Naegleria Fowleri: Barricading the brain against the amoeba

October 26, 2014

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— File photo
— File photo
Naegleria fowleri lifecycle stages
Naegleria fowleri lifecycle stages

The scare is back. The brain-eating amoeba, Naegleria Fowleri, has already claimed 12 lives this year — the oldest victim was a 57-year-old person and the youngest victim was a 9-month-old baby girl. Its latest prey was 25-year-old Humaira Bano from Karachi’s Malir locality. Following her demise, Karachi Health Director Dr Zafar Ijaz went on record to state: “It is unclear how Ms Bano came into contact with the deadly amoeba. She mostly stayed at home, and like other previous cases, she had no history of swimming”. So what exactly happened?

Naegleria Fowleri is a heat-loving amoeba, as defined by the Atlanta-based US Centres for Disease Control and Prevention, and is commonly found in warm freshwaters (ponds, lakes, swimming pools, underground and overhead water tanks). The amoeba lives by feeding on bacteria and is able to grow and survive at temperatures up to 46°C. It infects humans by entering the nose during water-related activities; once in the nasal canal, the amoeba travels to the brain via the olfactory nerve and transmits the fatal Primary Amoebic Meningoencephalitis (PAM) infection to its victim. Not many have successfully survived such attacks.

It is widely (and globally) believed that those swimming in poorly-chlorinated or un-chlorinated pools are more at risk of being infected by Naegleria Fowleri. But none of the 12 victims who died this year in Pakistan had a history of being swimmers.

In our context, Naegleria Fowleri enters the nose during ablution — a practice that is routine in most homes and mosques in Pakistan. This is problematic, since the amoeba enters homes and mosques through the pipeline that supplies water to them.


Naegleria Fowleri comes through our water supply lines, but the only defence against it is controlled chlorination. Will the government stand up?


Karachi’s water supply comes mainly from the Keenjhar Lake and the Hub Dam, both of which remain unprotected from Naegleria Fowleri. The amoeba enters water treatment plants through the water source, and enters the water pipelines unchecked because of inadequate filtration and chlorination at the treatment plants.

Once in the pipelines, the amoeba can easily proliferate due to three factors.

First, inadequate chlorine residual: low levels of chlorine that remain in water after initial application are called chlorine residuals. For effective chlorination, the turbidity (density) of water must be less than one Nephelometric Turbidity Unit (NTU). Chlorination will not be effective if turbidity is greater than five NTUs, because the microorganisms hide themselves within the suspended particles to escape disinfection.

But free chlorine in water distribution systems is consumed by various water-borne substances, biofilms, and by the walls of the pipeline.


In our context, Naegleria Fowleri enters the nose during ablution — a practice that is routine in most homes and mosques in Pakistan. This is problematic, since the amoeba enters homes and mosques through the pipeline that supplies water to them.


Microorganisms have a strong natural preference to attach themselves to the inert and living surfaces for survival. They produce a slimy (sticky) material that enables them to attach to the surfaces. In ageing pipelines, as exist in Karachi, the colonies of microorganisms attach themselves to the interior of the pipelines, forming what is known as biofilms. They are a common phenomenon; they can easily be seen on any old pipe taken out freshly from the water distribution system.) The concentration of chlorine, therefore, decreases as it travels through the distribution system, an aspect known as chlorine decay.

In Karachi’s context, a free chlorine residual of 0.5 milligrams per litre (mg/l) would be required, at all points in the city’s water distribution system and up to the farthest end, to inactivate Naegleria Fowleri. For example, the Karachi Water and Sewerage Board (KWSB) water treatment plant is located at COD hills. If the water distribution system is laid up to Keamari, then Keamari would be the farthest end.

Such controlled chlorination is the only trusted defence mechanism that the city can fall back on to protect against the brain-eating amoeba.

The 0.5mg/l level is in accordance with World Health Organisation (WHO) guidelines. As per the WHO’s Drinking Water Guidelines (2011): “For effective disinfection, there should be a residual concentration of free chlorine equal to, or greater than 0.5 mg/l, after at least 30minute contact time at pH less than 8.0. Chlorine residual should be maintained throughout the distribution system.”

There should be a minimum of 30 minutes of contact time of chlorine with water at 20°C, at pH level of 5.5 to 7, for effective disinfection. pH, a measure of the degree of the acidity or the alkalinity of a solution, is defined as the negative logarithm of the hydrogen ion concentration. The effectiveness of chlorine disinfection reduces with increasing pH. At pH values of 8, 9 and above 9, the free chlorine residual level should be 0.6, 0.8 and 1.0 mg/l, respectively. Likewise, if the water temperature drops to 10°C, the contact time should be one hour.

The second factor that helps proliferation of the amoeba is intermittent water supply; this causes negative pressure in pipes, and dislodges the organisms from the biofilms when water supply resumes. Put another way, aging water pipelines are vulnerable to the development of biofilms inside the pipes. Biofilms possess the properties of bioaccumulation and bioabsorption. All kinds of organisms and microorganisms, like bacteria, viruses, protozoa (Naegleria Fowleri), fungi, algae and invertebrates attach themselves to biofilms.

The third factor is the frequent leaks in water supply and sewer lines, causing inflow of wastewater into the water supply lines.

Maintaining a chlorine residual of 0.5 mg/l up to the farthest end in the distribution system, does not mean that the KWSB should opt for excessive chlorination at water treatment plants. The issue is about controlled chlorination.

If more chlorine is added than needed, people living near treatment plants will get excessive levels of chlorine in their potable water. High chlorine levels (greater than 2mg/l) will cause taste and odour problems, corrosion of pipelines and, more importantly, would lead to the formation of trihalomethanes, which are strong carcinogens. The rational approach, in case of Karachi, would be to setup booster stations along the water distribution network, to maintain chlorine residual of 0.5mg/l.

Unfortunately, warding Naegleria Fowleri off is not entirely manageable at home — it is necessary for the government to step in. Frequent cleaning of overhead and underground tanks at home might give you clean water in taps, but in-house chlorination is tricky because too much chlorine turns water into a liquid with odour, it can cause skin and eye irritation, as well as health issues for children. It also causes erosion of the pipeline in the house. Cleaning of the house pipes is thus impractical. Tackling the brain-eating amoeba requires the government to step up.

F. H. Mughal is a senior environmental engineer, who works on water, sanitation and hygiene

Published in Dawn, Sunday Magazine, October 26th, 2014