BOZEMAN, Mont. -- Stable flies are the latest suspect that may be involved in the West Nile virus deaths of hundreds of pelican chicks at the Medicine Lake National Wildlife Refuge in northeast Montana. West Nile virus killed 800 to 1,000 pelican chicks in 2003, averaged 400 in each of the next three summers and more than 600 this year.
Veterinary entomologist Greg Johnson of Montana State University said earlier this year that he considered the possibility that lice were transmitting West Nile virus to pelicans. He became suspicious after collecting very few mosquitoes in 2006, but seeing pelicans continue to die at a high rate. Johnson discovered previously that the Culex tarsalis mosquito is the primary carrier of West Nile virus in Montana and that the Medicine Lake refuge was one of the hot spots for the virus.
Many of the dead pelicans at Medicine Lake had lice crawling inside and outside of their beak, Johnson continued. Mike Rabenberg, deputy refuge manager, said external parasites -- especially pouch lice and feather lice -- are common on the Medicine Lake pelicans. The lice may be more prevalent, he said, on pelicans that are sick or weakened.
The lice were cleared, however, after Johnson sent pelican tissue samples and lice to the Centers for Disease Control and Prevention in Fort Collins, Colo. The lab tested approximately 800 lice, but none was found to have West Nile even though most came from pelicans that tested positive.
Stable flies caught Johnson's attention when he came across a bird with blood on its neck and some flies feeding on the blood during the third week of July. Stable flies look like common house flies, but they have a painful bite. They come from a different family than horse flies or deer flies, however.
"This (the stable fly scene) was very unusual because stable flies are only reported to feed on domestic livestock, humans and companion animals," Johnson said. "There are no repor
|Contact: Evelyn Boswell|
Montana State University