February 3, 2012

In the Spotlight: Past Willdife Disease Investigations from USGS National Wildlife Health Center

USGS National Wildlife Health Center Quarterly Wildlife Mortality Report - July 2011 to September 2011

Mortality in captive Mississippi Gopher Frog larvae (Harrison County, Mississippi - View on GeoNames Map   )

In September, the USGS National Wildlife Health Center (NWHC) was contacted for assistance with an overnight mortality event involving approximately 2,400 newly hatched endangered larval Mississippi Gopher Frogs (Rana sevosa).

The tadpoles originated from portions of several egg masses that had been collected one week earlier from a single natural pond for captive propagation. No natural mortality among adults or egg masses was observed at the pond at the time of collection.

NWHC received representative specimens from each egg mass for diagnostic evaluation. Notable abnormalities in the 1-2 mm sized hatchlings from two egg masses included the presence of blisters and fluid accumulation in the skin and tails. Many of the tadpoles also had oddly curled tail tips. It could not be determined if these lesions occurred before death or represent post-mortem artifact.

In addition, some of the tadpoles appeared too underdeveloped to have hatched under normal conditions, suggesting that some of the eggs might have prematurely burst open releasing the tadpoles.

The cause of mortality is still under investigation although adverse husbandry conditions, such as exposure to acidified water, are one possible explanation for these findings. No fungi were observed and no viruses were isolated from pooled samples.

Mississippi Gopher Frogs, a federally-listed species since 2004, currently number less than 100 adults in two isolated populations in southern Mississippi. An undescribed systemic Perkinsus-like protozoan infection and chytridiomycosis are known disease threats to the remaining population, as is predation of egg masses by Caddisfly larvae and snakes.

Source: USGS National Wildlife Health Center, Quarterly Mortality Reports

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