Insights into Zika Virus History, Human Health Effects, and Control Measures

EnvironmEntal HEaltH insigHts 2016:10 Zika virus is named for the Zika Forest in Uganda and was first discovered in 1947 in primates. The first human cases of Zika virus infection were detected in 1952. From about 1960– 1980, human infections occurred across Asia and Africa, although infections were typically mild with limited symptoms. The first major human outbreak occurred in Micronesia in 2007. Zika was linked to a neurological disorder (GuillainBarré syndrome, or GBS) during a 2013–2014 outbreak in French Polynesia. In May 2015, the first human cases were reported in Brazil and a link to GBS was also reported. Other symptoms of Zika infection include rash, fever, conjunctivitis and joint pain. Only approximately 20% of infected individuals experience clinical symptoms (http://www.cdc.gov/zika/ symptoms/symptoms.html). Brazil reported an association between Zika viral infections and microcephaly in October 2015. Microcephaly is a disorder in which the head of a newborn child is disproportionally small relative to the body. It may result from a variety of chromosomal and environmental causes, including drug, alcohol, or radiation exposure and prenatal infections (rubella, herpes simplex, and likely Zika virus) (Merck Manual, 2016). As of August 3, 2016, evidence of mosquito-borne Zika virus transmission has been reported in 68 countries and territories and 14 countries or territories have reported microcephaly and other central nervous system (CNS) malformations associated with Zika virus. As of August 3, 2016, evidence of mosquito-borne Zika virus transmission has been reported in 68 countries and territories and 14 countries or territories have reported microcephaly and other central nervous system (CNS) malformations associated with Zika virus. From January 1, 2015 through September 7, 2016, there have been 2,920 U.S. travel-associated cases reported, 43 locally-acquired mosquito-borne cases reported and one laboratory acquired case reported for a total of 2,964 cases (24 sexually transmitted and seven with GBS association) (http://www.cdc.gov/zika/about/overview.html and http:// www.who.int/emergencies/zika-virus/timeline/en/). At the time of this report, all U.S. states except for Wyoming had confirmed traveler-related Zika virus cases. The first U.S. case of locally-transmitted (victim did not travel) mosquito-borne Zika virus was reported in Miami, Florida on July 29, 2016 and all local U.S. cases (as of September 7, 2016) have been restricted to the state of Florida. The U.S Territories of Puerto Rico, American Samoa and the U.S. Virgin Islands have reported (as of September 7, 2016) 15,809 local and 60 travel-associated cases of Zika virus infection. Zika virus is primarily spread through the bite of an infected mosquito of the species Aedes aegypti (the yellow fever mosquito) or Ae. albopictus (the Asian tiger mosquito). Maps showing the approximate distribution of these species in the U.S. show that Ae. albopictus is more widespread than Ae. aegypti, although caution is advised in interpretation, since mosquito surveillance may be inadequate in some areas (Hahn, et al. 2016). These species of mosquitoes lay eggs primarily in artificial containers holding standing water. Aedes aegypti females prefer to blood feed on humans, while Ae. albopictus females are opportunistic feeders, blood feeding on a variety of hosts, including humans. Both Ae. aegypti and Ae. albopictus are primarily active and blood feed in the daytime. When mosquitoes bite a person infected with the virus, they may become infected; however, not all mosquitoes can become infected with and transmit viruses. Mosquitoes that are competent vectors (ie, able to transmit Zika virus) can pass the virus to humans through their subsequent blood meals. A pregnant woman who is bitten by a Zika virus-infected mosquito may pass the virus to her fetus, which may result in microcephaly and/or other complications in the developing fetus and newborn child. Zika virus may also be passed through sexual contact, even if the infected person shows no symptoms. Zika virus may also be transmitted through transfusion of infected blood and laboratory exposure, although the exact mechanism of the laboratory transmission is unclear (http://www.who.int/ topics/zika/en/, http://www.cdc.gov/zika/transmission/index. Insights into Zika Virus History, Human Health Effects, and Control Measures