ZIKV: Additional Information on Transmission

 Microcephaly:  Zika virus or Guillain-Barré syndrome?

ZIKV is transmitted primarily by Aedes aegypti mosquitoes (1,7). Aedes albopictus mosquitoes also might transmit the virus. Aedes aegypti and Ae. albopictus mosquitoes are found throughout much of the Americas, including parts of the United States, and also transmit dengue and chikungunya viruses.

In addition to mosquito-to-human transmission, Zika virus infections have been documented through:

• Intrauterine [in mother’s womb, or uterus] transmission resulting in congenital infection
• Intrapartum [during the act of birth] transmission from a viremic mother to her newborn
• Sexual transmission
• Blood transfusion
• Laboratory exposure

There is a theoretical concern that transmission could occur through organ or tissue transplantation, and although Zika virus RNA has been detected in breast milk, transmission through breastfeeding has not been documented.

The Brazil Ministry of Health has reported a marked increase in the number of infants born with microcephaly in 2015, although it is not known how many of these cases are associated with Zika virus infection. Guillain-Barré syndrome also has been reported in patients following suspected Zika virus infection. Studies are under way to evaluate the risks for Zika virus transmission during pregnancy, the spectrum of outcomes associated with congenital infection, and the possible association between Zika virus infection and Guillain-Barré syndrome.

There is no commercially available test for ZIKV. The virus testing is performed in the United States at CDC and four state health department laboratories.

Source: Hennessey M, Fischer M, Staples JE. Zika Virus Spreads to New Areas — Region of the Americas, May 2015–January 2016. MMWR Morb Mortal Wkly Rep 2016;65:55–58. DOI: http://dx.doi.org/10.15585/mmwr.mm6503e1

What is Guillain-Barré syndrome (GBS)?

Guillain-Barré syndrome (GBS) is a rare disorder in which a person’s own immune system damages their nerve cells, causing muscle weakness and sometimes paralysis. GBS can cause symptoms that usually last for a few weeks. Most people recover fully from GBS, but some people have long-term nerve damage. In very rare cases, people have died of GBS, usually from difficulty breathing.

• The background rate for GBS in the U.S. is about 80 to 160 cases of GBS each week, regardless of vaccination.

What causes GBS?

Many things can cause GBS; about two-thirds of people who develop GBS symptoms do so several days or weeks after they have been sick with diarrhea or a respiratory illness. Infection with the bacterium Campylobacter jejuni is one of the most common risk factors for GBS. People also can develop GBS after having the flu or other infections (such as cytomegalovirus and Epstein Barr virus). On very rare occasions, they may develop GBS in the days or weeks after getting a vaccination.