.trashed-1730560018-PARASITOLOGY LECT 2.pptx

Study of parasites life cycle, transmissions, treatment and prevention

1. AMOEBIASIS Amoebas are primitive unicellular microorganisms with a relatively simple life cycle which can be divided into two stages: • Trophozoite – actively motile feeding stage. • Cyst – quiescent, resistant, infective stage. Their reproduction is through binary fission, e.g. splitting of the trophozoite or through the development of numerous trophozoites within the mature multinucleated cyst. Motility is accomplished by extension of pseudopodia (“false foot”)

2. AMOEBA INTESTINAL AMOEBAE FREE LIVING AMOEBA a. Entamoeba histolitica b. Entamoeba dispar a.Naegleria fowleri c. Entamoeba.coli b.Acantamoeba spp d. Entamoeba palecki c.Balamuthia mandrillaris e. Entamoeba hartmanii f. Entamoeba.gingivalis g. Entamoeba gingivalis h. Endolimax nana i. Iodomoeba butschilli NOTE:all intestinal amoeba are non pathogenic Except E . histolitica NOTE:All free living amoeba are opportunistic

3. HISTORY AND DISTRIBUTION OF E.histolitica E. histolytica was discovered by Lösch in 1875, who demonstrated the parasite in the dysenteric feces of a patient in St. Petersburg in Russia. In 1890, William Osler reported the case of a young man with dysentery, who later died of liver abscess. Councilman and Laleur in 1891 established the pathogenesis of intestinal and hepatic amoebiasis and introduced the terms ' amoebic dysentery ' and ' amoebic liver abscess '. E. histolytica is worldwide in prevalence, being much more common in the tropics than elsewhere. It has been found wherever sanitation is poor, in all climatic zone from Alaska (61°N) to straits of Magellan (52°S). It has been reported that about 10% of world population and 50% of the inhabitants of developing countries may be infected with the parasite. The infection is not uncommon even in affluent countries, about 1% of Americans being reported to be infected It is the third leading parasitic cause of mortality, after malaria and schistosomiasis.

4. Morphology E. histolytica occurs in 3 forms Trophozoite Precyst Cyst

5. Trophozoites Viable trophozoites vary in size from about 10-60μm in diameter. Motility is rapid,progressive, and unidirectional, through pseudopods. The nucleus is characterized by evenly arranged chromatin on the nuclear membrane and the presence of a small,compact, centrally located karyosome. Trophozoite is the vegetative or growing stage of the parasite . It is the only form present in tissues. It is large and actively motile in freshly-passed dysenteric stool, while smaller in convalescents and carrriers. The parasite, as it occurs free in the lumen as a commensal is generally smaller in size, about 15–20 µm and has been called the minuta form. The cytoplasm is usually described as finely granular with few ingested bacteria or debris in vacuoles. In the case of dysentery,however, RBCs may be visible in the cytoplasm, and this feature is diagnostic for E.histolytica

6. cyst stage The cyst is spherical in shape about 10–20 µm in size. The early cyst contains a single nucleus and two other structures—a mass of glycogen and 1–4 chromatoid bodies or chromidial bars, which are cigar-shaped refractile rods with rounded ends .The chromatoid bodies are so called because they stain with hematoxylin, like chromatin. As the cyst matures, the glycogen mass and chromidial bars disappear and the nucleus undergoes 2 successive mitotic divisions to form 2 and then 4 nuclei. The mature cyst is, thus quadrinucleate . The cyst wall is a highly refractile membrane, which makes it highly resistant to gastric juice and unfavorable environmental conditions. The nuclei and chromidial bodies can be made out in unstained ilms, but they appear more prominently in stained preparations. With iron hemotoxylin stain, nuclear chromatin and chromatoid bodies appear deep blue or black, while the glycogen mass appears unstained. When stained with iodine, the glycogen mass appears golden brown, the nuclear chromatin and karysome bright yellow, and the chromatoid bodies appear as clear space, being unstained.

7. metacyst trophozoite The nuclei in the metacyst immediately undergo division to form 8 nuclei, each of which gets surrounded by its own cytoplasm to become 8 small amoebulae or metacystic trophozoites. If exystation takes place in the small intestine, the metacystic trophozoites do not colonize there, but are carried to the caecum. The optimal habitat for the metacystic trophozoite is the submucosal tissue of caecum and colon, where they lodge in the glandular crypts and grow by binary ission Some develop into precystic forms and cysts, which are passed in feces to repeat the cycle. The entire life cycle is, thus completed in one host.

8. Trophozoite,Precyst , unnucleated,binucleated and multinucleated cyst stages

9. Infective form : Mature quadrinucleate cyst passed in feces of convalscents and carriers. The cysts can remain viable under moist conditions for about 10 days. Mode of transmission : Man acquires infection by swallowing food and water contaminated with cysts. As the cyst wall is resistant to action of gastric juice, the cysts pass through the stomach undamaged and enter the small intestine. Excystation: When the cyst reaches caecum or lower part of the ileum, due to the alkaline medium, the cyst wall is damaged by trypsin, leading to excystation. The cytoplasm gets detached from the cyst wall and amoeboid movements appear causing a tear in the cyst wall, through which quadrinucleate amoeba is liberated. This stage is called the metacyst LIFE CYCLE

10. Trophozoites then multiply in the small intestine by binary fission to produce cysts that exit via human stool. Several trophozoites remain inside the lumen of the small intestine. The rest attach themselves to the intestinal mucosa, enter the bloodstream and further grow in the extraintestinal regions of the host like lungs, liver, brain. NB :In most of the cases, E. histolytica remains as a commensal in the large intestine without causing any ill efects. Such persons become carriers or asymptomatic cyst passers and are responsible for maintenance and spread of infection in the community. Sometimes, the infection may be activated and clinical disease ensues. Such latency and reactivation are the characteristics of amoebiasis.

