Female Aedes aegypti mosquito hard at work feeding off a human host. This daytime biting mosquito is the primary vector for transmitting Flavivirus Dengue (DF) and Dengue hemorrhagic fever (DHF). Image courtesy CDC / James Gathany
Which Mosquito Diseases Do We Need to Worry About in Houston?
We want to scare you, just a little bit. At least just enough to take mosquito-borne diseases and mosquito control seriously.
That’s because we are now have three different mosquito-borne diseases that are of concern in Houston: West Nile virus, Chickungunya virus and Dengue virus.
Mosquito Diseases: West Nile Virus Activity in Houston and Harris County
Since first arriving in the U.S. in 1999, West Nile virus has established itself in many areas of the country, including Texas. The Center for Disease Control (CDC) has created an online mapping tool, called ArbotNET, which tracks areas where West Nile is active. We’ve made a screen shot using the mapping tool to show the total number of West Nile cases in our region.
The West Nile Virus Can Cause Two Different Human Diseases
The first is called West Nile neuroinvasive disease (WNND). It’s the more severe form of the illness; it can cause headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis.
The second disease caused by West Nile virus is West Nile fever (WN fever). Symptoms of WN fever include (obviously!) fever as well as headache, body aches, and occasionally a skin rash on the trunk of the body and swollen lymph glands. According to the Texas Department of State Health Services,
The Texas Department of State Health Services released its own update on September 16 with a detailed breakdown on West Nile virus activity in Houston. To date, they report that Harris County has had twenty confirmed cases of WNND and five confirmed cases of WN fever so far in calendar 2014.
We will look at West Nile in more detail in a future update.
Mosquito Diseases: Dengue Virus Activity in Houston and Harris County
Dengue virus is a huge problem world-wide. The CDC estimates as many as 400 million people contract the virus each year, primarily in the tropics. Below we have another screen capture taken from the CDC Disease Mapping tool showing where Dengue virus (DENV) has been detected.
If you look closely, you will see the active selection on the mapping software is set to DENV(imp). This selection show cases believed to be “imported” by visitors or tourists who contracted the virus elsewhere (generally in the tropics) and brought it with them to the Houston area (rather than having contracted it by local mosquito infection).
Visitors to Puerto Rico, Latin America, Southeast Asia and the Pacific islands need to be especially alert for these areas are high risk for the disease.
The CDC has not yet identified any locally acquired Dengue virus infections in Texas during 2014. There is in fact some debate among area health officials whether Dengue virus may now be sufficiently established in the Houston region to enable transmission via local mosquitoes. Most agree that if it’s not the case today then it’s only a matter of time.
Both the Dengue virus and the Chikungunya virus (discussed below) are transmitted by Aedes mosquitoes (as shown in the photograph at the top of this article). These type of mosquitoes are active during the day, so you shouldn’t drop your guard and only worry about mosquito protection during the early morning and dusk hours.
Like West Nile Virus, the Dengue Virus Can Cause Two Different Diseases in Humans
The most common disease is Dengue Fever, also commonly called breakbone fever. This disease can bring on symptoms like fever, headache, muscle and joint pain, as well as a skin rash that looks similar to measles. To date there is no vaccination to prevent or medication to treat Dengue virus diseases.
Less common is a more severe, life-threatening disease called Dengue Hemorrhagic Fever. Patients who contract it can bleed and lose blood plasma as the skin and organs develop hemorrhages.
We will investigate Dengue in more detail in a future article.
Mosquito Diseases: Chikungunya Virus Activity in Houston and Harris County
Like the Dengue virus, Chikungunya virus can cause fever and debilitating joint pain. The virus — once limited to Southeast Asia and Africa — reached the Caribbean islands toward the end of 2013, where it has since infected thousands of people.
Chikungunya virus has also reached Texas this year for the first time. However public health officials contend that all cases of Chikungunya virus infection in our area have been imported from elsewhere, e.g. those who contracted the virus did so outside of the continental United States.
