Ranavirus ecology in common frogs (Rana Temporaria) from United Kingdom: transmission dynamics, alternate hosts and host-strain interactions.

Abstract

The ranaviruses (Family: Iridoviridae) are a group of emerging pathogens in amphibians. Ranavirus(es) were introduced to the UK in the late 1980s and have been associated with mass mortality events in common frogs (Rana temporaria) in south east England. While the signs associated with the disease are well known in common frogs, little is known about the ecology of the disease in any amphibians in the UK. This thesis begins the process of the eludication of the ecology of the ranavirus in common frogs. To test the two different hypotheses for the transmission/maintenance of ranavirus(es) in North American amphibians, investigations into the life history stages of common frogs (Rana temporaria) affected by the ranavirus were undertaken. Eggs and tadpoles were screened using standard molecular methodologies for the presence of the virus. No infections were found in eggs (n = 720), one infection was found in a tadpole (n = 288), but adults were commonly infected with the virus. A mathematical model was developed to investigate if the ranavirus could be maintained in populations of common frogs when only adult-to-adult horizontal transmission of the ranavirus occurred. Under certain circumstances, the virus can persist for long periods of time when this occurs. This is the first attempt to mathematically quantify the dynamics of a ranavirus. The potential of alternate or reservoir hosts of the ranavirus(es) in the UK were also examined. This permitted for the identification of new amphibian host and for the isolation and characterization of ranaviruses from different hosts. Phylogenetic analyses revealed that all of the viral isolates were genetically similar at both loci examined. Experimental work examining the association between ranavirus isolates from different hosts in common frog and common toad (Bufo bufo) tadpoles was also performed. At low doses, isolates from common frogs caused higher mortality in common frog tadpoles than isolates from common toads. However, in common toad tadpoles, no such relationship was observed.