Geneva: Yesterday, public health officials investigated a report over the Zika virus spread that an American had been infected through sexual contact and Brazil said 4,074 cases of infants with severe birth defects could be linked to the virus. The widening scare comes two days after the World Health Organization (WHO) declared a global health emergency because of the growing number of Zika-linked cases of microcephaly, a condition in which the baby is born with an abnormally small head and an underdeveloped brain.

On Wednesday, the agency once more warned regions beyond Latin America to be on guard, including Europe but also Africa and Asia, the areas with the world’s highest birth rates. So far, the WHO said the virus has been transmitted in at least 32 countries, from South America to the Western Pacific. There were new concerns about the possibility of sexual transmission after health officials in Texas said the first known case of Zika virus transmission in the United States was likely contracted through sex rather than a mosquito bite.

But the focus by public health officials in terms of stemming the outbreak remains the Aedis aegypti mosquito, the tropical insect known to be the primary source of contagion. Ben Neuman, a virologist at Britain’s University of Reading said, “Control measures need to focus on the major source of Zika, which is still overwhelmingly mosquitoes”. He added, “If you swap enough bodily fluid, most viruses can probably be sexually transmitted to some extent”.

Although Tuesday’s report of a sexual transmission in Dallas adds to evidence that bodily fluids might also transmit the disease, scientists and public health authorities said far more research is needed to determine how much sexual contact might be needed for contagion. Officials are scrambling to measure the severity of an outbreak that began in northeast Brazil early last year, before spreading across the country and into the rest of the Americas, a region that had never before suffered from Zika infections.

Late on Tuesday, the Brazilian health ministry said the number of newborns with microcephaly linked to the virus had increased to 4,074 as of Jan 30, from 3,718 a week earlier. One of the key challenges in terms of measuring the severity of Zika and its believed complications is that the illness shows symptoms in only one of five people who are infected with it.