Summary
Highlights
Balantidium coli is the only ciliate pathogenic to humans and the largest protozoan parasite affecting man. It causes balantidiasis, an infection acquired by ingesting fecally contaminated food or water, often from pigs (its natural host). Trophozoites are large, pear-shaped, covered in cilia, and possess a large kidney-shaped macronucleus and a small dot-like micronucleus. Cysts are spherical to oval and contain a prominent macronucleus. It causes ulceration in the large intestine, with symptoms including severe diarrhea with blood and mucus.
The video starts by comparing Bacillary Dysentery and Amoebic Dysentery, highlighting their causative agents, symptoms, and microscopic differences. Bacillary dysentery is caused by bacteria (e.g., Shigella, Salmonella, E. coli) and presents acutely with fever, malaise, and prominent vomiting. Amoebic dysentery, caused by Entamoeba histolytica, has a more gradual onset, with milder abdominal cramps and less common vomiting. Key microscopic distinctions include the presence of Charcot-Leyden crystals and trophozoites with ingested red blood cells in amoebic dysentery.
Entamoeba dispar is morphologically identical to E. histolytica but is non-invasive and non-pathogenic. E. moshkovskii is found in sewage and brackish water, also being morphologically similar but non-pathogenic. E. hartmanni is a smaller, non-pathogenic species often referred to as the 'small race' of E. histolytica. Differentiation primarily relies on size and the absence of ingested red blood cells in their trophozoites. In routine hospital settings, E. histolytica and E. dispar are often reported together unless ingested red blood cells are observed.
Entamoeba polecki is common in Papua New Guinea, primarily affecting pigs and monkeys, but can infect humans. Its cysts have angular or pointed chromatoidal bars and are consistently uninucleated. The general life cycle of non-pathogenic intestinal amoeba is straightforward: ingestion of cysts, multiplication as trophozoites in the intestines, and release of cysts and trophozoites in stool. Unlike E. histolytica, these do not invade other organs.
Entamoeba coli cysts are large (15-25 µm), spherical to oval, and can contain up to eight nuclei. Their trophozoites have sluggish motility and eccentric karyosomes. Endolimax nana cysts are small (5-10 µm) and oval, lacking peripheral chromatin or chromatoidal bodies, with a large, irregular karyosome described as 'blood-like.' Iodamoeba buetschlii cysts (10-12 µm) are notable for a large iodine-staining glycogen vacuole and a 'basket' nucleus appearance. Reporting non-pathogenic amoeba is important as their presence indicates fecal contamination of food or water sources.
Entamoeba gingivalis is the only amoeba that ingests white blood cells and lacks a cyst stage, primarily found in the mouth but occasionally in the vagina. Free-living amoebae like Naegleria, Acanthamoeba, and Balamuthia are opportunistic pathogens that cause severe infections, particularly in immunocompromised individuals. They are usually harmless in their natural environment but become pathogenic when they infect humans.
Naegleria fowleri is the causative agent of Primary Amoebic Meningoencephalitis (PAM), often called the 'brain-eating amoeba.' Infection occurs through inhalation of contaminated water, typically during swimming in warm freshwater. It has two trophozoite forms: amoeboid (infective to humans) and flagellate. The disease is rapidly fatal, resembling bacterial meningitis in early stages. Diagnosis involves CSF examination for motile trophozoites and specific culture using non-nutrient agar with E. coli.
Acanthamoeba species cause Granulomatous Amoebic Encephalitis (GAE), primarily in immunocompromised individuals, and Acanthamoeba keratitis in contact lens wearers or those with eye trauma. Trophozoites are characterized by spine-like pseudopods (acanthopodia). Cysts have a distinctive double wall with an outer wrinkled layer and an inner polyhedral layer. Diagnosis involves CSF or corneal scraping examination, microscopy, and culture, noting its ability to tolerate higher saline concentrations than Naegleria.
Balamuthia mandrillaris causes Balamuthia Amoebic Encephalitis (BAE), similar to GAE, and is also prevalent in immunocompromised patients. Its trophozoites have finger-like or broad pseudopods, and its cysts feature three distinct wall layers (ectocyst, mesocyst, endocyst) identifiable by electron microscopy. Definitive identification requires advanced techniques. Recently discovered free-living amoebae like Sappinia pedata, Sappinia diploidea (with two nuclei connected by a filament), and Paravahlkampfia francinae have been implicated in isolated human infections.
Diagnosis of Balantidiasis relies on routine stool examination, with wet preparations from fresh or concentrated material being recommended to clearly visualize the organisms. Permanent stains can obscure internal morphology due to dark staining, making identification difficult. The large size of B. coli can sometimes lead to confusion with helminth eggs. The key distinguishing feature is the large, kidney-shaped macronucleus observed in both trophozoites and cysts.