“Consider the difference in size between some of the very tiniest and the very largest creatures on Earth. A small bacterium weighs as little as .0000000001 gram. A blue whale weighs about 10000000 grams. Yet, a bacterium can kill a whale… . Such is the adaptability and versatility of microorganisms as compared with humans and other so-called higher organisms, that they will doubtless continue to colonise and alter the face of the Earth long after we and the rest of our cohabitants have left the stage forever. Microbes, not macrobes, rule the world.”—Bernard Dixon.

When a general medical practitioner talks about amoeba, he is usually referring to an organism that causes amoebiasis, an infection which is almost worldwide in distribution and which is caused by the protozoon Entamoeba histolytica. Recurrent bouts of diarrhoea, abdominal cramps, loss of appetite, and liver abscess are some of the symptoms that enable a physician to diagnose that a particular patient has amoebiasis. In making a positive diagnosis of amoebiasis, the doctor is also aided by laboratory findings. In our country lakhs of people, particularly those who have to be away from home frequently on tours of long duration, suffer from amoebiasis which can be successfully treated by a drug such as Metronidazole or tinidazole or any of the 15 or more other amoebicides which are widely prescribed by doctors. If a complication arises, such as an abscess in the liver, doctors resort to chemotherapy.

There is, however, another kind of free living amoebic organism called Naegleria which causes a fatal disease known as primary amoebic meningo encephalitis or PAM, for which no cure has been found yet. The  Naegleria invades the central nervous system through the nasal passage where it affects the olfactory nerves and enters the protective layers of the brain and the cerebral cortex. There it eats up the brain tissue causing death. Autopsies have revealed that the brain of the patient would have become as soft as jelly and full of haemorrhage.  Until today, no satisfactory treatment has been discovered. Scientists are baffled not only by the potency of the organisms and their resistance to all known drugs but also by their erratic occurrence. It is not known why some swimmers go unharmed (the disease affects only swimmers in lakes and rivers), while others get infected.

All over the world people do enjoy jumping into a lake on a hot summer day to take a refreshing bath. But a few swimmers or bathers can be unlucky as to be attacked by the deadly amoeba that reside in great concentrations at the bottom of rivers or lakes. A few years ago a young boy was admitted to a hospital in Florida with high fever. The boy had been in perfect health until two days earlier when he had suddenly begun to complain of a severe headache. Since the doctors came to know that he had been swimming in a lake they decided to check his spinal fluid for the presence of pathogenic amoebas. The test proved positive indicating the presence of Naegleria. Despite prompt medical attention and various kinds of therapy, the boy died in a few days.

A study of the pattern of the disease shows that no latitude on the globe has been spared. Cases of PAM (all of them fatal) have been reported from India to Australia, the Czech republic to Nigeria. The victims are usually healthy and young individuals who develop flu­like symptoms signalling the onset of PAM following a refreshing swim in a lake or a river. It is now known that people subject to the greatest risk are those who swim along the bottom of the water stirring up the sediments where these organisms reside in large numbers and possibly in a more virulent form.

The amoebas also appear to thrive only in temperatures of 98°F of and over. While pathogenic amoebas may be present throughout the year in the rivers of the tropical regions, in the United States the season for amoebic infections occur in June, July and August. Scientists are not clear as to why certain waters sustain the organisms while others with comparable temperatures do not. There is pre­liminary evidence to indicate that increased populations of bacteria enhance the proliferation of pathogenic Naegleria. One scientist believes that pollution causes a breakdown in the natural integrity of the ecosystem, that may well be responsible for these amoebic infections. In his view, organically polluted streams and ponds may contain enough bacteria to activate the amoebic cysts.

The amoebas, present in water, feed on the bacteria and reproduce in the water and invade the brain of the swimmer. However, since there is evidence to show that amoeba-related diseases had appeared as early as 1909, the pollution theory cannot perhaps be fully accepted.

Public health measures introduced even till now in response to this new threat posed by the virulent pathogenic amoebas have not been on a very large scale. All such efforts have till now been concentrated on common causes of epidemic in which several people have become infected from the same source. A few years ago when it was suspected in Czechoslovakia, that amoebic infections had caused 16 fatalities over a six-year period and that the infections could be traced to amoebas proliferating in the cracked walls of a swimming pool, the walls were entirely re-built. Since then no amoebic infections have been reported there.

Similarly in California, after two fatalities, were traced to a spring in San Bernardino National park, signs were placed, warning bathers that swimming there could be dangerous. Ironically a nudist group in the area, believing that it was some kind of move to prevent them from bathing in the nude, kept pulling down the warning sign. In Richmond, in the state of Virginia, a lake believed to have been the source 18 fatal infections, was closed down permanently by a court order.

Physicians as well as health and medical workers generally agree that solutions to the problem posed by these pathogenic amoebas are generally unwieldy. It is not possible to close down every river, lake and pool to swimming or to chlorinate all rivers lakes and pools. Scientists have therefore begun to realise that the situation demands increased research in helping doctors to diagnose the infection as quickly as possible and to find out the optimal growth medium of the amoebas so as to design suitable drugs that would kill them Some scientists are hopeful of discovering a natural predator that could be introduced into the contaminated lakes or pools so that they could devour the dreaded Naegleria.

Several drugs have been found to be effective against Naegleria fowleri in the laboratory conditions. However, their effectiveness is unclear since almost all infections have been fatal, even when people were treated with similar drug combinations. Recently, two people with Naegleria infection survived after being treated with a new drug called miltefosine that was given along with other drugs and aggressive management of brain swelling (these may be isolated cases of success).

Therefore it has not yet been established how effective a drug miltefosine is.

Humankind has always been reluctant to enter unexplored waters out of fear of crocodiles or even man-eating fish such as pirahna. But only recently has science discovered that deep in the bottom of rivers and lakes lurk microscopic organisms that can prove even more fatal. However, despite all that had been given in this chapter, the moral of story is not that one should refrain from going for a swim. In fact, the scientists who are actually studying the deadly Naegleria amoebas have not given up the occasional dip in the local swimming pool. They only advocate that swimmers should take suitable precautionary measures such as using effective nose guards or plugs if one intends to swim at the bottom of a lake or river or even unfamiliar swimming pools. One very elementary precaution is that after coming out of the water one should blow one’s nose, and inhale steam.


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