How it began
In 1947 scientists carrying out routine surveillance for yellow fever in the Zika Forest, near Entebbe in Uganda, isolated a previously unknown virus from samples taken from a captive sentinel rhesus monkey. The feverish monkey, number 766, had been held in a cage on a platform in the forest canopy. The virus was named after the forest.
How it works
The method was sentinel surveillance. Monkeys were caged on tree platforms where forest mosquitoes would bite them, and their blood was tested when they developed fever. In 1948 the same virus was recovered from the mosquito Aedes africanus caught on a tree platform in the forest, which showed how it traveled. Zika virus is a member of the family Flaviviridae.
How it spread
Between 1969 and 1983 the known range of the virus expanded to equatorial Asia, including India, Indonesia, Malaysia and Pakistan, where it was found in mosquitoes. In 2007 it caused its first large human outbreak on the Pacific island of Yap. Before then only 14 human cases had been documented worldwide. Outbreaks followed in French Polynesia and other Pacific islands in 2013 and 2014, and in Brazil from 2015.
What changed first
In 1952 the first human cases were detected in Uganda and Tanzania, in a study that found neutralizing antibodies to Zika virus in blood sera. For decades the infection was regarded as rare in humans, with mild symptoms. Within five years of the first isolation, the virus had been found in monkeys, in mosquitoes and in people.
What lasted
Because the virus had been isolated and described in Uganda decades earlier, health agencies could identify it when it reached the Pacific and the Americas. On February 1, 2016, the World Health Organization declared the association of Zika infection with clusters of microcephaly and other neurological disorders a Public Health Emergency of International Concern.
