Outbreak of Primary Amoebic Meningoencephalitis in Kerala

In recent months (May-August 2024), a rare, fatal form of amoebiasis, referred to as ‘Primary amoebic meningoencephalitis’ (PAM, PAME) was identified in Kerala. Five cases were recognized, all of which resulted in death. The last case was caused by Vermamoeba vermiformis (a free-living amoeba), while others were due to Naegleria fowleri infection.

We are familiar about amoebic dysentery caused by Entamoeba histolytica. Rarely, Acanthamoeba may cause severe corneal inflammation (keratitis) among those wearing contact lenses, while Entamoeba gingivitis, a protozoan parasite living in oral cavity, can lead to persistent gingivitis.^1,2

Four cases of PAM, three in children and one in an adult, were first identified in Adelaide, Australia by Fowler and Carter. Autopsy findings indicated that the causative agent likely entered the CNS through the olfactory nerve filaments.³ The first reported case of PAM in India was recorded in Kolkata in 1971, involving two children.⁴

A fatal case of PAM in a 5-month-old infant was reported from Mangaluru in 2002 and well water used for bathing was found to be the source.⁵ First case of PAM in Kerala was reported in Alappuzha, in 2016. High mortality rate was due to the rapid onset of illness, delayed diagnosis and lack of effective treatment protocol.⁶ In Tamil Nadu, a case of PAM in a 47-year-old male was reported, who probably contacted the infection while bathing in a river and he responded to administration of Liposomal

Amphotericin B and Azithromycin.⁷ A case of PAM in a 20 year old male with acute leukemia in remission, without any history of swimming, was reported from Haryana in 2009 and the patient met a fatal end.⁸ Jain et al. reported a case of acute meningoencephalitis caused by N. fowleri who made full recovery following treatment with Amphotericin B, Rifampicin and Omidazol.⁹

Singh et al. reported a case of an 8-year-old boy in Delhi with Naegleria meningitis. The patient was treated with Amphotericin B and Rifampicin in 1998 and survived.¹⁰ Kaushal et al. reported a case of a 36-year-old person with a history of bathing in the village pond, succumbing despite the treatment.¹¹ Gupta et al. reported a case of primary amoebic meningoencephalitis in 2015,  while Mittal et al. reported a case of an infant diagnosed with PAM infection in Faridabad, Haryana in 2019.^12,13

Thus, multiple cases of PAM have been reported from various parts of India, affecting individuals from infancy to middle age. Many of them did not provide a history of swimming or diving, but reported bathing using well water, or tap water. The response to the treatment has been variable. Though the reports suggested positive response to the treatment in the initial five decades, there have been reports of unresponsiveness to treatment in the recent years, which is intriguing.

Popularly known as ‘the brain-eating amoeba’, Naegleria fowleri is an amoeboflagellate which is responsible for an acute fulminant, rapidly fatal infection of the central nervous system (CNS),  that has been termed as ‘Primary amoebic meningoencephalitis’. The condition is considered as a rare, neglected one.

Naegleria fowleri, a species of Naegleria, is a one celled, amoeboflagellate, that is ubiquitously distributed worldwide in different warm aquatic environments, mud and soil. It is found in warm freshwater lakes, water ponds, hot springs, irrigation canals, poorly maintained swimming pools, and rivers.² This thermophilic amoeba grows in fresh water bodies of tropical and subtropical climates, with high temperature and humidity. N. fowleri was found in various water bodies in Rohtak and Jhajjar districts of Haryana. About 107 water samples from the trapped debris of water reservoirs were screened. Among these, 43 (40%) samples showed the presence of free living amoeba after incubation for 14 days at 37^oC, while one sample showed the growth of N. fowleri and another sample showed growth of N. australiencis.¹⁴

The infection can be acquired from water-related activities such as swimming, jumping or diving. The condition often affects children and young persons, mostly male, who are active and healthy. The pathogen was also isolated from a swimming pool in Bombay (now called Mumbai).¹⁵ N. fowleri was also found in pond water and sewage water in Calcutta (now called Kolkata).^16,17

Although N. fowleri is commonly found in the environment, rarely it causes an infection. N. fowleri is a heat-loving, single-celled amoeba in the phylum of protozoa (single-celled infective organism) called ‘Percolozoa’. It has been noted as a free-living organism in freshwater and soil, and it thrives by consuming organic matter and bacteria. The organism passes through three different stages in its life cycle, such as cyst, flagellate, and amoeboid trophozoite. Cysts are highly stable and can withstand any environment. The f lagellate form is an intermediate stage that has the ability to move quickly from a hostile surrounding. The amoeboid trophozoite form is the active, eating, and reproducing phase. Animals and humans are considered ‘accidental hosts’.

Naegleria are ‘thermophilic’ and exhibit marked activity in warm water during summer months. They are found in both tropical and temperate climates throughout the world. They get encysted in situations where the water temperature is cool; often the protective cyst forms are found in the sediment at the bottom of lakes. In such surroundings, they can survive winters. The most infectious form is the trophozoite form. However, cysts may assume an infectious state within few hours when the conditions get favourable. The flagellated form can become a trophozoite within minutes.

Often the organism has been reported in poorly chlorinated and unchlorinated swimming pools. Its presence has been noted in water parks using nonchlorine-based water treatment methods. It is important to note that N. fowleri cannot survive in saltwater. It is not found in the ocean.

