Microbiology 3 - Parasitology.pdf

Microbiology Parasitology Microbiology| Parasitology Contents : Definition 3 Parasite 4 Host 9 Protozoa 17 Entamoeba histolytica 19 Naegleria fowleri 39 Microbiology| Parasitology Definition : Parasitology is the area of biology concerned with the phenomenon of dependence of one living organism on a...

Microbiology Parasitology Microbiology| Parasitology Contents : Definition 3 Parasite 4 Host 9 Protozoa 17 Entamoeba histolytica 19 Naegleria fowleri 39 Microbiology| Parasitology Definition : Parasitology is the area of biology concerned with the phenomenon of dependence of one living organism on another. Medical parasitology deals with: 1. The parasites which infect man. 2. The diseases they produce. 3. The response generated by the human against parasite. 4. Various methods of diagnosis, prevention and treatment. Microbiology| Parasitology Parasite : A parasite is an organism (mainly infectious agent except for virus, bacteria or fungus) that is entirely dependent on another organism, referred to as its host, for all or part of its life cycle and metabolic requirements. It is of two types: Microparasite & Macroparasite. Microbiology| Parasitology Microparasite It is small, unicellular and multiplies within its vertebrate host, often inside cells. Ex: protozoa Macroparasite It is large, multicellular This category includes helminths. Ex: Fasiola hepatica Microbiology| Parasitology On the basis of their location : 1. Ectoparasites: Organisms which live on the surface of the skin or temporarily invade the superficial tissues of the host (e.g. Louse (plural is lice) such as human head lice (pediculosis capitis). The infection by these parasites is known as infestation. 2. Endoparasites: Organisms that live within the body of the host. All protozoan and helminthic parasites of human are endoparasites. The invasion by endoparasites is known as infection. Microbiology| Parasitology On the basis of host : Obligate parasites: Organisms that cannot exist without a host (Ex. Toxoplasma gondii) Facultative parasites: Organisms that may live either a parasitic or free-living existence (Ex. Naegleria fowleri, Acanthamoeba spp.) Microbiology| Parasitology Accidental or incidental parasites: Organisms that attack an unusual host (Ex. Echinococcus granulosus in man). Aberrant parasites: Organisms that attack a host where they cannot live or develop further (Ex. Toxocara canis in man). Free-living: The term free-living describes the non-parasitic stages of existence which are lived independently of a host. Ex. hookworms such as: Ancylostoma duodenale and Necator americanus have active free-living stages in the soil. Microbiology| Parasitology Host : An organism which harbors the parasite and provides the nourishment and shelter to the latter. Type of Host Definitive host: This is the host in which sexual reproduction of the parasite takes place. The definitive host is the mammalian host. Ex. Felines are final host for Toxoplasma gondii. Microbiology| Parasitology Intermediate host: The host which alternates with the definitive host and in which the larval or asexual stages of a parasite are found. Some parasites require two intermediate hosts for completion of their life cycle. Ex. the first IH for Clonorchis sinensis is snail while second IH is a freshwater fish. Microbiology| Parasitology Paratenic host: A host in which larval stage of a parasite survives but does not develop further. It is often not a necessary part of the life cycle. Such as fleas. Reservoir host: A host which harbors the parasite and serves as an important source of infection to other susceptible hosts. Epidemiologically, reservoir host are important in the control of parasitic diseases. Ex. The women genital tract (Bartholin glands) is the only reservoir for the Trichomonas vaginalis. Microbiology| Parasitology Host - parasite relationships : Commensal Parasites are parasites which do not harm their hosts Entamoeba coli. Pathogenic Parasites Pathogenic Parasites are those which cause diseases to their hosts. Entamoeba histoloytica. Symbiosis an association in which both host and parasite are so dependent upon each other that one cannot live without the help of the other. Neither of the partners suffers from any harm from this association. Microbiology| Parasitology Vector: an agent, usually an insect that transmits infection from one human host to another. 1. Mechanical vector: transfer parasite between hosts but is not essential in the life cycle of the parasite. Ex. e.g. a housefly that transfers amoebic cysts from infected food that is eaten by humans. 