Primary Amoebic Meningoencephalitis (PAM)

Vijithkumar V
Sep 25
4 min read

Primary Amoebic Meningoencephalitis (PAM) is a highly fatal (acute) disease that affects the central nervous system—particularly the brain. This is an acute infection, meaning once the infection begins, symptoms manifest very quickly. The rapid progression is due to the increased load of the pathogen in the host body, along with the genetic material and proteins of the pathogen acting swiftly inside the host, producing hazardous changes in a very short time.

A human brain infected by Naegleria fowleri is shown in a zoomed bubble. — *Naegleria fowleri* infection of the brain. Picture credits: Times of India

The causative agent of PAM is a unicellular organism called Naegleria fowleri. Naegleria fowleri is generally referred to as an amoebo-flagellate organism. Its major biological feature is that, in its life cycle, the organism passes through several different structural and functional stages. These include the cyst stage, trophozoite stage, and flagellated stage (1).

In the flagellated stage, the organism has pseudopodia (temporary limb-like projections formed for directional movement) as well as flagella (2). In the trophozoite stage, however, the organism becomes pathogenic and capable of causing PAM. Clinical samples obtained from the nasal passages or cerebrospinal fluid of a patient with PAM typically reveal the organism in its trophozoite stage (1).

Like amoebo-flagellates, certain bacteria and viruses can also cause meningitis, but the mechanism of infection, physiological disturbances in the host, and biochemical changes in body fluids differ significantly between them (1).

Bacteria and amoebo-flagellates are both unicellular organisms, but differ structurally and genetically. Bacteria are unicellular prokaryotes (3), while amoebo-flagellates are unicellular eukaryotes (2). The defining feature of eukaryotes is the presence of a distinct, membrane-bound nucleus (4).

Free-living bacteria exist, but most of them are parasitic (living in and exploiting host organisms), while some are symbiotic (living in hosts without causing harm). Amoebo-flagellates, although capable of surviving as free-living organisms, become parasitic upon entry into the human body and cause disease. They are mostly encountered in freshwater ecosystems such as ponds, pools, canals, and lakes—and more recently, their presence has also been suspected in well water.

What distinguishes Naegleria fowleri and PAM from other forms of meningoencephalitis caused by viruses and bacteria is its extremely high fatality rate. Global studies indicate that PAM has a mortality rate of approximately 98%.

Epidemiology of PAM in Kerala

According to scientific records published until 2024, a total of eight confirmed PAM cases were reported in Kerala between 2016 and 2023, mainly from the central and northern districts of the state. Unfortunately, all these patients died (1).

The district-wise breakdown is as follows:

- Alappuzha – 2 cases

- Thrissur – 2 cases

- Malappuram – 3 cases

- Kozhikode – 1 case

The first case of PAM in Kerala was reported in 2016 from Alappuzha.

Owing to the rapid and acute progression of PAM, in some cases, correct diagnosis is possible only at autopsy. Additionally, misdiagnosis and reporting errors lead to under-reporting of actual case numbers.

Recent Case Reports (2025)

On August 14, 2025, three consecutive PAM cases were reported in Kozhikode district (5).

- A 9-year-old girl from Thamarassery died due to the infection.

- A 3-month-old baby from Omassery and a 40-year-old man from Annassery were also infected.

The infant’s condition remained very critical. Following the death of the girl, her two siblings were also tested, and her 7-year-old brother was later confirmed positive (6).

Subsequently, two more cases were reported from Malappuram district:

- An 11-year-old girl from Chelari, diagnosed at Kozhikode Medical College. Reports confirmed that her health remained stable.

- A 67-year-old woman from Vengara, who unfortunately succumbed to the infection.

It was confirmed that the 11-year-old girl developed infection following bathing in a local water reservoir near her home. The amoebal strain identified from the water sample matched that from the child’s clinical sample, substantiating the infection caused by Naegleria fowleri (7).

The Three-Month-Old Infant Case

The case of the 3-month-old infant continues to puzzle the medical community. For infection by Naegleria fowleri, contaminated water must come into contact with the nasal mucosal lining (1). Initially, well water from the infant’s household was suspected, but later it was found that the amoebal strain in the water was different from that detected in the infant.

This led to new hypotheses:

- PAM does not always require exposure to water.

- The source of infection and entry route may vary.

- Other pathogenic amoebae, such as Acanthamoeba and Balamuthia mandrillaris, can also cause encephalitis, potentially via soil or dust exposure (8, 9).

Current Status in Kerala (as of August 2025)

According to an article published in The Print on August 20, 2025, Kerala has reported a total of 37 PAM cases (covering cases from 2024 to August 24, 2025).

- 13 deaths occurred in 2024

- 2 deaths occurred up to August 24, 2025 (10)

- Total deaths: ~15 (~40%)

This suggests that the mortality rate in Kerala (~40%) is significantly lower than the global average (~98%).