Charmo University Medical Parasitology Lecture Notes PDF

Charmo University COLLEGE OF SCIENCE Department of Medical Laboratory Science Medical parasitology -Lecture 2 Protozoa/Amoeba classification...

Charmo University COLLEGE OF SCIENCE Department of Medical Laboratory Science Medical parasitology -Lecture 2 Protozoa/Amoeba classification Entamoeba histolytica Saturday, October 12, 2024 1  Lec.2:Phylum Protozoa (Animal-like Protista) Characteristic features of protozoa: (Proto) stands for Primitive - (Zoa) means Animal o The protozoa are unicellular eukaryotic microorganisms with no cell walls. o They have all the structural features (specialized organelles) that help them in their essential life activities. o Many protozoa live singly, but many others live in colonies. o Only a few of the many thousands of protozoan species are pathogenic for humans. Reproduction is generally by: Asexual Reproduction: (Mitotic binary fission) is a type of asexual reproduction in which the fully grown parent cell splits into two halves and produces two new daughter cells. Sexual reproduction: (Meiotic) It occurs in some protozoal species such as Sporozoa. Saturday, October 12, 2024 2  General Characteristic of Intestinal Protozoa (Amoeba) o Amoeba is a single- celled (protozoan) organism that constantly changes its shape. “Amoeba” “Amoibe” (Greek word) = “change”. o They constantly change their shape due to presence of cytoplasmic extensions called pseudopodia single (pseudopodium). o The cytoplasm of Ameba is bounded by a membrane and can be differentiated into an outer ectoplasm and inner endoplasm. o Pseudopodia are formed by the Ameba by thrusting out ectoplasm, followed by endoplasm. o These are employed for locomotion and engulfment of food by phagocytosis. o All Amebae have a Trophozoite stage in which they multiply by binary fission as long as the environmental conditions are favorable. Many species have an encysted stage that is more resistant to unfavorable conditions and allows transfer from one host to the next. Saturday, October 12, 2024 3  Classification of Clinically Important Protozoa: Many of these protozoa have both stages (1)- Trophozoite (Diagnostic stage), A motile, the active, reproductive &feeding stage (2)- Cyst (Infective stage), A dormant & highly resistant to environmental stress. The protozoa are classified according to their: (1)- Mode of locomotion (how they move): (2)- Site where infection occurs: 4 Saturday, October 12, 2024  Amoebae Classification Based on Habitat: Amoebae are classified as Intestinal Amoebae and Free living Amoebae. o Intestinal Amoebae: They in habitat in the large intestine of humans and animals. - Pathogenic: Entamoeba histolytica - Nonpathogenic: Entamoeba dispar, Entamoeba moshkovskii, Entamoeba coli Entamoeba gingivalis, E. hartmanni, Endolimax nana. o Free-living Amoebae: They are small free living & opportunistic pathogens. Examples are : - Acanthamoeba species - Naegleria fowleri (They are producing meningoencephalitis and other infections). - Balamuthia mandrillaris Saturday, October 12, 2024 5  Protozoa Classifications: (1)- Class/ Rhizopoda 1-) Class Rhizopoda: The parasites of this class move by pseudopodia and multiply by binary fission. The only parasite of this class which is pathogenic to human begins is Entamoeba histolytica. A Trophozoite: It is a moving, feeding, and multiplying stage of protozoan life cycles. There are not male & female Trophozoites, they multiply a sexually. A cyst: It is a stage of many protozoan parasites that survive well in the environment. Cysts of human parasites are infective to humans. Saturday, October 12, 2024 6  1)- Entamoeba histolytica o E. histolytica is worldwide but more common in warm areas (tropical & subtropical countries). E. histolytica has three subs species- such as E. dispar, E. moshkovskii & E. bangladeshi o E. histolytica is the pathogenic species causing amoebic dysentery (Amoebiasis), and a wide range of other invasive diseases, including amoebic liver abscess, where as other two are considered as nonpathogens that colonize the large intestine. o It infects the human as well as cats, pigs and monkeys; o It has finely granular, somewhat viscous endoplasm and a clear ectoplasm. o Pseudopodia are broad finger-like (lobopodia) that extend from the ectoplasm. o There are many food vacuoles containing parts of epithelial cells, Bacteria and sometimes many R.B.Cs. o The nucleus is rounded, vesicular, surrounded by a delicate nuclear membrane, studded on its inner surface with minute regular chromatin granules. o In the Centre of the nucleus, there is a single dense bead-like chromatin