Rio de Janeiro: Unusually wet weather, poor sanitation and a public health service weakened by economic crisis are contributing to an outbreak in Brazil of Zika, a mosquito-carried virus linked to a surge in cases of children born with brain damage, health experts say.
Researchers believe the virus - first thought to be relatively innocuous - may have arrived in Brazil during the 2014 football World Cup, carried by visitors from French Polynesia, where an outbreak had just occurred.
The effects of the emerging Zika virus
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The effects of the emerging Zika virus
The US Centers for Disease Control says there is growing concern about the mosquito-borne Zika virus after a surge in cases of a rare brain defect among babies in Brazil.
"The virus found the perfect conditions in Brazil: a very efficient vector that loves human blood, millions of susceptible victims with no antibodies, ideal climate, and lots of places to breed," said Ricardo Lourenço, who studies tropical infectious diseases at Brazil's Oswaldo Cruz Institute.
The virus - which is also affecting Colombia and 20 other countries and territories in the Americas - is raising global alarm ahead of the 2016 Olympic games in Rio de Janeiro.
Brazil and Colombia have warned pregnant women to take precautions against mosquito bites, and other women not to get pregnant until the effect of Zika on unborn children is better understood.
"We are doing this because I believe it's a good way to communicate the risk, to tell people that there could be serious consequences," said Alejnadro Gavira, Colombia's health minister, who called on women to delay pregnancies six to eight months.
The Colombian health ministry has told state health providers to treat pregnant women who are infected with the Zika virus as high-risk pregnancies, and to provide scans during the entire pregnancy.
On Friday, US health officials said three people in New York state, including one from Queens, tested positive for Zika.
All three had travelled to places outside the United States. Besides the person from New York City, the patients were from Nassau and Orange counties. One person has fully recovered, and the two others are recovering without complications, according to a statement the State Health Department issued Friday.
Health officials said the virus's symptoms - including fever, rash, joint pain and red eyes - are typically mild and last as long as a week. Some may not even realise they have been infected. About 1 in 5 people who have been bitten by an infected mosquito will grow ill, with symptoms usually appearing within a few days.
The Centres for Disease Control and Prevention in the United States has warned pregnant women not to travel to Brazil and 13 countries in Latin America and the Caribbean where the virus is quickly spreading.
But Marcos Espinal, head of the Pan American Health Organisation's communicable diseases department, told the Thomson Reuters Foundation in a telephone interview from Washington that "travel restrictions will not stop the spread of Zika" and it is likely to reach throughout Latin America.
"It's a mosquito that is endemic in the whole of Latin America and the Caribbean, and the population of the Americas was not exposed to the virus, so there's no immunity to it," he said.
Colombia has the second highest infection rate after Brazil, with more than 13,500 people infected with the Zika virus and the disease could hit as many as 700,000, its health minister said.
"This is a new and emerging phenomenon and we still don't know all of its consequences," he told local media this week.
Unlike dengue, which can cause high fever and join pain, Zika produces symptoms - such as mild fever and rash - that are often so light people don't know they have the disease, health experts say.
But the spread of the virus in Brazil has coincided with a surge in infants born with birth defects - and a possible rise in cases of Guillain-Barre syndrome, a rare condition in which the body's immune system attacks its nerves.
Threat to newborns
Brazil's Health Ministry said on January 20 that 3,893 cases of microcephaly, a rare congenital condition in which babies are born with an abnormally small head, have been associated with Zika.
The cases have appeared in nearly all Brazilian states. Infants likely contracted the virus from their mothers who were infected while pregnant, the ministry said.
The condition leads to irreversible neurological damage that affects movement and vision.
Although microcephaly has not been definitively connected with Zika, experts believe there is a link, as the virus has been found in brain tissue and amniotic fluid from babies who were born with microcephaly or died in the womb, Brazil's Health Ministry said.
In Colombia, there are 560 known cases of pregnant women who are infected with the Zika virus, and who are being closely monitored by health workers. So far no cases of newborns suffering from microcephaly have been recorded.
Challenges to gaining control
Bringing the epidemic of the little-known virus under control will be hugely difficult for Brazil, as the country grapples with a surge in numbers of Aedes aegypti mosquitoes this year in response to unusually wet weather in many parts of the huge nation, said Nancy Bellei, head of clinical virology at Brazil's Infectology Society.
"This is the worst time to deal with an epidemic of a virus we know very little about," she said in a phone interview. "The government is trying to raise awareness and fight the mosquito but we won't achieve control in the short term under the current circumstances."
The mosquito that transmits Zika also carries dengue, yellow fever and chikungunya and thrives in humid, tropical climates. It breeds in stagnant water, which is more likely to collect during heavy rainfall in everything from abandoned tyres in garbage dumps to residential water tanks recently installed to get residents through a record Brazilian drought.
Extreme weather swings linked to climate change and a strong El Nino phenomenon this year may be contributing to the outbreak, some experts believe.
The worst recession in more than a century in this country of 200 million also had led government to cut budgets for public health and sanitation services, limiting its ability to respond, Bellei said.
In its fight against the mosquito, the government has asked the army to help sanitation agents in their search for mosquito breeding sites.
The Pan American Health Organisation, the regional arm of the World Health Organisation, has said the key to containing the Zika outbreak is to get rid of the places where mosquitoes lays their eggs in water, and for people to use repellent and sleep under mosquito nets to prevent mosquito bites.
It is urging governments across the region to step up campaigns to raise public awareness about how to control mosquitoes.
Colombians, like others in the region, are being told to cover and regularly clean water tanks, to empty or cover any other containers that can hold water and to unblock drains that can accumulate standing water.
Authorities in Colombia's northern city of Cucuta, where 1700 cases of Zika have been registered, have announced they will start spraying some homes and streets with insecticide to kill mosquito eggs.