Zika, a mosquito-borne virus that arrived in Brazil in May 2015, has since spread into 17 other countries in the Americas. Until October, Zika was not thought much of a threat: only a fifth of infected people fall ill, usually with just mild fever, rash, joint aches and red eyes. Since then, though, evidence has been piling up that it may cause birth defects in children and neurological problems in adults. On January 15th America’s Centres for Disease Control and Prevention (CDC) advised pregnant women not to travel to countries where Zika is circulating.
There are two factors for rapid transmission (documented in other countries): (1) Since this is a new virus to the Americas, the entire population is susceptible, lacking defenses to Zika virus; and (2) The Aedes mosquito is widespread in the Region, given the climatic conditions, temperature, and humidity in tropical countries.
Countries begin reporting when they detect the circulation of the virus in their territories. However, maintaining a case count is difficult because symptoms of the disease tend to be mild and not everyone affected is seen by health services.
The virus was first isolated in 1947, from a monkey in the Zika forest in Uganda. Since then it has caused small and sporadic outbreaks in parts of Africa and South-East Asia. In Brazil, for reasons yet unclear, it quickly flared into an epidemic after its arrival, infecting as many as 1.5m people.
The yellowfever mosquito Aedes aegypti. For info: This image is a work of the Centers for Disease Control and Prevention, part of the United States Department of Health and Human Services, taken or made as part of an employee’s official duties. As a work of the U.S. federal government, the image is in the public domain. https://en.wikipedia.org/wiki/Zika_virus#/media/File:Aedes_aegypti_CDC-Gathany.jpg
In Brazil, forty-nine babies with suspected microcephaly (babies born with a small head) have died. In five of these cases an infection with Zika virus was found.
The most common symptoms of Zika virus infection are mild fever and exanthema (skin rash), usually accompanied by conjunctivitis, muscle or joint pain, and general malaise that begins 2-7 days after the bite of an infected mosquito.
Zika virus is transmitted to people through the bite of an infected Aedes mosquito. In general, the Zika virus needs a vector (a means of transportation) to infect people. That vector is the mosquito. Zika can be transmitted through blood, but this is an infrequent mechanism.
Treatment consists of relieving pain, fever, and any other symptom that inconveniences the patient. To prevent dehydration, it is recommended to control the fever, rest, and drink plenty of water. There is no vaccine or specific drug for this virus.
Anyone not previously exposed to the virus and who lives in an area where the mosquito is present, and where imported or local cases have been reported, may be infected. Since the Aedes mosquito is found throughout the Region (except in continental Chile and Canada), it is likely that outbreaks will occur in other countries that have not yet reported any cases.
Prevention
Prevention involves reducing mosquito populations and avoiding bites, which occur mainly during the day. Eliminating and controlling Aedes aegypti mosquito breeding sites reduces the chances that Zika will be transmitted. An integrated response is required, involving action in several areas, including health, education, and the environment.
To eliminate and control the mosquito, it is recommended to:
- Avoid allowing standing water in outdoor containers (flower pots, bottles, and containers that collect water) so that they do not become mosquito breeding sites
- Cover domestic water tanks so that mosquitoes cannot get in
- Avoid accumulating garbage: Put it in closed plastic bags and keep it in closed containers
- Unblock drains that could accumulate standing water
- Use screens and mosquito nets in windows and doors to reduce contact between mosquitoes and people
To prevent mosquito bites, it is recommended that people who live in areas where there are cases of the disease, as well as travelers and, especially, pregnant women should:
- Cover exposed skin with long-sleeved shirts, trousers, and hats
- Use repellents recommended by the health authorities (and apply them as indicated on the label)
- Sleep under mosquito nets
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