Laboratory analysis found Zika infections in some patients with GBS in Brazil, El Salvador, Suriname and Venezuela, and the WHO declared on 22 March 2016 that Zika appeared to be "implicated" in GBS infection and that if the pattern was confirmed it would represent a global public health crisis. Research
Mechanism
Research has been ongoing to better understand how Zika virus causes microcephaly and other neurological disorders.It may involve infection of the primary neural stem cells of the fetal brain, known as neural progenitor cells. The main roles of brain stem cells are to proliferate until the correct number is achieved, and then to produce neurons through the process of neurogenesis. Zika proteins NS4A and NS4B have also been shown to directly suppress neurogenesis. Infection of brain stem cells can cause cell death, which reduces the production of future neurons and leads to a smaller brain. Zika also appears to have an equal tropism for cells of the developing eye, leading to high rates of eye abnormalities as well.In addition to inducing cell death, infection of neural progenitor cells may alter the process of cell proliferation, causing a depletion in the pool of progenitor cells. A large number of cases of microcephaly have been associated with inherited gene mutations, and specifically with mutations that lead to dysfunction of the mitotic spindle.
These abnormalities can lead to intellectual problems, seizures, vision problems, hearing problems, problems feeding and slow development.Whether the stage of pregnancy at which the mother becomes infected affects the risk to the fetus is not well understood, nor is whether other risk factors affect outcomes. One group has estimated the risk of a baby developing microcephaly at about 1% when the mother is infected during the first trimester, with the risk of developing microcephaly becoming uncertain beyond the first trimester. Affected babies might appear normal but actually have brain abnormalities; infection in newborns could also lead to brain damage. Cause
Reservoir
Zika virus is a mosquito-borne flavivirus closely related to the dengue and yellow fever viruses. While mosquitoes are the vector, the main reservoir species remains unknown, though serological evidence has been found in both West African monkeys and rodents. Transmission
Transmission is via the bite of mosquitoes from the genus Aedes, primarily Aedes aegypti in tropical regions. It has also been isolated from Ae. africanus, Ae. apicoargenteus, Ae. luteocephalus, Ae. albopictus, Ae. vittatus and Ae. furcifer. During the 2007 outbreak on Yap Island in the South Pacific, Aedes hensilli was the vector, while Aedes polynesiensis spread the virus in French Polynesia in 2013.Zika virus can also spread by sexual transmission from infected men to their partners. Zika virus has been isolated from semen samples, with one person having 100,000 times more virus in semen than blood or urine, two weeks after being infected.