Friday, October 9, 2015

Mosquito bites/West Nile Virus

I hate mosquitoes. Yes I am aware that they are part of nature's vast food chain but that doesn't stop my loathing. For the record, it is a mutual dislike and fortunately I rarely get bitten. The rest of my family, both of my daughters in particular, are tasty targets, who they feast on when given the opportunity. Some loose studies that were trying to make sense of why mosquitoes target some people more than others postulate that the favored blood type seems to be O, followed by B. A is the least favorite (I am A-). 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 gotten the most media coverage lately. 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.

In 2014 in California:

  • There were 561 cases of the more serious form of West Nile neuro invasive disease
  • There were 31 fatalities, which exceeded all previous years.
  • The proportion of mosquitoes infected with WNV was the highest level ever detected in California
  • The prevalence of WNV infection in tested dead birds, 60 percent, was the highest ever detected in California

In 2015 as of last Friday we have had  311 confirmed cases. Luckily, most of these folks survived.

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 for getting terribly ill 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. With a warm October expected we likely have another month before it starts to slow.  80% of folks who get WNV have no idea that they are infected and feel perfectly fine. There are probably thousands of cases that go under the radar since we would never consider testing if someone is only showing mild symptoms of a mystery illness.  The unfortunate other 20% of infected 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.

So far this year, 2015, there have been 311 reported cases in 28 counties. San Francisco hasn’t had any cases reported, but you don’t have to travel too far to be in a county that has. (Marin, Alameda and Santa Clara to name a few.) 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.

Keep in mind that 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. The larvae are dependent on water for breeding.
  • 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 repellents. 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.

Mosquitoes don’t like fans! The nasty insects are lightweight enough that a good breeze may make it hard for them to zoom in on their target.

If you do 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. It is updated weekly.

I was in western Massachusetts last 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.
The helpful folks at the California Department of Public Health pointed out that even with the extended drought, the mosquito abatement districts are still seeing A LOT of mosquito activity due to more stagnant water.

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. If your little one is getting bitten, check the bedroom carefully. Look at the mattress and all the corners of the room; bites could be from spiders, fleas or other culprits

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
  • Mosquitoes can sense CO2 from up to 75 feet away.
  • Mosquitoes only fly as fast as 1-1½  miles per hour.
  • Mosquitoes love pregnant women (regardless of their blood type) possibly because they emit a little extra CO2.

Thanks so much to the Disease Section of the California Department of Public Health  for being such a great resource.

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