The Zika virus is causally linked to microcephaly, the birth defect that leads to abnormally small head size in infants, the U.S. Centers for Disease Control and Prevention declared Wednesday in The New England Journal of Medicine. The agency said it has not found any definitive new evidence but has weighed the accumulating data connecting the two conditions and concluded that it was solid enough to call causative.
Zika infection known as Zika fever, often causes no or only mild symptoms, similar to a mild form of dengue fever. Common symptoms of infection with the virus include mild headaches, Maculopapular rash, fever, malaise, conjunctivitis, and joint pains.
The illness cannot be prevented by medications or vaccines. It is treated by rest.
Zika virus got its name from the Zika forest of Uganda, where the virus was first isolated in 1947. Zika virus is related to Dengue, Yellow fever, and West Nile viruses.
Since the 1950s, Zika virus has been known to occur within a narrow equatorial belt from Africa to Asia. From the year 2013 – 2014, the virus spread eastward across the Pacific Ocean to French Polynesia, New Caledonia, the Cook Islands, and Easter Island, and in 2015 to Mexico, Central America, the Caribbean, and South America, where the Zika outbreak has reached pandemic levels.
Transmission by Mosquito
Zika is spread by daytime-active mosquitoes. It is primarily spread by the female Aedes aegypti mosquitoes .
Transmission Through Sex
Zika can be transmitted from a man to his sex partners. As of April 2016 sexual transmission of Zika has been documented in six countries – Argentina, Chile, France, Italy, New Zealand and the United States – during the 2015 outbreak.
All cases involve transmitting the Zika from men to women and it is unknown whether women can transmit Zika to their sexual partners.
Transmission During Pregnancy
In 2015, Zika RNA was detected in the amniotic fluid of two pregnant women whose fetuses had microcephaly, indicating that the virus had crossed the placenta and could have caused a mother-to-child infection.
As of early April 2016 two cases of Zika transmission through blood transfusion have been reported globally, both from Brazil.
Risk Assessment for Africa
The WHO said though no systematic surveillance has been in place for tracking Zika virus in Africa, sporadic cases have been reported on the continent for many years. The agency added that the virus may be endemic in many parts of the continent where Aedes aegypti, the main vector of the disease, is prevalent.
Though it’s possible that some portion of the African population may have some immunity, the strain spreading rapidly in the Americas may not be known to African populations and could lead to a more acute disease, the WHO warned. “Vigilance must also be maintained.”
In the current outbreak, Cape Verde is the only African nation to report cases, more than 7,000 of them from October through December 2015. However, the WHO said that, based on available data, the number of cases has been declining since December.
All countries in the African region are at risk for Zika virus transmission, because A. aegypti mosquitoes are widely distributed and transmit several arboviruses on the continent. The WHO said the mosquito has adapted to and flourishes in urban settings found in many African cities, where poor water storage and drainage conditions can increase breeding sites for the mosquitoes.
African countries vary in their access to healthcare and disease detection and management, and ones with strong health systems are likely to cope better with a Zika outbreak, according to the WHO. The agency looked at the vulnerability of 47 countries in the region based on composite measures of hazards, vulnerabilities, and lack of coping capacity.
The WHO said all of the countries are at some risk, but it added that nearly half (20) of the countries were categorized as high risk, with Comoros, Guinea-Bissau, Central African Republic, Madagascar, and South Sudan in the top five. The five countries with the lowest risk were South Africa, Namibia, Swaziland, Mauritius, and Ghana.
The agency urged countries to take actions based on its risk assessment. For example, it said high-risk countries should be prioritized for health system support and vector control investments, and lower-risk countries should receive communication and general advisory support.