Zika Virus: What Happened When

 (Centers for Disease Control and Prevention, Pan American Health Organization)
(Centers for Disease Control and Prevention, Pan American Health Organization)

Since it was first discovered in Uganda in 1947, Zika virus was known mostly as a short-lived and mild illness. In 2015, that all changed. An outbreak in Brazil is suspected of causing cases of a serious birth defect, microcephaly, and a potentially crippling disease, Guillain-Barre syndrome.

As the mosquito-borne illness spreads across the Americas, scientists are trying to figure out what illnesses the virus is truly responsible for and why more people are getting sick.

We've put together a timeline to track the global response to Zika virus and scientists' understanding of how it affects people, with the most recent events at the top. (Find NPR's ongoing coverage here.) Check back, as we're regularly updating this list.

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More Photos:

This is a transmission electron micrograph (TEM) of Zika virus, which is a member of the family Flaviviridae. Virus particles are 40 nm in diameter, with an outer envelope, and an inner dense core. The arrow identifies a single virus particle.

This is a transmission electron micrograph (TEM) of Zika virus, which is a member of the family Flaviviridae. Virus particles are 40 nm in diameter, with an outer envelope, and an inner dense core. The arrow identifies a single virus particle.

Health workers fumigate in an attempt to eradicate the mosquito which transmits the Zika virus on January 28, 2016 in Recife, Pernambuco state, Brazil. Two two-man teams were fumigating in the city today. Health officials believe as many as 100,000 people have been exposed to the Zika virus in Recife, although most never develop symptoms.

Health workers fumigate in an attempt to eradicate the mosquito which transmits the Zika virus on January 28, 2016 in Recife, Pernambuco state, Brazil. Two two-man teams were fumigating in the city today. Health officials believe as many as 100,000 people have been exposed to the Zika virus in Recife, although most never develop symptoms.

Dr. Vanessa Van Der Linden, the neuro-pediatrician who first recognized the microcephaly crisis in Brazil, measures the head of a 2-month-old baby with microcephaly on January 27, 2016 in Recife, Brazil. The baby's mother was diagnosed with having the Zika virus during her pregnancy.

Dr. Vanessa Van Der Linden, the neuro-pediatrician who first recognized the microcephaly crisis in Brazil, measures the head of a 2-month-old baby with microcephaly on January 27, 2016 in Recife, Brazil. The baby's mother was diagnosed with having the Zika virus during her pregnancy.

A patient suffering from the Guillain-Barre neurological syndrome recovers in the neurology ward of the Rosales National Hospital in San Salvador, on January 27, 2016. Health authorities have issued a national alert against the Aedes aegypti mosquito, vector of the Zika virus which might cause microcephaly and Guillain-Barre syndrome.

A patient suffering from the Guillain-Barre neurological syndrome recovers in the neurology ward of the Rosales National Hospital in San Salvador, on January 27, 2016. Health authorities have issued a national alert against the Aedes aegypti mosquito, vector of the Zika virus which might cause microcephaly and Guillain-Barre syndrome.

Marilla Lima had Zika virus while pregnant. Her 2 1/2-month-old son, Arthur, has microcephaly — a birth defect characterized by a small head and severe brain damage.

Marilla Lima had Zika virus while pregnant. Her 2 1/2-month-old son, Arthur, has microcephaly — a birth defect characterized by a small head and severe brain damage.

An Aedes Aegypti mosquito is photographed on human skin in a lab of the International Training and Medical Research Training Center (CIDEIM) on January 25, 2016, in Cali, Colombia. CIDEIM scientists are studying the genetics and biology of Aedes Aegypti mosquito which transmits the Zika, Chikungunya, Dengue and Yellow Fever viruses, to control their reproduction and resistance to insecticides.

An Aedes Aegypti mosquito is photographed on human skin in a lab of the International Training and Medical Research Training Center (CIDEIM) on January 25, 2016, in Cali, Colombia. CIDEIM scientists are studying the genetics and biology of Aedes Aegypti mosquito which transmits the Zika, Chikungunya, Dengue and Yellow Fever viruses, to control their reproduction and resistance to insecticides.

Dr. Anthony Fauci, director of NIH/NIAID, listens as Dr. Anne Schuchat, Principal Deputy Director of the CDC, speaks. President Obama is asking Congress for more than $1.8 billion in emergency funding to help fight Zika. The money would be used to expand mosquito control programs, speed development of a vaccine, develop diagnostic tests and improve support for low-income pregnant women.

Dr. Anthony Fauci, director of NIH/NIAID, listens as Dr. Anne Schuchat, Principal Deputy Director of the CDC, speaks. President Obama is asking Congress for more than $1.8 billion in emergency funding to help fight Zika. The money would be used to expand mosquito control programs, speed development of a vaccine, develop diagnostic tests and improve support for low-income pregnant women.

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