Zika Virus

Zika virus is a tropical disease that is usually spread by mosquitoes. The symptoms are mild compared to many tropical diseases and include fever, conjunctivitis (pinkeye), rashes, and aching joints. Up to 80% of the people infected show no symptoms at all, but the virus is believed to cause severe birth defects.

The CDC notes that "Brazil has been having a significant outbreak of Zika virus since May 2015. Officials in Brazil have also noted an increase in the number of babies with congenital microcephaly (a birth defect in which the size of a baby’s head is smaller than expected for age and sex) during that time."[1] But they've also stated that "Additional studies are needed to determine the degree to which Zika might be linked with microcephaly." [1]

The disease vector that carries zika virus and transmits it to humans is the mosquito Aedes aegypti. This species is commonly known as the yellow fever mosquito and acts as a vector for dengue and chikungunya as well. They are aggressive biters during the day. Aedes species have a broad geographical range, which has been expanding into more temperate climates over the past few decades, which may be partly attributable to climate change.

Although the mosquito vector is by far the most common route of transmission, Zika can also be spread through infected blood or sexual contact. As with many blood-borne pathogens, transmission from mother to child during birth is possible but rare.

The sexual transmission of Zika will further extend the virus' range into temperate climates.

Currently, there is no medication to cure Zika and no vaccination to prevent it. Cases are usually mild, with symptoms resolving within a week, and are treated like other mild viral illnesses: with rest, fluids, and acetaminophen or ibuprofen. The most effective way to prevent the virus is to avoid or exterminate the mosquito vector. Traditional methods like window screens, mosquito nets, and pesticides should all be employed.

Additionally, engineers are targeting the DNA of Aedes aegypti as a way of programming the mosquitoes to self-destruct. This method of pest control involves genetically modifying males mosquitoes so that their offspring die soon after birth. Experiments on this "self-limiting genetic technology" have been underway since 2014 in areas of Brazil where dengue fever is rampant, and mosquito populations have dropped as much as 80% in those areas [2].

Zika cases in the western hemisphere were first reported in Brazil in May of 2015, and have spread rapidly since. As of early 2016, dozens of countries and territories were affected.

CDC map of Zika virus cases, January 15, 2016. [3]

Zika outbreaks are not new. The virus was first isolated and described in 1947 in Uganda. It has been reported throughout Africa, Southeast Asia, and the Pacific Islands. In May of 2015, the virus was reported in Brazil, and a cluster of rare neurologic disorders followed. Zika's subsequent spread through dozens of countries in the Western hemisphere prompted the World Health Organization (WHO) to declare Zika a "Public Health Emergency of International Concern" on February 1, 2016 [4].

Several Latin American governments have issued statements suggesting women in Zika-affected areas avoid getting pregnant until 2018. In many of these countries, women have limited access to healthcare and particularly to contraception. The United Nations High Commissioner for Human Rights issued a statement on February 5, 2016 that "upholding women’s human rights is essential if the response to the Zika health emergency is to be effective" [5].

Even though most cases of Zika are mild, pregnant women and their unborn children are considered especially high risk patients. Infection with the virus is strongly correlated to severe birth defects including microcephaly, though it has not yet been proven that Zika is the cause of these often fatal abnormalities.

Microcephaly is a condition where infants are born with abnormally small heads and is usually accompanied by irreversible brain damage. Other symptoms may include hyperactivity, poor coordination, seizures, and delayed speech or movement. The WHO expert committee concluded the recent cluster of microcephaly cases in Brazil "constitutes an 'extraordinary event' and a public health threat to other parts of the world" [4].

Illustration showing the difference between an infant with microcephaly and average head size at birth. [6]

Patients infected with Zika are also at risk for developing the autoimmune disease Guillain-Barré Syndrome (GBS). In GBS, the patient's own immune system attacks the peripheral nervous system. Symptoms start with tingling and weakness in the limbs, and can progress to full paralysis.

[1] Centers for Disease Control. Question and Answers: Zika virus infection (Zika) and pregnancy. Retrieved February 20th, 2016, from http://www.cdc.gov/zika/pregnancy/question-answers.html

[2] Carvalho DO, Mckemey AR, Garziera L, et al. Suppression of a Field Population of Aedes aegypti in Brazil by Sustained Release of Transgenic Male Mosquitoes. PLoS Negl Trop Dis. 2015;9(7):e0003864. http://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0003864 Accessed February 10, 2016.

[3] Image from https://commons.wikimedia.org/wiki/File:CDCmapofZikavirusdistributionasof15January2016.png under Creative Commons licensing for reuse and modification.

[4] World Health Organization. WHO Director-General summarizes the outcome of the Emergency Committee regarding clusters of microcephaly and Guillain-Barré syndrome. Retrieved February 10, 2016, from http://www.who.int/mediacentre/news/statements/2016/emergency-committee-zika-microcephaly/en/

[5] UN News Centre. Upholding women’s human rights essential to Zika response – UN rights chief. Retrieved February 10, 2016, from http://www.un.org/apps/news/story.asp?NewsID=53173#.VrrVjJMrLuQ

[6] Image from https://commons.wikimedia.org/wiki/Category:Zika_virus#/media/File:Microcephaly-comparison-500px.jpg under Creative Commons licensing for reuse and modification.