Suspect mosquito found in county |

Suspect mosquito found in county

Janet Urquhart
Aspen Times Staff Writer

Culex tarsallis, a species of mosquito that can carry West Nile Virus and transmit it to humans, was trapped last week outside Carbondale.

Local environmental health officials have been setting traps to collect mosquitoes and watching for the culex tarsallis, but they aren’t sure if the species is capable of living at higher altitudes.

It has not yet been found in Aspen, but two of the mosquitoes were identified in a batch of bugs collected Wednesday night along Highway 133 south of Carbondale.

“Those are the ones that we’re looking for as possible transporters of the disease,” said Carla Block, senior health specialist for Pitkin County. “You know what – they’re around.”

It was the first night the county had set out the traps, according to Block. The city of Aspen has been trapping mosquitoes for several weeks but has yet to find a culex tarsallis. It can be identified under a microscope by a white band around its proboscis – the tube it pokes into a victim’s flesh to draw blood.

There is no way of knowing whether the pair of mosquitoes collected in the midvalley carry the virus, according to Block.

The Colorado Department of Public Health and Environment requires a much larger sampling of mosquitoes in order to run its test for West Nile, she said.

There are a number of mosquitoes that can carry West Nile Virus. Only some of them feed on birds, which carry the virus, as well as mammals, meaning they might transmit it to people. Of those mosquitoes, only the culex tarsallis might thrive at higher altitudes, but no one knows for sure – hence the surveillance measures in Aspen and Pitkin County.

Carbondale is at about 6,100 feet in elevation, while Aspen is at about 7,900 feet.

Aspen recently sent in a sample from a dead bird for testing; it did not have the virus, according to Lee Cassin, head of the city’s Environmental Health Department.

The virus, originally transported from Africa, first appeared in Colorado late last summer. It was blamed for 193 deaths nationwide last year, from among 3,399 documented cases of the virus in people. In Colorado, none of the 13 documented cases proved fatal, though 93 horses died from the virus.

Experts believe many people contract the virus without ever knowing it, or suffer only minor, flu-like symptoms, including fever and muscle ache. Nonetheless, health officials urge everyone to use repellent to protect themselves from mosquito bites.

Janet Urquhart’s e-mail address is

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