Increased faecal contamination of ground water sources and widespread environmental pollution of waterbodies is emerging as one of the significant public health problems that the State will have to prioritise as multiple cases and deaths due to amoebic meningoencephalitis are being reported across all districts in Kerala.

Amoebic meningoencephalitis has emerged as the single infection claiming the highest number of lives in the State, with 121 cases and 30 deaths reported as of May 23 this year.

Clinical, microbiological and environmental investigations in the State have increasingly pointed to contaminated domestic water sources , especially household wells, storage tanks, and surface ponds, as the likely source of exposure.

Environmental drivers

Several environmental drivers such as the rise in ambient temperature seem to be favouring the persistence and increased density of free-living amoeba (FLA) such as Acanthamoeba in these waterbodies

Acanthamoeba, which causes granulomatous amoebic encephalitis (GAE), usually enters through minute skin breaks or wounds or through the inhalation of contaminated water aerosols and then disseminates via the blood stream to the brain.

Unlike in the case of Naegleria fowleri, which causes an acute infection and death within the initial few days, the course of encephalitis caused by Acanthamoeba is chronic.

“Thepatient may go through a cycle of vague symptoms, skin, sinus, respiratory infections for months before presenting with a neurological illness at the hospital. All clinically suspected cases of encephalitis are now tested for amoeba, but in many cases, the organism may not become visible in light microscopy. What turned around the management of amoebic meningoencephalitis—and the reduction of mortality from the 75-90% to less than 30%—in Kerala is the widespread use of molecular diagnosis (PCR), which enabled treatment using multidrug regimen,” a senior doctor points out.

Globally, 60-70% of the cases of meningoencephalitis have remained undiagnosed. It is because of active case search and increased detection that the number of amoebic encephalitis cases seem to be on the higher side in the State, health officials say. They point out that only 20 % of the Cerebrospinal Fluid (CSF) samples tested are yielding a positive diagnosis.

“Cases have been reported in immunocompetent as well as immunocompromised individuals, like the elderly, cancer or dialysis patients. We get many cases from the border districts in Tamil Nadu also,” they say.

Infectious disease experts say that the problem of amoebic meningoencephalitis is not something that can be resolved easily because FLA are ubiquitous in the environment. “We do not have all answers,” says a senior doctor.

Well water

However, going by the patient history in hundreds of cases reported in the State in the last two years, well-water does seem to be an independent risk factor because the quality is highly compromised, they point out.

High levels of faecal contamination (presence of E.coli/coliform bacteria) has been reported in over 70% of the open wells in the State by agencies like the Centre for Water Resources Development and Management (CWRDM). A study in the urban areas in Thiruvananthapuram in 2018 had also reported that coliform contamination was prevalent in 73% of wells and that well chlorination and cleaning practices were inadequate. More than 77% wells had septic tanks within 7.5 m radius.

From the public health point of view, the increasing incidence of amoebic meningoencephalitis as well as water-borne diseases like Hepatitis A should be taken as a wake up call to improve water quality surveillance and public health communication on basic water safety measures.

The authorities should also ensure that the guidelines which were issued regarding the chlorination of water sources, including swimming pools in clubs, resorts, and hotels, are being followed so that these do not pose a risk to the public.