2. Biological vector: Is the vector in which the parasite undergo development, then it is essential in the life cycle of the parasite. Microbiology| Parasitology Zoonosis: term describe a disease that transmit from animals to humans, either directly or indirectly Ex. leishmaniasis, hydatid cyst and fascioliasis. Microbiology| Parasitology Sources of Infection : Contaminated soil and water, Freshwater fishes, Crab and crayfishes , Raw or undercooked pork & Beef, Watercress. Housefly (mechanical carrier), Dog , Cats. Man…. Portal of Entry Into the Body: Mouth, skin, Sexual contact, Kissing, Congenital, Inhalation Protozoa Microbiology| Protozoa Protozoa are single-celled animals; each cell performs all of the necessary functions of life, majority of which are free-living. Microbiology| Protozoa Classification of the protozoa: Human parasites in the Kingdom: Protista. Subkingdom: Protozoa are classified under four phyla: 1. Sarcomastigophora (containing amoeba and flagellates). 2. Apicomplexa (containing Sporozoa). 3. Ciliophora (containing Ciliates). 4. Microspora. Microbiology| Protozoa Entamoeba histolytica : Was first described by Losch in1875. Geographical distribution higher incidence in tropical and subtropical regions that have poor sanitation and contaminated water. Risk groups include: Male homosexuals, Travelers and recent immigrants and Institutionalized populations. Microbiology| Protozoa Habitat Trophozoites of E. histolytica reside in mucosa and submucosa of large intestine of man Morphology 1. Trophozoite 2. Precyst 3. Cyst Microbiology| Protozoa 1. Trophozoite Cytoplasm is either a clear outer ectoplasm or an inner finey granular endoplasm Movement: long finger-like pseudopodial extensions It is the only form present in tissue Has a spherical nucleus Microbiology| Protozoa 2. Precyst It is oval with a blunt pseudopodium projecting from the periphery. Food vacuoles disappear. 3. Cyst (it found only in stool, do not found in tissue) It is spherical thick chitinous wall Has1–4 nuclei Microbiology| Protozoa Life cycle : One host only Infection occur by ingestion of mature quadri-nucleate cysts (may remain viable in a humid environment and stay infective for several days). In the small intestine : cyst wall lysed by trypsin Note: Flies and cockroaches can also serve as vectors for the transmission of E. histolytica cysts. Microbiology| Protozoa By division the 4 nuclei become 8 Cytoplasm becomes separated into small parts surrounding each nuclei, thus from each mature cyst eight small amoebulae (metacystic trophozoites) are produced. During growth, E. histolytica secretes a proteolytic enzyme of the nature of histolysin which brings about destruction and necrosis of tissue and produces flask-shaped ulcers At this stage, a large number of trophozoites are excreted along with blood and mucus in the stool leading to amoebic dysentery. Microbiology| Protozoa Encystation: The trophozoites, in the lumen of the large intestine, discharge undigested food particles and transform into precysts and then into mature quadri-nucleate cysts. Excystation: occurs only after mature cyst has been taken in suitable host and reach a suitable level of intestine so amoeba becomes active, rapture the cyst membrane and escapes and started to multiply by binary fission and colonization inside host digestive tract. Microbiology| Protozoa Microbiology| Protozoa Pathogenicity : Intestinal amoebiasis confined to gastrointestinal tract Incubation period of 1–4 weeks the amoebae invade the colonic mucosa, producing characteristic ulcerative lesions and a profuse bloody diarrhoea (amoebic dysentery). Ulcer: generalized or local Microbiology| Protozoa Complications : When destruction is not limited to the submucosa but extends deeper into the muscular layer Local peritonitis Perforation and generalized peritonitis Pericaecal or pericolic abscess Sloughing and gangrene of large gut Microbiology| Protozoa E. histolytica may also cause amoebic appendicitis and amoebomas. The latter are pseudotumoural lesions whose formation is associated with necrosis inflammation and oedema of the mucosa and sub-mucosa Microbiology| Protozoa Extraintestinal amoebiasis : Trophozoites of E. histolytica are carried by the portal vein from the base of the amoebic ulcer in the large intestine Multiply in the liver lead to cytolytic action cause obstruction of the portal venules resulting in anaemic necrosis of hepatic cells. Microbiology| Protozoa This complicated with 1. Amoebic liver abscess 2. Pus of liver abscess 3. diffusion to many direction [include, right-sided liver abscess, left-sided liver abscess and liver abscess situated on the inferior surface] Microbiology| Protozoa Pathogenicity depend on: 1. Virulence of strain 2. Resistance of the host (depends on the innate immunity). 