Health officials say it is now “high season” for Zika virus transmission for many countries below the equator.
The World Health Organization said Friday that the Zika virus has spread to 47 countries. The virus spreads primarily through mosquito bites, and the WHO is concerned that because it is now the high season for transmission of Dengue, another mosquito-borne virus, it may also be a time for higher transmission rates of Zika.
“We believe this will be the high season for Zika transmission as well,” said Bruce Aylward, WHO executive director for outbreaks and health emergencies, during a Friday press conference in Geneva.
For the U.S., health officials are worried about the spread of Zika from mosquitoes in the summer, especially in warmer southern states. Zika causes a mild illness, but growing evidence links it to a birth defect called microcephaly that causes babies to be born with abnormally small heads.
Now, there is more evidence of a link between Zika and Guillain-Barre Syndrome, a neurological disorder that can cause temporary paralysis. A new study published earlier this week in the Lancet journal analyzed cases of the syndrome in French Polynesia, which had a Zika outbreak in 2013-14.
The study found that 100 percent of people who had the syndrome in the country had evidence of a Zika infection, Aylward said.
“This is the strongest evidence so far that this is a virus that can cause consequences,” he said.
The WHO noted that of the 47 countries, nine have reported a potential association between Zika and Guillain-Barre. Those countries are mainly in South America and include El Salvador, Colombia and Brazil.
Aylward conceded that it is difficult to pin down the number of total cases of Guillain-Barre linked to Zika. “Right now the data is still relatively piecemeal,” he said.
That is because the WHO has to separate the number of cases of Guillain-Barre that would occur normally and those linked to Zika, he added.
Aylward speculated there were about 100-200 excess cases in each of the nine countries, but didn’t give a total number. He emphasized that Guillain-Barre is still very rare, and about one in 5,000 people get it.
Data on the link between microcephaly and Zika is coming in much more slowly because of the nature of the birth defect. Aylward said they believe pregnancies are most vulnerable to the birth defect in the first trimester, so the WHO won’t know for months whether there is a spike.
