Entamoeba histolytica - Host Immunity, Epidemiology, Reservoir, Source, Transmission, Treatment, Prevention, Control
Host Immunity of Entamoeba histolytica
The host immunity in response to Entamoeba histolytica infestation includes:
Non-immune defense mechanism
Specific immunity
Non-immune defense mechanism
The non-immune defense mechanism is an important role in resistance against Entamoeba histolytica infection i.e. amoebiasis:
Gastric acid barrier- kills amoebic trophozoites
rapid intestinal movement – reduces the time for the trophozoites to the intestinal mucosa
colonic mucin – prevents the amoebic trophozoites from adhering to the intestinal epithelial cells
Specific immunity
Once the Entamoeba histolytica infection is cured, host resistance to subsequent infestation is developed and includes specific immunity - both humoral and cell-mediated immunity
Humoral immunity
humoral immunity is responsible for the presence of circulating antibodies in the serum during the first week of infestation
among all the classes of antibodies produced, IgG is the most prevalent one
the complement system present in the serum initiates the lysis of the trophozoites but the amoeba protects itself – partly with the help of amoebic lectin present on their surface
the Entamoeba histolytica lectin binds with the C8 and C9 components of the complement system which inhibits their assembly and prevents the C5b-9-mediated lysis
in the case of primary amoebiasis, humoral antibodies eliminate the parasite from the intestine and protect the host from further infection as well as further damage
Cell-mediated immunity (CMI)
cell-mediated immunity (CMI) is mediated by antigen-specific blastogenic responses
produces lymphokines such as interferon-g (IFN-g) which induces the killing of the Entamoeba histolytica trophozoites by macrophages and depends on contact, oxidative pathways, non-oxidative pathway, and the production of nitric oxide (NO)
cytokines such as tumor necrosis factor (TNF) and IFN-g activates the amoebicidal activity of neutrophils
CD8+ lymphocytes are also an important immune response in killing the trophozoites
CMI is not responsible for host immunity in cases of initial amoebic invasion which has been evidenced by the lack of severity of amoebic disease in AIDS patients
it also plays an important role in limiting the invasion of Entamoeba histolytica and protecting the host from recurring infection
Epidemiology of Entamoeba histolytica
Epidemiologically, Entamoeba histolytica is worldwide in distribution
the third cause of death by parasite next to malaria and schistosomiasis
prevalence ranges from 1% to 10% in developed countries and 50% to 80% in developing countries
Reservoir, Source of Entamoeba histolytica
the main source of infection is food and water (wells, ponds, springs) contaminated by human feces containing Entamoeba histolytica cyst
sometimes piped water supply is contaminated after it comes in contact with sanitary drains as a result of defective plumbing in an urban setting
since there are no animal reservoirs, infected humans, especially asymptomatic cyst carriers are the main reservoir for the parasitic infection
Transmission of Entamoeba histolytica
Vectors – arthropods such as flies and cockroaches may mechanically transmit the Entamoeba histolytica cysts from the feces to water and food
Fecal-oral route
Entamoeba histolytica infection is transmitted after the consumption of food and/or water contaminated with the cyst
unhygienic handling of food by food handles including cook, waiter, etc can also cause transmission of the infestation
in tight community settings such as hospitals, orphanages, mental hospitals, and refugee camps, the amoebae are transmitted among individuals if personal hygiene is poor
use of human feces as fertilizers to grow vegetables, crops can also be blamed for transmission
consumption of raw vegetables, especially if not properly washed
Sexual contact
Entamoeba histolytica infection is transmitted via sexual intercourse, mostly in male homosexuals
the transmission also occurs through anilingus, the practice of oral-to-anal contact
Treatment of Entamoeba histolytica
The treatment for Entamoeba histolytica is based on:
the eradication of amoebae using amoebicides
replacement of electrolytes, blood, fluids
None of the amoebicidal drugs available are effective against the parasite present in all infected organs such as the liver and lungs. There are two types of amoebicidal drugs- luminal amoebicides and tissue amoebicides.
Luminal amoebicides
luminal amoebicides act on the Entamoeba histolytica present in the mucosa of the lumen
only effective against both trophozoites and cysts if present in the lumen of the intestine
as they can kill cysts and prevent the recurrence of the infestation, these drugs are always used to treat any type of amoebiasis
Eg: diloxanide fluorate, diiodohydroxyquin, paromomycin
Tissue amoebicide
tissue amoebicide only affects Entamoeba histolytica present in the host tissues such as the liver, colonic mucosa
acts on trophozoites but not the cyst form of the amoebae
can be administered orally or parenterally
Eg: metronidazole, tinidazole, emetine hydrochloride, chloroquine, tetracycline, erythromycin, metronidazole (Drug of choice but is contraindicated in pregnant women)
Prevention, Control of Entamoeba histolytica
Prevention, Control of Entamoeba histolytica are done by:
Individual prophylaxis
Individual prophylaxis of Entamoeba histolytica is done by
improved personal hygiene such as proper washing of hands with soap after defecation and before eating food
treatment of water before drinking such as boiling, filtering the water used in a 0.22-micrometer membrane, iodination with tetracycline hydro per iodide
drinking bottled water while traveling to areas endemic to amoebiasis as chlorine treatment cannot kill the cysts
if salad is to be consumed, treat the vegetables with acetic acid or vinegar for 15 minutes
not performing sexual acts that involve fecal-oral contact
Community prophylaxis
Community prophylaxis of Entamoeba histolytica is done by
improvement of the water management system to avoid fecal contamination
improvement of sanitation by installing latrines for proper disposal of human feces