3. State of nutrition of the host. 4. Infection with other agents (free of other infections mean less susceptible to infection). 5. Some drugs may irritate the intestinal wall so irritated intestine is more susceptible to infection. 6. Bacterial flora (metabolic processes can enhance the invasiveness). Microbiology| Protozoa Symptoms : Fever, chills, and diarrhea, sometimes bloody or white mucus and often with cramps. Some people may have only mild abdominal discomfort or no symptoms at all. Symptoms can start 2 or more weeks after infection. Microbiology| Protozoa Laboratory Diagnosis : Intestinal amoebiasis Stool examination scrapings from ulcerated areas are examined by macroscopic (should be distinguish from Bacillary Dysentery) to demonstrate motile trophozoites or cyst Stool culture is useful especially in the cases of chronic and asymptomatic intestinal infections Microbiology| Protozoa Biopsy specimens should also be submitted for histopathologic studies. DNA probe and polymerase chain reaction (PCR). Blood examination It shows moderate leukocytosis Serological tests: include 1. Indirect haemagglutination (IHA) 2. Indirect fluorescent antibody (IFA) test 3. Enzyme-linked immunosorbent assay (ELISA). Microbiology| Protozoa Hepatic amoebiasis 1. Diagnostic aspiration 2. Liver biopsy 3. Blood examination 4. Stool examination 5. Serological tests Microbiology| Protozoa Treatment : For asymptomatic infections, paromomycin or iodoquinol are the drugs of choice. For symptomatic intestinal or extraintestinal infections, the drugs of choice are metronidazole or tinidazole, immediately followed by treatment with paromomycin or iodoquinol. Failure of metronidazole therapy may be an indication for surgical intervention. Microbiology| Protozoa Parasite Properties Entamoeba dispar Morphologically identical to E. histolytica. It must be separated by isoenzymatic, immunologic or molecular analyses. Also E. histolytica under microscope appear to contain ingested RBC, while dispar not Entamoeba hartmanni Some consider this a separate species. It differs from E. histolytica by being smaller in size. Entamoeba coli Distinguished from E. histolytica by having an eccentric endosome, and mature cysts with 8 nuclei. If chromatoidal bodies are present, they have splintered ends, rather than rounded as in E. histolytica. Endolimax nana This is a very small amoeba (6-15um) with a large, eccentric endosome and thin nuclear envelope. Mature cysts contain 4 nuclei. Iodamoeba butschlii Both the trophozoite and cyst have one nucleus with a large endosome. The cyst contains a large glycogen vacuole that stains darkly with iodine. Microbiology| Protozoa Pathogenic and opportunistic free-living amoebae Naegleria fowleri : Found in warm freshwater and in the soil near warm-water discharges of industrial plants, and in unchlorinated or minimally-chlorinated swimming pools. Microbiology| Protozoa Morphology : N. fowleri has two stages – motile trophozoites and non-motile cysts The trophozoites produce broadly rounded lobopodia. The trophozoites can also transform to a flagellated form. Microbiology| Protozoa Cysts relatively thin cyst wall, single-walled, spherical. a feature that makes N. fowleri cysts susceptible to desiccation. Trophozoites encyst when conditions are appropriate and, later, excyst in a favourable environment. Microbiology| Protozoa Life cycle and pathogenicity : Infection acquired by contamination during swimming in freshwater lakes or inhalation of dust containing infective forms. The amoeboid forms invade the nasal mucosa, cribriform plate and travel along the olfactory nerves to brain primary amoebic meningoencephalitis (PAM). The disease usually results in death within 72 hours of the onset of symptoms. Microbiology| Protozoa Microbiology| Protozoa Diagnosis Diagnosis relies on identifying trophozoites by microscopic examination of fresh cerebrospinal fluid specimens or histologic sections of CNS tissue, and on culturing, if necessary. Treatment At present there is no satisfactory treatment for PAM. Antibacterial antibiotics and antiamoebic drugs are ineffective.