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Zika Virus Timeline

2016-02-07

Zika virus was first described in Uganda in 1947.  It was detected only because blood viruses in monkeys were being studied.  Even in people, there are few symptoms.  The virus spread to the Pacific Islands from Africa and Asia, then to South America in 2013-15.

Zika is thought to be spread by mosquito bites.  The symptoms are described as “mild” and last about 4-7 days; they consist of fever, joint pain, rash, and conjunctivitis (red eyes) in about 1 in 5 exposed people, with headache and muscle pain at times.  The incubation period is probably a few days to two weeks.  Fatalities are said to be “rare” (unless you are affected.)

The greatest concern is for women who are pregnant when they become acutely ill with Zika.  An increase in the incidence of microcephaly in epidemic areas of Brazil was reported and the Brazilian Ministry of Health established a registry of cases in the fall of 2015.  Of 37 cases reported, 35 could not be attributed to known causes; one had cytomegalovirus and one had a genetic anomaly.  Most (71%) of the mothers reported an acute illness with fever and rash during the pregnancy, and all were negative for syphilis, CMV, etc., etc.  The historical incidence of microcephaly at birth was about 0.5 per 10,000 births but a new estimate could not be given.

A detailed timeline of the known spread of the Zika virus is available from NPR here.  First detected in the Zika forest in Uganda, it was followed in Central African countries until 1981.  Asian countries, from India to the Phillipines, were also found to have cases in the fifties to the eighties.  In 2007, the virus jumped to Yap Island and infected virtually all of its seven thousand residents.  In 2013-14, the virus continued across the Pacific, finally to Easter Island, and then in 2015 it appeared in South America.  There are estimates of at least a million Brazilians infected already.

Then, in 2015, a woman gave birth in Hawaii after having been in Brazil while pregnant.  The infant had microcephaly.  More than a dozen imported cases of Zika in adults have been found in the US during the course of 2015.  A Centers for Disease Control report published in Morbidity and Mortality Weekly Report on Zika and microcephaly is here.

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