GENEVA/BRASILIA/WASHINGTON/LEINSTER, IRELAND – The World Health Organization voiced concern on Wednesday over the reported sexual transmission of the Zika virus in Texas amid worries that such infections could make efforts to combat the virus linked to severe birth defects in Brazil even tougher.
The virus, spreading quickly across the Americas, is usually transmitted by mosquitoes. But health officials in Dallas County reported on Tuesday that the first known case contracted in the United States was a person infected after having sex with somebody who had returned from Venezuela.
The WHO declared a global health emergency on Monday, citing a “strongly suspected” casual relationship between Zika infection in pregnancy and microcephaly, a condition marked by abnormally small head size that can cause permanent brain damage in newborns.
Health ministers from across South America gathered in Uruguay’s capital, Montevideo, to discuss the public health emergency and how the region can coordinate its fight against the outbreak.
There is no treatment or vaccine for Zika.
Sexual transmission could add a new dimension to the threat Zika poses, but WHO spokesman Gregory Hartl stressed that “almost a 100 percent of the cases” are transmitted by the bite of a mosquito.
“This reported case in the U.S. of course raises concerns,” Hartl said at the U.N. agency’s headquarters in Geneva. “This needs to be further investigated to understand the conditions and how often or likely sexual transmission is.”
But he said that for the WHO “the most important thing to do is to control people’s exposure to mosquitoes.”
The WHO estimates as many as 4 million people could become infected in the Americas.
Hartl called the Texas case only the second worldwide linked to sexual transmission, referring to media reports about a case of an American man who returned from Senegal in 2008 and is suspected of having infected his wife. The medical literature also has a case in which the virus was detected in semen.
“If you swap enough bodily fluid, most viruses can probably be sexually transmitted to some extent,” said Ben Neuman, a virologist at Britain’s University of Reading.
Florida Gov. Rick Scott declared a public health emergency in four counties with travel-related cases of the Zika virus, and ordered state officials to increase mosquito control efforts in some of the state’s most heavily populated locales, including Miami and Tampa.
Scott directed state officials to pay special attention to mosquito spraying in residential areas.
In addition, the U.S. Centers for Disease Control and Prevention, which has urged pregnant women to consider delaying travel to locations with ongoing Zika transmissions, added Jamaica and Tonga to its travel alert.
The WHO said the virus has been transmitted in at least 32 countries, from South America to the Western Pacific.
Late on Tuesday, the Brazilian health ministry said the number of newborns with microcephaly it suspects are linked to the virus had increased to 4,074 as of Jan. 30, from 3,718 a week earlier.
Researchers have identified evidence of Zika infection in 17 of these cases, either in the baby or in the mother, but have not confirmed that Zika can cause microcephaly.
The WHO warned member states in Europe on Wednesday that the risk of the virus spreading into the region increases with the onset of spring and summer.
“Now is the time for countries to prepare themselves to reduce the risk to their populations,” said the WHO’s Europe chief, Zsuzsanna Jakab. “Every European country in which Aedes mosquitoes are present can be at risk for the spread of Zika virus disease.”
The Pan American Health Organization, the WHO’s arm for the Americas, said it needed an estimated $8.5 million to help countries in the region respond to the Zika threat.
Brazilian Health Minister Marcelo Castro said U.S. experts will travel to Brazil next week to start work on the development of a Zika vaccine and come up with a timetable for the effort.
A number of drug developers and universities are attempting to produce a vaccine. Experts have said a vaccine is months or even years away.
Japan’s leading drugmaker, Takeda Pharmaceutical Co. Ltd., said it has created a team to investigate how it might help make a vaccine, a day after France’s Sanofi SA said it would launch a Zika vaccine program.
Pfizer Inc., Johnson and Johnson and Merck & Co. Inc. said they were evaluating their technologies or existing vaccines for their potential to combat Zika.
Indian biotechnology company Bharat Biotech said it was working on two possible vaccines.
The rising number of cases has stirred concern ahead of the Olympic Games in August in Rio de Janeiro in August, when Brazil’s second-largest city will host tens of thousands of athletes and tourists from around the world.
In its brief lifespan, the mosquito that carries the Zika virus is caught in a race: Will it pass the disease to humans before it dies?
Weather might make the difference. Scientists say the hotter it gets, the more likely the insect can spread disease.
As the temperature rises, nearly everything about the biology of the Aedes aegypti mosquito — the one that carries Zika, dengue fever and other diseases — speeds up when it comes to spreading disease, said entomologist Bill Reisen of the University of California, Davis.
“With higher temperatures you have more mosquitoes feeding more frequently and having a greater chance of acquiring infection. And then the virus replicates faster because it’s hotter, therefore the mosquitoes can transmit earlier in their life,” Reisen said. The thermodynamics of mosquitoes are “driven by temperature.”
