More than 30 travellers returning to the US have been diagnosed with the untreatable Zika virus so far

An untreatable virus has already been detected in a number of US travellers returning from ares where the disease is spreading.

The Zika virus has been detected in 31 travellers returning to the US in 11 states and DC, the Centres for Disease Control and Prevention said on a conference call with reporters Thursday, although it added that it expects those numbers to rise.

The CDC also said that state-specific data should be forthcoming, according to CDC Principal Deputy Director Anne Schuchat.

So far, the virus has been identified in a number of states in people who recently travelled to areas where Zika is being transmitted locally. Local transmission of the virus, which is spread by a type of mosquitoes called Aedes aegypti, has been documented in Puerto Rico (19 cases) and the US Virgin Islands (one case) as well. There is no vaccine or treatment available for the virus, though the National Institute of Allergy and Infectious Diseases expects early trials of a potential Zika vaccine to start by the end of 2016.

Once infected, only about 20% of people with Zika ever show symptoms, which most commonly include fever, rash, joint pain, and red eyes.

“For the average American not travelling, this is not something they need to worry about,” Schuchat said. But, pregant women or women who are trying to get pregnant should consider postponing to places where the disease is being spread.”

One reason Zika is troubling is because it has been linked with birth defects. After some mothers showed symptoms of the virus during their pregnancy, their babies were born with abnormally small brains, a condition known as microcephaly. The CDC recently published a set of working guidelines for pregnant women travelling to areas where local transmission is happening. These include monitoring themselves and their unborn children.

Zika virus outbreakMario Tama/Getty ImagesA baby born with microcephaly.

The CDC and other government organisations are working to determine if this link is a causal relationship. It’s proving difficult because babies recently born with microcephaly may have been infected with the virus a while ago. Government agencies including the CDC are working to develop better ways to diagnose the virus in people who are no longer presenting Zika symptoms.

Again, no local transmission of the virus has been documented in the US yet — so far it has only been diagnosed in people who’ve recently travelled to Zika hot spots. The CDC anticipates that local transmission will happen, but it will be similar to outbreaks of dengue and chikungunya, which have been relatively contained to southeastern states in the US.

The US, Schuchat, has a lot going for it in terms of preventing mosquito bites, such as air conditioning, window screens and less densely populated urban areas.

It may be a while before research can definitively establish that the Zika virus causes the birth defects, and it’s possible that the birth defect could be because of another factor unrelated to the virus.

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