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Americas battle Zika virus
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Health authorities in the Americas are on alert as mounting evidence suggests that Zika virus infection — a usually asymptomatic and mild disease that is increasing in the Western Hemisphere — may be responsible for thousands of birth malformations and neurological syndromes.
In a recent statement, WHO Director-General Margaret Chan, MD, declared a cluster of microcephaly and neurological complications in countries reporting Zika virus outbreaks a Public Health Emergency of International Concern and called for a coordinated international response to contain the epidemic.
Although Zika virus is primarily transmitted through the bite of an infected mosquito, the CDC recently determined the virus also can be acquired through sexual contact. These findings are supported by two previously published case studies.
Zika virus was first detected in the Americas in February 2014, according to WHO. Last year, outbreaks were reported in Cape Verde, Brazil and Colombia. Since then, the virus rapidly spread to the United States Virgin Islands, Dominican Republic, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela, the Commonwealth of Puerto Rico, Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana and Samoa.
As Zika virus continued to escalate in Brazil, the country’s Ministry of Health reported an unusual increase in the number of cases of microcephaly — a condition that affects newborns in which the occipitofrontal circumference is smaller than average. Brazilian health authorities linked the rare neurological condition to Zika virus after they discovered Zika RNA in blood and tissue samples from an infant born with microcephaly who died. As of mid-January, the country reported nearly 4,000 suspected cases of microcephaly, including several deaths.
CDC officials confirmed that there is strong evidence to suggest Zika virus infection may increase the risk for microcephaly, and recommended that pregnant women postpone travel to areas with ongoing Zika virus transmission. During a telebriefing, Lyle R. Petersen, MD, MPH, director of the CDC’s Division of Vector-Borne Diseases and an Infectious Disease News Editorial Board member, said an unconfirmed increase in microcephaly also was observed during an outbreak that occurred in French Polynesia, which affected more than 30,000 people.
“We believe this is a fairly serious problem,” Petersen said. “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.”
In addition, the virus has been associated with a steep rise in Guillain-Barré syndrome (GBS), a rare disorder in which the body’s immune system damages nerve cells, causing muscle weakness and occasionally paralysis. Several countries with heightened Zika virus activity such as French Polynesia, Brazil, Venezuela and El Salvador have reported an abnormal number of GBS cases, according to the European Center for Disease Prevention and Control.
The Pan American Health Organization (PAHO) anticipates that Zika virus transmission will eventually spread to every country in the Americas where the Aedes aegypti mosquito vector is found, which includes all regions except for Canada and continental Chile.
“One of the interesting things about this outbreak, especially if you compare it to other ones such as the West Nile outbreak in 1999 or even when chikungunya came to the Caribbean in 2013, is that Zika virus has exploded,” Shannan Rossi, PhD, predoctoral fellow from the Institute for Human Infections and Immunity at the University of Texas Medical Branch, told Infectious Disease News.
Rossi warned that transmission may surge during the upcoming rainy reason. Moreover, Chan said conditions accompanying this year’s El Niño weather pattern could further increase the global mosquito population.
“In the next couple of months, I really think we’re going to see a lot more countries declaring themselves to have Zika outbreaks,” Rossi said. “We’re just seeing the tip of the iceberg now.”
Countries attempt to control Zika outbreaks
At this time, health officials representing some Zika-endemic countries such as Brazil and El Salvador have advised women to delay pregnancy. Although there have been no locally transmitted cases in Jamaica, the country’s Ministry of Health also advised women to postpone pregnancy for 6 to 12 months, if possible.
“Given how quickly the outbreak is moving, it doesn’t surprise me that Jamaica has already made this announcement,” Rossi said. “These countries are put in a bit of a pickle. If they say there’s no need to worry, and then the link [between Zika virus infection and microcephaly] does turn out, they don’t want to be caught behind the eight ball. You don’t want to seem unsympathetic, but you also don’t want to cause undue alarm.”
The CDC held two news conferences to address the growing epidemic, but said the risk for a widespread outbreak of Zika virus would be minimal in the United States. So far, the U.S. is free of local transmission outside of the Virgin Islands; however, there has been one case of microcephaly possibly linked to Zika virus in Hawaii, and more than 30 Zika virus infections were reported in the U.S. among returning travelers, including pregnant women, since 2015.
“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.”
Nevertheless, President Barack Obama recently emphasized the need for rapid developments in diagnostics, vaccines and therapeutics. Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, reported that NIAID researchers are working on two vaccine candidates to prevent Zika virus infection.
“We already have existing vaccine platforms to use as a sort of jumping off point,” Fauci said during one of the CDC news conferences. “First, a DNA-based vaccine using a strategy very similar to what we employed for ... the West Nile virus. This vaccine was found in a phase 1 trial to be both safe and immunogenic. Second, a live-attenuated vaccine building on similar and highly immunogenic approaches used for the closely related dengue virus.”
More evidence needed
Despite recent reports, many researchers say more data is needed to confirm that poor health outcomes are associated with Zika virus infection.
“So far, what we don’t have is the smoking gun link between Zika virus infection and the outcome of microcephaly in infants,” Rossi said. “With a little bit more research on the bench, it is probably going to turn out to be the case.”
An initial analysis in pregnant women suggested the risk for Zika virus infection is associated with the first 3 months of pregnancy, Brazil’s Ministry of Health reported. However, there is evidence that the risk can continue into the second trimester, according to Cynthia Moore, MD, PhD, director for the Division of Birth Defects and Developmental Disabilities at the CDC.
“There are many causes of microcephaly,” Moore said during the telebriefing. “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.”
The condition also may be triggered by rubella infection in nonimmune pregnant women, Andrew Bonwit, MD, division of pediatric infectious diseases at Loyola University Medical Center, told Infectious Disease News.
“That would be the main thing that I would be concerned about,” he said.
To further investigate Zika virus, 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, 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.
Another area of research is to determine whether the risk for Zika virus is increased in women, Moore said.
“The level of concern is high, as is the level of uncertainty,” Chan said during a WHO briefing. “Questions abound. We need to get some answers quickly.” – by Stephanie Viguers
- References:
- DCHHS. DCHHS Reports First Zika Virus Case in Dallas County Acquired Through Sexual Transmission. http://www.dallascounty.org/department/hhs/press/documents/PR2-2-16DCHHSReportsFirstCaseofZikaVirusThroughSexualTransmission.pdf. Accessed February 2, 2016.
- Foy BD, et al. Emerg Infect Dis. 2011;doi:10.3201/eid1705.101939.
- Lucey DR, et al. JAMA. 2016;doi:10.1001/jama.2016.0904.
- Musso D, et al. Emerg Infect Dis. 2015;doi:10.3201/eid2102.141363.
- Petersen EE, et al. MMWR Morb Mortal Wkly Rep. 2016;65:30-33.
- Schuler-Faccini L, et al. MMWR Morb Mortal Wkly Rep. 2016;65:59-62.
Disclosure: The researchers report no relevant financial disclosures.