ZIKA VIRUS INFORMATION
Zika virus (ZIKV) is a member of the virus family Flaviviridae and the genusFlavivirus. It is spread by daytime-active Aedes mosquitoes, such as A. aegyptiand A. albopictus. Its name comes from the Zika Forest of Uganda, where the virus was first isolated in 1947.[4] Zika virus is related to the dengue, yellow fever,Japanese encephalitis, and West Nile viruses. Since the 1950s, it has been known to occur within a narrow equatorial belt from Africa to Asia. From 2007 to 2016, the virus spread eastward, across the Pacific Ocean to the Americas, leading to the2015–16 Zika virus epidemic.
The infection, known as Zika fever or Zika virus disease, often causes no or only mild symptoms, similar to a very mild form of dengue fever. While there is no specific treatment, paracetamol (acetaminophen) and rest may help with the symptoms.As of 2016, the illness cannot be prevented by medications orvaccines. Zika can also spread from a pregnant woman to her fetus. This can result in microcephaly, severe brain malformations, and other birth defects. Zika infections in adults may result rarely in Guillain–Barré syndrome.
In January 2016, the United States Centers for Disease Control and Prevention(CDC) issued travel guidance on affected countries, including the use of enhanced precautions, and guidelines for pregnant women including considering postponing travel. Other governments or health agencies also issued similar travel warnings, while Colombia, the Dominican Republic, Puerto Rico, Ecuador, El Salvador, and Jamaica advised women to postpone getting pregnant until more is known about the risks. Zika is pronounced /ˈziːkə/ or /ˈzɪkə/.
Transmission
The vertebrate hosts of the virus were primarily monkeys in a so-called enzooticmosquito-monkey-mosquito cycle, with only occasional transmission to humans. Before the current pandemic began in 2007, Zika "rarely caused recognized 'spillover' infections in humans, even in highly enzootic areas". Infrequently, however, other arboviruses have become established as a human disease and spread in a mosquito–human–mosquito cycle, like the yellow fever virus and the dengue fever virus (both flaviviruses), and the chikungunya virus (a togavirus).Though the reason for the pandemic is unknown, dengue, a related arbovirus that infects the same species of mosquito vectors, is known in particular to be intensified by urbanization and globalization. Zika is primarily spread by Aedes aegypti mosquitoes, and can also be transmitted through sexual contact[32] or blood transfusions. The basic reproduction number (R0, a measure of transmissibility) of Zika virus has been estimated to be between 1.4 to 6.6.
In 2015, news reports drew attention to the rapid spread of Zika in Latin America and the Caribbean. The countries and territories that were identified by the Pan American Health Organisation as having experienced "local Zika virus transmission" at that time were Barbados, Bolivia, Brazil, Colombia, the Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Saint Martin, Suriname, and Venezuela. As of August 2016, more than 50 countries have experienced active (local) transmission of
Virus isolation in monkeys and mosquitoes, 1947
The virus was first isolated in April 1947 from a rhesus macaquemonkey that had been placed in a cage in the Zika Forest ofUganda, near Lake Victoria, by the scientists of the Yellow Fever Research Institute. A second isolation from the mosquito A. africanus followed at the same site in January 1948. When the monkey developed a fever, researchers isolated from its serum a"filterable transmissible agent" that was named Zika in 1948.
First evidence of human infection, 1952
Zika had been known to infect humans from the results of serological surveys in Uganda and Nigeria, published in 1952: Among 84 people of all ages, 50 individuals had antibodies to Zika, and all above 40 years of age were immune. A 1952 research study conducted in India had shown a "significant number" of Indians tested for Zika had exhibited an immune response to the virus, suggesting it had long been widespread within human populations.
It was not until 1954 that the isolation of Zika from a human was published. This came as part of a 1952 outbreak investigation of jaundice suspected to be yellow fever. It was found in the blood of a 10-year-old Nigerian female with low-grade fever, headache, and evidence of malaria, but no jaundice, who recovered within three days. Blood was injected into the brain of laboratory mice, followed by up to 15 mice passages. The virus from mouse brains was then tested in neutralization tests using rhesus monkey sera specifically immune to Zika. In contrast, no virus was isolated from the blood of two infected adults with fever, jaundice, cough, diffuse joint pains in one and fever, headache, pain behind the eyes and in the joints. Infection was proven by a rise in Zika-specific serum antibodies.
Spread in equatorial Africa and to Asia, 1951–1983
From 1951 through 1983, evidence of human infection with Zika was reported from other African countries, such as the Central African Republic, Egypt, Gabon, Sierra Leone, Tanzania, and Uganda, as well as in parts of Asia including India, Indonesia, Malaysia, the Philippines, Thailand, Vietnam and Pakistan. From its discovery until 2007, there were only 14 confirmed human cases of Zika infection from Africa and Southeast Asia.
Micronesia, 2007
Main article: 2007 Yap Islands Zika virus outbreak
In April 2007, the first outbreak outside of Africa and Asia occurred on the island of Yap in the Federated States of Micronesia, characterized by rash, conjunctivitis, and arthralgia, which was initially thought to be dengue, chikungunya, orRoss River disease.Serum samples from patients in the acute phase of illness contained RNA of Zika. There were 49 confirmed cases, 59 unconfirmed cases, no hospitalizations, and no deaths.
Americas, 2015–presen
Main article: 2015–16 Zika virus epidemic
As of early 2016, a widespread outbreak of Zika was ongoing, primarily in the Americas. The outbreak began in April 2015 in Brazil, and has spread to other countries in South America, Central America, Mexico, and the Caribbean. In January 2016, the WHO said the virus was likely to spread throughout most of the Americas by the end of the year;and in February 2016, the WHO declared the cluster of microcephaly and Guillain–Barré syndrome cases reported in Brazil – strongly suspected to be associated with the Zika outbreak – a Public Health Emergency of International Concern. It is estimated that 1.5 million people have been infected by Zika in Brazil,with over 3,500 cases of microcephaly reported between October 2015 and January 2016.
A number of countries have issued travel warnings, and the outbreak is expected to significantly impact the tourism industry. Several countries have taken the unusual step of advising their citizens to delay pregnancy until more is known about the virus and its impact on fetal development.With the 2016 Summer Olympic Games hosted in Rio de Janeiro, health officials worldwide have voiced concerns over a potential crisis, both in Brazil and when international athletes and tourists, who may be unknowingly infected, return home and possibly spread the virus. Some researchers speculate that only one or two tourists may be infected during the three week period, or approximately 3.2 infections per 100,000 tourists.
