Vandals and thieves have increasingly been attacking Fairfax County’s mosquito traps, impeding efforts to monitor the presence of the potentially-deadly West Nile virus, officials said today.

The Fairfax County Health Department Environmental Health Unit said about 20 of its 70 sites have been disturbed since the yearly monitoring program began in May. Many of these sites contain multiple traps, meaning there have been between 40 and 60 traps disturbed so far this year.

“It’s one of these things where you’re trying to do something for public good and you have it interrupted by vandalism, it doesn’t make a lot of sense,” said health department spokesman Mike Andrews.

The traps catch mosquitoes to be tested for the West Nile Virus. Fairfax County has had 22 human case of West Nile virus since 2002, with two resulting in death, said Dr. Jorge Arias, environmental health supervisor for the health department.

In some cases, the traps, which are mostly on county land near residential areas, have been torn apart or burned. Others have had their ropes cut or their batteries stolen--requiring $150 to $200 replacements.

“There have been other instances where people open the holding container to liberate the mosquitoes,” Andrews said. “It’s like the Free Willy movie, you know, liberate the mosquitoes.”