Zika Resource Center

Zika Resource Center

January 18, 2016
4 min read

CDC: New evidence supports link between Zika virus infection, microcephaly

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During a telebriefing Friday evening, CDC officials said there is strong evidence to suggest that Zika virus infection may increase the risk for microcephaly, and they are recommending that pregnant women postpone travel to areas with ongoing Zika virus transmission.

Early last week, CDC researchers tested samples provided by Brazilian health officials from two pregnancies that ended in miscarriages and from two infants with microcephaly — a condition that affects newborns in which the occipitofrontal circumference is smaller than average — who died shortly after birth. The results showed that Zika virus was present in the brain of both full-term infants. A genetic sequence analysis revealed that Zika virus strains in all four cases were similar to the strain circulating in Brazil. All four mothers reported symptoms of Zika virus during their pregnancies such as a fever and rash.

Lyle Petersen

Lyle R. Petersen

After these reports, the CDC issued a level 2 travel alert for people who plan on visiting countries with heightened Zika virus activity, including Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela and the Commonwealth of Puerto Rico. On Jan. 22, the CDC extended the travel alert to Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde and Samoa.

“We believe this is a fairly serious problem,” Lyle R. Petersen, MD, MPH, director of the CDC’s Division of Vector-Borne Diseases and Infectious Disease News Editorial Board member, said during the telebriefing. “The virus is spreading fairly rapidly throughout the Americas. Because of this growing evidence that there’s a link between Zika virus and microcephaly, which is a very severe and devastating outcome, it [is] important to warn people as soon as possible.”

Credit: CDC

Figure 1. Countries with past or current evidence of Zika virus activity as of January 2016.

Source: CDC

Out of an abundance of caution, the CDC recommends that pregnant women in any trimester should avoid traveling to the affected areas. Pregnant women and women trying to become pregnant who must travel should consult their health care provider and strictly follow steps to prevent mosquito bites, which include the use of mosquito repellents with at least 20% DEET; wearing long-sleeved shirts and long pants; remain in screened or air-conditioned rooms; use a bed net when sleeping in an area exposed to the outdoors; and drain standing water inside and outside the home.

“Because specific areas where Zika virus transmission is ongoing are difficult to determine and likely to change over time, CDC will update this travel guidance as more information becomes available,” Petersen said. “Check the CDC website frequently for the most up-to-date recommendations.”

Zika virus infection in the US

On Friday, the CDC linked a case of microcephaly in Hawaii to Zika virus infection, according to the state’s health department. The mother of the infant likely transmitted the virus during pregnancy when she was residing in Brazil in May 2015. Neither the infant nor the mother are infectious, and there is no risk for Zika transmission in Hawaii, the health department said. The virus typically remains in the bloodstream for less than a week, according to Petersen.

“This case further emphasizes the importance of the CDC travel recommendations,” Sarah Park, MD, state epidemiologist at Hawaii’s Department of Health, said in a press release.

Locally transmitted Zika virus infection has not been reported in the United States outside of the U.S. Virgin Islands; however, cases of Zika virus have been reported in returning travelers, according to the CDC. Fourteen U.S. travelers were infected with Zika virus from 2007 to 2014, and 12 were identified between 2015 and now, Petersen said during the telebriefing.

“We’re not able to predict how much Zika virus will spread in the United States,” Petersen said. “Many areas of the United States have mosquitoes that can become infected with and transmit Zika virus. However, recent chikungunya and dengue outbreaks in the United States suggest that Zika outbreaks in the U.S. mainland may be relatively small and focal.”

Although other mosquito-borne infections such as malaria and dengue used to be widespread in the U.S., Petersen said the use of window screens and state and local mosquito control efforts helped eliminate outbreaks in the mainland.

More studies needed to assess poor outcomes associated with Zika virus infection

According to Brazilian health authorities, more than 3,500 microcephaly cases, including several deaths, were reported in Brazil between October 2015 and January, Petersen said. An unconfirmed increase in microcephaly cases also was observed during an outbreak that occurred in French Polynesia, which affected more than 30,000 people. An initial analysis suggested the risk for Zika virus infection is associated with the first 3 months of pregnancy, according to Brazil’s Ministry of Health. However, there is evidence that the risk can continue into the second trimester, Cynthia Moore, MD, PhD, CDC director for the division of birth defects and developmental disabilities, said during the telebriefing.

“There are many causes of microcephaly,” Moore said. “Some are genetic causes, some are other environmental causes, such as alcohol exposure during pregnancy, and there are other infectious causes of microcephaly. Several viruses can give you pretty much the same picture that we’re seeing now with the babies that have been exposed to Zika virus, so just saying microcephaly or severe microcephaly doesn’t always point you to the cause of the problem.”

To determine the origin of these microcephaly cases, Petersen said some major trials are either planned or are underway. For one study, Brazilian researchers will follow women to assess their pregnancy outcomes. In an upcoming case-control study conducted by the CDC and Brazilian authorities, the researchers will examine a sample of women infected with Zika virus who give birth to babies with or without microcephaly to identify antecedent risk factors.

“We’re hoping another area of our research or inquiry is to figure out exactly how much the risk for women is increased,” Moore said.

Research efforts also will examine an association between Zika virus and Guillain-Barré syndrome, a rare disorder in which the body’s immune system damages nerve cells, causing muscle weakness and occasionally paralysis, according to the CDC. The European Center for Disease Prevention and Control reported that 42 patients in French Polynesia and 121 patients in Brazil with suspected Zika virus infection were diagnosed with Guillain-Barré syndrome.

Disclosure: The researchers report no relevant financial disclosures.

* This article was last updated on Jan. 22.