Brazilian scientists could be close to producing a reliable test for the Zika virus that can spot traces of the disease even months after sufferers have recovered.

If scientists succeed, it could represent a major breakthrough for public health authorities in Brazil looking for a definitive connection between a Zika epidemic in the country and an outbreak of thousands of cases of the birth defect microcephaly.

Zika has spread rapidly through the Americas in recent months, causing fear and panic, especially among pregnant women. The World Health Organization said Zika could affect 3 million to 4 million people within a year, and President Obama has called for urgent action.

Luis Ferreira, a microbiologist at the University of Sao Paulo who is part of a “Zika network” of 42 laboratories, said the new test could be ready in a few weeks.

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The Brazilian government blames the incidence of microcephaly on Zika, but the U.S. Centers for Disease Control and Prevention and the World Health Organization have not positively confirmed the link. The CDC, however, has warned pregnant women against traveling to countries with outbreaks of Zika infections.

The Brazilian government is investigating 3,448 suspected cases of microcephaly, it said in a bulletin this week. Beyond those, it has discounted 462 cases and confirmed 270 as being microcephaly. However, it has been able to confirm the presence of Zika in only six of the 270 established cases.

This is because of the lack of a widely available method to test for the virus months after parents may have been infected, Ferreira said. The virus can be detected in the blood of victims for a few days and in their urine for a few months.

Currently, complex tests can spot traces of the virus in antibodies but take up to 10 days, because the antibodies produced are similar to those of dengue, another disease spread by the Aedes aegypti mosquito.

This week Lyle Petersen, director of the CDC’s vector-borne disease division, said that current tests cannot differentiate between the antibodies humans produce in response to the two diseases.

Paolo Zanotto, a microbiologist at the University of Sao Paulo who is coordinating the Zika network said the team is waiting for a protein from Senegalese researchers that may be able to tease out the differences between antibodies produced against dengue and Zika.

As the World Health Organization decides whether to declare the Zika virus outbreak a global public health emergency, here's a look at other pandemics that made it to our shores. (Gillian Brockell/The Washington Post)

In Brazil, Zika infection has often been wrongly diagnosed as dengue or chikungunya. Zika has also been associated with hundreds of cases of the rare Guillain-Barré syndrome, which can cause paralysis.

Mirdad Kazanji, director of the Pasteur Institute in French Guiana, who has been working with the Zika network, said the test is crucial to establishing a definite link between Zika and microcephaly.

“To do that, you need the diagnostic test first, to show that the virus is already present here,” he said.

At a Zika network conference at the University of Sao Paulo, Kazanji said the virus had first been found in a rhesus monkey in Uganda in 1947 by researchers studying yellow fever. It spread to Yap Island in French Micronesia, which saw an outbreak in 2007. An outbreak in French Polynesia followed in 2013-2014, but it was only after the Brazil outbreak that researchers there found evidence of a spike in local microcephaly cases, Kazanji said in a presentation.

Kazanji worked for 10 years in Africa, where the only person he saw with the disease was his wife. In contrast, the Brazilian government says that 400,000 to 1.5 million people may have been infected in less than a year.

Kazanji said this is because Africans had built up resistance to Zika but Brazilians had not.

“The people there, they own immunity,” Kazanji told The Washington Post. “But the virus arrived at this naive region where it is not Africa; the people have no immunity.”

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