Zika virus, the latest mosquito-borne virus to hit the United States, joins a long list of other infections the insects can carry, like malaria, dengue fever, chikungunya and West Nile.
“Mosquitoes literally drink blood, and by doing so ingest microbes directly and can pass them directly into the bloodstream of others,” says Dr. Amesh Adalja, an infectious disease physician at the University of Pittsburgh Medical Center’s Center for Health Security. “They are very mobile and can move over distances a few miles allowing them to have some trajectory in finding their blood meals and spreading disease in the process.”
It’s the female mosquitoes we really have to worry about, since they’re the ones that ingest blood, which provides nutrition needed for their eggs.
In 33 years of practice, Rio de Janeiro obstetrician and gynecologist Isabella Tartari Proenca has helped countless expectant mothers through the anxieties of pregnancy and childbirth. But ever since an exotic virus called Zika hit Brazil a few months ago, she’s run out of assurances. “I get calls and text messages all day long,” Tartari told me. “My patients are terrified.”
Since May, when the national health ministry confirmed the first cases of Zika virus, the mosquito-borne disease has swept the country, infecting at least half a million people. While most victims escape with a low-grade fever, skin rashes and achy joints, some dire complications have ensued. Suspected to be among them is microcephaly, a condition that leads to exceptionally small infant head size, which causes lasting neurological damage and can lead to death.
Zika has since spread across Latin America. By Dec. 22, Brazilian authorities had confirmed 2,782 cases of microcephaly this year, a fivefold increase over the yearly average since 2010; 80 babies whose mothers tested positive for Zika were stillborn or died shortly after birth.
According to Janet McAllister, an entomologist with the U.S. Centers for Disease Control and Prevention (CDC), not all mosquitoes are good at transmitting disease, but the ones that are have evolved to live closer to humans. “Some of these species have even developed a preference for feeding on humans over other animals,” she says. “Mostly, those that will bite humans have become very good at taking blood from us without us noticing. Some prefer to bite at night when we are sleeping. Others, those that bite during the day or early evening, have chemicals in their saliva that allow them to bite without us noticing it right away. That way, they can get their meal and leave more disease-causing organism before the itching starts.”
Diseases spread by insects “are the next big threat to the Western Hemisphere, including the U.S.,” said Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston.
Dengue, chikungunya and Zika are spread by the same species of mosquito known as the Aedes and can be found in much of the USA, said Amesh Adalja, a senior associate at the Center for Health Security at the University of Pittsburgh Medical Center.