To date, the CDC disease mapping tool hasn’t been updated to include Chikungunya virus infections. But the Texas Department of State Health Services announced on September 9th that they had identified 19 cases of Chikungunya across Texas, with 4 cases confirmed in Harris County and one each in Brazoria County and Montgomery County.
Indicative of the heightened level of concern about this new disease, the U.S. Defense Advanced Research Projects Agency (DARPA) is conducting a contest with a $150,000 award for the best epidemiological / mathematical model predicting how this mosquito-borne Chikungunya virus will spread across the Americas.
Checklist on How to Avoid Getting Infected by Mosquito-Borne Diseases
1. Avoid Bites from Mosquitoes in Daylight Hours too, Not Just at Dusk
Back before West Nile virus arrived in Houston, you may have learned that mosquito bites at dawn and dusk were the ones to really worry about, because the mosquito species active in the evening and early morning were considered the most likely to transmit encephalitis and malaria. This is true. But since the arrival of West Nile virus we have to worry about daytime mosquito activity too. Many types of mosquitoes can harbor West Nile virus, including Aedes aegypti, which is active in the day. Now that we are at risk for Dengue and Chikungunya, both of which are transmitted by Aedes aegypti, it’s even more important to avoid mosquito bites during daylight hours.
2. When Outside Use Mosquito Repellent and Wear Protective Clothing
The CDC has a guide for effective mosquito repellent use. They recommend choosing products with one of the following ingredients: DEET, picaridin, IR3535, certain varieties oil of lemon eucalyptus or para-menthane-diol.
Caution: Do not use permethrin products (not on the list) on your skin.
Wear socks, long pants and long-sleeved shirts when possible. This will help prevent mosquito bites. If some of these are made of thin fabrics, the mosquito may bite anyway, so apply mosquito repellent to thin fabrics.
3. Analyze Your Environment and Think Like a Mosquito
While the shorter-lived male mosquitoes are feeding on flower nectar and sweet juices, the female mosquitoes are searching for blood to nourish the eggs they develop. They use chemical sensors to detect carbon dioxide and lactic acid (and sometimes sweat) up to 30 yards away.
They are on the lookout for movement — this indicates you are alive! And, if you wear clothing that contrasts with your surroundings, you’ll be a more noticeable target to mosquitoes as well.
Finally mosquitoes can detect heat sources from a distance — they can sense warm-blooded animals, like us humans.
So if you have been working in the yard, you are a prime target due to exhaling Co2 and sweating! If you plan on working for a long time, it would be ideal if you could take a break partway to rinse off in the shower, change clothes and re-apply mosquito repellent before going out to work again.
The female mosquito needs to find still standing water to lay her eggs, which can total up to as many as 500 during her lifetime. The water needs to be still for about a week for the mosquito larvae to develop into young adults.
If You Were a Mosquito, Where Would You Look for Still Water?
You’d look for still water in the alley — discarded car tires are the best mosquito hatchery ever devised. Or maybe you’d find still water in mud puddles, stopped up drains or gutters, flower pot drip plates or even large upturned magnolia leaves lying on the ground. All are ideal locations for mosquito reproduction. Think like a mosquito and drain the water from these areas at least once a week.
If you can’t drain the water for some reason (like a rain-barrel collecting water from your gutters example), consider some other options:
- Buy a couple of goldfish who will gladly eat the larvae that hatch
- Add a pump and fountain to make the water flow
- Use non-toxic mosquito ‘dunks’ in the water
- Add a little vegetable oil to the the surface of the water to prevent mosquito larvae from hatching
Concerned About a Mosquito Bite? Give Dr Brewton a Call for an Appointment
It’s hard to avoid getting bitten by mosquitoes even with these tips from the CDC. So if you have a concern about a mosquito bite, call us at (713) 529-9224 and schedule a same day doctor appointment. We are open Monday through Friday from 8:30 a.m. to 5 p.m.
As always, if you are having an urgent medical emergency, call 911 immediately.