body, the karyosome (centric karyosome). Saturday, October 12, 2024 7  Morphology of the Entamoeba histolytica Morphologically E. histolytica occurs in three stages: - Trophozoite - Precyst - Cyst The parasite has 2 distinct stages (Trophozoite & Cyst) which are commonly recognized in the feces of the patient, but only the Trophozoite is present in the tissue. The Trophozoite lives in the last part of the small intestine & in the large intestine stuck with mucosa, especially in the caecum, sigmoid rectal area. The Trophozoite grow & multiply continuously in the intestine, but sometimes it is encysting in the intestine, whenever, the Trophozoite will discharge the undigested food and become spherical, and then it secretes a delicate, solid membrane and become a cyst. The Cyst contains a nucleus (the same one of the Trophozoite), glycogen mass and some chromatoid bars. The nucleus will divide into 2 nuclei then each of them divides once again, So, the mature cyst typically has 4 nuclei. The cyst is spherical or may have an oval shape. Saturday, October 12, 2024 8 Entamoeba histolytica - (A) Trophozoite; (B) Precyst; (C) Cysts Saturday, October 12, 2024 9  Life Cycle of E. histolytica  E. histolytica completes its life cycle in single host, i.e. human.  Infective form: Mature quadrinucleated cyst is the infective form. It can resist chlorination, gastric acidity and desiccation and can survive in a moist environment for several weeks.  Trophozoites and immature cysts can be passed in the stool of amoebic patients, but they cannot serve as an infective form as they are disintegrated in the environment or by gastric juice when ingested. The mode of Infection from ingestion of Amoebic cysts are: o Contaminated water or food. o Fecal- oral route (most common) o Sexual contact, or Vector. Saturday, October 12, 2024 10  Life cycle stages of E. histolytica 1. Cysts ingested with foods or drinks. 2. They pass through the stomach, and in the duodenum, the cyst wall will be destroyed by the effects of digestive enzymes. 3. They transform into Trophozoite in the small intestine. 4. Trophozoites invade the mucosa of the large intestine, causing tissue damage, increased secretions and eventual bloody diarrhea. 5. When these cysts are evacuated in the faeces of the infected patient, they will arrive in the environment, and the cycle will be repeated. Saturday, October 12, 2024 11  Pathogenesis of Amebiasis o Trophozoite of E. histolytica is the major invasive form and possesses many virulence factors that play role in the pathogenesis of intestinal as well as extraintestinal amoebiasis.  Pathogenesis of Intestinal Amoebiasis, Trophozoites invade the colonic mucosa producing characteristic ulcerative lesions (Amoebic ulcer) and profuse bloody diarrhea (amoebic dysentery). Males and females are affected equally with a ratio of 1:1.  Pathogenesis of Extraintestinal Amoebiasis o (Amoebic liver abscess, Anchovy sauce pus) Cross section of liver showing Amoebic liver abscess Saturday, October 12, 2024 12  Symptoms (Clinical Features) of Amoebiasis 1)- Asymptomatic Amoebiasis 2)- Intestinal Amoebiasis: (Incubation period varies from one to four weeks) Intestinal Amoebiasis is characterized by four clinical forms such as:  Amoebic dysentery: It should be differentiated from bacillary dysentery by these symptoms: Chronic: Abdominal discomfort or soft stool for variable periods may suddenly develop into - Bloody diarrhea with mucus and pus cells. Acute: Frequent dysentery with necrotic mucosa and abdominal pain.  Amoebic appendicitis: Presented with acute right lower abdominal pain.  Amoeboma: It presents as a palpable abdominal mass.  Fulminant colitis: Presents as intense colicky pain, rectal tenesmus, more than 20 motions/day, fever, nausea, anorexia and hypotension. 3)- Amoebic Abscesses: Presents with fever with weight loss, sweating and weakness, rarely jaundice, & cough - Liver - tender hepatomegaly - Hematologic spread - Hematomegaly - Right Upper Quadrant RUQ pain - Other sites: Lungs or Brain 13  Investigations & Laboratory Diagnosis of Intestinal Amebiasis o The typical stool In amebic dysentery consists of exudates, mucous, blood and may be little fecal material and we are mainly looking for the cyst stage. In the liquid stool, the Trophozoite may also be found, but only the cyst stage is present in the solid stool. For the diagnosis procedure, the fresh stool sample is required to prepare the wet mounts. Concentrates from fresh stool can be used for the wet mounts, with or without iodine stain. For permanently stained preparations we use trichrome stain. Concentration procedures, however, are