TOM FUDGE: I am Tom Fudge, this is KPBS Midday Edition. Hot and humid weather provides the perfect breeding ground for mosquitoes, and that is causing concern for San Diego health officials. The second dead bird in the county has tested positive for West Nile virus, which is carried by mosquitoes. So far only one person in San Diego has been diagnosed with the virus, but health workers are concerned that number may grow. Joining me to discuss the potential threat of disease and how to protect yourself are my guests, Steve Waterman and Chris Conlan. Thank you for coming in. Doctor Waterman, what is West Nile virus? STEVE WATERMAN: West Nile virus is an infectious disease, a virus that is related to a number of other viruses like yellow fever viruses, which are all transmitted by mosquitoes, and it causes disease in a certain percentage of people. Many people are not symptomatic when they become infected. TOM FUDGE: Is it deadly? STEVE WATERMAN: It is less than 1% fatal overall. Most people have a mild flu illness. But it does cause encephalitis, or inflammation in the brain, in a small percentage of people, about 10%. They can have a higher mortality rate. TOM FUDGE: The overall mortality rate of 1% since quite low. If you get West Nile virus, do you vomit? What typically happens? STEVE WATERMAN: Typically it is a sudden onset of high fever, headache, and it's very flulike without the cough and runny nose of the flu. You get a high fever and feel bad for a few days, and then it goes away. Or you may not have any symptoms at all. TOM FUDGE: Do weather patterns contribute to the outbreaks? STEVE WATERMAN: They definitely do. It's a summer born disease. I think the real message to the public about West Nile virus, is that elderly people over fifty or sixty and people with chronic diseases like diabetes and high blood pressure and kidney disease, they are at higher risk for the severe inflammation of the brain. You don't want to be bitten in the summer by mosquitoes. TOM FUDGE: Chris, Doctor Waterman invited you to talk about weather patterns. CHRIS CONLAN: Whenever we have this unusual weather with high humidity and rainfall and we got last weekend, it certainly increases the potential events. There is an incubation phase with the mosquito and the virus itself when it first picks up the infection. The hotter weather actually speeds up the incubation phase a little. It makes that mosquito effective at a younger age and more likely to find someone. Whenever the weather does just that, it makes us a little more nervous. TOM FUDGE: We've been in a drought. Would that reduce the number of mosquitoes we would see? CHRIS CONLAN: Not necessarily. One of the things that is hard to wrap your head around, drought is not necessarily a mosquito killer. Certain areas that might otherwise have not been breeding because they were flowing, when the outcomes those areas stop flowing and stagnate. That causes new breeding instead. You have to change your way of thinking, it's not so much more or less. TOM FUDGE: Is stagnant water the problem in terms of mosquitoes breeding? CHRIS CONLAN: Mosquitoes can't breed in flowing water, they need still water to do that. Different species prefer different types, but it has to be still. TOM FUDGE: A hawk was found to have West Nile virus. This is recently? CHRIS CONLAN: This was last week. We use birds as an indicator of the prevalence of the virus in the county. We can't say exactly where they got the infection, they may have got it and flu often died elsewhere. But the number of birds give us a good idea of how prevalent the virus is at any given time. TOM FUDGE: So the mosquito is the vector, but it is frequently given to birds and they typically are animals that carry them? STEVE WATERMAN: The main cycle is between birds and mosquitoes. Humans are what are called a dead-end hosts. Horses can also be dead-end hosts. CHRIS CONLAN: Not as bad as it sounds. STEVE WATERMAN: Humans don't transmit between themselves, in other words, it does not go between human to human. Humans are not usually viremic for it to be passed from mosquito to human to human. The birds keep the cycle going. TOM FUDGE: I think this hawk was the second bird the season that this is for West Nile. Is that a cause for concern? CHRIS CONLAN: It is still early in the season. West Nile is a disease of the warmer months, typically from July to mid-September. We are early on and there is a potential for this to get worse. TOM FUDGE: What areas of the county do you look at when you get concerned about West Nile virus? CHRIS CONLAN: We really look at all areas of the county. Anywhere where people are. When we see birds testing positive, we get concerned. You can have mosquitoes anywhere in the county, depending on where people live. TOM FUDGE: Chris, I think one person has been infected with this, that we know of. CHRIS CONLAN: That we know of, as Doctor Waterman mentioned, many people are not symptomatic. It's probably very underreported. TOM FUDGE: Are there other animals that carry it? STEVE WATERMAN: The ecology of West Nile virus is really interesting. There are a lot of different animals that have shown to be infected, but again, birds are the main species, and close seem to be a species that is killed easily by West Nile virus. If you see dead crows in your neighborhood, call Chris's shop and use the new app that enables you to take a picture and send it to the environmental health department. TOM FUDGE: Your telephone number and your website on our website, but how do people get in touch with you if they find a dead crow? CHRIS CONLAN: You can always go to our web page, contact us through email, call the office directly at 888-694-2888. Now we have a new mobile app that people can use as well, and you can download that from the local app store or from the county website. TOM FUDGE: Steve, you have an interesting job, you are with the US-Mexico unit of the CDC, what do you do? STEVE WATERMAN: I am part of a division