Global health officials are racing to better understand the Zika virus behind a major outbreak that began in Brazil last year and has spread to more than 60 countries.
Zika is transmitted to people through the bite of infected female mosquitoes, primarily the Aedes aegypti mosquito, the same type that spreads dengue, chikungunya and yellow fever. Aedes aegypti mosquitoes are found in all countries in the Americas except Canada and continental Chile. The virus can also be transmitted through sex, from either a male or female partner who has been infected, and a few cases of apparent infection via blood transfusion have been reported.
There is no treatment for Zika infection. Companies and scientists are racing to develop a safe and effective vaccine, but a preventative shot is not expected to be ready for widespread use for at least two or three years.
The US Centers for Disease Control and Prevention concluded that Zika virus infection in pregnant women can cause the birth defect microcephaly. The condition is defined by unusually small heads that can result in developmental problems and other severe brain abnormalities in babies.
The World Health Organization has said the ‘most likely explanation’ is that Zika virus infection during pregnancy is a cause of congenital brain abnormalities including microcephaly. In addition, the agency said that Zika infection in children and adults can trigger Guillain-Barre syndrome, a rare neurological disorder that can result in paralysis.
Brazil has confirmed more than 2,200 cases of microcephaly believed to be linked to Zika infections in pregnant women. It is investigating 3,173 suspected cases of microcephaly.
Current research indicates the greatest microcephaly risk is associated with infection during the first trimester of pregnancy, but health officials have warned an impact could be seen in later weeks. Recent studies have shown evidence of Zika in amniotic fluid, placenta and fetal brain tissue.
People infected with Zika may have a mild fever, skin rash, conjunctivitis, muscle and joint pain and fatigue that can last for two to seven days. As many as 80 per cent of people are infected never develop the symptoms.
Controlling Zika's spread requires eliminating mosquito breeding sites and taking precautions against mosquito bites such as using insect repellent and mosquito nets. US and international health officials have advised pregnant women to avoid travel to Latin American and Caribbean countries, sections of Miami, Florida in the United States and Singapore where they may be exposed to Zika.
They are also advising that men and women who have traveled to Zika outbreak areas use condoms or abstain from sex for six months to prevent sexual transmission of the virus.
Active Zika outbreaks have been reported in more than 60 countries or territories, most of them in the Americas, according to the U.S. Centers for Disease Control and Prevention. Brazil has been the country most affected.
Americas (50): Anguilla, Antigua and Barbuda, Argentina, Aruba, The Bahamas, Barbados, Belize, Bolivia, Bonaire, Brazil, British Virgin Islands, Cayman Islands, Colombia, Costa Rica, Cuba, Curaçao, Dominica, Dominican Republic, Ecuador, El Salvador, French Guiana, Grenada, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Montserrat, Nicaragua, Panama, Paraguay, Peru, Saba, Puerto Rico, Saint Barthelmy, Saint Lucia, Saint Martin, Saint Vincent and the Grenadines, Saint Eustatius, St. Maarten, St. Kitts and Nevis, Suriname, Trinidad and Tobago, Turks and Caicos, United States, US Virgin Islands and Venezuela.
Asia, Oceania and Pacific Islands (10): American Samoa, Fiji, Kosrae, Federated States of Micronesia, Marshall Islands, New Caledonia, Palau, Papua New Guinea, Samoa, Singapore and Tonga.
The Zika virus is found in tropical locales with large mosquito populations. Outbreaks of Zika have been recorded in Africa, the Americas, Southern Asia and the Western Pacific. The virus was first identified in Uganda in 1947 in rhesus monkeys and was first identified in people in 1952 in Uganda and Tanzania, according to the WHO.
Zika has also been associated with other neurological disorders, including serious brain and spinal cord infections. The long-term health consequences of Zika infection are unclear. Other uncertainties surround the incubation period of the virus and how Zika interacts with other viruses that are transmitted by mosquitoes, such as dengue.