Faulkner continued, "There's another threat from mosquitoes in California that's potentially much worse, and that's the Southeast Asian tiger mosquito. It carries encephalitis and a few other things. It's constantly being introduced to the state in these shipments of 'Heavenly Bamboo' -- they sell it at the Del Mar fair -- where you have these little bamboo stalks. They're shipping it in water in vast amounts, and the mosquitoes are coming with it. They've been intercepted a number of times in the past few years, and they've become established in a couple of places. It's mainly nurseries, but they're trying to get them under control."
A phone call interrupts our conversation. When Faulkner hangs up the other line, he explains its significance to the topic at hand. "That was Jim Lang. He's with County Environmental Health. They've had a big turnover of employees recently, and he's one of their last entomologists. He says that it looks like the state does everything -- collects dead birds, sends them to a lab in San Bernardino, and does the necropsies on them there."
Even though Faulkner says the West Nile virus is inevitable for San Diego, he cautions against panic. "At this point I wouldn't be too concerned about it, just because there are so many things we don't know about it yet. We haven't narrowed down which mosquito is actually carrying it. Florida, which faces a potentially big problem with it, has 77 species of mosquitoes down there, and they're not sure which ones will carry it. We do know that a couple of them in this area are definite potential carriers, particularly the genera Aedes and Culex. But which ones are doing it, we don't know.
"We also don't know which hosts the mosquitoes will prefer. Humans may be a second or third choice. Maybe a bird or smaller mammal will be preferred. They have to bite more than once to transfer the disease. But if you only get one mosquito bite, you'd better make sure that you're the first person that mosquito has bitten. Mosquitoes are very opportunistic. They'll contract it in their body, then spread it in the next blood meal that they take. And if they don't get a full blood meal, which would expand their abdomen enough to let them know that the eggs will mature, they'll go for another host. The disease can build up in the body of the mosquito, and that's how they transfer it. There's a term called 'transovarian transmission' of pathogens, which means it goes from the ovaries of the female mosquito into the eggs, which would mean that the larvae would already be infected when they become adults, but I don't know if that's true for this particular disease. What I know about mosquitoes is probably more extensive than what I know about the West Nile virus."
One person who does know a lot about the West Nile virus is Dr. Leland Rickman, associate clinical professor of medicine for the infectious diseases division at UCSD Medical School. "It's a virus that can cause severe clinical symptoms in patients who acquire it. The virus has been around for a long time; however, in the United States, it was just recently recognized back in 1999. It's been traveling from the northeastern United States across the country, and so far, in California we haven't seen any cases. As of now, it's spread over 30 different states."
West Nile virus gets its name from the West Nile region of Uganda, where it was first isolated in 1937. "It was probably around before that, although we didn't have the technology to detect it. It has a worldwide distribution, but it's most commonly found in Africa, parts of Asia, the Middle East, and Europe. But 1999 was the first time it was recognized in the Western Hemisphere."
The "severe clinical symptoms" Dr. Rickman spoke of include meningitis and encephalitis. "These are infections of the brain or the lining surrounding the brain and spinal cord. It can cause a milder form of illness -- there's a large spectrum of illness, from asymptomatic infection, i.e., not knowing that you've caught it, to severe encephalitis and, potentially, death."
Fortunately, the odds of catching encephalitis when bitten by an infected mosquito are long. "Among patients and people who are infected, only about 1 in 150 actually develop severe disease. You have to be bitten by a certain type of mosquito, and that mosquito has to be carrying the virus. So, depending upon how much virus is circulating in that area, the chances of one mosquito actually transmitting the virus to a person can be remarkably low. For example, in California, where no virus has been detected, if you've got a thousand mosquito bites, you wouldn't get the virus, because there's no virus yet. It depends on how many of the vectors -- which are birds in this case -- are carrying the virus in their bloodstream."
Dr. Rickman is hesitant about saying "It's only a matter of when" about the West Nile virus. "That's a common term used for a lot of emerging infectious diseases. We basically don't know if or when it will arrive. We do have the mosquito vector here, but there is no virus identified so far in California. The birds -- who are actually the reservoir for the virus -- migrate, and they usually migrate in a north-to-south direction, and some of the migration paths for some of the more important bird reservoirs don't come over California.
"I live in San Diego, and I'm not alarmed at all at this point."