11. Pathogenesis and clinical features E. histolytica causes intestinal and extraintestinal amoebiasis . Incubation period is highly variable. On an average, it ranges from 4 days to 4 months. Amoebiasis can present in different forms and degree of severity, depending on the organ afected and the extent of damage caused a.Intestinal Amoebiasis The lumen-dwelling amoebae do not cause any illnesss. They cause disease only when they invade the intestinal tissues. This happens only in about 10% of cases of infection, the remaining 90% being asymptomatic.

12. Intestinal amoebiasis cont’ Mucosal penetration by the amoeba produces discrete ulcers with pinhead center and raised edges. Sometimes, the invasion remains superficial and heals spontaneously. More often, the amoeba penetrates to submucosal layer and multiplies rapidly, causing lytic necrosis and thus forming an abscess. The abscess breaks down to form an ulcer . Amoebic dysentery occurs when E. histolytica trophozoites invade the wall of the large intestine and multiply in the submucosa, forming large flask-shaped ulcers . The amoebae ingest red cells from damaged capillaries. Occassionally, a granulomatous pseudotumoral growth may develop on the intestinal wall from a chronic ulcer. This amoebic granuloma or amoeboma may be mistaken for are malignant tumor.

13. clinical features of intestinal amoebiasis The typical manifestation of intestinal amoebiasis is amoebic dysentery. This may resemble bacillary dysentery, but can be diferentiated on clinical and laboratory grounds. Compared to bacillary dysentery, it is usually insidious in onset and the abdominal tenderness is less and localized . The stools are l arge, foul-smelling, and brownish black , often with bloodstreaked mucus intermingled with feces. The RBCs in stools are clumped and reddish-brown in color. Cellular exudate is scanty Charcot-Leyden crystals are often present. E.histolytica trophozoites can be seen containing ingested erythrocytes. The patient is usually afebrile and nontoxic. In fulminant colitis, there is conluent ulceration and necrosis of colon. The patient is febrile and toxic. Intestinal amoebiasis does not always result in dysentery. Quite often, there may be only diarrhea or vague abdominal symptoms popularly called ‘uncomfortable belly’ or ‘growling abdomen.’ Chronic involvement of the caecum causes a condition simulating appendicitis.

14. EXTRA INTESTINAL AMOEBIASIS -a moebic liver abscess Occasionally E. histolytica amoebae are carried to the liver in the portal circulation and form abscesses, usually in the rightlobe. Capillary system of the liver acts as an efficient filter and holds the trophozoites . Trophozoites multiply inside liver cells and carry on cytolytic actions. This leads to obstruction to the circulation and produces thrombosis of the portal venules (sinusoids) resulting in anaemic necrosis of the liver cells,progressive destruction of concentric layers of liver cells occurs. the centre of the abscess contains a viscous pink-brown or grey-yellow fluid consisting of digested liver tissue. It is referred to as ‘pus’ but contains very few pus cells. As part of treatment (not diagnosis) the fluid may be aspirated and sent to the laboratory to examine for trophozoites. Amoebic liver abscesses are more common in adults than in children with a higher frequency in men (3 to 1 rate). There is pain and tenderness over the liver, wasting, and fever with chills and night sweats. Patients with large or multiple abscesses may become jaundiced and anaemic. There is usually a raised white cell count with neutrophilia and a significantly raised ESR. There is pain and tenderness over the liver, wasting, and fever with chills and night sweats. Patients with large or multiple abscesses may become jaundiced and anaemic. There is usually a raised white cell count with neutrophilia and a significantly raised ESR. Right-lobe abscesses can penetrate the diaphragm and cause lung disease (pulmonary amoebiasis ) Other lesions include:Cerebral amoebiasis

15. Pulmonary amoebiasis Very rarely, primary amoebiasis of the lung may occur by direct hematogenous spread from the colon bypassing the liver, but it most often follows extension of hepatic abscess through the diaphragm and therefore, the lower part of the right lung is the usual area affected . Hepatobronchial fistula usually results with expectoration of chocolate brown sputum . Amoebic empyema develops less often. The patient presents with severe pleuritic chest pain, dyspnea, and non-productive cough.

16. Diagnosis It rests on  finding either trophozoites in diarrheal stools or cysts in formed stools.  Diarrheal stools should be examined  within one hour of collection  to see the ameboid motility of the trophozoite . The trophozoite   characteristically contain ingested red blood cells.  Characteristics of Stool Macroscopic appearance of stool : Offensive dark brown semisolid stool, and mixed with blood, mucus and much fecal matter. General microscopic examination : Presence of charcot -Leyden crystals. E. histolytica  infection is distinguished from bacillary dysentery by the lack of high fever and absence PMN leukocytosis

17. Prevention and Control 1. Cooking of food and vegetables 2. Hand washing after defecation and before eating 3. Safe water supply (treatment, boiling, filtration, etc.) 4. Control of mechanical vectors like flies 5. Avoid use of night soil as a fertilizer proper sanitary disposal of faeces . 6. Treatment of infected individuals and health education

18. Treatment Three classes of drug are used in the treatment of amoebiasis. Luminal amoebicides: Diloxanide furoate, iodoquinol, paromomycin, and tetracycline act in the intestinal lumen but not in tissues. Tissue amoebicides: Emetine, chloroquine, etc. are efective in systemic infection, but less efective in the intestine. Dosage of chloroquine in amoebic liver abscess is 1 g for 2 days followed by 5 g daily for 3 weeks. Both luminal and tissue amoebicides: Metronidazole and related compounds like tinidazole and ornidazole act on both sites and are the drug of choice for treating amoebic colitis and amoebic liver abscess.