DECATUR, Ala. (AP) — Fogger trucks that ply many neighborhoods with mosquito-killing pesticides in the evenings likely do little to control the possible carriers of the Zika virus, according to an Auburn University researcher and a state health official.
The problem is in the timing of treatment — known as ultra-low-volume spraying — according to Derrick Mathias, an assistant professor at Auburn University who is researching mosquitoes as possible vectors for the Zika virus.
Mathias said the trucks used in many towns and cities across the state do a good job killing species such as the southern house mosquito, which is active in the evenings and known to spread diseases such as the West Nile virus.
But the Asian tiger mosquito, which is considered to be the most likely vector for a Zika outbreak in Alabama, is only active during the day.
"With this type of mosquito, the burden is more on the homeowner to address problems on their properties," said Cheryl Clay, an Alabama Department of Public Health official who heads the vector control division for the city of Huntsville.
Simply adjusting the hours that fogger trucks operate isn't an option because that could kill beneficial insects that pollinate crops and other plants, according to Mathias. Additionally, the chemical that most fogger trucks use — a synthetic derivative of chrysanthemum plants — breaks down quickly in sunlight.
Even mosquito control programs like the one in Decatur that distributes pellets laden with larvae-killing bacteria into standing water may fall short when it comes to the Asian tiger mosquito.
That's because the species prefers to breed in water collected in small containers and tree holes that aren't likely to be treated with the pellets, according to Clay.
"It takes very little water, even as little as a teaspoon," she said.
Both Clay and Mathias said the best way to control the Asian tiger mosquito is simply for property owners to eliminate standing water, scrubbing the sides of containers to remove mosquito eggs.
According to the state health department, residents should make sure water is not allowed to stand for more than two days in items such as gutters, bird baths, improperly stored tarps, wading pools and pet dishes.
Eliminating all the possible breeding sites promises to be a challenge. Clay said mosquitoes are known to breed in the internodes of bamboo. The health department even advises residents to make sure vases in cemeteries aren't holding water.
According to Mathias, commercial operations that spray shrubs and other areas where mosquitoes rest also can be effective, but it is important they don't spray flowering plants to protect beneficial pollinators such as bees.
The owners of two local companies that offer that service — known as barrier spraying — as part of a wider service designed to make properties unfavorable for mosquitoes said they have seen an increase in demand this year.
In Huntsville, Daniel Smartt, owner of Mosquito Squad Huntsville, estimated that as many as 10 percent of new customers mention the Zika virus as a concern when they sign up for mosquito control services.
"I'm sure it has more of an effect than that, but the customers aren't mentioning it specifically," he said.
In Decatur, Heath Legg, owner of Superior Mosquito Defense, said they're treating about 200 homes in the area per week and expect that to climb to about 300 per week before mosquito season ends in early October.
Most customers are interested in simply alleviating the annoyance of mosquitoes, he said, but some specifically have requested the service due to fear of Zika virus.
"There are a lot of people concerned, especially couples that are planning on having children or couples that are already pregnant," he said.
While researchers are concerned over the potential of the Asian tiger mosquito to spread the Zika virus, there has never been a documented case of the species transmitting the disease in the wild — though it has been shown to transmit Zika in a laboratory setting.
"We really don't know how good it is at transmitting the virus under normal conditions," Clay said.
In countries with Zika outbreaks, the disease is spread primarily by the aedes aegypti, also known as the yellow fever mosquito. That species largely has been pushed out of Alabama by the Asian tiger mosquito.
Mathias said scientists have discovered the male Asian tiger mosquitoes attempt to breed with female aedes aegypti, rendering the females sterile.
"We don't think aedes aegypti is here anymore," he said.
According to Clay, the last aedes aegypti found in Madison County was in 1990.
All known cases of the Zika virus in the United States were acquired by travelers in other countries or by people who had sexual contact with people who acquired the virus in other countries.
There are no known cases of mosquito transmission in the United States, but Mathias said aedes aegypti mosquitoes are still present in southern Florida, making it the most likely place for that to happen.
"Florida is kind of the canary in the coal mine," he said. "That's where we think it will happen first."
According to the Alabama Department of Public Health, just six Alabama residents have tested positive for the virus, including one in Morgan County as of June 13. A total of 91 tests had been submitted to the Centers for Disease Control and Prevention for Alabama residents with seven tests still pending.
Researchers aren't sure how well the Asian tiger mosquito can transmit the virus from person to person. While the aedes aegypti prefers humans, the Asian tiger mosquito is opportunistic, feeding on most mammals, which could be a factor, Mathias said.
Additionally, unlike countries where Zika outbreaks are ongoing, the United States has no primate population to help spread the disease. That's important because most mosquitoes travel only a few hundred yards in their lifetimes, making widespread transmission unlikely.
"I'm being cautious and saying don't let your guard down, but this is not like West Nile," Mathias said.
The West Nile virus was able to spread throughout much of the United States because birds served as carriers.
While mosquito fogger trucks and municipal control measures may not be effective against the Zika virus, they still play an important role in controlling other diseases, particularly West Nile virus.
In Decatur, Director of Street and Environmental Services Rickey Terry estimated the city spends no more than $10,000 to $15,000 a year on its mosquito control program, which runs two trucks in the evenings throughout the mosquito season.
"It's a minor thing in our budget," he said.
Without the mosquito controls, he said attendance at outdoor recreational events that benefit the city, such as those as Point Mallard Park, would be impacted by the annoying insects.
According to the CDC, the most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis. The symptoms are usually mild, so many people do not realize they've been infected.
Zika infection during pregnancy can cause serious birth defects. Once a person has been infected, he or she is likely to be protected from future infections, according to the CDC.
Information from: The Decatur Daily, http://www.decaturdaily.com/decaturdaily/index.shtml