A Texas Doctor Again Puts on His Hat as Virus Hunter
The Aedes species of mosquito carries several viruses, and is the object of study as well as scorn in Dallas County.
Dr. Christopher Perkins just started his job as director of Dallas County Health and Human Services in 2012 when an emerging disease took root in Texas. The West Nile virus, spreading across the United States on the wings of mosquitoes, infected thousands of people in Dallas county — more than anywhere else in the nation.
It was to be an unwelcome pattern in his career. “I was here for West Nile in 2012, Ebola in 2014 and now it’s Zika in 2016,” he says. “But these are things I’ve trained for. The same skill sets we use for other pubic health issues translate to emerging diseases.”
Perkins took a break from meetings with Centers of Disease Control specialists and county officials on Friday to speak to the Observer about the new emerging threat, the Zika virus. The CDC says Zika is primarily transmitted through the bite of an infected Aedes species mosquito, but unlike other fevers it can also be transmitted by sex.
The symptoms — fever, rash, muscle and joint aches, and pinkeye — are pretty mild and patients beat the virus within one week. However, Zika infection in pregnant women is associated with fetal congenital deformities and deaths.
Texas has 10 cases of Zika virus disease, and all but one patient caught it while abroad. The exception involved a Dallas County resident who had sexual contact with someone who seemingly acquired infection while traveling. On Thursday, Dallas County officials said they are investigating four more possible cases, each of which also seemed to have caught the virus while out of the country.
“The vast majority of cases will occur when people are bitten by infected mosquitoes [rather than sexual contact],” Perkins says. “So the best defense is to avoid being bitten."
The focus of the county's response is squarely focused on keeping people and mosquitoes separate. On Friday afternoon the county advised Dallas County residents to use insect repellents (“DEET All Day, Every Day”), wear long, light-colored clothes and drain any standing water around the home or workplace. The Aedes species feeds during the day, but they get particularly active when the sun sets and rises, so the county is advising limited outdoor activities during dusk and dawn.
The rationale is not only to keep people from being infected; it’s to keep people from infecting mosquitoes. Those bites pass the virus both ways, and once the insects are infected, a "vicious cycle" begins, he says.
Preventing the virus from becoming entrenched in the local mosquito population should be easier here than in South and Central America. “In tropical areas, Zika and other viruses can spread to non-human primates,” Perkins says. “Also, it’s spreading in less developed countries, without screen windows or air conditioning. A person here doing an outdoor activity could be bitten once or twice. In the tropics, that’s 20 to 30 times.”
According to Perkins, low temperatures have kept Aedes mosquitos dormant in DFW, as they wait for warmer late spring and summer months. "But we know they are here,” Perkins says.
A different mosquito species spreads West Nile, and because of that, Perkins says “we know more about that population.” So the county is charting the population of the Aedes in North Texas. There’s only one way to do that — trap them.
Mosquito traps are not just mason jars filled with water and brown sugar. The county uses fabric bag traps, made by BG-Sentinel, that mimic a mosquitoes’ prey. The trap takes in and releases air like a mammal breathing, and is baited with a cocktail of chemicals that mimic the profile of human skin. (In other words, instead of saying “Eat at Joe's” to passing mosquitoes, the chemicals announce that Joe himself is on the menu.)
The researchers are not yet charting the spread of infected mosquitoes, just the details of the possible carriers. “We’re trying to establish a baseline for Aedes population, to learn more about their behavior,” Perkins says.
If Zika or any other such virus becomes entrenched in the local mosquito population, it becomes time for what public health experts call “control measures.” Those include spraying insecticide to kill adults and larvicide to exterminate the young. If things get bad enough, mosquito-thick areas could be sealed off. Or, as the CDC charmingly puts it, “During outbreaks a combination of containment and large-scale vector control may be used to minimize vector-human contact.”
DFW's previous run-ins with infectious disease—courtesy of a large airport and excellent terrain for mosquitoes—have made the county better prepared for outbreaks, he says. “We already had a cousin here that gave us a good preparation for Zika,” he says. Perkins and his team had been chasing another virus called Chikungunya that, like dengue fever, is spread by the same species of mosquito. But the Zika virus has given the county “more urgency” to study the pest, he says.
But the CDC says that trapping and testing mosquitoes isn’t the best way to track an outbreak of Zika. “Mosquito-based surveillance is the preferred method for monitoring or predicting West Nile virus outbreaks, it is not the preferred method for monitoring or predicting [Zika virus] outbreaks,” reads “For these, it is more efficient to detect cases in people.”
That’s where public education comes in, Perkins says, which explains why he was talking to an alternative weekly while a public health crisis is underway. “That’s one area where the region is helped by the past," he says. "People here know that part of public health is personal responsibility.”
For all the water tipped from tires and sprays of repellant, the biggest awareness campaign focuses on area doctors who are on the front line. Perkins says it’s vital for the county to let them know when to test their patients. For the time being, a patient’s travel history will be the biggest indicator to a doctor if a blood sample needs to be sent to the CDC for testing.
But Zika is a virus that is good at hiding. Its mild symptoms make it hard to detect, since many infected people won’t seek medical treatment. Mild symptoms also mean carriers won’t be sick enough to knock them out of commission, making sexual contact more likely. The county is advising pregnant women to ask partners who have travelled to the tropics to use a condom during sex, or to not bother getting laid at all.
Perkins did point out a thin silver lining to the Zika emergence. He says these outbreaks are a chance for his staff to take center stage. "Public health means air quality, sexually transmitted diseases, food inspection, and everything," he says. "When we have an outbreak it makes people more aware of the health department."
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