ENC Health Currents: Controlling Mosquito Populations After Hurricane Florence

Oct 3, 2018

According to the CDC, the best way to avoid getting sick from viruses spread by mosquitoes is to prevent mosquito bites by wearing long-sleeved shirts and pants, using insect repellent and limiting time outdoors at dawn and dusk when mosquitoes are most active.
Credit CDC

Record rainfall and historic flooding from Hurricane Florence has caused a terrible mosquito problem here in Eastern North Carolina.  Last week, Gov. Cooper ordered $4 million dollars to fund mosquito control efforts in 27 counties.  Jared Brumbaugh has more on the multi-layer approach to studying and eradicating mosquitoes.

Trenton resident Melba Metts lost her home to flooding during Hurricane Florence.  She’s staying with her daughter as she sorts through her belongings and tries to salvage what she can.  But Metts says mosquitoes are hampering her recovery.

“We stay in the house most of the time, I mean.  You run to the car, I mean you can’t walk out on the porch without getting swarmed by them.”

Metts and about 300 people waited in line at a farm and garden center in New Bern Saturday morning.  The business was giving away two mosquito eradicators to each person.  Metts says she’s concerned about the diseases mosquitoes might carry. 

“She’s mixed up some sprays, my daughter has and been spraying that stuff but it’s just not working.  So we’ll do anything, however long we have to stand to get what we think might work.”

An increase in mosquito populations after a hurricane isn’t unusual. President of the North Carolina Mosquito and Vector Control Association Stephanie Richards says there are several different species of floodwater mosquitoes in Eastern North Carolina.

“Floodwater mosquitoes will lay their eggs in woodland pool areas and just in any kind of flooded field situation. When the waters come up and we have a lot of rainfall, when we have some flooding like associated with the hurricane, the eggs will hatch and then they’ll, the adults will emerge in large numbers.”

Richards says they’re also seeing an increase in mosquito species that lay their eggs in containers.

ECU students Adam Vang helping Brandon Grigsby with Columbus County Environmental Health gather mosquito data to support a potential application for FEMA funding for insecticide treatments.
Credit Melinda Fields

“We actually have a research study going on in a neighborhood in a suburban neighborhood in Winterville, so we’re seeing definitely an uptick in our floodwater mosquito species in our traps.  We also work with Pitt County Environmental Health.  Mr. Jim Gardener is the vector control manager for the county and he’s seeing an uptick in his trap counts as well.”

Richards says landing counts, which is the number of mosquitoes that land on a person in one minute,  surpass 100 mosquitoes in some parts of Pitt County.   

“So, probably, usual conditions, depending on the location and the species that you’re looking at, you don’t want to get more than five mosquitoes landing on you in a minute.”

In Columbus County, west of Wilmington, landing counts are 100-200 mosquitoes per minute.  Richards, who is also an associate professor in the environmental health program at ECU, says her students set traps last week across Columbus County to identify which species are most prevalent. The information will be provided to the Health Department so they can apply to FEMA for assistance for mosquito spraying.

“Counties that don’t have mosquito surveillance or control programs are really hurting right now and scrambling for what to do, especially since the citizens are calling them asking for help.”

Several communities in Eastern North Carolina have ramped up mosquito control efforts since Florence, including the city of Kinston and Pitt and Beaufort counties.  Richards says some municipalities are applying to conduct aerial insecticide spraying.  She says her organization is distributing donated larvicide briquettes to tamp down the mosquito population before they become vectors for diseases.

“So the ones that are coming off right now, the adults that have hatched and they’re emerging right now so they may not have had their blood meal yet.”

In addition to smaller floodwater mosquitoes, Pitt County is repoting some of the large woodland pool mosquitoes (see image for size comparison) that blood feed on large mammals, including humans.
Credit Stephanie Richards

Health officials say the species of mosquitoes that hatch after a storm are considered nuisance mosquitoes and don’t transmit disease.  State Public Health Veterinarian Carl Williams says historical data shows that cases mosquito-borne illnesses like Eastern Equine Encephalitis or West Nile Virus don’t increase after hurricanes.

“These floodplain and salt marsh mosquitoes really do not have high capacity to vector these diseases and what we have seen in the past, and other states have documented this as well, is that following a hurricane or tropical storm, you don’t really see increases in arbovirus illness.”

However, Williams says the species of mosquitoes that do serve as vectors are still present.

“It’s just that they’re overwhelmed by other mosquitoes that we don’t normally see except in the time after a hurricane or tropical storm.” 

According to the Centers for Disease Control, the types of mosquitoes that can spread viruses may increase two weeks to two months after a hurricane, especially in areas that did not flood but received more rainfall than usual. 

“We usually see arboviral disease transmission from August through October.  So we are in the classic middle of our arboviral disease transmission."

There were 21 cases of La Crosse encephalitis last year, an arboviral illness geographically associated with the southwestern part of the state.  In Eastern North Carolina, West Nile and Eastern Equine Encephalitis are viruses of primary concern.  According to the latest statistics from the State Department of Health and Human Services, there’s been no reported human cases of EEE as of July 2018.  The CDC reports three West Nile cases, in Catawba, Cumberland and Currituck Counties.  President of the North Carolina Mosquito and Vector Control Association Stephanie Richards says bridge vectors are responsible for the transmission of EEE.

“When there’s a lot of Eastern Equine Encephalitis in bird populations, there are occasions when mosquitoes that blood feed on both birds and humans or other animals like horses can bridge, they’re called bridge vectors, so they can bridge the virus out of the swampy areas into the human or equine populations.  And in Eastern North Carolina this year, we have had several horse cases of Eastern Equine Encephalitis.  So it is out there in the swampy areas.”

Richards says mosquito control programs have collected mosquito samples in Brunswick County that have tested positive for EEE.  If a human becomes infected, EEE can cause flu-like symptoms within 4-10 days after being bitten.  Inflammation of the brain can cause headaches, high fever, chills and vomiting.  About one-third of people who are infected with EEE die, and those who survive have mild to severe brain damage.  State Public Health Veterinarian Carl Williams says EEE is very rare with only a few cases in the U.S. each year.  He says many mosquito borne illness, including EEE, are asymptomatic.

A petri dish containing hundreds of mosquitoes, mostly floodwater mosquitoes, from Pitt County traps collected after Hurricane Florence.
Credit Stephanie Richards

“If you get infected, there’s a high likelihood that you won’t develop any illness. But if you do, you would go to your physician at which point if they suspect a arboviral illness based on maybe the season of the year, especially in the southwestern part of the state, a geographic association with areas of transmission, they would order serologic tests.  And those are specific tests that can be done to measure the anti-body response against those specific pathogens.”

Since there are no vaccines for humans to protect against EEE or West Nile, Williams say the best way to protect yourself is to prevent mosquito bites by wearing long-sleeved shirts and long pants, using insect repellants and reducing mosquito breeding areas around your home.  Some relief may be on the way as temperatures cool.  Mosquitoes become less active in colder weather and when temperatures fall below 50 degrees, mosquitoes die off.