Now that Zika has established itself in the U.S. mosquito population, it’s likely to prove tough to eradicate.
Like dengue fever, chikungunya, and West Nile Virus that were once seen only as exotic tropical diseases, Zika is likely to become one of the U.S. public health concerns that regularly drive American cities to spray for mosquitoes – the world’s deadliest animal.
“Zika is now here,” Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, said Friday in marking the moment when the virus went from being a concern only of travelers in Latin America and the Caribbean to something that can strike people enjoying their own backyards or a dinner on a restaurant patio.
Frieden had warned members of Congress in February that once the Zika virus took root, it could spread as rapidly as the chikungunya virus did in 2014, when the disease, also carried by mosquitoes, swept across Puerto Rico in just three months.
Zika is now here.
Dr. Tom Frieden, Centers for Disease Control and Prevention
He was more circumspect on Friday when talking to reporters about four new Zika infections in South Florida – the first known cases of the virus being transmitted by mosquitoes in the continental United States. He said he didn’t expect widespread expansion in the United States. But he also stressed that people who live in warm areas where mosquitoes are prevalent should use insect repellent with Deet and wear clothing that covers their arms and legs.
The U.S. arrival of Zika was no surprise to the bug and scientific community. The virus has exploded across the hemisphere, and travel-related cases were being reported daily in the United States. It had been expected in time that a mosquito would be infected and transmit the disease – scientists just didn’t know when.
That it happened in the summer made sense, considering that’s when mosquitoes are most active. Similar summer outbreaks of dengue and chikungunya – which are carried by the same Aedes aegypti mosquito – also occurred in the summer.
And summer is when West Nile Virus outbreaks, spread by a different mosquito species, occur across the United States.
Epidemiologists say they can’t be certain that the four South Florida cases are the only locally acquired cases in the United States. A major challenge of identifying the Zika virus is that the symptoms are so mild. They include a fever, headache and possible red eyes. But most people don’t ever realize they have the disease.
The uncertainly about the virus has only fueled fears, particularly among expectant mothers – the mild disease represents a major threat to their unborn children. Zika has been linked to a huge increase in the incidence of microcephaly in newborns that results in a smaller-than-normal head and an underdeveloped brain. Brazil has reported more than 4,000 incidents of the defect in the months since Zika was first detected there. A dozen microcephalic babies have been linked to Zika infections in the United States.
History shows that Zika likely will be part of our lives for the foreseeable future.
Paul D. Roepe, co-director of the Center for Infectious Disease at Georgetown University, points to the sporadic outbreaks of dengue and chikungunya, both of which also are carried by the Aedes aegypti mosquito.
I would bet you a $100 is going to turn out very similar to the stories that we’ve seen played out over the last decade or so with dengue and West Nile.
Paul D. Roepe, Center for Infectious Disease at Georgetown University
Chikungunya was discovered in about 450 people who traveled through Florida in 2014. Eleven people contracted the virus in Florida. Dengue fever struck Key West in 2009, infecting 27 people, and again in 2011, infecting 66 people.
But there are still many unknowns about Zika, including whether it can be spread by other animals, as birds carried West Nile virus across the United States.
West Nile first appeared in New York City in 1999. It then spread south and west, becoming endemic in the lower 48 states, where it has killed more than 1,700 people.
Scientist are cautious about making comparisons between West Nile virus and Zika. For one, the two viruses are spread by different species of mosquito – West Nile’s host is the Culex group. For another, birds are major sources of West Nile virus, providing a huge population of potential sources for mosquito infection. Mosquitoes and humans are the only known animals to have been involved in the spread of Zika.
Chris Barker, an epidemiologist with the School of Veterinary Medicine at the University of California, Davis, said he believes the spread of Zika will be limited because the Aedes aegypti mosquitoes that are most likely to spread it are dependent on warm wet conditions that exist in most of the United States only in the summer.
Air conditioning and window screens will help limit its spread, he said.
But Roepe said another concern is if Zika takes hold in other Aedes mosquitoes, such as the albopictus variety, a tough species that thrives not only in warm and moist climates, but also can survive snow and other intemperate weather.
“Like any other infectious disease expert, we study history very, very closely,” Roepe said. “This story I would bet you $100 is going to turn out very similar to the stories that we’ve seen played out over the last decade or so with dengue and West Nile.”