Micro 11 Ex 2

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Severity of disease caused by parasites often depends on

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Infectious dose
Chronic repeat infections that increase pathogen burden
Immunopathology resulting from host immune response

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Amoebae
Entamoeba histolytica generally causes

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free living amoeba. Diarrhea, occasionally invasive disease

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Flagellates
Giardia intestinalis: generally characteristics

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motile via lashing flagella. Mild diarrhea to severe maladsorption syndrome

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Flagellates
Trichomonas vaginalis: generally characteristics

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motile via flagella. Urogenital tract infections, vaginitis

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Sporozoa (also called Coccidia or Apicomplexans)
Cryptosporidium species general characteristics

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mild to severe gastrointestinal disease

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Entamoeba histolytica has 2 life cycles

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Motile feeding stage (trophozoite)
Quiescent, resistant, infectious stage (cyst)

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Entamoeba histolytica Divides by

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binary fission (trophozoite) or through the generation of multiple trophozoites within a single multinucleated cyst.

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Cyst forms under conditions of

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low humidity and/or drop in temperature

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In asymptomatic patients Entamoeba histolytica remains in the patient in

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lumen of colon and multiplies

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What is the diagnostic phase of Entamoeba histolytica

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Trophozoite and cysts found in feces

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Severe diarrhea in patients with Entamoeba histolytica is oberserved when the parasite

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invades the wall of the colon and multiplies. This is the extraintestinal access stage of the parasite

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What are the paths that the parasite may take once in the extraintestinal stage?

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It can go to organs lke lover, lungs. etc. Or it can return to the lumen where cysts will be formed

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The infectious stage of Entamoeba histolytica is

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cyst

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Entamoeba histolytica incidence

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-Worldwide distribution. Incidence higher in tropical areas that have poor sanitation & contaminated water.

-Seen where human waste is used as fertilizer – can also be passed along by flies and cockroaches.

-. It resembles a lot of the commensal organism.

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Outcome of infection
with Entamoeba histolytica is

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Carrier state
Intestinal amebiasis
Extraintestinal amebiasis

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Abdominal pain, cramping, colitis with diarrhea - several bloody stools per day.
this is

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Intestinal amebiasis results from localized tissue destruction in large intestine

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fever, leukocytosis, rigors. Liver is usually involved and may develop abscesses.
this is

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Extraintestinal amebiasis results in systemic signs

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Entamoeba histolytica - Intestinal amebiasis
diagnosis

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ID of trophozoites and cysts in stool and trophozoites in tissue is diagnostic.
Parasites are concentrated in abscesses, not uniform in stools. May need to examine several stools.
Antigen detection assays of stool or serum are currently most sensitive.

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Entamoeba histolytica -Extraintestinal amebiasis
diagnosis

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Sometimes diagnosed by scanning procedures for liver
Serological tests combined + microscopic examination of abscess material.
Stool is usually negative for cysts for extraintestinal infections.
PCR and immunology-based tests are being developed

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Entamoeba histolytica - treatment & prevention

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Treatment:
Metronidazole is the drug of choice.

Prevention:
Can limit infection by sterilizing and filtering water – in countries were disease is common, boil water and avoid ice cubes, raw vegetables and fruits

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Giardia intestinalis (The happy pathogen) Life cycle consists of

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cysts & trophozoites. Cysts is the infectious form. 10-25 organisms needed to cause infection

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Giardia intestinalis invasion

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Trophozoites are released into the duodenum & jejunum. Attach to intestinal villa via sucking disc.

Extraintestinal infection is rare.

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Where is Giardia intestinalis found?

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World wide distribution – wilderness streams, lakes, mountain resorts. Maintained by reservoir animals such as beavers and muskrats.

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Giardiasis occurs following consumption of

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of contaminated water, ingestion of contaminated food, or person-to-person via oral-fecal route.

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Incubation period is 1-4 weeks (average ~10 days).

Sudden onset of really foul smelling watery diarrhea, cramps, flatulence. Stools are packed with fat.

Blood and pus are rarely present in stools (absence of tissue damage).

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: Giardia intestinalis

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Giardia intestinalis resolves

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Spontaneous recovery usually occurs after 10-14 days. May be chronic in patients with immunoglobulin A deficiency or intestinal diverticula

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Giardia intestinalis - diagnosis

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Examination of stool samples by microscopy for cysts & trophozoites – need one specimen per day for 3 days as organism may appear one day and not the next.

Fecal antigen tests are also available

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Giardia intestinalis - treatment & prevention

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Drug of choice: metronidazole.

Prevention: Boil water. Municipal water supplies need properly functioning filters as cysts are resistant to chlorination

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Most infected women are asymptomatic or have a scant watery vaginal discharge.

Vaginitis can occur with more extensive inflammation and can be associated with itching, burning, and painful urination.

Men are primarily asymptomatic carriers and serve as reservoirs for infections in women – but sometimes can experience UTI symptoms.

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Trichomonas vaginalis

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Trichomonas vaginalis
morphology

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Has 4 flagella & a short undulating membrane that provides motility.

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Trichomonas vaginalis exists only as

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trophozoite and is found in the urethras and vaginas of women and urethra and prostate glands of men

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where is Trichomonas vaginalis found?

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Worldwide distribution with sexual intercourse being the primary mode of transmission.
Occasionally transmitted by fomites (toilet seats).
Infants may be infected during passage through infected birth canal.

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Trichomonas vaginalis in low income men and women can be a severe problem because

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it must be up to 50%. It is associated with premature births.

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Trichomonas vaginalis - diagnosis

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Microscopic examination of vaginal or urethral discharge for trophozoites = method of choice.

Can use fluorescent antibodies to aid detection

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Trichomonas vaginalis tx

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Treatment drug of choice: metronidazole. Both partners must be treated. Drug resistance has been reported.

Second drug of choice is there is resistance, Nitazoxanide. This drug interacts with anaerobic metabolism

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Infection may result in asymptomatic carriage, or a mild, self-limiting diarrhea without blood that usually resolves in ~10 days in healthy individuals.

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Cryptosporidium species

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Cryptosporidium species in AIDS patients

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can have 50 or more stools per day with massive fluid loss – this can last for months to years. Disseminated cases can occur in AIDS patients

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Cryptosporidium species found in

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Intracellular parasite found just within the brush border of intestinal epithelial cells.

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Cryptosporidium species replication

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Attaches to the surface of cells and replicates through a series of processes (merogony, gametogony, sporogony) resulting in the production of infectious oocysts (infectious stage)

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Cryptosporidium species may exists as

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either excyst within the GI tract or may be excreted into the environment

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Cryptosporidium species are contracted most usually in

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related to water supplies like in public pools and contaminated water. Waterborne infection is an important route of infection – organism is resistant to chlorination and ozone.

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Cryptosporidium species most commonly affecting humans

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C. hominis and C. parvum.

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Cryptosporidium species spread can occur

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Zoonotic spread occurs as well as person-to-person spread through oral-fecal and oral-anal routes.

Veterinarary workers and animal handlers are at high risk for infection, as are day care centers

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Cryptosporidium species - diagnosis

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Can be detected via microscopic examination of stool samples by either stains or immunofluorescence – need to examine at least 3 samples. Immunoassays for detecting antigens in fecal samples also exist.

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Cryptosporidium species - treatment

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Spiramycin may help control the diarrhea in early AIDS patients, but this is ineffective in late stage patients.

Supportive fluid replacement therapy must be used.

Hard to prevent transmission from animals – good hygiene and sanitation help in avoiding infection.

No broadly effective therapy currently exists for managing infections in immunocompromised patients.