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HomeIndiaWhy Nipah virus keeps returning to Kerala, how its symptoms have changed

Why Nipah virus keeps returning to Kerala, how its symptoms have changed

The zoonotic virus Nipah, which claimed 17 lives in 2018 when Kerala witnessed its first outbreak, has returned to the state for the fourth time in the last five years. Six cases have so far been detected in 2023, all in the north Kerala district of Kozhikode.On both occasions, it was Dr A S Anoop Kumar, an expert on infectious diseases and tropical fevers, who was instrumental in detecting the virus, leading to timely containment of the outbreak. Dr Anoop, Director, Critical Care, of Aster MIMS Hospital’s North Kerala Cluster, had also served as a member of the state government’s expert advisory panel on Covid-19 management.

In an interview with The Indian Express, Dr Anoop compares the 2018 outbreak in Kerala with the recent cases, explains why more studies are needed on Nipah and narrates how, after a family of four was admitted to MIMS Kozhikode, his team meticulously investigated the disease, isolated patients and ensured Nipah protocols kicked in.

nipah Dr Anoop compares the 2018 outbreak in Kerala with the recent cases

Why does Kerala, particularly Kozhikode, see repeated infections of Nipah?

This can be explained in two ways. In the 2018 outbreak, it was proven that bats in the Kozhikode area have the Nipah virus. Then, the same strain of the virus was isolated from all cases, showing that bats are the source of infection. This could be one reason for the repeated presence of the virus. At the same time, there is data that shows the presence of the virus in bats in other states as well. One reason why other states are not reporting Nipah could be because they don’t have a higher index of suspicion and nobody has tested samples for Nipah. But in Kerala, even when we are slightly suspicious (that there might be an infection), we take all precautions, collect samples and identify cases. We have been diagnosing cases whenever we are suspicious or come across unusual findings. It’s possible that this is not happening in other states.

Could the higher cases be the result of fruit bats in Kerala being a reservoir of the virus?

All fruit bats in India are reservoirs of the Nipah virus. We have data to show that except certain parts of Kashmir, all Indian states have bats with the presence of the virus. But we don’t have scientific data on whether fruit bats in Kerala have a higher density of the virus in their bodies. No documents are available comparing the density of the virus across bats in various regions. So, we can say that Kerala is suspecting more, testing more and identifying more cases.

Why is Kerala ‘suspecting’ more cases?

There are many reasons for this. The health care system in Kerala is more developed, people here are more aware and more demanding. When a disease is not diagnosed, people here start questioning the clinician. That puts pressure on the treating clinicians. Public awareness, dedication of health care professionals and health care infrastructure put together help us diagnose cases.

Nipah Kozhikode: Health workers collect clinical samples and investigate the home of a Nipah virus victim, in Kozhikode, Friday, Sept. 15, 2023. (PTI Photo)(PTI09_15_2023_000328A)

After outbreaks in West Bengal in 2001 and 2007, we haven’t heard anything from that state.

We don’t know the exact reasons for that. In West Bengal, Nipah was retrospectively diagnosed after the outbreak. Cases were not diagnosed when they were active. I was in touch with clinicians in that area. I was told they were screening only when there is a high index of suspicion. That could be one reason. Also, it’s possible that the source of infection may not be in that area, which is also protecting people.

Clinically, how are the Nipah symptoms in 2018 different from what you are seeing in 2023?

Majority of the Nipah cases that have been reported from different parts of the world since 1998 have had mainly encephalitis symptoms. Even during the 2018 outbreak in Kerala, all the patients had encephalitis symptoms — they came to the hospital with fever and later developed unconsciousness and neurological issues. This time, the patients have been showing mainly respiratory symptoms and developing severe pneumonia. They did not have many encephalitis symptoms. We developed suspicion only because there was a clustering of cases and a few unusual symptoms. The index case, who died on August 30, had fever, which progressed into severe pneumonia and later multi-organ failure. He had no symptoms of encephalitis. His case was concluded as viral pneumonia, which is very common.

What does this clear shift in clinical symptoms indicate?

There is obviously some genetic variation or a slight mutation in the virus or its variant. The National Institute of Virology, Pune, should be able to find out whether this time we had the same strain as in 2018 or if the virus has undergone any mutation.

Can you take us through the events that led to the detection of the virus this time?

Four members of a family were admitted to our hospital (MIMS Kozhikode) — three in the paediatric department and an adult in the pulmonology department. We were told that a person in the family had died on August 30. That made us suspicious about a clustering of a disease and so the dead person was reckoned as the index case. We formed a multi-disciplinary team, analysed symptoms and looked into the background. We realised that this family was from near the epi-centre of the Nipah outbreak in 2018. They also exhibited some abnormal clinical features. One of them had seizures.