of the CDC that works with migrants from foreign countries, and we work with the ports of entry at Tijuana, San Ysidro, and all the way through Texas. We work with persons coming into the United States that may have infectious diseases, and we also do surveillance projects with local health departments like San Diego County, looking for emerging infectious diseases like West Nile virus. TOM FUDGE: What are the other vectorborne diseases that you have been concerned about looking at the US-Mexico border? STEVE WATERMAN: We live in an interesting part of the world. In Mexicali, in recent years, there have been outbreaks of Rocky Mountain spotted fever, which can be fatal illness transmitted by ticks, which are often found on the stray dogs. Very close to us in Mexicali, there was a very recent case of Rocky Mountain spotted fever in Imperial county. That person died, so that is a disease that we are on a lookout for. TOM FUDGE: That is very interesting, have you heard of that Chris? CHRIS CONLAN: That is one of the other diseases that our group is monitoring. We test ticks for that when we get them. TOM FUDGE: I wanted to ask one of you a little bit of the history of West Nile virus. Steve, maybe you're the one to answer this question. When did West Nile arrive in California, and where did it come from? STEVE WATERMAN: It arrived in 1999 it mysteriously, in Long Island. Gradually it worked its way across the country and first arrived in California in 2001 or 2002, I can't remember the exact year. California since then consistently has had hundreds of cases in a year. We have not had a high year like that since 2012. TOM FUDGE: I think we talked a little bit about this before, about where mosquitoes breed. What are the places that people need to monitor? CHRIS CONLAN: Absolutely, the county knows about the bigger sources around town, but we cannot go in every backyard, really need the public to help out and take personal responsibility for their backyards. Anything that can hold water for a week or more can be a potential breeding source for mosquitoes. TOM FUDGE: Okay, that is one way to protect ourselves. Do you have any other tips for us? CHRIS CONLAN: Yes absolutely. Make sure your screen doors were not full of holes, wear mosquito repellant, wear longer sleeves and pants, and avoid peak mosquito hours at dust to dawn. TOM FUDGE: The mortality rate is not high, but are there lingering affects of the disease? STEVE WATERMAN: Yes, particularly in persons who develop encephalitis. Elderly people and those with chronic diseases, they can have long-term neurologic effects, which might cause them to have to live in assisted living or chronic rehab. They may have lingering paralysis. It's a serious disease, even if it is not always fatal. TOM FUDGE: Chris, anything to add on that? CHRIS CONLAN: What he said is absolutely true. We actually had a former colleague of ours who had it and he was very fatigued for a long time before he finally got over it. TOM FUDGE: How concerned should we be in California about West Nile virus, given the history we have seen? CHRIS CONLAN: It is a cyclic disease. We see some years it is very low and some years it gets very high. It is difficult at times to predict what will be a bad year, versus what will be a low year. I don't think anyone wants to get sick. We would encourage everyone to take this step to prevent being bitten and to prevent breeding mosquitoes on your own property. TOM FUDGE: In the state of California, do we know how many infected persons there are? CHRIS CONLAN: There were about fifty-seven reported cases in humans, so far. But we have a long ways to go. TOM FUDGE: And two recent deaths? CHRIS CONLAN: Yes, recent fatalities as well. TOM FUDGE: Steve Waterman, do you have anything to add to that? STEVE WATERMAN: Again, it can be fatal. About 10% of the encephalitis cases, I think any elderly person what information of the brain. I think following mosquito prevention advice during the summer months is really important. TOM FUDGE: Thank you both very much.
Hot and humid weather provides the perfect breeding ground for mosquitoes — and that's causing concern for San Diego County health officials as our region continues to experience warm weather and high humidity.
Just last week, a second dead bird tested positive for West Nile virus in unincorporated El Cajon.
The dead hawk was found two weeks after a Santee man was diagnosed with the disease. He's the first person in the county in two years to contract West Nile, a disease transmitted by mosquitoes.
The California Department of Health reported 16 new human cases of the disease last week in Butte, Fresno, Madera, Orange, Sacramento, Stanislaus and Tulare counties.
Chris Conlan, the supervising vector ecologist with the San Diego County Department of Environmental Health, said these reports raise alarm. But he said it's not a major threat yet.
"It's a definite sign that things could potentially progress to get a little bit worse, so people should be taking the proper precautions to prevent themselves from getting mosquito bites," he said.
Conlan said people should wear bug repellant, long sleeves and long pants to deter mosquitos. He also wants people to dump out anything around their homes that hold water, which can create a mosquito breeding ground.
He said it's difficult to say whether the recent heat and rainfall might be leading to more occurrences of the disease.
"We know heat does play a role, and the fact that we recently got rain could potentially increase the number of mosquitos," he said.
The public should report dead crows, ravens, jays, or birds of prey on the county website, or by calling (858) 694-2888, Conlan said.
San Diego County has also developed an app called Fight the Bite that allows residents to report mosquito breeding and dead birds for testing.
"We use testing to help monitor progression of the disease," Conlan said. "The more positive birds we find, the more concerned we get."
