Till the year 2018, only 381 cases of primary amoebic meningoencephalitis (PAM) – the dreaded brain infection that has been making news in Kerala – were reported across the world. Only seven people had survived the disease. In 2024, the number of survivors worldwide were reported to be 11, before the disease broke out in Kerala. But contradicting all available data on the disease, Kerala reported 19 cases of amoebic meningoencephalitis in four months. This was unusual, considering that until 2023, only 3.7 cases were reported every year worldwide. What's even more unusual is that 14 of the 19 infected persons have recovered, putting the mortality rate at around 26% for a disease that is globally known to kill more than 90% of those infected.
Amoebic meningoencephalitis is a fatal brain infection caused by free-living amoeba found in freshwater, soil, sewage, and even unchlorinated swimming pools. PAM is a type of the disease, caused by the amoeba naegleria fowleri. Usually a person is infected when they come in contact with water containing amoeba, which then enters the body through the nose and reaches the brain.
It is known to be rare, occurring mostly in warmer regions, and until 2012, mostly reported from Australia, the United States, Britain, Czechoslovakia, Thailand, and Mexico, according to WHO. The first known case in Kerala occurred in Alappuzha in 2016, and since then seven more cases were reported before the sudden spike in 2024. All eight people who were infected before 2024 had succumbed to the disease, according to a report published in March in the Journal of Communicable Diseases.
But then it took eight years for these eight cases to be reported, against the 19 in a few months of a single year. Last Wednesday, 10 people who were infected with amoebic meningoencephalitis were discharged from the Thiruvananthapuram Medical College, leading the Health Department to call it a historic achievement.
The Thiruvananthapuram story
All 10 were admitted after the disease was diagnosed in a 27-year-old man who died in July. “He had a history of brain surgery, and he suffered a cardiac arrest. By the time he came to us, it was too late,” says Dr Aravind Reghukumar, Head of Department of Infectious Diseases at the Medical College.
Here again is an anomaly – amoebic meningoencephalitis is known to mostly affect children and, in rare cases, young people in their early 20s. The first five cases that were reported in Kerala this year – between May and July – were of children between the ages of five and 14. Three of them died, while the other two survived. They were from the northern parts of Kerala – two boys from Kozhikode, one boy from Thrissur, one girl from Kannur, and the youngest of all, a five-year-old girl from Malappuram.
“All five of them had come into contact with different sources of water bodies. No second case was reported from the same pond or waterbody these children were infected from. But in Thiruvananthapuram, several cases were reported from the same pond (Kavinkulam in Neyyattinkara). This is a disease that is known to occur only in one in 26 lakh people who get exposed to amoeba-infested water. So when we found a cluster of patients from the same pond, we tried to investigate how that happened,” Dr Aravind says.
After the death of the first patient – the 27-year-old who had a history of brain surgery – six more people who had bathed in the same pond as him were diagnosed with the disease. The first case was not thought to be unusual, given the patient’s history. But soon after, his cousin was admitted with similar symptoms.
“We didn’t think it would be amoebic meningoencephalitis when we sent the sample for testing, given that it is sporadic and the chances of infection was only one in 26 lakh. We were very surprised to get a positive result,” Dr Aravind recalls.
Investigations were conducted to check if there was a high-risk factor common to these people who bathed in the same pond and if there were others exposed to the same risk. Those who were thus identified were tested, and all of them were diagnosed with the disease. All of them, including the deceased man, were friends – males aged between 20 and 41.
Dr Aravind says that it was a process of snowball sampling in which people affected by a rare disease are studied for common histories that may have led to their condition. He cites the example of the outbreak of fusarium meningitis in Mexico in 2023, when snowball sampling helped them identify that all the people with the infection had undergone procedures under epidural anaesthesia at a certain centre. They began testing everyone who had had the procedure since January and were able to diagnose the condition early.
The same method was applied in Thiruvananthapuram, helping the doctors at Medical College to make an early diagnosis of the disease in six people, give them timely treatment, and cure them. Amoebic meningoencephalitis can only be cured with early diagnosis and proper treatment. The availability of the drug Miltefosine in combination with four other medicines has also played a role in the success of the treatment.
However, there were also three other cases reported in Thiruvananthapuram, in which the patients had nothing to do with the Kavinkulam pond. By then, anyone with meningitis was tested for the disease. This helped identify the three other cases, which included two women and a man again in the age group of 20 to 30. One of them had come in contact with water in a stream in Navaikulam, and another had a head injury and also had contact with well water.
“It does not really make a difference, tracing the source. Free-living amoeba is in every freshwater and in soil. In the case of PAM, caused by the amoeba called naegleria fowleri, the incubation period is 14 days, and the infected persons may be able to trace the source. If the infection is caused by another kind of amoeba, it may take months for the symptoms to manifest, and we may not be able to trace the source,” Dr Aravind says.
He is talking about the two kinds of amoebic meningoencephalitis – PAM, which leads to death within days without early treatment, and granulomatous amoebic encephalitis (GAE), caused by other kinds of amoeba, which takes time to progress but can be equally deadly.
In the first five cases reported in Kerala this year, the infection of a 13-year-old girl in Kannur was caused by Vermamoeba vermiformis, and her symptoms manifested only months after she was infected. Other than naegleria and vermamoeba, a genus called acanthamoeba has also been identified among patients in Kerala.
However, the amoebae responsible for the infection in all the cases have not yet been traced. Kerala does not have the facility to do the PCR (polymerase chain reaction) tests that can identify the amoeba. Every time, the sample is sent to Pondicherry. In the one health action plan that is being prepared by the Health Department, one of the proposed measures is to make the state self-sufficient to test the samples.
Why Kerala
It is not that the disease is prevalent only in Kerala, Dr Aravind says, but that other states may not be detecting it or have not released data about it. Global warming is purported to be one of the reasons for the presence of more amoeba in freshwater, but that is true for every place. Additionally, only 30% of cases of meningoencephalitis (amoebic or otherwise) are diagnosed worldwide. In fact, West Bengal hospitals released information about cases of amoebic meningoencephalitis last year.
In July, Kerala became the first state to release technical guidelines for the disease. Among the guidelines, what is most important to follow is the behavioural change necessary to prevent the infection, more than general instructions such as avoid swimming in contaminated water, Dr Aravind says. “It can even come from tap water. What is required is that you don’t allow water to enter the nose; you can use nose plugs for it. You should also avoid diving into water, since that can cause the amoeba to come to the surface.”
A technical workshop was conducted in late August with Health Minister Veena George and experts from the Indian Council of Medical Research (ICMR), Indian Institute of Science (IISc), AVM institute Pondicherry, IAV Kerala, Department of Environmental Engineering Kerala University, and State Pollution Control Board, among others, taking part. The focus was to understand the increasing occurrences of amoebic meningoencephalitis in Kerala. It was decided to have an action plan for early diagnosis and treatment, conduct campaigns with local self-government for awareness, collaborate with other departments and identify the reasons for the growth of amoeba in freshwater, and send samples to IISc for genomic sequencing.