Test detects antibodies against Zika virus
Agência FAPESP/DICYT A diagnostic test capable of detecting the presence of specific antibodies against Zika virus in blood samples has been developed by researchers at the University of São Paulo’s Biomedical Science Institute (ICB-USP) in Brazil.
The researchers – Paolo Zanotto, Luís Carlos de Souza Ferreira and Edison Luiz Durigon – belong to the São Paulo Zika Virus Research Network (Rede Zika), a task force set up in late 2015 with FAPESP’s support.
“The test will help clarify the link between infection by Zika virus and microcephaly,” Durigon stated. “We will know how many of these mothers were infected by zika and whether microcephalic babies have antibodies against the virus. It will also give us an idea of the actual extent of the epidemic and how the virus is spreading across Brazil.”
The group developed a way of producing recombinant Zika virus NS1 protein from genetically modified bacteria of the species Escherichia coli and adapted the enzyme-linked immunosorbent assay (ELISA) deployed by labs around the world to test for HIV, hepatitis and rubella, among other diseases, using the recombinant protein.
According to Durigon, the test detects both IgM antibodies, produced during the acute phase of the infection, and IgG antibodies, which confer long-term protection against the virus. It has been validated in samples from patients in São Paulo as well as women in Itabaiana, a town in Sergipe State, which has one of the highest incidence proportions of microcephaly in Brazil.
The methodology confirmed that most of the eight mothers of microcephalic babies in the town are seropositive for Zika virus, and the same findings were obtained for their babies.
“These initial tests showed us that the method is specific and does not cross-react with antibodies against dengue or yellow fever, which was our main worry,” Durigon said. “We now have to assess how the method works in real life. We are in touch with Fiocruz and Instituto Adolfo Lutz to ask them to use the test on their patients.”
According to Durigon, rather than patenting the methodology or using it as a basis for a commercial kit, the group plans to distribute the recombinant protein free of charge, first to the centers that belong to the Zika Network and soon afterward to the public health system.
“The Butantan Institute, in partnership with the São Paulo State Technological Research Institute (IPT), will mass-produce recombinant NS1,” he said. “Initially, I believe it will be used to test pregnant women because they are most at risk. Once the Butantan Institute has ramped up production, it will be possible to distribute the test to all of the labs in Brazil’s public health system. I expect this to be done quickly.”
According to Durigon, no other technique is currently available for this purpose in Brazil. “Imported methods are arriving, and some kits use the same protein as our test,” he said. “However, these kits would be extremely expensive for our health system to buy.”
Members of the Zika Network selected the development of a serological test as a research priority when they met at FAPESP on February 16.
“Until now, we could not even be sure an epidemic was actually under way because it was not possible to measure the number of cases or know how the virus was circulating. The diagnostic test has been made a priority because of these reasons,” Durigon said.
The only tests currently available are real-time PCR molecular assays that detect DNA from the virus in secretions up to five days after infection.
“These acute cases are only the tip of the iceberg,” Durigon said. “Patients who develop a moderate condition can take as long as a week to go to a doctor. If so, the PCR test will not be positive, but the IgM test will.”
In addition to showing how many mothers with microcephalic babies have had the disease, the test will also show how many pregnant women are currently infected so that they can be properly cared for.
“Moreover, blood banks can use the test to screen out asymptomatic donors who are carrying the virus or have been infected in the past, just as they currently do for hepatitis and HIV,” Durigon said.