First Human Cases of Mosquito-Borne Disease Found in the United States

Three states — North Carolina, Idaho and Rhode Island — reported the first cases of an unusual mosquito-borne disease in the United States this summer, Centers for Disease Control and Prevention officials said Thursday.

The three individuals, who did not have any known interactions with each other, were acquired from single pools of stagnant water. Each case involved at least one mosquito-born encephalitis virus. Two of the three patients were children and had no previous history of health problems. The other patient was an adult, reported by local health officials.

An unusual cluster of cases in North Carolina is of particular concern, the CDC said, as the state has been found to be among the best at containing this kind of encephalitis virus. The state has recorded three previous human cases of the disease between 2012 and 2016.

“West Nile virus virus has long been a challenge in North Carolina,” said Patricio Caceres, a retired CDC expert in encephalitis and associated viruses who is currently a professor at the University of North Carolina. (Caceres is not affiliated with the current investigation.) “But we may have perhaps the best immunology on the scale of the country, with more people equipped to act quickly and act definitively in response to infections — even when they’re relatively rare.”

Illnesses connected to mosquitoes and places where mosquitoes do not like to bite are exceptionally rare, and many of the cases reported so far involve only one infected mosquito. More than two dozen places — including Florida, Louisiana, Maryland, Louisiana, Mississippi, Missouri, New York, Oregon, Texas, Pennsylvania, Virginia and Washington, D.C. — continue to monitor and treat for these kinds of incidents.

The most deadly and widespread threat from mosquitoes in the United States comes from a species known as the Western Culex mosquito. This mosquito is the main vector for the Zika virus, although it has not been linked to that disease. In recent years, mosquito-borne illnesses have also been linked to dengue, chikungunya and yellow fever.

Much of the current focus on insect-borne diseases in the United States will center on Zika. As previously reported by The New York Times, the virus has been found in the brains of people infected in the United States, although it does not affect their neurological functions. The virus also remains highly resistant to vaccine.

For now, the current outbreak of Zika in Florida is less the primary issue and more an inconvenience for tens of thousands of Americans. The first wave of reported cases in Broward County in South Florida in July was considered relatively mild, leading local officials to announce a few days ago that the outbreak had been contained. Since then, though, Broward officials have stepped up their communications with the public and opened two call centers, where residents can report cases of disease. “More and more, it’s really a way to get people more involved,” Nancy Bordeaux, Broward County’s public health director, told The New York Times.

An outbreak is occurring elsewhere in the country. And it’s nowhere near over yet. CDC officials anticipate three to four cases of the Zika virus for each person infected, which could mean a total of 100 people infected each month. (By comparison, an outbreak in Florida of West Nile virus, which causes encephalitis, killed 17 people and infected about 300 in 2014.) This outbreak has also prompted health officials in Australia and other parts of the southern hemisphere to increase surveillance efforts and quarantine efforts on some animals.

Although Florida currently leads the nation in the spread of Zika, mosquito-borne infections in the United States do not mean the issue is over. “In the event of an outbreak anywhere in the country, we know we’ll have to work very quickly,” said Erin Chilcoat, a CDC spokeswoman.

The country’s current lead on mosquito-borne diseases has begun to change as new areas of the country have taken action to prevent their spread. State and local efforts to tackle the problem will continue.

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