Is that salamander virus flying?

Investigators say that they have dismissed fish and frogs as suspects in the mysterious spread of a virus among salamander colonies in the western United States and Canada. Birds remain under suspicion, however, says Elizabeth Davidson of Arizona State University in Tempe. Her colleague Danna Schock points out that outbreaks lie along a migratory flyway, and birds might carry the virus on their feet.

In the 1990s, scientists studying salamander die-offs in the San Rafael Valley in Arizona at first mistook viral outbreaks for the bacterial disease called red leg. In 1996, Davidson and her colleague James Jancovich realized that red leg was in fact a secondary infection and the real culprit was a pathogen new to science.

This microbe belongs to the group of iridoviruses, so called because they can turn sick insects an iridescent blue. The Arizona discovery was the first iridovirus found to attack a salamander. Since then, iridoviruses have been fingered for killing salamanders in Utah, North Dakota, Wyoming, and Saskatchewan.

Laboratory tests have failed to turn up evidence that fish or frogs catch and spread the iridoviruses, Davidson reports. For more leads, scientists are sequencing viral genomes from several outbreaks. Teams are also surveying water holes, which is quite a task. "You're up to your knees in mud the consistency of chocolate pudding and then up to your waist in water," she says. "If you're not powerful, you can't get out."