Generation of a long-lasting, protective, and neutralizing antibody response to the ranavirus FV3 by the frog Xenopus

Xenopus serves as an experimental model to evaluate the contribution of adaptive immunity in host susceptibility to emerging ranaviral diseases that may contribute to amphibian population declines. It has been previously shown that following a secondary infection with the ranavirus frog virus 3 (FV3), adult Xenopus more rapidly clear FV3 and generate specific anti-FV3 IgY antibodies. We have further evaluated the potency and persistence of the Xenopus antibody response against FV3. Frogs inoculated with FV3 (without adjuvant) up to 15 months after priming produce specific, thymus-dependent anti-FV3 IgY antibodies detectable from 10 days to 8 weeks post-infection. These antisera from boosted frogs are neutralizing in vitro and provide partial passive protection to susceptible larvae when they are injected a few minutes before FV3 inoculation. These results with Xenopus suggest that other anuran amphibians are likely to develop effective long-lasting protective humoral immunity after an initial viral exposure.