Suspected links between the Zika virus and two neurological disorders, microcephaly in babies and Guillain-Barre syndrome, should be confirmed within weeks, the World Health Organization (WHO) said on Friday.
A sharp increase in birth defects in Brazil has triggered a global health emergency over the mosquito-borne virus, which had previously been viewed as a relatively mild illness, and has spurred a race to develop a vaccine and better diagnostic tests.
The WHO said U.S. government scientists and an Indian biotechnology firm were currently front-runners in the race to develop a vaccine. The U.N. agency for the first time advised pregnant women to consider delaying travel to Zika-infected areas.
Brazil, centre of the Zika outbreak that has spread to more than 30 countries, is hosting the Rio 2016 Olympics, an event expected to draw hundreds of thousands of athletes, officials and spectators.
“It seems indeed that the link with Zika virus (and microcephaly) is becoming more and more probable, so I think that we need a few more weeks and a few more studies to have this straight,” Marie-Paule Kieny, WHO Assistant Director-General for Health Systems and Innovation, told a news briefing.
Studies of pregnant Latin American women who are confirmed as having had the Zika virus and due to deliver their babies soon should yield evidence, Kieny said, adding data also was being collected from studies in French Polynesia and Cape Verde.
Kieny said areas hit by the Zika virus had also seen increased cases of the neurological disease Guillain-Barre, adding: “The direct causality has still to be demonstrated but the association in time and in location seems to be clear.”
Guillain-Barre syndrome, in which the body’s immune system attacks part of the nervous system, causes gradual weakness in the legs, arms and upper body and sometimes total paralysis.
In a statement, the WHO reiterated it was not recommending any general travel or trade restrictions related to the Zika virus, but added: “Women who are pregnant should discuss their travel plans with their healthcare provider and consider delaying travel to any area where locally acquired Zika infection is occurring.”
Researchers in Brazil are scrambling to determine whether Zika has caused a big rise in the number of cases of microcephaly, or abnormally small heads in newborns, with more than 4,000 suspected cases of the condition reported to date. Brazil has confirmed more than 400 of those cases as microcephaly and has identified the presence of Zika in 17 babies but a link has yet to be proven.
Still, many scientists are convinced that the link is real and new evidence of Zika in the brain of an aborted foetus, reported on Wednesday, has added to the case.
On vaccines, Kieny said it would take at least 18 months to start large-scale clinical trials of potential preventative shots.
“Two vaccine candidates seem to be more advanced: a DNA vaccine from the U.S. National Institutes for Health (NIH) and an inactivated product from Bharat Biotech in India,” she said.
The NIH is working on a DNA-based vaccine that uses the same approach as one being developed for West Nile virus. Bharat said last week its experimental vaccine would start pre-clinical trials in animals imminently.
Overall, about 15 groups are working on Zika vaccines, including France’s Sanofi, as well as researchers in Brazil, who announced a new partnership with the University of Texas on Thursday.
The road to developing a preventative shot against the disease is strewn with hurdles, however, not least because the group viewed as most at risk are pregnant women.
Improved diagnostic tests also are viewed as critical to fighting the disease and Kieny said new test kits were being rapidly developed and could be available in weeks. The virus causes symptoms in only about one-fifth of people it infects.
VIRUS LINGERED IN SEMEN
Although Zika is predominantly spread by mosquito, scientists are looking into possible transmission by blood and sexual contact, which would complicate efforts to contain the outbreak.
British health officials reported on Friday that the virus was found in the semen of a British man two months after he was first infected, suggesting it may linger in the semen long after symptoms of the infection fade.
Researchers at Public Health England said the 68-year-old man became infected with the virus in 2014 in French Polynesia. He was tested for while he still had a fever and low levels of Zika were detected in blood samples.
Subsequent tests of semen showed positive results at 27 days and 62 says after the start of Zika symptoms. The findings were reported in a letter in Emerging Infectious Diseases published by the U.S. Centres for Disease Control and Prevention.
The researchers said the man had low levels of virus in initial blood tests. Subsequent tests of semen showed positive results at 27 days and 62 says after the start of Zika symptoms, with higher levels of the virus in the semen than the initial blood tests.
“Our data may indicate prolonged presence of virus in semen, which in turn could indicate a prolonged potential for sexual transmission” of this virus, the researchers from Public Health England and the National Institute for Health Research in Liverpool wrote.
The WHO has advised women, and particularly pregnant women, to protect themselves from mosquito bites in Zika-affected areas and also to practice safe sex through the use of condoms.