Protozoan of the Intestinal Tract

Epidemiology of Entamoeba histolytica

• protozoan: Amoeba

• Worldwide distribution with highest incidence in the tropical and subtropical regions (freshwater contaminated with human feces)

  • Endemic in Central/South America, Africa and Asia

  • 10% of population carries the protozoan

  • ~50 million with 100000 deaths/annually

  • Prevalence in the US is 1 to 2% of the population

• Human and animal reservoir (dogs, cats, cattle and pigs)

Risk factors for Entamoeba histolytica

• sexually active homosexually men

• Immigrants

• Tourists

• Institutionalized persons

• HIV positive individuals

Life Cycle of E. histolytica

• infection occurs through ingestion of cysts (infective stage) in fecally contaminated food, water or hands (exposure to infectious cysts/trophozoites in fecal matter during sexual contact may also occur)

• Cyst excyst in the small intestine and trophozoites are released which migrate to the large intestines

• Trophozoites may remain in the intestines or invade the intestinal mucosa/blood vessels causing extraintestinal disease

• Trophozoites multiply and produce cysts and both are passed in the stool (diagnostic stage)

• Cysts survive in the external environment and are infectious while the trophozoites degrade (if ingested do not survive the gastric environment)

Clinical Syndrome of Entamoeba histolytica

• mostly asymptomatic

  • About 10% become symptomatic = amebiasis

• Mild symptoms: Loose stools, stomach pain, and stomach cramping

• Severe symptoms: Amebic dysentery (stomach pain, bloody stools, and fever)

• Rarely, E. histolytica invades the liver and forms an abscess; or spreads to other parts of the body, such as the lungs or brain

Diagnosis of Entamoeba histolytica

• microscopy:

  • E. histolytica trophozoites and cysts in stools using trichrome stain

  • Trophozoites in tissue

• Immunodiagnosis

  • Antigen detection

  • Antibody detection

• Molecular analysis

treatment and prevention of Entamoeba histolytoca

• metronidazole for the invasive trophozoites along with a lumenal amoebicide for those still in the intestine (paramomycin is the widely most used)

• Prevention by eradicating fecal contamination of food and water through improved sanitation, hygiene, and water treatment

• Amebic cysts are not killed by soap or low concentrations of chlorine or iodine; therefore, boil water and vegetables should be washed with a detergent soap and soaked in acetic acid or vinegar for 10-15 minutes before consumption

• avoid sexual practices that involve fecal-oral contact

Epidemiology of Giardia lamblia

• protozoan: Flagellate

• Worldwide distribution; most common intestinal protozoan in the US (highest incidence rates in Northern states)

  • Developed countries: 2% adult and 6% children

  • Developing countries: 33%

• Has been found in as many as 80% of raw water supplies from lakes, streams, and ponds and in as many as 15% of filtered water samples

• animal reservoir

Risk factors for Giardia lambila

• travel to countries where giardiasis is common

• people in childcare settings

• those who are in close contact with someone who has the disease

• people who swallow contaminated drinking water

• people who have contact with animals who have the disease

• men who have sex with men

• people with B cell immunodeficiency

Life Cycle of Giardia

• infection occurs through the ingestion of cysts (infective stage) in fecally contaminated food, water or hands

• cysts excyst in the small intestine and trophozoites are released which migrate to the large intestines

• trophozoites multiply and produce cysts and both are passed in the stool (diagnostic stage)

• cysts survive in the external environment and are infectious while the trophozoites degrade (if ingested do not survive the gastric environment)

Clinical Syndrome of Giardia lambia

• infectious dose - ingestion of one or more cysts may cause disease

• symptoms begin 1 to 3 weeks after becoming infected

• 50% of infected individuals can be asymptomatic carriers

• mild diarrhea to severe malabsorption

  • profuse watery diarrhea and foul-smelling flatulence

  • greasy stool that can float

• normally illness lasts 2 to 6 weeks, but there are cases of chronic infection lasting months to years

  • recurrent abdominal pain

Diagnosis of Giardia lambia

• microscopic examination of stool specimens for cysts and trophozoites using:

  • trichrome stain or immunoflorescent stain

• immunodiagnosis

• molecular analysis

• Giardia species may occur in “showers” with many organisms present in the stool on a given day and few or none detected the next day; test at least 3 stools separated a day or 2 apart

Treatment and prevention of Giardia

• metronidazole is the drug of choice (for disease patients as well as asymptomatic carriers) (cure rate of 85-90%)

• fluids to prevent dehydration

• education and good hand hygiene

• avoid contaminated water/food (boil and properly functioning filtration systems)

• avoid sexual practices that involve fecal-oral contact

Epidemiology of Cystoisopora (Isospora) belli

• protozoan: coccidian (sporozoa)

• worldwide distribution; common infections in tropical and subtropical areas

• unknown incidence rate

  • outbreaks in daycare centers and mental institutions'

• human reservoir

Life Cycle of C. belli

• infection occurs through ingestion of sporocysts-containing oocyts (infective stage) in fecally contaminated food/water

• sporocysts excyst in the small intestine and release their sporozoites which invade the epithelial cells

• both asexual and sexual reproduction occurs with production of oocysts

• oocysts are excreted in the stool (diagnostic stage)

Clinical Syndrome of Cystoisopora belli

• rare infections in immunocompetent individuals; more common in immunocompromised patients (AIDs patients)

• asymptomatic carriers to mild or severe gastrointestinal disease (leading to dehydration) (rare tissue invasion possible)

Diagnosis of Cystoisospora belli

microscopic examination of concentrated stool sediment using modified acid-fast or safranin stain

Treatment and prevention of Cystisopora belli

• trimethoprim-sulfmethoxazole

  • inhibits synthesis of dihydrofolic acid

  • use of trimethoprim-sulfamethoxazole for prophylaxis against Pneumonocystis in HIV-infected patients diminishes the likelihood of developing Cystoisoporiasis

• education and sanitation

• avoid sexual practices that involve fecal-oral contact

Epidemiology of Cryptosporidium sp.

