Sickness can cause progressive muscle weakness

The epidemic of an estimated 300,000 to 1 million cases of Zika virus infection in South America was recently declared an international public health emergency by the World Health Organization.

While this virus was first discovered in 1947, it was only the cause of small and sporadic outbreaks in Africa and southeast Asia prior to 2007. Since 2007, the virus has slowly marched across the South Pacific Islands, and it reached South America in 2013 or 2014.

Zika virus is similar to other viruses that are transmitted by mosquitoes, especially West Nile virus, which has spread across the United States since 1999. For both Zika virus and West Nile virus, approximately 80 percent of people have no symptoms of infection and never know they have been infected.

Similarly, approximately 15-20 percent of people who are infected with Zika virus develop fever, muscle and joint aches, rash and generally feel miserable for about five to eight days, much like the syndrome of West Nile Fever.

A small number of patients (believed to be less than 1 per thousand) develop Guillain-Barre Syndrome, which is a neurologic disease with progressive muscle weakness due to interference in the conduction of nerve signals to muscles.

What apparently distinguishes Zika virus infection from other mosquito-transmitted viruses is its ability to cause damage to the brain of infants during pregnancy.

While this is a strong association at the present time and further research is necessary to establish a causative relationship, the 20-fold increase in microcephaly (small head size) and severe neurologic impairment among infants born in Brazil during 2015 remains a unique and unexplained feature that has caused numerous governments to recommend that women delay pregnancy until such time as the epidemic abates or further information is known.

Mosquitoes are the major source of Zika virus spread and most efforts to control the epidemic are focused on mosquito control through environmental spraying and the use of person protection such as mosquito repellents containing DEET, avoidance of mosquitoes, wearing long sleeves and long pants and emptying of standing water that may be a breeding place for mosquitoes. Several research projects are ongoing to use genetically modified mosquitoes that prevent mosquito breeding, and these may offer a unique mechanism of disease control. Sexual transmission of Zika virus has been reported, but this is believed to be a minor mode of transmission.

Even so, public health agencies have recommended that travelers from South American countries with significant Zika virus activity should avoid unprotected sexual contact for a period of 28 days after leaving the areas with Zika virus activity.

The possibility of local transmission of Zika virus in the United States is high, since the mosquitoes capable of spreading Zika virus are present throughout the continental United States. However, local transmission of Zika virus by mosquitoes has not been confirmed in the continental United States at this time.

Until additional information is available, travelers to Central and South America should exercise routine precautions to reduce mosquito exposure while traveling.

LEARN MORE:

Additional information of Zika virus and the epidemic in South America can be found at: www.cdc.gov/zika/index.html.

John A. Vanchiere, M.D., Ph.D. is a professor of pediatrics, chief of pediatric infectious diseases for LSU Health Sciences Center – Shreveport.