By Rose Hoban
It’s cold in North Carolina right now. So people aren’t sitting on their porches swatting at mosquitoes.
But even when the weather warms up and the local bloodsucking bugs start flying, the question for many people is: Is it possible to get the Zika virus in North Carolina?
The answer, according to researchers from UNC-Chapel Hill, is, essentially, “No.”
“There’s not zero risk of anything, but I wouldn’t worry about transmission of Zika in the U.S.,” said Aravinda de Silva, an infectious-disease researcher at UNC who specializes in dengue virus, another mosquito-borne virus in the same family as Zika.
Though there are mosquitoes in the U.S. capable of carrying Zika, de Silva said there’s an exceedingly slim chance of someone in this country getting Zika from a mosquito.
There have been small outbreaks of dengue in Key West and along the Texas-Mexico border. But da Silva said Zika diagnoses in the U.S. will overwhelmingly come from travelers who bring it home from their Caribbean or Latin American vacation.
“Let’s put the U.S. aside for a moment. There’s more globally; all these people living in endemic areas,” he said. “There are huge populations living in these large urban centers, millions and millions of people who are at risk of getting dengue, and those same populations are at risk of getting Zika.”
“If it wasn’t for the microcephaly, it wouldn’t be unique,” said UNC infectious-disease specialist David Weber, referring to a strongly suspected link between Zika infection in pregnant women in Brazil and a sharp uptick in a birth defect known as microcephaly.
“Otherwise, [Zika] is just a mild illness, which is why there’s been so little research,” he said.
According to da Silva and Weber, who both presented last week, researchers from the university are mobilizing to study the disease.
Even as the UNC researchers were presenting, a study was released in the New England Journal of Medicine showing direct links between even mild Zika infections in pregnant women and the birth defect. What is disturbing to the authors of that study was that only about a third of the women tested actually had a fever; the rest never knew they were sick.
Air conditioning and window screens
Zika is closely related to dengue, which has been spreading widely in Latin America and the Caribbean for the past few years. Commonly known as “breakbone fever,” dengue usually causes mild fever. But in a limited percentage of patients, its muscle and joint pains can be just plain awful.
Yet out of the estimated 390 million cases of dengue worldwide in 2013, only 794 were diagnosed in the U.S. Most of those were travelers who acquired the disease while abroad.
There has been some local transmission in the U.S., but the spread has been limited. Even in places in the U.S. like Key West and along the Texas-Mexico border where there are the right kind of mosquitoes – namely, Aedes aegypti and Aedes albopictus – and the weather is warm enough, there’s reduced risk of those bugs actually carrying disease from one person to another.
“This has mostly to do with lifestyle factors such as air conditioning and window screens, which limit the spread of mosquito-borne viruses here,” said Helen Lazear, a UNC microbiologist who studies mosquito-borne diseases, during last week’s presentation.
In a recent Key West dengue outbreak, there were only 28 confirmed cases of locally transmitted disease between August 2009 and March 2010.
More than the U.S.
Lazear floated the suspicion that prior infection with dengue, as is common in Brazil and other countries where Zika is currently raging, can actually make Zika cases worse.
According to Lazear and da Silva, Zika triggers the immune response created after a person has gotten dengue.
“Unfortunately, dengue and Zika are too close and it’s very difficult with the [existing test] to see whether someone is having a dengue or a Zika infection,” da Silva said.
That makes it harder for researchers to actually confirm that a patient has Zika while they’re still sick. Instead, the best diagnosis is made using sensitive DNA-based testing; but that’s expensive and needs to be done in a lab.
UNC researcher Sylvia Becker-Dreps, who has been doing epidemiology research in Nicaragua for a decade, will be leading a collaboration between UNC and a university in that country to study Zika.
“Right now, it’s mostly a naîve population; they’re only starting to get their first cases, something between 300 and 600 cases detected in Nicaragua,” Becker-Dreps said.
The idea is to help the government with its response, but resources in that country are poor and Becker-Dreps said the ministry of health is only testing every tenth blood sample it receives.
She said one of the most important things to do is monitor what happens with pregnant women as the disease spreads across Nicaragua.
“The rainy season begins in May,” she said. “So the epidemic is only arriving now in Nicaragua. Then wait nine months and see.”
It’s important to understand what’s happening with Zika now, da Silva said, because inevitably the disease will make the jump to Asia, with its megacities of tens of millions of people.
“You have huge populations living in these large urban centers, millions and millions of people who are at risk of getting dengue, and those same populations are at risk of getting Zika,” he said.
Even if only a small proportion of pregnancies in Zika-infected women in those megacities end with babies having birth defects, it could still be tens of thousands of cases.
Staffing up
Closer to home, state public health officials are leveraging the publicity around Zika to beef up their surveillance and response capacity around bug-borne diseases.
North Carolina was one of the only states in the country to have a small cadre of entomologists, embedded in the Division of Public Health, to track mosquito-borne diseases and other diseases carried by bugs, known as “vector-borne” diseases.
But the vector-borne disease branch was eliminated during budget cutting in 2010 and 2011.
Now the Division of Public Health is looking for two entomologists, one to be based in Raleigh and the other to do fieldwork throughout the state, according to Danny Staley, who heads the division.
Essentially, that’s the same level of staffing as in the older program.
Staley said a number of counties, including New Hanover and Brunswick, have active vector-control programs. Those counties have historically been mosquito hot spots.
Staff go out, either in response to complaints or to known hot spots, he said, and look for birdbaths or containers with larvae.
Staley said spraying has fallen out of favor as the preferred method of mosquito control. Instead, public health interventions are more targeted: Teams go to hot spots, look for larvae, trace the feeding patterns of the mosquitoes and monitor what happens after they apply larvacide or drain waters.
“You can have three or four broods coming off of one container in a day,” Staley said.
He said the newly hired state-level entomologists will coordinate with local departments and will track what’s happening statewide to prepare for “new and novel viruses that are coming our way.”
“Last year, it was chikungunya; a few years earlier, it was West Nile virus,” Staley said.
As happens often in public health efforts, funds get cut when there’s no disease activity; then when there’s an outbreak, agencies scramble to rebuild.
“I will say that North Carolina is not unique in this situation,” Staley said. “In Florida and other states, there are similar situations; programs that were once very popular have faded.”
The entomologist job postings closed last week. Staley said the division is “aggressively” moving to get the new hires in place before North Carolina’s mosquitoes get active.
Republish our articles for free, online or in print, under a Creative Commons license.