• protozoan: coccidian

• worldwide distribution

  • presence in immunocompetent hosts: 1-3% in developed countries; 7-10% in developing countries (2.9 to 4.7 million cases in Africa/Asia within 202,000 deaths)

  • in the US, an estimated 748000 cases of cryptosporidiosis occur each year

• human and animal reservoirs

Risk factors for Cryptosporidium sp

• animal handlers

• children in daycare centers (especially those under 2)

• elderly patients

• foreign travel

• immunocompromised individuals

• contact with positive patients

Life Cycle of Cryptosporidium

• infection occurs through ingestion of sporocysts-containing oocysts (infective stage) in fecally contaminated food/water

• sporocysts excyst in the small intestine and release their sporozoites which invade the epithelical cells

• both asexual and sexual reproduction occurs with production of oocysts

• oocysts are excreted in the stool (diagnostic stage)

Clinical Syndrome of Cryptosporidium sp

• incubation period of 2-10 days

• asymptomatic carriage to acute watery diarrhea for 1 to 2 weeks (healthy individuals); abdominal pain, nausea, mild fever

• 50 or more stools per day and tremendous fluid loss which can last for months to years (immunocompromised individuals); abdominal pain, nausea, mild fever

• shedding of oocysts on average of 9 to 12 days post infection

• extraintestinal infection (ex. gallbadder)

Diagnosis of Crytosporidium sp.

• microscopic examination of stool specimens for oocysts using:

  • modified acid-fast/safranin stain or immunofluroscent stain

• immunodiganosis

• molecular anaylsis

Treatment and prevention of Crytosporidium sp.

• nitazoxanide

• fluid replacement

• education and sanitation

• treatment of contaminated water supplies

Epidemiology of Cyclospora cayetanensis

• protozoan: coccidian

• worldwide distribution

  • endemic in at least 27 countries with prevalence ranging from 3.3% in Mexico to 41.6% in Peru (average prevalence of 3.5%)

  • ~16000 cases per year in the US

• human reservoir

Life Cycle of Cyclospora

• infection occurs through ingestion of sporocysts-containing oocysts (infective stage) in fecally contaminated food/water

• sporocysts excyst in the small intestine and release their sporozoires which invade the epithelial cells

• both asexual and sexual reproduction occurs with production of oocysts

• unsporulated oocysts are excreted in the stool (diganostic stage)

• oocysts sporulate in the environment and become infectious

Clinical Syndrome of Cyclospora cayetansis

• incubation period is 1-14 days

• clinically indistinguishable from cryptosporidiosis and cystoisosporiasis

• mild nausea and watery diarrhea that lasts 6-7 weeks (in immunocompromised the diarrhea may last for months)

Diagnosis of Cyclospora cayetanesis

• microscopic examination of stool specimens for oocysts using:

  • modified acid-fast/safrainin stain

• molecular analysis

Treatment and prevention of Cyclospora cayetanensis

• trimethoprim-sulfamethoxalzole and fluid replenishment

• improved personal hygiene and sanitation

• care when visiting areas where the protozoan is endemic (generally tropical and sub-tropical regions such as Peru, Brazil, Haiti)

• treatment of contaminated water supplies

Epidemiology of Dientamoeba fragilis

• protozoan: flagellate (yet does not possess flagella)

• worldwide distrubition

  • estimated prevalence in developed countries = 2-5%

  • higher rates (19-69%) in those living in crowded conditions

  • most common age at which infection has been reported in children is 5-10 years

• as more common or more common than giardia

• human reservoir

Life Cycle of D. fragilis

• infection occurs through ingestion of trophozoite (infective stage) in fecally contaminated food/water (possible transmission via helminth eggs)

• trophozoites multiply in the large intestine

• trophozoites are shed in the stool (diagnostic stage)

Clinical Syndrome of Dientamoeba fragilis

• most infections are asymptomatic disease (75-85% of infected individuals)

• some patients develop abdominal discomfort, intermittent diarrhea, weight loss (duration 1 to 2 weeks)

Diagnosis of Dientamoeba fragilis

examination of stool specimens for trophozoites (cyst stage?)

Treatment and prevention of Dientamoeba fragilis

• iodoquinoal

• better sanitary conditions/reduce enterobius infections

Epidemiology of Blasocystis spp.

• protozoan: stramenophiles-alveolates-rhizaria super group (ex. diatoms and water molds)

• worldwide distribution

• reservoirs: humans, farm animals, birds, rodents, amphibians, reptiles, fish, and cockroaches

• very common!

Life Cycle of Blastocystis

• infection occurs through ingestion of cyst (infective stage) in fecally contaminated food/water

• replication occurs in the intestinal tract

• cysts and vacualor forms are shed in the stool (diagnostic stage)

Clinical Syndrome of Blastocystis

• debate on whether it causes gastrointestinal disease

• water or loose stools, diarrhea, abdominal pain, anal itching, weight loss, and excessive gas

Diagnosis of Blastocystis spp.

examination of the cyst forms present in trichrome stained and unstained stool speciments

Treatment and prevention

• metronidazole

• education and sanitation