New Delhi: The fresh outbreak of the lethal Nipah virus in Kozhikode, Kerala, has seen five confirmed infections and two deaths. Nearly 700 are on the list of ‘suspected infection’, including 76 who have been identified as high-risk contacts.
Nipah’s high mortality — 40-75 percent, according to the World Health Organization — has sent the state and central governments rushing to limit its spread.
The latest case is a 24-year-old healthcare worker who had come in close contact with one of the earliest patients in the current outbreak, which was confirmed earlier this week.
This is the sixth outbreak of the deadly Nipah virus in India, first recognised in 1999 in Malaysia. The first two outbreaks in India were reported from West Bengal.
Nipah’s most lethal attack in India was the first one, in 2001 — when 66 cases, the highest so far, were recorded in West Bengal and 45 died.
In 2007, the disease struck five people in West Bengal, killing all. There was, however, a gap of over a decade before the virus struck humans again, this time in Kerala — it led to 18 cases and 17 deaths in Kozhikode and Malappuram.
All outbreaks of the disease since 2018 have been reported only from Kerala.
Next year, during the second outbreak of Nipah virus in the state, this time in Ernakulam, there was only one case and they survived. In 2021, the only confirmed patient, in Kozhikode, succumbed to it.
A study, experts say, has found evidence of the presence of the Nipah virus in bat populations in several other states. The concentration of human infections in a certain area, they add, could be explained by cultural factors and the human-animal interaction in that geography.
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The virus, disease, management and risk factors
Nipah is a zoonotic virus (transmitted from animals to humans) but can also be transmitted through contaminated food or directly between people.
During the first recognised outbreak in Malaysia, which also affected Singapore, most human infections resulted from direct contact with sick pigs or their contaminated tissues. Transmission is believed to have occurred via unprotected exposure to secretions from the pigs, or unprotected contact with the tissue of a sick animal.
Infected people, in the beginning, develop symptoms such as fever, headaches, myalgia or muscle pain, vomiting and sore throat. A few, however, can stay totally asymptomatic as well.
Among those exhibiting symptoms, the initial signs of the disease can be followed by dizziness, drowsiness, altered consciousness, and neurological signs that indicate acute encephalitis (inflammation of the brain).
Some patients can also experience atypical pneumonia and severe respiratory problems, including acute respiratory distress and encephalitis. Seizures occur in severe cases, progressing to coma within 24 to 48 hours.
The incubation period (the gap from infection to the onset of symptoms) is believed to range from 4 to 14 days but, in some cases, it has been reported to be as long as 45 days.
Most people who survive acute encephalitis manage to recover but long-term neurological conditions have been reported in them. Nearly 20 percent of patients are also left with residual neurological consequences such as seizure disorder and personality changes.
A small number of people who recover subsequently relapse or develop delayed-onset encephalitis.
Dr Anita Mathew, director-internal medicine with Fortis Hospital in Mumbai, said the outbreak over the last several years had been triggered by eating contaminated fruits and vegetables, through body fluids, excretory material, saliva, and secretions of infected animals or fruit bats.
Once a person has the virus, others in close contact can also get infected, the clinician added.
“The natural source of the Nipah virus are fruit bats,” she said . “The understanding is that rapid urbanisation and encroaching the original cores, where fruit bats stay, is possibly causing the disease to spike over to humans.”
There are currently no drugs or vaccines specific to Nipah virus and intensive supportive care is recommended to treat severe respiratory and neurological complications.
Also, according to the WHO, close unprotected physical contact with Nipah virus-infected people should be avoided.
Overall, the evidence of Nipah virus has been established in several animals and across various countries but the disease in humans has been reported only from Malaysia, Singapore, Bangladesh and India.
Why Kerala repeatedly?
A scientist with the Indian Council of Medical Research (ICMR), the apex body in India for the formulation, coordination and promotion of biomedical research, told ThePrint that an ongoing project by the National Institute of Virology (NIV) to assess the spread of Nipah virus in India has found evidence of its presence in bat populations in at least nine states and one Union Territory.
These are Karnataka, Maharashtra, Bihar, Assam, Meghalaya, Puducherry, Tamil Nadu and Goa, apart from Kerala and West Bengal.
“The answer to the question as to why the disease in humans has been limited to certain states only may lie in the eating pattern or links between animals and humans — due to cultural reasons,” said the scientist, adding that a project carrying out tests in the bat population in other states is still underway
Senior virologist Dr Shahid Jameel, who is a fellow at Green Templeton College, University of Oxford, and a visiting professor at the Ashoka University, said Nipah is primarily spread by fruit bats.
“And bats don’t fly long distances — deforestation and climate change bring bats closer to humans. It’s possible that bats in that area (where the outbreak is being reported from) carry the virus,” he told ThePrint.
Jameel also underlined that drinking fresh toddy or sweet tree sap in the morning is cultural to some areas, while bats also drink the same at night. This may lead to contamination and transmission of the virus between bats and humans, as was the case in the first two outbreaks of the disease in India,” he said.
“Also,” said Jameel, “There is a possibility of higher respiratory transmission even though it’s not very efficient. There is also an element of seasonality because in some seasons bats shed more viruses — it could be heat or other stresses. It’s also linked to pregnancy and pup-rearing in bats.”
Pathogen with pandemic potential?
Responding to a query regarding the Nipah infection in the assembly, Kerala Health Minister Veena George said Wednesday that the virus strain seen in Kerala was the Bangladesh variant, which has a high mortality rate, but is less infectious, according to media reports.
The ICMR scientist quoted above said that, so far, three distinct Nipah virus variants have been identified — the Malaysia M genotype, Bangladesh B genotype, and India I genotype.
“In the samples from Kerala tested at NIV during the outbreaks so far, the virus variant appears to be India I genotype,” the scientist said.
Jameel said that the worries about Nipah’s pandemic potential are not far-fetched.
“This virus definitely has pandemic potential, especially with deforestation bringing bats closer to humans and global warming increasing heat stress on bats with increased virus shedding. We should work on a Nipah vaccine,” he said.
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