The three people found infected with the Zika in Ahmedabad, Gujarat have no history of travel to Zika-affected countries. The implication of this is that that the transmission of the Zika in Ahmedabad could be local and that the disease is already prevalent in the area, said experts. This view is based on recent analyses of a 1954 report that indicated that Zika virus could have circulated in the India in the past. However, its findings are inconclusive.

Zika is a viral disease transmitted by the bite of an Aedes mosquito and can also be sexually transmitted. The Zika virus generally causes a mild and temporary infection in adults with symptoms like fever and rashes. But Zika infections have also been linked to incidences of Guillain-Barré syndrome, a nervous system disorder caused by a person’s own immune system attacking nerve cells, causing muscle weakness, and sometimes, paralysis. The biggest danger from the Zika virus is to pregnant women and their foetuses. Zika infections in pregnant women can lead to congenital defects in in their newborns such as microcephaly, in which the brain of the infant is small and underdeveloped.

As per guidelines issued by the Government of India to prevent and control Zika, the Integrated Disease Surveillance Programme should track clustered cases of acute febrile illness, which are people having fever, chills and joint pain. The programme is supposed to do this by gathering data from communities and hospitals. Surveillance for Zika also involves looking for people who have travelled to areas with ongoing transmission such as Brazil and Mexico.

“We checked if the patients travelled to these countries within the incubation period of the infection,” said Dr AC Dhariwal, director of National Centre for Disease Control. “Since there was no history of travel, the transmission is presumed to be local.”

Dhariwal said that the Zika virus strain found in the three Ahmedabad cases is of Asian origin. This strain was one of the many found in Brazil, which had one of the biggest outbreaks in 2015 and an abnormal rise in the cases of microcephaly.

“But the same strain was also found in Singapore last year,” clarified Dhariwal. “The cases were milder there.”

In response to queries by Scroll.in, a spokesperson for the World Health Organisation country office in India said in an email that cases of Zika in India are not unexpected since all countries with Aedes mosquitoes are at risk for local Zika virus transmission.

“Although Zika is no longer a Public Health Emergency of International Concern, WHO maintains that vigilance to Zika needs to remain high,” said the spokesperson in an email response. “Reporting of Zika cases reflects the country’s efforts to implement key WHO recommendations related to surveillance as well as their commitment to the International Health Regulations, which requires all member countries to report public health events to WHO.”

India did report the cases to WHO but more than four months after the first case in the country was confirmed.

Zika always hiding in India?

The Zika virus belongs to a family of viruses called flavivirus. The other such viruses include dengue and chikungunya.

The World Health Organisation, in its review of the history of Zika, records that the virus has been detected in mosquitoes found in equatorial Asia, including India, Indonesia, Malaysia and Pakistan. Despite this, India does not feature in the organisation’s list of countries with evidence of Zika before 2015.

Between 1969 and 1983, Zika virus was detected in mosquitoes found in equatorial Asia, including India, Indonesia, Malaysia and Pakistan. (Image: WHO)

A 1954 surveillance report indicates that Zika virus could have circulated in the India in the past. The report was prepared by KC Smithburn from Rockefeller Foundation in New York, JA Kerr who was the director of the Virus Research Centre – which has since been renamed the National Institute of Virology – in Pune and PB Gatne who was Bombay state’s medical officer. The researchers reported the detection of antibodies against the Zika virus in samples collected from people in Bharuch district, then in Bombay state and now in Gujarat and Nagpur. This would mean that the people tested developed immunity against the disease.

This report is inconclusive because, as virologists point out, an antibody test is not as accurate as the polymerase chain reaction test that is now used for genetic analysis and identification of viruses.

Moreover, the presence of these antibodies it could “be a result of cross-reactivity with other flaviviruses (such) as dengue (which) was also found prevalent in these areas,” according a 2016 paper published in the Indian Journal of Medical Research.

However, the antibody test was the only test available in 1954.

The Indian Journal of Medical Research paper authored by scientists from the National Institute of Virology said, “The major concern is that, once endemicity is established, ZiV (Zika Virus) can exist in its natural eco-cycle for a significant period with a potential to emerge as a pathogenic human agent.”

Another analysis published by the American Society for Microbiology in 2016 points to the presence of Zika in India in 1952 highlighting the possibility of the virus may having been circulating and having become endemic here.

So, it is possible that the virus has been present in the Indian ecosystem.

The government seems to believe that theory. “The paper indicates that the virus has been in circulation for many years,” said Dhariwal.

Dr Pradip Awate, Maharashtra’s epidemiological officer, said: “Looking at the environmental presence of the vector, that is the Aedes mosquito, it is possible that the virus was locally present.”

Awate said that since four out of five people infected with Zika will not show any symptoms, it may not have been detected earlier. He hopes that Maharashtra’s strengthened vector control to combat dengue and chikungunya will help subdue Zika too. Additionally, he said, 11 hospitals in the state are tracking microcephaly cases.

A more effective virus?

Currently, the strain of virus that has infected the three people in Ahmedabad seems to be a mild one.

“All three patients survived, including the high risk group of pregnant women,” said Dr Om Shrivastava, a consultant infectious disease specialist in Mumbai. “There were also no adverse clinical events despite the infection. That is good news.”

However, the government has to be cautious, said Shrivastava, since the full extent of medical complication caused by the Asian strain may still be unknown. “Also, the presentation of the antigen in the mosquito differs from season to season and year to year,” he added.

A health worker attends to a patient with Guillain–Barré syndrome. Brazil reported 49 cases were confirmed of Guillain–Barré syndrome. Of these cases, all but two had a prior history of infection with Zika, chikungunya or dengue. (Photo: WHO/PAHO)

Zika is from the flavivirus family, like Dengue, Chikungunya and Japanese Encephalitis. The presence of these in the environment can make Zika more dangerous, said Dr Shailendra Saxena who heads the Centre for Advanced Research at King George’s Medical University in Lucknow.

This is because of a phenomenon called antibody-dependent enhancement between similar viruses. A person who has contracted dengue will have antibodies against the dengue virus in his blood even after he recovers. If this person were now to be infected by the Zika virus, these antibodies may attack the infecting Zika virus but will be unable to inactivate it – a process that only makes the Zika virus stronger and more efficient and lead to a more severe infection.

“In that situation, the prognosis of the disease may be worse,” said Saxena. “That is why we need to more cautious and need to be more aggressive while doing surveillance in the country.”

Besides, the monsoons have only just hit Kerala and will spread across the country over the next few weeks and months. With the rains, the Aedes mosquitos will become more active. Dr HC Gera, who retired as the Integrated Disease Surveillance officer in Chandigarh said, “Post monsoon, the disease could spread.”