US scientists ‘missed’ any UK Zika cases

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Has the US government really already missed any more potential cases of the Zika virus transmitted in the UK?

On 10 February, US experts warned that Zika could be spread to the UK during a specialised clean-up in New Jersey.

But Dr Michael Fport, a neuroscientist at Loughborough University, says their conclusion – that there has been no local spread of the virus in the UK – was based on just one week’s worth of data.

US researchers took samples from two New Jersey parks as part of what was known as a Mosquito Elimination Programme.

They compared the chikungunya and Zika virus chains of infection to patterns seen in the tropics and wrote a report on the work.

The plot shows the timing of the infection chains.

They concluded that local transmission of Zika between two samples, taken from 8 and 13 February, “could be widespread and has occurred among several New Jersey parks”.

And that could still be true – Dr Fport says that the mosquitoes carrying Zika virus are only one generation old, meaning that this particular type of mosquito is probably replicating at “a massive scale, and many different species of Aedes mosquitoes carry and transmit Zika”.

Dr Fport points out that having stopped the virus within the first two weeks of virus-infected cells multiplying, the mosquitos will have also infected healthy people within a week’s time.

Image copyright Aerosol Mail / Health News/Graham/Werlin/Fisher

“The probability of transmission in the next 24-48 hours would be very low, and even if transmission occurred, the virus would only be transmitted from person to person by mosquitoes that bite people,” Dr Fport said.

“The fact is that if a mosquito bite an infected person they would pick up Zika and be highly infectious for the first days, but would be no longer infectious for at least a day – a point that we have known for decades,” he told the BBC.

The problem is that Dr Fport says that “if a mosquito bit a person three weeks earlier or later, a period of 24-48 hours, that person would have no evidence of the virus in them”.

Dr Fport acknowledges that “we are entirely reliant on the observations of the people who actually did the work at the time, and these (lack of) observations would affect our ability to statistically model the events”.

Image copyright CDC Image caption The virus in the Zika virus was named after Aedes aegypti, a family of mosquitoes (see diagram) which is also known to spread chikungunya and dengue viruses

Nevertheless, he says: “There is no reason to think that the particular virus that has been circulating in New Jersey has spread from either of the people who collected the samples outside New Jersey to people within New Jersey, or the UK.

“It is impossible to know whether this particular mosquito is present in the UK, or in Northern Ireland, and therefore it is too soon to know whether there is any evidence for Zika in these areas.”

Dr Fport says “the leading candidate” for the virus was Aedes albopictus, or the Aedes mosquito.

“It does not occur in the UK, the Scottish Highlands, the UK is the best place in the UK to isolate these insect species.

“It is reasonable to assume that by 10 February 2019, we had had no import of that particular species from the US.”

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