The Zika virus, on the wings of Aedes mosquitoes, has spread rapidly throughout the Americas, prompting the World Health Organization (WHO) to declare the virus a World Health Emergency. Just how worried should you be about Zika, and how much of a danger does the virus pose to you and your family?
Fortunately, for most otherwise healthy children and adults, an infection with Zika virus (resulting in acute Zika virus disease) is usually mild. Indeed, as many as 75% of those infected with Zika experience no symptoms at all. For the remaining 25% who do develop symptoms, as described by the Centers for Disease Control and Prevention in its Morbidity and Mortality Weekly Report (MMWR), the symptoms of acute Zika virus disease include fever, rash, conjunctivitis (eye inflammation), and arthralgia (joint pain). Although these symptoms can be unpleasant, they are usually self-limiting and do not require aggressive treatment. Symptoms typically last several days to a week.
Currently, in the United States, Zika virus is also very difficult to acquire. The virus is transmitted primarily by mosquito bite, although sexual transmission has also been reported (the virus was found in the semen of an infected man as much as two months after he became infected). Your doctor might suspect Zika virus infection if you have traveled to a region where Zika virus is present and report any of the symptoms described above in the two weeks following your trip. This is because, whereas the incubation period for Zika virus infection is not exactly known, it is thought to be approximately two weeks, with symptoms usually developing 2-10 days after infection.
Zika virus is not currently endemic to the mosquitos of the United States, meaning that the virus is not circulating in the United States. There have been zero cases of locally acquired, mosquito vector-borne Zika virus infections in the United States as of February 2016. Although it is possible that Zika could spread in the United States, many experts consider such spread to be unlikely. This is because the closely related Degue virus, which is also spread by Aedes mosquitoes, has never become endemic to the United States.
Though the fact that Zika usually causes mild disease and the fact that is unlikely to be acquired in the United States is reassuring, Zika should not be dismissed entirely. Indeed, the virus can in fact be dangerous to women who are pregnant, and that is because the virus has been associated with microcephaly in the fetuses of women who are infected. Microcephaly is a neurodevelopmental disorder marked by small head circumference; the condition typically indicates that a baby’s brain has not developed fully. In severe cases of microcephaly, a baby may be severely developmentally delayed and/or severely intellectually disabled.
Because of its potential association with microcephaly, pregnant women and their sexual partners are strongly encouraged to avoid exposure to Zika virus and to mosquito bites for the duration of pregnancy. Because it has been reported that Zika can be transmitted through intercourse, it is also recommended that men who may have been exposed to Zika virus wear condoms during sex with their female partners who are or may become pregnant.
Although microcephaly is perhaps the most worrisome condition that may be caused by Zika virus infection, acute Zika virus disease has also been associated with development of Guillain-Barré syndrome. Guillain-Barré syndrome is a condition in which the body’s immune system attacks the nervous system, resulting in progressive muscle weakness. Symptoms of Guillain-Barré usually start as weakness and tingling in the lower extremities that can gradually spread up the rest of the body. In severe cases, Guillain-Barré syndrome can result in paralysis. Treatments for Guillain-Barré syndrome can include blood plasma exchange and immunoglobulin therapy, which is intended to lessen the immune response that the body has produced against the nerves. Sufferers of Guillain-Barré syndrome often require physical therapy as a result of the condition’s neurological effects.
While Zika virus may seem like a new virus, it has actually been known since 1947. The virus was first identified in a monkey near the Zika Forest in Uganda, which lends the virus its name. Zika first moved outside of Africa in the late 2000s and 2010s, causing outbreaks in Yap Island and French Polynesia. Cases of Zika virus infection were not identified in the Americas until May 2015, when an outbreak occurred in Brazil. The virus is thought to have been imported to Brazil from Asia during the 2014 World Cup. Since then, Zika virus has spread to an additional 22 countries in the Americas.
Zika virus is a flavivirus, making it a close relative of yellow fever virus, dengue virus, Japanese encephalitis virus, and the more familiar West Nile virus. The virus circulates in Aedes sp. mosquitoes, enabling human-to-human transmission. It is not currently known whether Zika virus has a non-human reservoir host that it infects, although a reservoir host is likely. Other flaviviruses typically have reservoir hosts including monkeys and birds.
The fortunate thing about Zika’s being a flavivirus is that vaccines to other flaviviruses already exist; making genetic alterations to those vaccines in order to create a vaccine that may protect against Zika is not particularly difficult. As a result, it may be possible to have a Zika vaccine ready for human trials by the end of 2016.
Knowing what effects Zika virus can have and a bit of the history of the virus is certainly helpful for avoiding unnecessary panic, but Zika virus absolutely deserves the attention it has been getting. Zika will be one of the major public health stories to watch in 2016.