Which organism is known to cause primary amoebic meningoencephalitis?

Naegleria fowleri is well-known as the causative agent of primary amoebic meningoencephalitis (PAM), a rare but serious infection of the brain typically associated with warm freshwater and poorly maintained swimming pools. This free-living amoeba can enter the body through the nasal passages, often when individuals are swimming or diving in contaminated water, and then migrate to the brain, causing severe inflammation and rapid neurological decline.

Acanthamoeba, while also a free-living amoeba, is primarily associated with keratitis and can cause granulomatous amebic encephalitis in immunocompromised individuals rather than PAM. Entamoeba histolytica is a protozoan parasite primarily known for causing amoebic dysentery and liver abscesses, acting mainly in the gastrointestinal tract. Giardia lamblia is another protozoan that causes giardiasis, a gastrointestinal infection characterized by diarrhea and is not involved in central nervous system infections.

Therefore, Naegleria fowleri stands out clearly as the organism associated specifically with primary amoebic meningoencephalitis.