Wednesday, June 04, 2003
I appreciate your comments. West Nile is here to stay. But rather than downplay the reportage of the terrors of this disease, I wish you would warn as well as (or instead of) dismissing them.
“Most people who get bitten by an infected mosquito won’t even know they have an illness ( less than one percent who are infected develop serious complications). It is not a public health threat on a par with SARS, or even influenza.”
Dr. Michael Bunning and Dr. Catherine Chow at the CDC recently completed a study where I live (Slidell, Louisiana). They found, after sampling 1,226 individuals, a 1.8% infection rate, and incidences of inflammations of the brain and spinal column were about three times higher than expected. They estimate that at around one in 51 people infected, instead of the expected one in 150 to 200 people infected.
Whether those numbers hold elsewhere remains to be seen.
I don’t dismiss the potential complications of West Nile Virus infection, only the public health implications of them. Disabling and fatal complications of any illness are tragic on an individual basis. But, as a matter of public health concern, what matters is how frequently those complications occur. There are a lot of diseases carried by mosquitoes and other insects that can cause neurological damage and other complications, including death. (Lyme disease, Rocky Mountain Spotted Fever, Eastern Equine Encephalitis, to name a few.). But, like West Nile, they aren’t carried by the majority of insects and their incidence is very low compared to other diseases such as influenza. Their complication rates are also low. So, while it’s important to be aware of the disease, it isn’t nearly the public health problem that other, more established, diseases are.
Granted, the study in Slidell, Louisiana found higher rates of infection and complications than those seen nationally:
Based on a federal study of Slidell residents, the rate of severe complications from West Nile virus is at least three times higher than previously believed.
"It's not what we expected," state epidemiologist Raoult Ratard said Friday. "We need to understand why, and nobody knows."
Until they complete more studies, state and federal officials won't know whether the Slidell results are an aberration or whether they are the first hint that national estimates have been off by a factor of at least three.
It’s important to remember that Slidell is in a region of the country that had higher rates of West Nile virus cases last summer than other regions - swampy Louisiana, where mosquitoes are more of a public health problem than they are in, say, Montana. It’s safe to say that if you live in a region teaming with mosquitoes you’re more likely to get bitten, and not only to get bitten, but to be bitten by an infected mosquito. It’s highly unlikely that national estimates are off by a factor of three, but instead that the findings in Slidell are an aberration of the climate and geography:
The data came from a study the Centers for Disease Control and Prevention conducted last year by drawing blood from 1,226 randomly selected Slidell residents. They found a 1.8 percent infection rate, or about one in every 55 people.
Given that Slidell has 25,695 residents, the survey results in an estimate of 463 people infected, Ratard said.
Ratard couldn't say whether that number is out of line with expected infection rates because most people with healthy immune systems unknowingly fight off the disease. That makes reporting such rates difficult without the kind of wide-scale blood sampling done last year on the north shore
....In addition to the high number of reported West Nile infections last year in St. Tammany Parish, Slidell was picked for the survey because of its climate to determine whether that might make a difference, said Dr. Michael Bunning, the study's director.
Of course, the fact that the higher rate is due to the climate doesn’t do much to comfort people who live near those swamps, and stories like these are heartbreaking:
Two gentlemen to my knowledge have lost all or most of their vision, as has a co-worker I have never personally met. Another gentleman known to my family is severely, possibly permanently, impaired. All of us are, months after contracting WNV, far less able, physically and mentally, than we were.
Most of the time, I feel as if the lights have gone dark inside my head. I have been under medical work restrictions, and have learned a disgustingly depressing new vocabulary that includes polite terms for abhorrent realities. For example, the genteel “viral encephalopathy,” for the more jarring “brain disease.”
Prevention: I don’t argue that nothing should be done to protect against West Nile Virus, but only that public actions should be proportional to public risk. For example, dead birds don’t have to be collected and tested for the virus. We know the virus is in the mosquito population now from coast to coast, so testing birds won’t help control the virus. It probably isn’t necessary for every city to spray for mosquitoes, either. But it probably is necessary for especially swampy areas to invest in mosquito control and good drainage.
It’s also a good idea to use insect repellent if you’re spending any amount of time in situations that put you at risk for mosquito or other insect bites - i.e. camping, hiking, etc. With that in mind, The Medical Letter has a good summary of insect repellents in this week’s issue. (Unfortunately only available by subscription, so I’ll summarize it.)
The best repellents remain those that contain DEET. Not only does it repel mosquitoes, but it repels ticks, chiggers, fleas, and flies, too. Products with less than 20% DEET in them provide protection for 1 to 3 hours. (The less DEET, the less time.) Higher concentrations can provide protection for up to 12 hours, but concentrations over 50% probably don’t confer any longer protection.
A commercial version of the insect repellent used by the Army is now available. Called Ultrathon, it can protect against mosquitoes for 6 to 12 hours, depending on the type and numbers of mosquitoes in the environment.
Extra protection can be had by spraying your clothing, sleeping bags, and tents with permethrin, a chemical that’s most familiar as a lotion and shampoo to treat lice and scabies. It comes as a spray that doesn’t stain clothing and stays on for up to twenty washings. It’s poorly absorbed through the skin, and toxic side effects have not been reported, although skin irritation can occur if you’re sensitive to any of the ingredients.
Many people are reluctant to use DEET-containing repellents because the risk of toxic reactions if over-applied, especially in young infants. For the chemically averse, there are some plant-based repllents out there, although they require more frequent application than DEET-based products. Citronella based products, such as Natrapel are popular, but my experience has been that they smell bad. There’s also a eucalyptus-based product that can provide up to four hours of protection. (I’m not sure how that smells.) And, although I’ve never tried it, I’ve got to wonder about the odor of a coconut-geranium-soybean repellent. (Their website claims that they’re as effective as DEET products, but click on the link to the data and you’ll find that DEET protected for 300 minutes compared to 95 minutes for the soybean oil.)
And then, there’s always Avon’s Skin So Soft. Some say that its ability to repel mosquitoes is only an urban legend, but I found it very effective when my children were small and we lived near a mosquito-infested city pond. It comes in all sorts of incarnations now - lotions, sprays, bath oils, some with sunscreen added, some with insect repellents added - but I just used plain old Skin So Soft moisturizer. The disadvantage is that it needs to be re-applied after about an hour, and that you need to know an Avon salesperson to get it. It still doesn’t work as well as the DEET-containing products, which I now use on the kids since they’ve gotten older.
For more information on mosquitoes and repellents, click here.
posted by Sydney on 6/04/2003 11:42:00 AM 0 comments