When we were having a discussion about these four cases, another patient was brought to us on September 11, referred from a hospital. He had viral pneumonia, but died of cardiac arrest soon after reaching our emergency department. The death of a healthy 40-year-old raised our suspicion. This patient did not have any contact with the four-member family who was already under our investigation. But we kept probing and realised that this 40-year-old (who died on September 11) was in another hospital to meet one of his relatives. We already knew that the August 30 death (the index case, a member of the four-member family under treatment at MIMS, Kozhikode) had taken place at the hospital where this 40-year-old had gone to meet a relative. So, we painstakingly went after the discharge summary of the 49-year-old person who died on August 30, collected his admission time and other details. We came to know that there was an overlap of time between the two — the 49-year-old and the 40-year-old — at that hospital. So we considered the person who died on August 30 as the index case. We did not hand over the body of the 40-year-old to his relatives and followed the protocol involved in handling the body of a Nipah victim. That is why we were able to prevent any spread from that patient’s body. At the same time, we collected samples from the dead and the other four suspected cases. All patients were isolated and Nipah precautions were taken. The entire exercise took only a day.

Over the last five years since the first outbreak, how far has the system in Kerala evolved to take on the virus?

After the Covid-19 pandemic, the system is very smooth in handling such outbreaks. Now, health workers are used to handling a high-priority viral pathogen with all precautions. The public are also aware about the practices to be followed such as wearing masks and social distancing. During the 2018 outbreak, people were scared to see men in PPE burying a Nipah victim – that was a first in the country. This time around, better awareness has helped people lead normal lives in Kozhikode while sticking to protocols. Besides, after Covid-19 there are more molecular labs which can test Nipah and many other viruses. Now, when we get a viral pneumonia case, we test for most viruses. When everything is negative, we look for rare viruses like Nipah.

In 2018, the transmission of the Nipah virus took place mainly in health care institutions. This time, too, a health worker was infected and another person got the infection from a hospital.

In all past outbreaks, spreading of the disease has happened at health care institutions. In 2018, infection control practices were not up to the mark in government hospitals. But after Covid-19, infection control measures have improved. That may be a reason why a major outbreak has not happened this time. In 2021, Nipah was limited to a single case mainly because the person had encephalitis symptoms, but no respiratory symptoms. When respiratory symptoms are there, the chances of transmission are high.

If there is a proper infection control practice, transmission in hospitals should not happen. Because this is not an airborne transmission, but mainly a droplet transmission. There might have been some breach in infection control policy this time, leading to the infection of a health worker and another getting the infection from a health care institution.

By now, do we have enough research material on Nipah?

We need more studies in this sector. We have two persons who tested positive and survived in 2018 and 2019. We need to study whether they have more antibodies or their immunity is lasting or whether we can develop monoclonal antibodies using their serum. Also, more studies are required on exposed persons, both symptomatic and asymptomatic. We should look into their symptoms and find whether asymptomatic spread is happening or not. We still need to find many answers. There have been high-risk exposed persons who did not develop any symptoms. We need to see if genetic factors played a role in protecting such persons from the virus. In 2018, my team members and I were highly exposed to five patients (who died by the time the virus was detected) without any protection.

To what extent are monoclonal antibody therapies effective in treating Nipah patients?

Monoclonal antibodies are not going to help treat existing patients. Data about monoclonal antibodies are mainly about Hendra virus which is similar to Nipah. In those cases, the therapy was used for those exposed to the virus, but before they developed symptoms. Monoclonal antibodies may be effective in the initial stages of the infection. In the 2018 outbreak, we used (the antiviral) Ribavirin and it was not useful… So, this time we are using Remdesivir for the adult patient.

Is Nipah virus seasonal?

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The viral load in fruit bats goes up and the spillover happens during their roosting season from June to November. This period has a high risk of transmission from bats to humans. We don’t know what actually induces that spillover in bats — whether it is ecological variation or whether it has got to do with some kind of scarcity of food or any other change. We need more research on what are the triggering factors which induce the spillover of the virus and also what is the mode of transmission from bats to humans.

What areas do we need to focus on to prevent future outbreaks?

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Disease surveillance is the most important area we should focus on. Fever deaths and undiagnosed cases of encephalitis, respiratory diseases that have tested negative for various other viruses, should be compulsorily tested for Nipah. There should be a proper screening of persons with encephalitis and proper diagnosis. Undiagnosed fever deaths should be investigated. There should be enough testing facilities in Kerala.

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