First diagnostic test kit for Zika virus already created

Aedes aegypti. - Photo - James Gathany, CDC

Aedes aegypti mosquitoes spreads Zika virus. – Photo: James Gathany, CDC

If all goes well and as expected, the validation process of the first diagnostic test kit capable of diagnosing Zika, dengue and chikungunya simultaneously will be completed by the end of this month. The test kit has already been created. And if the final validation process also goes off well, about 500,000 test kits could be available in Brazil by the end of the year, Dr. Ana Bispo, Head of the Flavivirus Laboratory at the Oswaldo Cruz Foundation (Fiocruz), in Rio de Janeiro, Brazil told the WHO Bulletin.

“The test has great potential for improving epidemiological vigilance because it shows which virus is circulating at a specific time in a given area. The test could also be particularly useful in the first days of infection, when the symptoms of Zika, chikungunya and dengue are so similar that it is difficult for doctors to distinguish between dengue and Zika,” she was quoted as saying.

The diagnostic test is a simple, ready-to-use PCR test — Nucleic Acid Test for Dengue, Chikungunya and Zika viruses. All that a technician has to do is to extract the RNA of the virus and add it to the three different reagents meant for Zika, dengue and chikungunya.

The causal link

A causal link between Zika virus and microcephaly is yet to be established despite a strong association found between the virus and microcephaly — the virus has been found in the placenta and amniotic fluid of mothers and in the brains of foetuses and newborns.  “The latest evidence suggests that Zika virus infection during pregnancy may be linked to microcephaly in newborn babies. No scientific evidence to date confirms a link between Zika virus and microcephaly,” a February 12 WHO Zika situation report notes. Even the February 26 WHO Zika situation report states: “Evidence that neurological disorders, including microcephaly and GBS [Guillain-Barré syndrome], are linked to Zika virus infection remains circumstantial, but a growing body of clinical and epidemiological data points towards a causal role for Zika virus”.

In November 2015, Dr. Bispo’s team was the first to detect Zika virus genome in the amniotic fluid of two pregnant women (from Paraíba state) who had a medical condition consistent with Zika virus infection.  Though ultrasound images initially showed that both the foetuses were normal, microcalcifications of the brain were soon seen. Amniocentesis tests to check for the virus in the amniotic fluid turned a positive result for Zika virus.

Dr. Bispo is doubtful if anything other than Zika virus could be causing the increasing number of microcephaly cases seen in Brazil. “The majority of women who have delivered babies with microcephaly report that they have had a medical condition consistent with Zika, especially during the first trimester,” she said. “It is hard to establish a causal link between Zika and microcephaly, because it is difficult to detect the virus when the baby is born.”

The challenges

Detecting the virus antibodies in the baby with microcephaly or Guillain-Barré syndrome becomes almost impossible as things stand now due to the non-availability of specific serological test for Zika virus antibodies. The problem is compounded in the case of Guillain-Barré syndrome — “when the symptoms appear (usually 12 to 15 days after Zika virus infection) patients are no longer in the acute phase of Zika disease,” she said.

Currently, diagnosis of Zika virus relies on the molecular detection of viral RNA.  But the problem is that the viral RNA is present only during a brief period of viraemia. Because the clinical symptoms are nonspecific, most cases remain undiagnosed, making it even more difficult to find the link between microcephaly and Zika virus infection.  “It is essential to have reliable and more sensitive and specific serological tests, without or with minimal cross-reactivity with other infections, particularly, dengue fever, yellow fever, and other flaviviruses,” notes a February 23 Comment piece in The Lancet.

According to the WHO Bulletin, a case–control study involving 300 pregnant women is being done at Fiocruz to find the causal link between microcephaly and Zika virus. Besides Fiocruz, a similar case–control study is under way at the Aggeu Magalhães Research Center, a branch of Fiocruz in Pernambuco state, where an exceptionally high number of microcephaly cases was reported last year.

Dr. Bispo does not think that Zika virus will be a problem when the Olympic Games get under way in Brazil in August this year. Dengue, which was prevalent in 2014, did not create a problem when the World Cup was held that year.  The reason: the event was held in the winter. “Mosquitoes that hibernate need warm weather to become active: the Aedes shuts down for winter and so we did not have a big problem with dengue during the World Cup,” she told the WHO Bulletin. “The government is working hard on prevention so that visitors to Brazil — apart from pregnant women — need not worry.”

Published in the Hindu on March 1, 2016