The Zika virus behind the ongoing outbreak in Rajasthan is closely related to the virus that caused the Brazilian outbreak, according to Balram Bhargava, Director General of the Indian Council of Medical Research (ICMR). Dr. Bhargava told The Hindu that the National Institute of Virology (NIV) had fully sequenced the Rajasthan virus’ genome, and this is the first time a Brazilian-like strain has been detected in India. Before this, a strain from a patient in Gujarat, sequenced partially by the NIV, was found to be close to a Malaysian Zika strain, isolated in 1966.
Different from Gujarat
The Rajasthan outbreak is different from the Gujarat cases in several important ways. Firstly, this is the largest in India, having affected 72 people. Before this, only four Zika cases were detected by the NIV in 2016-17, despite widespread surveillance. These included three cases in Gujarat and one in Tamil Nadu. Secondly, in Gujarat and Tamil Nadu, the virus did not seem to be moving efficiently from person to person, via mosquitoes. Though researchers tested several people apart from the confirmed cases then, they were unable to find other infections, said Arunkumar Govindakarnavar, who heads Karnataka’s Manipal Centre for Virus Research. Thirdly, even though the ICMR has screened 50,000 mosquitoes at 8 sites across India since 2016, it did not detect the virus in mosquitoes until the Rajasthan outbreak, Dr. Bhargava said.
“The current outbreak seems to be triggered due to uncontrolled mosquito breeding. Vector control is the key to prevention of outbreaks in future,” he said.
Though the virus is spreading quickly, most Zika cases have been mild, with 60 out of 72 patients healthy after treatment. There have been no deaths.
The biggest risk that officials are being watchful about is Congenital Zika Syndrome, in which babies of Zika-infected mothers are born with impairments such as microcephaly - an abnormally small head. Dr. Bhargava said pregnant women were being screened carefully for Zika infections in Rajasthan.
Microcephaly was first linked to Zika during the Brazilian outbreak. This outbreak, which spread to 28 countries, was unusual because of its size, as well as the number of microcephaly cases. Even though Zika has been in Asia for several years, outbreaks here were small and saw no microcephaly. In contrast, at its peak, northeast Brazil saw 49.9 cases of microcephaly for every 10,000 births, compared to a historical normal of 2 per 10,000, according to a 2017 study in The Lancet . Eventually, researchers suggested several likely reasons behind the unusual Brazilian outbreak. Among them, the Brazilian population had never been exposed to Zika, and lacked protective immunity. Also, experiments showed that the south American strain was better at being transmitted through mosquitoes than older strains. One of the factors behind the improved transmission was a mutation called A188V in the viral genome, according to a 2017 Nature study. This mutation is not present in the Rajasthan strain.
The NIV found another mutation called S139N in the Rajasthan strain, however. In a 2017 study published in Science , Chinese researchers linked this mutation to microcephaly. But this study has not be replicated by other researchers, said Kristian G Andersen, a Zika genomics researcher at California’s Scripps Research Translational Institute. Further, researchers have hypothesised that the unusual spike in microcephaly cases in Brazil could be due to other causes, such as co-infection with dengue. For now, Andersen says, S139N is not a cause for worry in Rajasthan.
