In: Biology
Compare Entamoeba, Acanthamoeba and Naegleria. Based on incidence, which of these parasites is a threat to humans and clinically which is the most serious? Explain why your answer is not the same for both questions.
Amoebae are characterized by possessing clear protoplasm which form pseudopodia. These pseudopodia are the means by which these organisms move and engulf bacteria and red blood cells for feeding purposes. They are reproduce by binary fission. Amoebae exist in two forms: Trophozoite form, actively motile, feeding form, multiplying by simple binary fission. Cyst form, dormant, non-feeding resistant stage. The most common amebas seen in the intestinal tract are Entamoeba histolytica/dispar, Entamoeba coli, Entamoeba hartmanni, Endolimax nana and Iodamoeba bütschlii. Of these only Entamoeba histolytica is of medical importance. It causes amoebiasis. However , other intestinal amoebae are of interest mainly because their trophozoites may be difficult to distinguish from those of E. histolytica by light microscopy. There are some potentially pathogenic free living amebas that can cause disease in man e.g. Naegleria fowleri, Acanthamoeba spp. and Balamuthia mandrillaris.
Entamoeba histolytica has more incidence than naegleria fowleri and acanthamoeba but it is less fatal than both of these .
Disease by entamoeba - intestinal amoebiasis 1. Acute dysenteric amebiasis, may have explosive liquid stools daily, containing much blood and mucus and may be accompanied with fever, dehydration, abdominal cramps, tenesmus, painful spasm of the anal sphincter, is a sign of rectal ulceration. Amebic ulcers may develop in the large colon and can also be found in the rectal area. 2. Chronic dysenteric amoebiasis, mild gastrointestinal disturbances with recurrent attacks of dysentery with alternation of constipation and localized abdominal tenderness .
Disease by naegleria fowleri -
The infection follows penetration of water containing the amoeboid form of N. fowleri into the nasal cavities. From there the lamina cribriforma of the ethmoid bone is penetrated, probably through phagocytosis of the olfactory epithelium. via the first cranial nerve, the infection spreads to the lowermost part of the frontal cerebral lobes leading to rapidly fatal infection known as primary amoebic meningoencephaltitis ( PAM). The amoebae reproduce rapidly in the cerebrospinal fluid. There is virtually no inflammatory reaction. Haemorrhagic necrosis of the base of the brain, cerebral cortex and the olfactory lobes develops. The incubation period is 2 - 15 days. Early in the infection, upper respiratory distress, severe headache, sore throat, runny or stuffy nose, altered smell and taste occur. Later on when CNS affected; symptoms of meningeal irritation occurs as fever, vomiting and neck stiffness. Mental confusion and coma occur after 3 to 6 days. Most infections are lethal.
Disease by acanthamoeba - Man acquires infection by inhalation of dust containing the trophozoites and cysts . the trophozoites reach the lower respiratory tract and from there invade the CNS through the blood stream. Also the infection can be acquired through direct invasion of injured or ulcerated skin or eye. Acanthamoeba species are responsable for several clinical problems: 1. Granulomatous amoebic encephalitis. 2. Keratitis . 3. Disseminated lesions, including skin ulcers, but also lesions in adrenals, kidneys, liver, spleen, thyroid …….
Thus naegleria fowleri is most lethal to humans and entamoeba is least .