The Nipah virus in Kerala may have mutated due to climatic stress: Expert

The Nipah virus that has yet again gripped Kerala may have become deadlier due to climate stress. The Bangladesh strain of the virus currently circulating in Kerala has a high case fatality rate compared to the Malaysia strain, killing nine out of 10 people affected, epidemiologist Raman Gangakhedkar told news website News18.

With five infections and two deaths reported, the mortality in India is around 90 per cent, according to experts.  

The strain of the virus that caused the outbreak in 2018 was related to the Bangladesh strain but was significantly different from it and is to be classified as a different cluster, Kerala’s former health secretary Rajeev Sadanandan told Down to Earth. “The virus has been circulating locally since then in the fruit bat population and could have mutated from 2018, due to climatic stress.”

A study had previously confirmed that heat had made the dengue virus more infectious in Kerala, he told DTE. “But we will know for sure once the sequencing is completed by the National Institute of Virology in Pune.” 

Similarly, another question to be looked at is whether climate change caused a change in the hormone pattern of the fruit bat which led to a change in seasonality of the infection which used to be from December to June, the expert added.

Gangakhedkar, former head of epidemiology and communicable diseases at the Indian Council of Medical Research, who was at the forefront of the country’s efforts in tackling previous NiV outbreaks in Kerala, said in the interview with News18, that identifying the index patient and everyone who came in contact with the patient was key. In 2018, more than 2,000 people were traced within three days, he told the news organisation.

As of Saturday, state health minister Veena George said 1,192 are on the contact tracing list and 97 people have been tracked. 

On September 10, 2023, doctors who treated the four relatives of the deceased 49-year-old Mohammed Ali observed a red flag based on the family’s residence in Maruthonkara Gram Panchayat in Kozhikode, close by in proximity to the 2018 epicentre of the NiV outbreak.

Experts are currently collecting fluid samples from bats and fruit trees in the region. Pteropus medius (Indian fruit bat) is considered a reservoir and an intermediate host of the zoonotic RNA virus. 

A detailed investigation to find the source of NiV infection was carried out by National Institute of Virology, Pune during the 2018 and 2019 outbreaks, which showed the presence of NiV and anti-NiV antibodies in the fruit bats around the vicinity of the infected in Kerala.

While the spillover to humans was reported in Kerala and West Bengal in 2001, the virus has been found in other Indian states too in the Pteropus medius species. 

According to a recent Pune-based study by the Indian Council of Medical Research’s National Institute of Virology, NiV was detected in the bat population in nine Indian states and one Union territory. These are Kerala, Tamil Nadu, Karnataka, Goa, Maharashtra, Bihar, West Bengal, Assam and Meghalaya and Pondicherry.

Sadanandan told DTE: 

All the bats from the route between Kerala to West Bengal could have been infected because this species doesn’t fly farther than 50 km.  Hence, the only way to transmit the virus long term is to infect a chain of bats in different locations. 

“The percentage of virus-infected bats which was above 20 per cent in 2018 would have gone up manifold as bats can transmit to other bats without being affected by it,” the expert added.

On the repeated outbreaks in Kerala, public health researcher Sunil Raina told DTE: “A possible higher circulation of the virus in bats and more human-animal-environment interactions in Kerala due to rapid expansion of urban areas as also the fact that Kerala has previous experience and good surveillance in place, makes Kerala report Nipah Virus often. However, with urbanisation increasing in other states, a potential for spillover is always there resulting in reporting of Nipah outbreaks in the future.”

Sadanandan said the fruit bats need not be linked to forests, as they are fruit-eating bats, are very naturalised and live in human habitats too.

India has requested the import of 20 doses of monoclonal antibodies, namely m102.4, from Australia for treatment on a compassionate basis. It was originally developed for Henipavirus (bat-borne viruses of the same family). So far, it has only been proven to be safe in a small phase I trial and used on 14 people so far. 

During the 2018 NiV outbreak in Kozhikode, 20 doses of m102.4 were imported from Queensland, but they were not used as the outbreak ended before the antibodies arrived, Rajiv Bahl, director-general of the Indian Council of Medical Research, said in a press conference September 15, 2023.

Raina told DTE, “This is the first time the monoclonal antibody has been used to treat the Nipah virus in India. The research community only started thinking about it in 2013. Patients from the previous outbreaks in India were treated with supportive therapies.”