haemorrhagic disease. In these cases, usually there
are no external lesions. Diagnosis is by virus culture followed by
identification using electron microscope or PCR.
There is currently no known prevention or control method.
A study in the UK has confirmed that ranavirus not only causes sudden
mass-mortality events, but also long term population declines. The
researchers examined wild common frog (Rana temporaria
) numbers in a
selection of populations around the country where ranavirus disease
had been previously reported since 1996. The finding was that half of
the populations has had repeated outbreaks of the disease. In almost a
quarter of the cases, frog numbers had dropped by 81 percent over the
last 12 years."