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Some populations recover without further mortalities, others
suffer recurrent mortalities, whilst some were completely
eliminated. At ponds where there were recurrent mortalities, the
overall size of the frog populations decreases. In addition,
analysis of the frogs’ immune systems revealed that frogs might
be adapting to ranavirus infection with ‘resistant’ frogs
becoming more widespread in infected ponds. Frogs may also
adjust their mating behaviour by either choosing to mate with
other healthy frogs or through an inability of sick frogs to
effectively compete for mates.
Although tadpoles are often badly affected by ranaviral disease
elsewhere in the world, and British tadpoles are susceptible to
ranavirus infection in the lab, spawn and tadpoles from British
ponds may be infected only rarely. Rather, infections here are
among adult frogs and computer modelling has shown that disease
could be maintained in individual ponds with infections
occurring in adult common frogs alone. However, the virus is now
known to infect toads and newts as well as at least one
introduced species so the possibility that other species are
involved in the persistence and spread of disease remains.
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