SAO PAULO • A little-known virus spread by mosquitoes is said to be causing one of the most alarming health crises to hit Brazil in decades: thousands of cases of brain damage in which babies are born with unusually small heads.
Many pregnant women across Brazil are in a panic. The government, under withering criticism for not acting sooner, is urging them to take every precaution to avoid mosquito bites. One official even suggested that women living in areas where mosquitoes are especially prevalent postpone having children.
"If she can wait, then she should," said Mr Claudio Maierovitch, director of the department of surveillance of communicable diseases at Brazil's Health Ministry.
The alarm stems from a huge surge in babies with microcephaly, a rare, incurable condition in which their heads are abnormally small. Brazilian officials registered at least 2,782 cases last year, compared with just 147 in 2014 and 167 the year before that.
At least 40 of the infants have recently died, and Brazilian researchers warn that cases could multiply in the months ahead. Those babies who survive may face impaired intellectual development for life.
Brazilian researchers say Zika, an obscure mosquito-borne virus that arrived in the country only recently, is to blame for the sudden rise in brain damage among infants.
But other virologists caution that more testing is needed to prove the link between the virus and brain damage, leaving the full extent of the threat to the country unclear.
"Why this may have happened in Brazil and not elsewhere is at this stage difficult to answer," said Zika expert Alain Kohl, a virologist at the University of Glasgow. "Perhaps it was never properly registered in other areas, or the situation in Brazil is indeed different."
He said it was possible that the link between Zika and microcephaly could be related to particular strains of the virus.
Zika has already reached several countries in Latin America, including Mexico, and the US Centres for Disease Control and Prevention warns that it could also spread in the US. There have already been cases diagnosed in the US in travellers who had visited affected nations.
"I cried for a month when I learnt how God is testing us," said Ms Gleyse Kelly da Silva, 27, a toll road attendant in Recife in north-eastern Brazil, describing how an ultrasound test had detected microcephaly in the seventh month of her pregnancy with her daughter Maria Giovanna, born in October. A few months earlier, Ms da Silva had sought medical help after experiencing some of Zika's symptoms: fever, joint pain and a red rash.
"I had never heard of Zika or microcephaly," said Ms da Silva, who has three other children. "Now I just pray that my daughter can endure life with this misfortune."
No one knows when the Zika virus made the leap to Brazil from its place of origin in Africa. Some researchers say it could have arrived during the 2014 World Cup. Others point to a canoe race weeks later when paddlers from French Polynesia, the site of a recent Zika outbreak, arrived in Rio de Janeiro.
Researchers say that Zika's spread to Brazil reflects how easily viruses are jumping from one part of the planet to another.
They are particularly worried that the disease is wreaking havoc in a region where the population has not encountered it before, and that climate change may be allowing such viruses to thrive in new domains.
The Brazilian government has stopped short of officially advising women not to get pregnant, but confusion and fear are spreading along with the virus.
Zika, named for the forest in Uganda where scientists discovered it in the 1940s, often goes unnoticed in the people it infects and was not considered especially life-threatening before spreading to Brazil.
But the advance of the virus is focusing scrutiny on the resilience of a worrisome pest: Aedes aegypti, the mosquito that carries Zika and other diseases, including yellow fever and chikungunya.
NEW YORK TIMES