The organism enters through the nose when the water contaminated with trophozoites make an entry into the nose.² Occasionally, the infection can occur through a damaged ear drum. Rarely contaminated tap water may cause the infection during nasal rinsing.¹⁸ The trophozoites enter the CNS through the nose, after insufflations of infected water. It gets attached to the olfactory nerves, passes through the cribriform plate of the ethmoid bone into the anterior cerebral fossae.¹⁹

The infection can lead to severe necrosis of the olfactory bulb and brain. Probably a chemical agent does not lure N. fowleri by chemotaxis towards the brain.²⁰ The infection is neither contracted by drinking water contaminated with N. fowleri, nor does it spread from person-to-person contact.

The trophozoites are found in an amoebic form. Amoeba is a unicellular organism without any fixed shape. They move by forming pseudopods and feed on bacteria and detritus. In hostile environments such as hypotonic water, it assumes a flagellate form to escape from the region, and if the environment continues to remain hostile, it assumes a cystic form.²

Naegleria is a facultative parasite that does not require any host to complete its life cycle and it reproduces by mitosis.

After an incubation period of 3 to 7 days, the infection suddenly presents with severe symptoms. It presents with frontal headache unresponsive to analgesics, high fever, runny nose, alteration in taste and smell, nausea, vomiting, and neck stiffness. Later the patient exhibits behavioural changes, sensitivity to light, and drowsiness. The condition can rapidly deteriorate within a week causing coma and death. The condition progresses through three stages during the course of the disease.

Stage I: Nasal (Precerebral) stage

Stage II: Olfactory stage

Stage III: Meningoencephalitis stage

Minimal inflammation is noted in the nose, while brain shows severe inflammation with infiltration of neutrophils, eosinophils, monocytes and macrophages.²¹ The detection of amoebae by the immune system is impaired as the agent is eukaryotic, similar to the host cell.

The diagnosis is made using microscopic and molecular methods (PCR and ELISA). The symptoms are non-specific and often confused with disorders such as bacterial & viral encephalitis, and pyogenic meningoencephalitis. These conditions must to be considered in differential diagnosis. The cerebrospinal f luid (CSF) obtained from lumbar puncture aids in establishing the diagnosis. The CSF comes out with very high pressure. There is elevated levels of protein and reduced levels of sugar. There is increased number of leucocytes with polymorphonuclear cell predominance. There can also be presence of red blood cells. A definite diagnosis is made by identifying motile trophozoites of 10 to 25 microns size with a single nucleus and a centrally located nucleolus without any peripheral chromatin, in the centrifuged wet mount preparation. The morphological features of the trophozoites are established using Wright-Giemsa stain. Enflagellation test is performed by addition of 0.5 mL CSF to 2 mL distilled water on a sterile flat-bottomed plate and is incubated at 37^oC. Microscopy undertaken at 15-minute intervals may show motile moving organisms exhibiting a unique flagellate pattern.²²

Magnetic resonance imaging (MRI) of the brain reveals the presence of one or more space-occupying lesions with ring enhancement.²³ Polymerase chain reaction (PCR) helps to determine the genetic material of the amoeba.

Autopsy reveals extensive hemorrhages and necrosis of the brain, especially on the frontal cortex.

PAM exhibits an extremely high mortality rate varying between 95-98% and the percentage of mortality has remained same over the last six decades.

There is no proven therapy for N. fowleri infection. The Centre for Disease Control and Prevention (CDC) has made recommendations to use the antifungal drug, Amphotericin B in high doses and must be administered intrathecally.²⁴ Many other drugs that have been tried in the treatment include Fluconazole, Chloramphenicol, Dexamethasone, Miconazol, Rifampicin, and Miltefosine.

Cure for this condition is very rare. Various studies have shown that the drugs may be effective if administered early. However, early diagnosis is often difficult and the condition progresses rapidly. PAE is a severe form of a rare disease.

In India, the cases do not appear to be water related as many of the reported cases did not provide a history of swimming. Many bathed using well or pond water. Climate change may play an important role in the spread of the disease.²⁵ Rai et al. reported a case of an 8-month old infant who was bathed regularly using pond water, had acquired the infection. The child responded to the treatment with Amphotericin B, Chloramphenicol and Rifampicin.²⁶

Public water supplies, swimming pools, and pools in theme parks should be meticulously cleaned and chlorinated regularly with levels high enough to protect against N. fowleri. Forced water at the level of nose must be avoided. Nasal irrigation should be carried out with water that is sterile. The risk of infection can be reduced by wearing nose clips while swimming. Bathing in stagnant water and diving in water should be avoided.

The condition takes a rapid course making it difficult to initiate specific treatment for the disease. Yadav and colleagues have reported a case of youngest survivor of Naegleria meningitis infection. A 25-day old baby received Amphotericin B, Rifampicin and Fluconazole for four weeks, made recovery without any residual disability.²⁷

Given the rapid progression of the infection and the associated high mortality rate, it is crucial to make every effort for early diagnosis and prompt treatment with specific medicines. The physicians should be aware of this condition when encountering cases of meningitis or meningo-encephalitis. This enables them to make an early diagnosis and initiate treatment with a broad range of drugs in a timely manner.

Conflict of Interest

None