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Aggressive Vector Control Helps Prevent West Nile in S.D., So Far

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Governor Arnold Schwarzenegger has declared a state of emergency in three Central California counties hard hit by West Nile Virus. Officials say the mosquito-borne illness appears to be spreading rapidly this year. Fortunately, the virus hasn’t gotten a firm toe hold in San Diego. That could be due in part to the County’s aggressive vector control program. KPBS Health Reporter Kenny Goldberg has the story.

Just behind a complex of movie theatres and restaurants in San Marcos, there’s a large open field. At one end of the field, a storm drain empties out into an area thick with cattails and other brush. This is where Skyler Perry goes to work.

Perry is one of San Diego County’s vector control technicians. His job: to find out where mosquitoes breed, and kill them. Perry walks up to a murky pond.

Perry: See, that’s not very clean water.

Goldberg: What is that -- algae?

Perry: Oh, that’s duckweed. The slimy stuff is the algae.

Goldberg: So are there mosquitoes in there?

Perry: We will find out, I use this dipper here, and just sample the water…looks clean right here. Let’s go further down and take a look.

Just down a rocky path, Perry finds more standing water.

Perry: Bingo. We’ve got about 20 larvae in the first dip. And you can see the different sizes -- that can tell you the age. And there are variety of different sizes right there, so we’ll just throw this one out, on the ground, and come back and treat that.

Perry goes to his truck, and gets a bucket of larvicide that looks like bird food. He walks back to the pond, and spreads larvicide on the surface of the water. Perry suspects there are other pools of standing water he can’t get to behind the eight-foot-tall cattails. So he grabs a backpack blower from his truck, and shoots larvicide over the brush. 

Perry is one of 18 full-time vector control technicians employed by the County Department of Environmental Health . A vector is a bearer or carrier of disease. These technicians travel throughout the region to test standing water, and to kill mosquitoes wherever they find them. In the peak summer months, the department expands its activities, to include aerial spraying of salt water lagoons and marshes.  

Chris Conlan is the department’s supervising vector ecologist. He says his division also monitors rats and mice for evidence of disease.  

Conlan: The mosquitoes are probably the greater threat, from a disease transmission standpoint, but also from an annoyance standpoint. I mean you don’t see rats and mice running around biting people, whereas mosquitoes are on the wing specifically after our blood. But, the rats and mice do harbor diseases that we have to monitor, because should that ever get out of control, we’ve got to know about it, so we can take steps to try to curtail it.

The department keeps an eye on dead birds, too. Just last week, the County announced that three more dead birds tested positive for West Nile Virus .  San Diego County has yet to register any human cases of West Nile in 2007. In fact, Conlan says the County has had only one human case ever.

Conlan: We’re really proud of our vector control program, we have a very proactive program here, and so we think that that’s probably got something to do with it.

San Diego’s mild climate may be another factor. For whatever reason, San Diego’s environment just doesn’t seem to be conducive to vector-borne diseases. Still, Conlan believes it pays to be vigilant. After all, West Nile Virus was unheard of in the U.S. before 1999. Since then, the virus has become the nation’s most widespread mosquito-borne disease.

Conlan: The concern that something like West Nile, you know, got over here and spread so fast, was a really good lesson. You know, hey, there could be other things out there that might be able to pull the same stunt. So we need to understand that there are other diseases that can be transported from other areas of the world, and we need to keep our eyes open.

For now, however, West Nile is keeping vector control departments throughout California busy. So far in 2007, the number of people who’ve been infected is three times higher than at the same time last year.

Kenny Goldberg, KPBS News. 

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