Islamabad, Jul 22 (IANS): At least four people have died in the port city of Karachi due to an amoebic infection caused by a deadly waterborne organism called naegleria fowleri, the World Health Organisation (WHO) has said.

All four deaths were caused by primary amoebic meningoencephalitis, an official of the Sindh health department told Dawn News.

A team from the WHO's Disease Early Warning System (DEWS) visited various government and private hospitals in the city to investigate the situation.

Three people died at the Liaquat National Hospital while one died at the Aga Khan University Hospital.

A microbiologist said it was not a new disease in Pakistan. The first such case was detected in 2005, and there were 17 patients in 2011.

Naegleria fowleri can invade and attack the human nervous system. Such an infection nearly always results in death. The case fatality rate is estimated at 98 percent.

Naegleria lives almost everywhere - in lakes, hot springs and unclean swimming pools.

A media report said people become infected when they wade through shallow water and stir up the bottom. If someone allows water to shoot up the nose, the amoeba can latch onto the olfactory nerve.

The amoeba destroys tissue as it makes its way up into the brain, where it continues the damage, by feeding on the brain cells.

Infected people have a stiff neck, headaches and fevers. In the later stages, they show signs of brain damage such as hallucinations and behavioural changes.

Another microbiologist said the amoeba could not be detected from contaminated stagnant freshwater, but only from the cerebrospinal fluid culture.

Sources of the infection may be the main water reservoirs meant for supplying water to Karachi, an expert said, and suggested scrutiny of the Karachi Water and Sewerage Board for 100 percent chlorinated water supply to residents.