The hotspots for this Zika outbreak also have been temperature and drought hotspots recently. Recife, Brazil, the largest city in the Zika-struck region, saw its hottest September-October-November on record, about 1.2 degrees Celsius (2.2 degrees Fahrenheit) above normal, according to NASA data. The state of Pernambuco had its hottest and driest year since 1998, according to the state weather agency. And globally, last year was the hottest on record.
Although it is too early to say for this outbreak, past outbreaks of similar diseases involved more than just biology. In the past, weather has played a key role, as have economics, human travel, air conditioning and mosquito control. Even El Nino sneaks into the game. Scientists say you can’t just blame one thing for an outbreak and caution it is too early to link this one to climate change or any single weather event.
Scientists have studied Zika far less than other mosquito-borne diseases, so for guidance they often look at dengue fever or chikungunya, which are transmitted by the same species of mosquito. Dengue infects as many as 400 million people a year, with a quarter of them sick enough to be hospitalized.
Zika was just declared a global public health emergency after being linked to brain deformities in babies in South America. Several thousand cases of microcephaly have been reported in Brazil since October, although researchers have so far not proven a definitive link to the virus. No vaccine exists for Zika.
In general, mosquitoes don’t live long, maybe 10 to 12 days on average, said Tom Scott, a University of California, Davis professor of both entomology and epidemiology. That’s also about how long it takes a virus to grow in the mosquito gut, making the bug infectious and able to spread the disease. Often the insect will die before it can get a chance to spread the disease.
Warmer air incubates the virus faster in the cold-blooded mosquito. So the insect has more time to be infectious and alive to spread the disease, Scott said.
Warmer temperatures also make the mosquito hungrier, so it takes more “blood meals” and can spread the disease to more people, Scott, Reisen and others said. And warmer temperatures generally increase the mosquito population.
Kristie Ebi, a professor of global health at the University of Washington, calls it “a temperature-driven eruption.”
That’s not the only role of weather.
El Nino, a natural warming of parts of the Central Pacific Ocean that changes weather worldwide, usually puts northeastern Brazil into a drought, as it did last year. Aedes aegypti does well in less-developed regions in droughts, because it lives in areas where poorer people store water in outdoor containers, said Jonathan Patz, director of the global health institute at the University of Wisconsin.
“As with all mosquito-borne viruses, climate is one of many factors that influence Zika transmission,” said Andy Monaghan, a scientist who works on public health impacts of climate change at the National Center for Atmospheric Research. “I think it is too early to say anything about the role of climate change in the ongoing Zika outbreak.”
However, Monaghan earlier this year presented a paper to the American Meteorological Society’s annual convention that predicts that eventually Aedes aegypti “will move northward in the U.S. due to future warming, which would expose people to the mosquito on a regular seasonal basis in states like Missouri, Tennessee, Kentucky, North Carolina, Virginia and D.C.”
Ireland on Wednesday urged men to wear a condom during sex for one month after returning from a country affected by the Zika virus, as Britain said returning travelers cannot donate blood for a month.
Britain’s health agency last Friday had already warned that travelers should practice safe sex.
“Zika virus can be passed between sexual partners in the man’s semen. This is especially likely if he developed symptoms of Zika virus disease,” read a statement from the Health Protection Surveillance Agency, the specialist diseases agency in predominantly Catholic Ireland.
The statement also warned that anyone with symptoms that could be due to Zika such as fever, headache, aches, rash or itchy eyes should practice safe sex for six months following the start of his symptoms.
Britain’s National Health Service Blood and Transplant agency said in a statement it would implement from Thursday a 28-day on blood donors returning from Zika-affected countries as a “precautionary measure.”
“The safety of the blood supply is paramount and it is important we implement any precautionary blood safety measures agreed here as a result of an increasing prevalence of infectious diseases found around the globe,” a spokeswoman said.
The warnings about the fast-spreading Zika outbreak came following a case of sexual transmission identified in Texas on Tuesday, confirming that the virus is not just spread by tropical mosquitoes.
There had been two previous suspected cases of sexual transmission, in 2008 and 2015.
Britain had warned on Friday that “a small number of cases of sexual transmission of Zika virus have been reported and in a limited number of cases the virus has been shown to be present in semen, although it is not yet known how long this can persist.”
“The risk of sexual transmission of Zika virus is thought to be very low,” Public Health England said in a statement.
It advised condom use for male travelers returning from Zika-affected areas “if a female partner is at risk of getting pregnant or is already pregnant.”
The statement said this should be for 28 days for travelers with no symptoms and six months “following recovery if a clinical illness compatible with Zika virus infection or laboratory confirmed Zika virus infection was reported.”
The World Health Organization has declared the spike in serious birth defects in South America an international emergency and launched a global Zika response unit.