San Diego As the hysteria over the West Nile virus moves westward, California appears to be the inevitable destination of the mosquitoes that carry the deadly virus. Even though San Diego has a relatively dry climate and is not known as a mosquito enclave, one local bug expert says that the question is not if the virus will get here, but when.
David Faulkner, 51, is a forensic entomologist. A research associate of the Museum of Natural History in Balboa Park, Faulkner's most recent notoriety came as an expert witness in the David Westerfield trial. A bug fanatic since the age of five, Faulkner has been doing forensic research since 1979. "West Nile virus is definitely coming this way, but it's probably not going to be as intense as in other parts of the U.S. -- particularly eastern parts of the U.S., where they have this thing called water! We don't have a lot of that in San Diego County, particularly with the drought, the Santa Ana conditions, and everything else we've had for the last couple of years."
Water is the link between the insect and the spread of the disease. "We have an artificial environment, because we supply our water from outside, and that will restrict the activity of the mosquitoes, which would obviously restrict the spread of the virus. The places where we traditionally have a lot of problems with biting insects would be more of the coastal areas, like the estuaries, because a lot of these mosquitoes are able to survive in brackish water. Any of the lagoon systems where you have polluted or unpolluted fresh water feeding it, you have a potential for mosquitoes surviving. That's where you're going to have a lot of problems."
Faulkner says that normally the County Department of Environmental Health (formerly known as Vector Control) would be responsible for addressing this kind of problem, although it might not be the agency that tries to control it. "Often the counties do interception, and the state does control. The federal government may also regulate how it is done. In mosquito control, they used to use oil and all these other things that they would put across water surfaces. Right now, the most common techniques involve using biological control agents. They have 'mosquito fish,' which are very effective in certain situations, and the other thing is a bacillus, or bacteria, that gets into mosquitoes and kills them as well as the larval stages. We don't do a lot of fogging or spraying. Under certain circumstances, they might try to do that, but you'd have to have a reason for doing it, because fogging and spraying is pretty heavy-duty. We have had malaria here in the past few years, which is also transmitted by mosquitoes. What usually happens is that people will come in who are infected, and if you already have mosquitoes and water, you have the potential for that occurring. Even though we've had about 40 malaria cases in San Diego, most of those were brought in. We only know of 2 that originated here, from people who had not been out of the country.
"First, you have the actual vector of the disease, which is the mosquito. Then you have the introduction of a causal organism, which in this case is the virus or malaria or encephalitis, or whatever it is. Then you have the habitat that they can survive in, which would be aquatic situations -- then you have the potential for having a problem. The thing about West Nile virus is that it is spread about by birds. They are what we would call the 'reservoir hosts.' I know that in Orange County and throughout the state, they biopsy a lot of dead birds to find out what they died of. If you have a large die-off in one area, then you have a suspicion that it could be an accidental or potential poisoning, but it could be something else. There's always the potential that it's a disease that's being carried. Chickens are being used, because you can do blood tests on them while they are alive. And we have a lot of chicken ranches around here, too, which I imagine are tested from time to time as well. So a mosquito that can bite a bird that is infected can then bite a person, and that's how it gets spread around. The birds are the ones that are moving the disease, but it's only when it affects people that we have a real concern."
Another problem unique to San Diego is the movement of its water supply in a drought season. "The mosquitoes, birds, and everything else are moving more to the urbanized areas, because that's where the water is right now. You can go out in the chaparral where it's dry, and you can't find a lot of these insects, but I can go out in the back yard at dusk, and two or three mosquitoes will come after me, mostly Aedes, which is a good biter, and it's because we have water around here. You may not even be aware of the water around. We water our plants and use the sprinklers. There can be small pools of water around that are persistent, and that's enough."
What the small pool of water is "enough" for is the mosquito's life cycle -- much of which depends on mosquito "bites," which are not really bites but blood feasts. "The adult mosquitoes will live two, maybe three weeks at the most. It's a tough life: they've got to find a host, a blood meal, a mate, water to deposit eggs in, and then start the cycle over. The host is what they feed on. Many types of insects are pretty specific as far as what kind of animals they can take a blood meal from. The reason for the blood meal in the female mosquito is for egg maturity. The better the egg mass, the better a blood meal the mosquito has had. They pierce the skin, they add an anticoagulant to keep from clogging up their mouth parts and tube, through which they are feeding, and that's what people react to -- the anticoagulant," Faulkner explains. "They have to find a mate then, and the population is a lot less dense than it would be in a more optimal environment -- say, where there were lots of animals and a water source. But if you take an area that's diverse, that has a lot of dry area -- like San Diego -- they have to find a mate, and after mating, they have to find a water source where they can lay their eggs.