S.C. mosquitoes likely to carry Zika, but health experts don’t expect major disease outbreak

Aedes Aegypti mosquito
Aedes Aegypti mosquito

It’s likely a matter of time before mosquitoes carrying the dreaded Zika virus show up in South Carolina and infect someone.

But while the virus is expected, some of the state’s top health officials remain skeptical that South Carolina will experience a sustained Zika crisis.

South Carolina’s cool winter climate, the types of mosquitoes found here and the state’s past experience with mosquito-borne disease threats provide hope that the state could dodge a significant Zika outbreak, they say.

“Will it eventually reach South Carolina? The answer is probably,’’ said Robert Ball, a former state epidemiologist who now teaches at the Medical University of South Carolina. “But it would be a small number of cases, and maybe a cluster. I wouldn’t (say) an epidemic or outbreak.’’

Of the approximately 60 species of mosquitoes in South Carolina, only two are known to carry the Zika virus – and the one most likely to spread it is not common in many areas of the state, experts said.

Other viruses that have surfaced in South Florida and Texas, such as dengue fever and chikungunya, have not been spread in South Carolina by mosquitoes, state epidemiologist Linda Bell said. Bell said that indicates what South Carolina can expect – or not expect – in the near future.

“We can draw on what we know about the behavior of this virus and other closely associated viruses,’’ said Bell, a doctor with the S.C. Department of Health and Environmental Control.

Even though locally transmitted cases “occurred previously with closely associated viruses in other states, it did not occur here,” Bell said. “The possibility exists, but if we had a local transmission, it’s unlikely we’d have sustained transmission or an outbreak.’’

Zika virus is a concern nationally because of the devastating effects it can have on babies. Women who are pregnant or who are considering getting pregnant run the risk of having babies with birth defects if the women are bitten by Zika-carrying mosquitoes. Babies born in other countries to some women bitten by Zika mosquitoes have abnormally small heads.

Health officials across the country are warning pregnant women to take extra precautions to avoid mosquito bites in case one of the insects is carrying the virus. The disease also is a threat to others because it has been tied to outbreaks of Guillain-Barré syndrome, a disease that can cause muscle weakness and breathing difficulties.

Nationally, about 2,000 cases of Zika virus have been documented, but until recently, all have been found in people who contracted the disease while traveling to other countries or through sex.

Last month, however, officials in South Florida found evidence that local Miami-area mosquitoes transmitted the virus to people.

Ball, formerly with DHEC, said he wouldn’t be surprised to find a few cases of the same problem around Charleston. That’s where most of the mosquitoes most closely associated with Zika virus live, said Ball and DHEC spokeswoman Jennifer Read.

“The Lowcountry is at greater risk than the Midlands and the Upstate,’’ Ball said.

The kind of mosquito most likely to carry Zika virus, the Aedes aegypti, prefers to bite people instead of animals, and tends to cluster near neighborhoods, mosquito experts said last week. The aegypti is known as the yellow fever mosquito.

But it isn’t as widely found in the Palmetto State as the Aedes albopictus mosquito, a cousin that also can carry Zika virus. In some areas, such as Richland County, the albopictus has driven the aegypti species out of town. Known commonly as the Asian Tiger mosquito, the albopictus – which is just as happy biting animals as people – began moving into central South Carolina in the 1980s, according to state officials and the Richland County Vector Control Department.

Read said South Carolina also may escape a major Zika crisis because, unlike in South Florida, the weather gets cold here in the winter. Mosquitoes have difficulty flying when the temperature drops below 50 degrees, and they are sluggish at temperatures between 50 and 60 degrees, Read said in an email to The State newspaper.

“Colder temperatures reduce the likelihood of being bitten by a mosquito,’’ she said.

Nonetheless, South Carolina officials say they are taking the Zika threat seriously. DHEC says it doesn’t want anyone to get infected.

Zika spreads after people bitten by infected mosquitoes in other countries return to the United States and are bitten by local mosquitoes. The local mosquitoes then spread the disease when they bite another person.

To combat the possibility of Zika virus spreading to South Carolina mosquitoes – and then infecting people – some local officials say they will move quickly to kill mosquitoes in neighborhoods where travelers infected with the disease live. Zika virus can stay in people’s blood for a few weeks after they are infected

In South Carolina, state officials have confirmed 32 cases of Zika in people, almost all of whom have returned from other countries carrying the virus. One of the 32 cases was sexually transmitted.

DHEC and some local mosquito control agencies have launched campaigns to educate people on ways to control the mosquito population and stop any potential spread of Zika virus. The Aedes species, including the aegypti and albopictus, are of concern because they lay eggs in small containers, such as bottle caps or pans containing potted plants, instead of swamps in wooded areas.

Reducing populations of Aedes mosquitoes is often as simple as tipping over pots of standing water near people’s homes or businesses. That destroys the habitat for laying eggs and can significantly reduce the mosquito population, which tends to stay in localized areas rather than traveling great distances, according to DHEC.

But some counties and cities also are using other methods to attack potential Zika virus threats. Spraying is the most common, either by handheld methods or from the backs of pickup trucks. Using a chemical spray kills adult mosquitoes.

More than once this summer, mosquito control workers have descended on Columbia-area neighborhoods and killed swarms of the biting insects to prevent the spread of the virus.

Some people carrying Zika had returned to Columbia from other countries, where they had contracted the disease, said Tammy Brewer, Richland County Vector Control chief.

Once state health officials told Richland County about the cases, workers went into the neighborhoods, trapped mosquitoes, sprayed insecticide and kicked over water-filled containers where Zika-carrying mosquitoes can breed, Brewer said. She declined to identify the neighborhoods they treated or to say how many cases were involved, but she said the number was small.

Brewer said her agency’s work thwarted the threat. The idea was to keep local mosquitoes from getting Zika virus from the infected people, then biting someone else and spreading the disease.

“It’s impossible to tell if you completely eliminated them,’’ she said. “But we definitely improved the situation. We absolutely believe that.’’

Not all counties, however, are prepared for the threat of Zika virus. In May, DHEC said two-thirds of the counties need to improve their efforts. But many of those counties are in the Upstate, which Ball said last week is less at risk for Zika-carrying mosquitoes.

Coastal counties, including Charleston and Beaufort, have aggressive programs to combat mosquitoes, according to DHEC. Horry and Georgetown counties also have active programs.

James Brock, who runs Horry County’s mosquito control program, said the Aedes aegypti mosquito has been found in his area, but he is unaware of any Zika-carrying mosquitoes there. Still, Horry County is home to Myrtle Beach, which attracts millions of visitors each year – and he’s on the lookout for signs of Zika, he said.

“The guy who used to be over our program is now down in Florida,’’ Brock said. “I’m constantly on the phone with him asking “What are you doing, what are you doing?’’’

How to reduce your risk of mosquito bites

▪ Use insect repellents.

▪ Ensure screens are placed over windows.

▪ Wear long sleeves and pants or permethrin-treated clothes.

▪ Empty any items that can hold water both inside and outside dwellings at least once a week. These items include tires, buckets, toys and trash containers.

Source: S.C. Department of Health and Environmental Control