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WHO Declares Zika Virus a Global Health Emergency, Sexual Transmission Reported in Texas


The World Health Organization said this month that clusters of microcephaly andneurological disorders including Guillain-Barré syndrome occurring in areas affected by Zika virus -- currently concentrated in Brazil and elsewhere in Central and South America and the Caribbean -- is a Public Health Emergency of International Concern.

Zika virus is transmitted by Aedes mosquitoes, the same species that transmit yellow fever and dengue. The current Zika virus outbreak is centered in Brazil, but prior outbreaks have occurred in Africa, Asia, and the Pacific Islands. Typically the virus causes mild illness with fever, rash, joint aches, and conjunctivitis lasting about a week; a majority of infected people have no symptoms.

However, an unusually large number of cases of microcephaly -- a congenital malformation in which infants have small heads, often accompanied by incomplete brain development -- have been reported in Brazil since the Zika virus outbreak; it is not yet known for sure whether the virus causes the condition. Guillain-Barré syndrome, in which the immune system attacks the nervous system, has been reported during prior Zika virus outbreaks.

"The experts agreed that a causal relationship between Zika infection during pregnancy and microcephaly is strongly suspected, though not yet scientifically proven," said WHO director-general Margaret Chan. "All agreed on the urgent need to coordinate international efforts to investigate and understand this relationship better."

There is currently no vaccine and no known treatment for Zika virus infection, so the best protective measure is to avoid mosquito bites. The U.S. Centers for Disease Control and Prevention (CDC) has issued a travel advisory warning pregnant women about traveling to affected areas. Some affected countries have advised women to delay becoming pregnant until more is known about the link between Zika virus and congenital abnormalities.

"NIAID researchers are working on vaccine candidates to prevent Zika virus infection," National Institute of Allergy and Infectious Diseases director Anthony Fauci said during a January 28 media briefing. "First, a DNA based vaccine using a strategy very similar to what we employed for another virus, the West Nile virus, as this vaccine was found in a Phase 1 trial to be both safe and immunogenic. Second, a live vaccine building on similar and highly immunogenic approaches used for the closely related dengue virus. While these approaches are promising, it is important to understand we will not have a widely available safe and effective Zika vaccine this year and probably not in the next few years."

So far all 35 Zika virus infection cases on the U.S. mainland (as of February 3) have occurred in people who have recently traveled in affected areas, while 9 cases have been locally acquired in U.S. territories including Puerto Rico and the U.S. Virgin Islands.

While most recent cases of Zika virus infection have been due to mosquito bites, mother-to-child and sexual transmission is also possible, according to the CDC. A documented case of sexual transmission was recently reported in Texas.

"There have been isolated cases of spread through blood transfusion or sexual contact and that's not very surprising," CDC director Tom Frieden told CNN. "The virus is in the blood for about a week. How long it would remain in the semen is something that needs to be studied and we're working on that now."

WHO recommends that surveillance for microcephaly and Guillain-Barré should be standardized and enhanced, development of new diagnostics should be prioritized, communication about risk should be enhanced, and mosquito control measures and appropriate personal protective measures should be "aggressively promoted."

"A coordinated international response is needed to improve surveillance, the detection of infections, congenital malformations, and neurological complications, to intensify the control of mosquito populations, and to expedite the development of diagnostic tests and vaccines to protect people at risk, especially during pregnancy," said Chan. However, she added, "the committee found no public health justification for restrictions on travel or trade to prevent the spread of Zika virus.



WHO. WHO statement on the first meeting of the International Health Regulations (2005) (IHR 2005) Emergency Committee on Zika virus and observed increase in neurological disorders and neonatal malformations. WHO statement. February 1, 2016.

MChan. WHO Director-General summarizes the outcome of the Emergency Committee regarding clusters of microcephaly and Guillain-Barré syndrome. WHO statement. February 1, 2016.

WHO. Zika virus fact sheet. Updated January 2016.

CDC. Zika Virus. Updated February 4, 2016.

EE Petersen, JE Staples, D Meaney-Delman, et al. Interim Guidelines for Pregnant Women During a Zika Virus Outbreak -- United States, 2016. Morbidity and Mortality Weekly Report 65(2):30-33. January 22, 2016.

JE Staples, EJ Dziuban, M Fischer, et al. Interim Guidelines for the Evaluation and Testing of Infants with Possible Congenital Zika Virus Infection -- United States, 2016. Morbidity and Mortality Weekly Report 65(3):63-67. January 29, 2016.

CDC Health Alert Network. Recognizing, Managing, and Reporting Zika Virus Infections in Travelers Returning from Central America, South America, the Caribbean, and Mexico. CDC Health Advisory. January 15, 2016.