not useful for demonstrating Trophozoites. o Stool culture- Polyxenic & axenic culture o Stool Antigen detection- (copro-antigen)- CIEP; ELISA;ICT. In addition, E. histolytica Trophozoites- can also be identified in aspirates or biopsy samples obtained during colonoscopy or surgery. o Serology- Amoebic antigen- ELISA - Amoebic antibody- IHA; ELISA; & IFA o Molecular diagnosis- Nested multiplex PCR & real time PCR. Saturday, October 12, 2024 14  Laboratory Diagnosis of Entamoeba histolytica o Intestinal Amoebiasis: Direct microscopic examination of the stool to recover motile Trophozoite (containing red cells are diagnostic of Amoebic dysentery). o In Extra-Intestinal Amoebiasis: Laboratory tests, including immunologically based procedures, may be used. Methods currently available include antigen tests, enzyme-linked immunosorbent assay (ELISA), indirect hemagglutination (IHA), gel diffusion precipitin (GDP), & indirect immunofluorescence. The differential diagnosis for E. histolytica intestinal Amebiasis includes: o Bacterial pathogens: Shigella, Escherichia coli, Salmonella, Campylobacter, and Clostridioides difficile o Inflammatory bowel disease o Ischemic bowel disease The differential diagnosis for E. histolytica extra-intestinal amebiasis includes: o Pyogenic liver abscess o Echinococcal disease 15 o Malignancy  Prevention & Treatment of Entamoeba histolytica Preventive measures are as follows:  A voidance of ingesting food and water contaminated with human faeces Treatment of asymptomatic persons who pass E. histolytica cysts in the stool may help reduce opportunities for disease transmission.  Vaccination Till now, there is no effective vaccine licensed for human use. However, colonization blocking vaccines are under trial targeting three E. histolytica specific antigens such as ( SREHP 170 kDa subunit of lectin antigen and 29kDa cysteine rich protein.  An important component of prevention is patient education through interprofessional communication. Physicians, nurse practitioners, nurses, and pharmacists should educate patients if they are traveling to endemic areas. Treatment: Metronidazole (Flagyll) is the first-line treatment.  Typical dosing for metronidazole is 500 to 750 mg orally 3 times a day for 7 to 10 days in adults foe intestinal amoebiasis and amoebic liver abscess.  Metronidazole can be safely used in children at a dosing of 35 mg/kg to 50 mg/kg per day divided into three doses.  Other measures include fluid and electrolyte replacement are used as a treatment. 16 Saturday, October 12, 2024  2)- Entamoeba coli o Entamoeba coli has a cosmopolitan distribution. o 2 stages: Trophozoite and cyst have a spherical shape, The ectoplasm couldn't be recognized from the endoplasm, and the food vacuoles contain bacteria and other enteric microbes. o The nuclear membrane is studded from the inner surface with large irregular chromatin granules with eccentric-large karyosomes. o The Trophozoite has a sluggish movement, shortly extended pseudopodia, and It lives in the lumen of the caecum and the lower level of the large intestine. o The mature cyst has 8 nuclei, the chromatoid bodies have an irregular sharp end (splinter-like). o The life cycle is similar to that of E. histolytica, except that the Trophozoite doesn’t attack the mucosa of the intestine, so it is described as non-pathogenic (commensal) ameba and its presence is evidence that the host has ingested fecal material. Saturday, October 12, 2024 17  Morphology of the Entamoeba coli Morphologically E. coli occurs in 2 stages: o The Trophozoite Same pseudopodia shape but larger than E. histolytica, nuclei with eccentric karyosome, other things such as ingested particles or RBC’s & glycogen mass are not clear. o The cyst larger than E. histolytica, with 4-8 nuclei; if 4 there is no confusion with E. histolytica because it’s bigger & the karyosome is eccentric. Saturday, October 12, 2024 18  3)- Entamoeba gingivalis o It is a parasite of the mouth of man and other mammals, including several species of monkeys and of dogs and cats. o It lives in/on the teeth, gums, and sometimes tonsils, only the Trophozoite stage has been described. o In most respects it is closely resembles E. histolytica, with a few to several fingerlike pseudopodia, finely granular endoplasm, and clear ectoplasm. o The nucleus contains a small karyosome that is central or slightly eccentric in position. o Endocytotic vacuoles are often numerous and the parasite will ingest bacteria, leukocytes and erythrocytes although it is not itself invasive. o No cysts are formed and transmission is entirely by oral to oral contact Saturday, October 12, 2024 19