U.S. mosquitoes now spreading Zika virus

The infections occurred in Miami, Florida
Jul 29, 2016 — 4:53 pm EST

A virus researcher works with Zika samples at the National Institute of Allergy and Infectious Diseases Vaccine Research Center. 

NIAID/ FLICKR (CC BY 2.0)

Four new cases of Zika infection have turned up in Florida residents who could not have caught the disease during foreign travel. They also were not exposed to others sick with the disease. That suggests they had to pick up the virus while living at home — from local mosquitoes.

Florida’s health department made the unsettling announcement on July 29.  These cases would be the first due to local mosquitoes in the continental United States.

“Zika is now here,” Tom Frieden said at a news briefing the same day. Frieden directs the U.S. Centers for Disease Control and Prevention in Atlanta, Ga.

No trapped mosquitoes have yet tested positive for the virus. Still, health officials suspect that mosquitoes within a small region in north Miami are to blame. “Everything we’ve seen so far indicates that this is mosquito-borne transmission,” Frieden said.

The local mosquitoes include Aedes aegypti (AY-dee E-JIP-tye). This is the same species that has been spreading the virus throughout Latin America. Florida’s small cluster of cases does not mean an epidemic is coming, Frieden said. The four infected people probably were bitten in early July.  Since then, Florida has stepped up efforts to stamp out mosquitoes. People have been going door-to-door to get rid of standing water, where mosquitoes can lay their eggs. Public health teams also have been spraying bug killers.

“We believe that widespread transmission in the continental U.S. is unlikely,” Frieden said. “But it’s not impossible.”

Two other mosquito-borne diseases, dengue and chikungunya, have spread locally in Florida in the past. But, Frieden noted, those diseases generally die out after infecting just one person.

Power Words

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Aedes aegypti    A species of mosquito that can transmit the viruses responsible for several tropical diseases, including dengue fever, yellow fever and West Nile disease.

Centers for Disease Control and Prevention, or CDC    An agency of the U.S. Department of Health and Human Services, CDC is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. It does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.

chikungunya    A tropical disease that has been crippling large numbers of people in Africa and Asia. It’s caused by a virus that is spread by mosquitoes. It recently has been spreading widely throughout warm nations. More than 3 million people have suffered through its initial flu-like symptoms. A large share may also go on to develop intense pain in their muscles and joints that can last months to years. There is no cure or vaccine.

continental United States     Also known as the lower 48 states, these are all U.S. states except Alaska and Hawaii. They all reside below Canada and above Mexico.

dengue    A potentially lethal infectious disease transmitted by mosquitoes. No vaccine yet exists to prevent infection with the virus responsible for the disease, which causes high fevers, severe headache, joint pain, pain behind the eyes, rash, bone pain and sometimes mild bleeding. A more severe form of the disease, known as dengue hemorrhagic fever can cause uncontrolled bleeding if not treated right away.

epidemic   A widespread outbreak of an infectious disease that sickens many people (or other organisms) in a community at the same time. The term also may be applied to non-infectious diseases or conditions that have spread in a similar way.

infection   A disease that can spread from one organism to another.

Latin America     Nations in the Americas south of the United States, most of which now speak Spanish as their native tongue. The major exception within this region: Brazil, which speaks Portuguese.

test positive   A term that indicates that some test has confirmed what it was looking for, such as a disease or poison.

transmission     (In medicine) To spread a disease or toxic agent.

virus     Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.

Zika virus     A virus that can be transmitted to humans via mosquitoes. About 20 percent of infected people get sick. Symptoms include a slight fever, rash and pinkeye and usually fade quickly. A growing body of evidence suggests that the virus could also cause a devastating birth defect — microcephaly. Evidence suggests it may also cause neurological conditions such as Guillain-Barré syndrome.

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