Zika virus is spread to people through mosquito bites and through human body fluid contact, as the contact as recently discovered by a case in Dallas County, Texas . The most common symptoms of Zika virus disease are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting from several days to a week. Severe disease requiring hospitalization is uncommon.
In May 2015, the Pan American Health Organization (PAHO) issued an alert regarding the first confirmed Zika virus infection in Brazil. The outbreak in Brazil led to reports of Guillain-Barré syndrome and pregnant women giving birth to babies with birth defects and poor pregnancy outcomes.
The scientic name, Flaminia Catteruccia, associate professor of immunology and infectious diseases at Harvard T.H. Chan School of Public Health, says the virus may have adapted to the human environment and mutated. The mosquito-borne Zika virus has been linked to a surge in cases of birth defects in Brazil, and is spreading in other countries in the southern hemisphere.
Zika is very similar to other viruses that are transmitted by the Aedes mosquitoes, including dengue and chikungunya. It was first discovered in 1947 in monkeys in Africa, and there have been several outbreaks since then. But it has not been studied much because, normally, the symptoms are quite mild—fever, headaches, joint pain. People get over it in a few days.
It seems like there is something different about the virus in the current outbreak in Brazil. It has coincided with a dramatic rise in cases of microcephaly, a birth defect that results in babies born with unusually small heads. The increase in babies born with this condition has been more than 20-fold compared with previous years—from maybe 150 cases to more than 3,000 cases in a few months.
All it takes is for an infected person to return from somewhere overseas (such as El Salvador or Brazil) and get bitten by a local mosquito that can carry it.
“That blood that has that virus is circulating in the body. If a mosquito bites them, that mosquito could bite someone else and the process goes on,” said Dr Barry Alto, from the Florida Medical Entomology Laboratory at the University of Florida.
“It could very well mean local mosquitoes are actually infected with the virus. And now we have a public health concern,” said Alto. But it’s unlikely the US will see a Zika epidemic like that currently facing Brazil and El Salvador, since authorities are closing monitoring what’s happening overseas and the mosquitoes are mainly limited to the south. “I don’t expect there to be as big an outbreak. The [US] infrastructure is potentially better equipped to deal with outbreaks,” said Alto.
The Zika virus spreads so fast because it never emerged in this part of the world. Hence there is no natural immunity available in the population and a lot of infections occur. Once this “first wave” of infections is over, the level within the population will fall drastically.
It is of course possible that the Zika virus has acquired a new mutation which adapts it better to humans and allows spreading much easier, but this is not yet known, since the situation in South America is still changing very fast with a lot of cases occurring and analysis going on. It still can be enough that the virus never emerged in Southern America and that there is no natural immunity available.