Rio de Janeiro: Brazilian government researchers working in the north-eastern state where the country has registered the biggest spike in cases of babies born with microcephaly say they have identified traces of Zika in 12 infants born with the birth defect.
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The World Health Organisation says they are concerned after a report that the Zika virus has been sexually transmitted in Dallas, Texas.
"It is a major breakthrough," said Lindomar Pena, a virologist and researcher on the taskforce studying Zika in Pernambuco.
The researchers tested 12 babies with microcephaly and, in their spinal fluid, found antibodies that the human body makes to fight viruses such as Zika, said Dr Pena, who led the study.
The news comes as the world grapples with the explosive spread of the virus that has no immediate treatment and no vaccine. Commercial blood tests that can detect the antibodies used to fight it have only just been cleared for commercialisation by Brazilian public health agency Anvisa.
In December, the Brazilian Health Ministry confirmed a link between the virus and the small-head condition based on tests carried out on a deceased baby from the state of Ceara whose blood and tissue samples showed traces of the virus. The ministry has since announced Zika has been found on the amniotic fluid of two pregnant women whose fetuses have been diagnosed with the condition.
Hawaii health officials have also said a baby recently born with microcephaly at an Oahu hospital was infected with the virus in utero. In reporting the laboratory confirmation from the US Centres for Disease Control and Prevention (CDCP), the Hawaii health department said the child's mother probably had a Zika infection while living in Brazil.
But that is still a fraction of the more than 4000 suspected cases of the rare congenital condition reported in Brazil in recent months – in part, scientists say, because the virus lives in the body only for a few days and is extremely difficult to detect months later.
This week, the World Health Organisation declared a global public health emergency over Zika and its suspected complications in newborns, but neither it nor the CDCP has scientifically confirmed the link.
Luciana D'Angelo, executive secretary for health surveillance for the Pernambuco state government, says the latest test results "strengthen the hypothesis that there is a relationship between Zika and microcephaly."
So far, Brazilian experts have scrutinised 1113 of the reports of microcephaly received since October and found 404 cases in which the condition may have been caused by Zika. The other cases either were linked to something else, such as a genetic factor, or did not turn out to be microcephaly at all.
Complicating the situation, also on Thursday, Brazilian officials said two people contracted the virus through blood transfusions, the first reports of such transmission in an outbreak that is projected to infect millions in the coming months.
Carmino Antonio de Souza, health secretary of Campinas, a city north-west of Sao Paulo, said both transfusions occurred during the first four months of 2015 but that the transmission wasn't confirmed until recently, according to the Wall Street Journal. One patient was a liver-transplant recipient and the other a gunshot victim.
Marcelo Addas Carvalho, director of the Blood Centre at the Sao Paulo state University of Campinas, said genetic testing confirmed that a man who received a blood transfusion using blood from a donor with Zika in March 2015 became infected with the virus. The patient later died from his gunshot wounds and not the Zika infection, local health officials and Dr Carvalho told the news service.
Worries about Zika in the blood supply have been a growing concern for health officials around the world. While there are no scientifically confirmed cases of transmission through the blood supply, it is theoretically possible and has been shown to occur with viruses in the same family.
The American Red Cross, as well as health officials in Canada and Britain, have been urging people who have travelled to regions affected by the Zika virus to wait at least 28 days before giving blood.
Susan Stramer, the vice-president of scientific affairs for the Red Cross, said this week that the organisation is also asking donors to immediately notify the organisation if they subsequently develop symptoms consistent with the Zika virus within 14 days of donating blood "so that we can quarantine the product".
On Thursday, a Red Cross spokeswoman said that the two reported cases in Brazil "are under investigation and will provide further information regarding the risk of transmission of Zika by blood transfusion".
"It wouldn't be surprising to see transmissions through blood on rare occasions," said Tom Skinner, a spokesman for the CDCP, saying it depends on how sick the donor is. The Zika virus usually clears the bloodstream within a week, researchers have said. Despite the devastating effects on children born with microcephaly and as-yet unknown further complications, doctors say the virus is not fatal and most infected people would not notice its mild symptoms.
Compared with the Dengue virus – which is transmitted by the same mosquito Aedes Aegypti and kills between 25,000 and 50,000 people worldwide every year – Brazilian doctors say there's cause for "concern but not panic" in dealing with Zika.
Washington Post with Fairfax Media, Reuters