Assistant Professor of Microbiology
Icahn School of Medicine at Mount Sinai
Zika virus has made a worldwide media splash in the last few years following reports out of Brazil that it was linked to a spike in babies born with severe brain damage called microcephaly. Though media attention has diminished, Zika still poses a threat to many countries, including the United States. There is no cure for Zika, but with the start of the mosquito season, being informed and taking precautions can help people avoid this potentially devastating viral infection.
Zika virus is a mosquito-transmitted pathogen closely related to West Nile, yellow fever, and dengue viruses. First identified in 1947 in monkeys in Africa, it caused little disease in humans until 2007, when a few dozen cases broke out on the Micronesian island of Yap. A few years later, it spread across the Pacific Islands and then to South America. Zika virus only recently started causing large outbreaks, most famously in Brazil.
Zika virus spreads to humans primarily through the bite of infected mosquitoes. But, unlike similar viruses, Zika can also be transmitted through unprotected sex with someone who is infected, even if they don’t have symptoms, and can pass from a pregnant woman to her fetus.
Anybody who lives in or travels to an area with active mosquito transmission of Zika virus or has sexual contact with individuals who have traveled to Zika-affected areas is at risk: Mexico, South and Central America, the Caribbean, and many other regions—including parts of the United States. In 2016, 224 cases of Zika virus disease, presumably transmitted by local mosquitoes, occurred in areas of Florida (Miami-Dade County) and Texas (Brownsville). The virus is also endemic in the U.S. territories, including Puerto Rico, where more than 36,000 cases arose last year. Many additional cases in the continental United States have been associated with travelers who have returned from places where Zika virus is active.
What health problems can it cause?
Death from Zika virus is exceedingly rare, but infection can still have severe health consequences:
Birth Defects. If a woman is infected during pregnancy, Zika virus can cause serious birth defects, like microcephaly and other brain abnormalities. Microcephaly is a condition where a baby is born with an unusually small head due to stunted growth and destruction of brain tissue in utero. It is associated with a significant delay in physical and intellectual development, including impairments in learning, hearing, and vision. Microcephaly is a severe outcome, but not every child whose mother is infected during pregnancy will be born with a birth defect.
Miscarriage. Infection during the beginning of the first trimester may result in miscarriage so early that women don’t know they are pregnant.
Developmental Issues. In babies born with no signs of birth defects, there may be a milder spectrum of adverse outcomes that we don’t know about yet, possibly in the areas of learning and social behavior. These types of problems don’t show up on an ultrasound and may only become apparent years later.
Male Fertility. There is evidence that the virus might impact male fertility, as it can persist in the testes and seminal fluid for months after recovery from symptoms.
Guillain-Barré Syndrome. Infection with Zika virus can also cause Guillain-Barré syndrome, a condition where the body’s immune system attacks nerve cells, resulting in muscle weakness and sometimes paralysis.
What are the symptoms of Zika infection?
Most people don’t have symptoms and thus don’t realize they are infected. When symptoms occur, they are mild and not specific to Zika, such as a fever, rash, or headache. A health care provider can order a blood or urine test to confirm infection for anyone concerned about Zika virus.
Unfortunately, no medicine is available yet to fight the virus. Most people will recover from Zika’s symptoms within a week. Researchers are working to develop therapies to treat it, as well as a vaccine to prevent it.
Rethink travel plans. The most effective way to prevent infection is to avoid traveling to areas where Zika virus is known to exist. The Centers for Disease Control and Prevention (CDC) website provides a world map showing locations where Zika is spreading, along with travel guidance for pregnant women and couples who are planning to conceive in the near future.
Protect yourself from mosquitoes. If you do go to Zika-affected areas, follow typical guidelines for avoiding mosquito bites, which include using insect repellent and wearing long sleeves and pants.
Practice safe sex. If you have sex with a partner who has spent time in an area with Zika, use condoms for protection. For couples who want to conceive, the CDC advises that they wait eight weeks if the woman was exposed to Zika and six months if the man was exposed to the virus.
What else should I know about Zika?
A study that my colleagues and I recently conducted at the Icahn School of Medicine at Mount Sinai suggests that prior infection with a virus related to Zika, such as West Nile or dengue, may put you at risk for developing worse Zika virus disease. We found that, compared with mice that were exposed to Zika virus alone, mice that were first injected with dengue or West Nile virus antibodies and then infected with Zika displayed a major increase in mortality and symptoms, and an overall worsening of Zika disease, including more virus in their blood, as well as the spinal cord and testes, organs known to be involved in Zika virus disease in humans.
Our results may explain why the Zika outbreak is causing such serious birth defects in South America; almost everyone there has previously been infected with dengue virus and thus has antibodies against it. Dengue is not a problem in the United States, but West Nile, which is spread by a different type of mosquito than the one that transmits Zika, is found in nearly every state. As we approach the months where the most West Nile virus activity is observed in the United States—July, August, and September—doctors and other health care providers need to pay close attention to people who have a history of West Nile virus infection due to its potential to enhance Zika virus disease. And everyone should protect themselves from mosquito bites.