Health services in Texas confirmed on Monday that a woman was diagnosed with the first case of Zika virus contracted from a mosquito bite. The patient, who lives in the city of Brownsville, near the border with Mexico, was reported to have had a positive test for genetic material from the Zika virus in her urine. However, there was no detectable Zika virus in her blood. This means that she is not contagious and cannot pass the virus to another person via another mosquito bite.

Health investigators who have come to this conclusion have ruled out a number of other risk factors that could have contributed to the woman contracting Zika. These factors could include having sexual or very close contact with a person who was from a Zika-affected area. They would also have looked at whether she had travelled to an area with a high prevalence of Zika virus in the human population. The patient is also not reported to be pregnant, which is fortunate as Zika has been associated with severe birth defects in babies.

The fact that Zika has finally crossed the Rio Grande is significant because it is the first time that the virus has been recorded in this area after being transmitted by a mosquito bite. It is not surprising that it has happened now, as the area where the woman lived has previously been affected by other mosquito-borne diseases, such as Dengue virus.

Also, because Zika sometimes does not cause significant symptoms, it is thought that many cases of Zika infection are not reported to health authorities. This could mean that there have been many more cases of Zika infection in the US than the 4,400 that have been reported to date.

The United States Centers for Disease Control and Prevention and state health officials are conducting an investigation. It is likely that there will be more cases of Zika reported in Texas, particularly now that people living there are more aware of its presence. However, the infection is not likely to become widespread in the US this winter, as the mosquito that carries the Zika virus, Aedes aegypti, cannot survive in colder climates.

This is also the case for the UK where it is generally much too cold for the mosquito to survive. The risk of Zika infection still remains for people travelling to Zika affected areas such as South America, or engaging in unprotected sex with people who have recently come from Zika-affected areas.

The recommendations for people travelling to the warmer areas of the US or South America this winter remain the same. Pregnant women should avoid areas where Zika is known to be actively spreading, such as some parts of Florida, including Miami. All people who live, or have to travel to these areas, should use an effective mosquito repellent and wear trousers and long-sleeved shirts to avoid being bitten. This is the most effective way of preventing infection with the virus.