Inland Empire Guards Against West Nile Virus

Riverside County has recorded its first human case of West Nile virus. This is only the second human case reported in the Inland Empire this year; a couple of years ago, there were more than a hundred. But even though the virus seems to be under control in Riverside County this year, KPCC's Inland Empire reporter Steven Cuevas reports officials from the health department and vector control are still on guard.

Steven Cuevas: Here's what we do know about that first human case in Riverside County: The person is just 36 years old, and now recovering at home after a stay in the hospital to treat the virus's debilitating flu-like symptoms. Health officials are still trying to figure out how that person got infected, says Riverside County's chief of public health, Dr. David Hirfendahl.

David Hirfendahl: And it's just another wake up reminder to everyone in Riverside County. That if they live in an area where they are stagnant water and mosquitoes that they are at risk.

Cuevas: By the end of summer two years ago, there were already about 100 confirmed human cases of West Nile in Riverside County. The numbers plunged last year, and this year, cases in other parts of the state are surging – but not in Riverside County. Dr. David Hirfendahl is not sure why.

Hirfendahl: It's the luck of the draw. I don't even know if we're doing any active spraying; you probably know better than I. That's a whole nother department. Are we actively spraying?

Cuevas: The answer is no – at least, not in the West Valley Vector Control area, which covers Ontario, Chino, Rancho Cucamonga, and other parts of San Bernardino County. But there is an aggressive attack against mosquitoes going on here.

Min Lee Cheng: See this here? This serves as a filter ...

[Sound of manhole cover being opened]

Cuevas: Min Lee Cheng is head of West Valley Vector Control. He's snooping into a storm drain at a Home Depot in Ontario with field inspector Richard Real.

[Sound of sewer lid getting popped open, clanking onto concrete]

Cheng: See this here, the water? And if it breeds mosquitoes, you are in trouble. Until you open it, you don't know it's here.

Cuevas: Turns out, there's ten feet of standing water here. Vector Control already treated this site once before. Home Depot was ordered to pump out the drain periodically.

Cheng: I think we're going to have write them a warning notice now, because we've already talked to them and they have not done anything.

Cuevas: If the store doesn't clean up its act, it could get slapped with a thousand-dollar-a-day fine. There's no shortage of surface mosquito breeding habitats around, either. That puddle of sprinkler runoff in the gutter outside your house is more than enough to get the critters cookin'. In a matter of days, they're hatched and prowling for "blood food," as they say in the vector control business. Then there are the usual stubborn bug-breeding suspects.

[Sound of water splashing in pool]

Cuevas: This year – thanks to the sinking real estate market – there are more backyard swimming pools than ever carpeted with algae and mosquito larvae.

Cheng: Okay, this is vacant home in Chino we just discovered and the pool is turning green, and the owners left not too long ago. So we are seeing more and more vacant homes in our area.
Cuevas: So we're gonna get in closer and see if there are any eggs?
Cheng: Yeah, we can jump over there ...

[Sound of Cheng and Cuevas climbing cyclone fence, moving through dry grass]

Cuevas: Neglected and abandoned swimming pools are proliferating in Riverside County like ... well, like mosquitoes. Vector Control has been overwhelmed. Staying on top of the problem requires air surveillance, foot patrols, and lots of follow-up.

[Sound of knocking on door, door opening]

Richard Real: It should be vacant, but you never know. (laughs) They left it unlocked!

Cuevas: Even with all this maintenance, Vector Control chief Min Lee Cheng says the night skies are still thick with mosquitoes. So why aren't we seeing more infected birds, horses, and humans?

Cheng: We think that in the early season, in March and May, the evening temperatures were low and the virus didn't get a chance to amplify. Plus, because of the drier season, the mosquito numbers were low in the early season, so the virus didn't have a chance to spread to nesting birds. So that's why we're not seeing as bad as Northern and Central California.

Cuevas: In other words, we just got off lucky.

Cuevas: So cases may be on the decrease this year, but mosquito sources are ...
Cheng: Are increasing. And we never know, next year if we have warmer night-time temperatures early in the season, we could see an explosion, because the virus is embedded in our ecosystem.

[Sound of birds, wind]