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Micro Test 3

Parasitology

QuestionAnswer
obligate when an organism can live only in association with a host
facultative when an organism can live both in or on a host as well as in a free form
those that benefit from the host without causing it any harm are known as commensals
Parasites which live inside the body are termed endoparasites
those parasites which exist on the body surface are called ectoparasites
the host in which a parasite lives as the larval and asexual stage is the intermediate host
The host in which the parasite lives its adult and sexual stage is the definitive host
Other hosts that harbor the parasite and thus ensure continuity of the parasite's life cycle and act as additional sources of human infection are known as reservoir hosts.
An organism (usually an insect) that is responsible for transmitting the parasitic infection is known as the vector
direct wet mount detects motile organisms (Giardia) usually in duodenal drainage , with saline or iodine
concentration formalin ethyl acetate sedimentation or zinc flotation method, with saline or iodine
Permanent Stained smear Trichrome or Iron-hemotoxylin stains
Thick and thin blood films for Plasmodium, Babesia, Trypanosomes etc
Entamoeba histolytica (Protozoa) the major cause of amebic dysentery
The metacyst divides into four and then eight amoebae which move to the large intestine
Iodoquinol is used to treat asymptomatic infections
metronidazole is used for symptomatic and chronic amebiasis
Trophozoite: This form has an ameboid appearance and  is usually 15-20 micrometers in diameter, although more invasive strains tend to be larger. The organism has a single nucleus with a distinctive small central karyosome .
Entameba histolytica cysts are spherical, with a refractile wall; the cytoplasm contains dark staining chromatoidal bodies  and 1 to 4 nuclei with a central karyosome and evenly distributed peripheral chromatin.
Entamoeba coli not pathogenic, larger troph usually 20-25 m, cyst 15-25 m ,>4 nuclei Commensal
Endolimax nana cyst 5-10 m , 4 nuclei, no peripheral chromatin Commensal
Giardia lamblia (flagellate) It is the most frequent protozoan intestinal disease in the US and the most common identified cause of water-borne disease associated with breakdown of water purification systems. Infection occurs by ingestion of cysts, usually in contaminated water.
Giardia cysts 9 to 12 m. ellipsoidal cells with a smooth well-defined wall. The cytoplasm contains four nuclei and many of the structures seen in the trophozoite.
Giardia Trophozoite a 12 to 15 m., half pear-shaped organism with 8 flagella and 2 axostyles arranged in a bilateral symmetry. There are two anteriorly located large suction discs. The cytoplasm contains two nuclei and two parabasal bodi.
Metronidazole is the drug of choice for Giardia
Trichomonas vaginalis colonizes the vagina of women and the urethra (sometimes prostate) of men. Wet prep or Giemsa stain of vaginal/urethral discharge, prostatic secretions or urine sediment.
Cryptosporidium parvum Found in the gastrointestinal tract of many animals and causes epidemics of diarrhea in humans via contaminated food and water. Humans are infected by ingestion of C. parvum oocysts containing many sporozoites.
Isospora belli rare infection of normal humans, although it is being seen in increasing numbers in AIDS patients. Infection via the oro-fecal route The infective stage of the organism is an oval oocyst which, upon ingestion, follows the same course as C. parvum.
Cyclospora cayetanensis outbreaks linked to ingestion of contaminated food.
Demonstration of oocysts in feces is usually made using modified acid fast stains or immunoassays.
Toxoplasma gondii cats are the definitive host, can cause serious congenital defects if mother is exposed to cat feces.
TRYPANOSOMA These are hemoflagellates and can be demonstrated in peripheral blood smears
T.brucei gambiense, rhodesiense, congolense AFRICAN - Causes African sleeping sickness Parasites invade all organs of the body including heart and CNS. Leads to apathy, mental dullness, tremors, convulsions and sleepiness, coma.
AMERICAN (Southern U.S., Mexico, Central and S. America)- T. cruzi causes Chagas disease-The vector is the reduvid bug. Chagas diease is a chronic or acute infection characterized by neurological disorders (including dementia). Chagas' disease is often fatal unless treated.
Four Plasmodium species are responsible for human malaria These are P. falciparum, P. vivax, P. ovale and P. malariae.
Plasmodium is transmitted by the female anopheline mosquito which injects sporozoites present in the saliva of the insect. Malaria can also be transmitted by transfusion and transplacentally.
The chill and fever follow a cyclic pattern (paroxysm). Fever is associated with severe headache, nausea (vomiting) and convulsions are indicative of which disease? Malaria
Without treatment, all species of human malaria may ultimately result in spontaneous cure except with P. falciparum
Chronic malaria results in splenomegaly, hepatomegaly and nephritic syndromes
Diagnosis of Plasmodium is based on detection of parasite in what? Giemsa stained blood smears.
Created by: Mgoodall