Friday, August 15, 2014

West Nile Virus

Please see the updated post on this topic 10/2015

I hate mosquitoes. Yes I am aware that they are part of the vast food chain but that doesn't stop my loathing. For the record, it is a mutual dislike and for some reason I rarely get bitten. The rest of my family, my daughter Lauren in particular, is one of their favorite treats, and they feast on her when given the opportunity. Even though I don't end up getting bitten, having a whining mosquito in the bedroom at night is a form of torture. What makes it worse is knowing that the bites are not just annoying, but they can be downright dangerous.

Of all the mosquito-borne illnesses, the West Nile virus is the one that has been in the local news recently. This is a mosquito borne illness that is thought to have originated in Africa (hence the name.) It has spread throughout the world and it was first detected in this country in 1999.  Unfortunately we now have it in most states, including California.

Mosquitoes get this virus from feeding on infected birds and then transmit it to humans. Humans are referred to as "dead end hosts"; they get the virus from being bitten by the infected insect but then can not spread it to each other. It is possible that it can be transmitted from blood transfusions, pregnancy or breast feeding but there are no known cases of infants who have gotten seriously ill from these transmissions.

The good news is that most of the time it is actually not such a big deal. Children under 5 seem to be at  relatively low risk and folks over 50 seem to get hit the hardest. It can be found year round but seems to peak in late summer/early fall. 80% of folks who get it have no idea that they are infected and feel perfectly fine. 20% of folks may have fever, joint pain, muscle weakness, stiff neck, diarrhea, vomiting, swollen glands, photo-phobia and/or a rash on the trunk. Not everyone will have every symptom. Most people showing these mild to moderate symptoms will recover completely, although there are reports that some of these folks can remain fatigued and achy for several weeks.
1% of infected people can get more serious neurological complications including encephalitis and meningitis. It can be fatal for those with serious cases. People with troubled immune systems are at the greatest risk. California has had 2 deaths from it so far this year.

The incubation period is usually between 2-14 days after the bite from an infected mosquito (most commonly 2-6 days.) There is, alas, no treatment beyond supportive care. It is thought that most people who have fought off the illness do end up with some level of immunity.

Any severe headache-fever-stiff neck combination always needs to be evaluated right away.  If West Nile virus is suspected there are blood tests that can help with the diagnosis.

Since there is no vaccination at this point, and no treatment, the key is prevention.

* Make sure that you have intact screens on all windows
* Get rid of any standing water that is around your house; do a double check to make sure there are no pots, bird baths...etc. that are places where mosquitoes can breed.
* Avoid being out and about during dusk and dawn when most of the biting happens.
* Try to wear (keep your child covered with) long pants/ long sleeves etc. Light colored clothing is recommended.
*If you are going into a heavy mosquito area use bug spray on exposed skin and clothing. The EPA has five registered insect repellants. Of those, there are three products that are more easily available.
  - DEET is one of the more popular options. It is considered safe for infants over the age of 2 months.
  - Oil of Eucalyptus is considered one of the least toxic options but interestingly, the age recommendation for it is for 3 years and older.
  - Picaridin is a newer option. It is odorless and is approved for children 2 years and older. It is great as a mosquito repellent but it is not thought to be as effective against ticks as Deet if you are going into the deep woods.

As with any new thing, do a little test patch on the skin to make sure there is no sensitivity before you widely spritz it. They all come in different concentrations. You will need to read the labels to see how often you need to reapply. Avoid contact with eyes. 

If you see any dead birds, give them a wide berth and report them to 1-877-968-2473 (WNV -BIRD) or online at That website also will give you the up to date numbers on how many West Nile virus cases there are  in California, county by county.

I was in western Massachusetts in early summer and there were simply swarms of mosquitoes and other nasty biting insects wherever we went. It made me realize how lucky we are here in San Francisco that it isn't as "buggy" as it seems to be elsewhere. If you are seeing mosquitoes around your house, San Francisco's Environmental Health Department will send an inspector  to investigate (415-252-3805.) They will check the area around your home (including sewers) to see if they can find  any breeding areas.

To be sure, we still do get patients covered in bug bites, but to date I have not seen any cases of diagnosed West Nile or mosquito borne illnesses among any of my patients. Some people seem to have much more of a reaction to bites than others; it does not appear that there is any correlation to the magnitude of the local reaction and exposure to the West Nile virus.

Thanks so much to Denise Bonilla, the Senior Public Health Biologist at the Vector-Borne Disease Section of the California Department of Public Health  for being such a great resource.

Here are some bonus facts about mosquitoes

*Both males and females make that awful whining noise, but only the females bite humans 
*Mosquitoes are especially attracted to people who drink beer *Mosquitoes love the smell of sweaty feet 

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