Popular Parasites

Not everything reported by the lab is pathogenic.  For instance, the following organisms do not need treatment:

• Iodamoeba butschii
• Chilomastic mesnili cysts
• Endolimax nana
• Blastocystis hominis
• Enamoeba hartmani
• Entamoeba coli

Specific Organisms:

Giardia lamblia

• Most prevalent parasite in the US (6% of population)
• Flagellated protozoan which lives in the duodenum
• Humans, dogs, beavers are hosts.  Spread in water and food.
• Presentations
• Asymptomatic
• Acute diarrhea (flatulence, nausea, anorexia)
• Chronic diarrhea (flatulence, distention, abdominal pain, weight loss).

Sometimes associated with chronic urticaria or cholangitis.
• Diagnosis
• Need to get several stool specimens because cysts are excreted intermittently.
• May need Enterotest (string test) or endoscopy
• Treatment
• Metronidazole, Furazolidone, Quinacrine
• May need to limit lactose temporarily

Amebiasis: Entamoeba histolytica

• Note that Entamoeba hartmani and Entamoeba coli are not pathogenic
• Resistant infectious cyst or mobile invasive trophozoite
• Spread by food, water and person-to-person
• Ingestion is followed by invasion of the intestinal mucosa then infection of the liver, pleura, skin, brain or lungs
• Presentations
• Asymptomatic cyst passer

Treatment: Iodoquinol, paromomycin, diloxanide furoate
• Mild to moderate intestinal symptoms

Intermittent diarrhea and abdominal pain
Treatment:  Metronidazole followed by iodoquinol or paronomycin
• Dysentery or extraintestinal disease

Acute cramping diarrhea which may contain blood and mucous
Fever, abdominal pain, headache, chills
Recurrent symptoms
Amoeboma (a mass of amoebas)
Liver abcess (which may be present even with negative stools)
Ulcerative lesions of the colon
Treatment: Metronidazole followed by iodoquinol
• Diagnosis
Stools for ova and parasites times three on different days (put into fixative)
Serologic tests
Ultrasound or CT liver masses

Malaria

• Transmitted via the Anopheles mosquito bite, transplacentally, or by infected blood transfusion
• Most of the pathology is due to parasitized red cells being sequestered in the microcirculation and leading to tissue anoxia and death
• Sickle cell disease and G6PD deficiency are associated with some protection from malaria
• Organisms
• Plasmodium falciparum

The most lethal (cerebral malaria, pulmonary edema, renal failure, shock, dysentery, Black water fever, hemolysis); Tertian fever -- every 2 days after mild prodrome, then can be fatal within two weeks.
• Plasmodium vivax

Severe prodrome then overall mild course; fever every 2 days; may relapse due to persistent hepatic stage (even 8 years after initial infection)
• Plasmodium ovale

Mild prodrome and overall course; fever every 2 days; may relapse due to persistent hepatic stage (but not as commonly as with vivax)
• Plasmodium malariae

Quartan fever every three days (splenomegaly, nephrotic syndrome, congenital malaria which appears like sepsis); longest incubation period; recrudescences may occur as long as 30 years after initial infection
• Presentations
• "Cold, hot and wet" stages with anemia and splenomegaly
• Paroxysmal, cyclical fever, headache, abdominal pain, nausea, splenomegaly (palpate gently since spleens are prone to rupture)
• Hemolytic anemia (pallor and jaundice), pneumonia, encephalitis, enteritis
• Leukopenia
• Nephrotic syndrome
• Diagnosis
• Thick and thin blood smears (repeated every 12 hours in falciparum to follow treatment response).
• Thick:  concentrates the parasites to detect organisms
• Thin: for mophologic speciation
• Treatment
• Chloroquin (unless from a resistant area); otherwise, mefloquin or quinine plus pyrimethamine-sulfadoxine or quinine plus tetracycline.
• Primaquin eradicates the hepatic phase
• Prevention
• Prophylactic chloroquin plus primaquin; or for resistant areas, mefloquin or doxycycline (begin one week before exposure, continue throughout exposure and then for 4 weeks after exposure)

Toxoplasmosis

• Cats, undercooked meats, blood transfusions, organ transplants, transplacentally
• Congenital toxoplasma
• Less severe disease if contracted later in pregnancy
• May be stillborn
• Feeding problems, fever, rash, petechiae, lymphadenopathy, splenomegaly, microphthalmia, seizures, cerebral calcifications, chorioretinitis
• Heterophile negative mononucleosis syndrome
• Myocarditis, pneumonia, encephalitis (...think AIDS)
• Diagnosis
• Fourfold rise in antibody titers or a rise from negative to positive
• Maternal antibodies will fall in a neonate whereas during congenital infection the serial titers will remain stable or rise for several months
• Treatment
• Pyrimethamine plus sulfadiazien plus folinic acid
• If CNS or ocular infection is present, corticosteroids

American Trypanosomiasis (Chagas Disease)

• Especially in Central and South America
• Protozoan hemoflagellate transmitted by reduvid bugs, blood-sucking insects
• Symptoms
• Local inflammation
• Unilateral eyelid swelling
• Nodular skin lesions
• Malaise, fever, myalgia, adenopathy, rash, hepatomegaly, splenomegaly, meningoencephalitis
• Tachycardia, arrythmias
• Megaesophagus, megacolon
• Congenital disease: low birth weight, hepatomegaly, meningoencephalitis
• Diagnosis
• Demonstrate the organism on blood smears
• Treatment
• Nifurtimox

Visceral Larva Migrans (Toxocariasis)

• Dog or cat tapeworm
• May be asymptomatic
• Fever, cough, wheeze, seizures, hepatomegaly, rales, rash, adenopathy
• Decreased visual acuity, strabismus, periorbital edema, blindness
• Eosinophilia, ELISA
• Treatment
• Thiabendazole or diethylcarbamazine
• Ocular larva migrans is treated with corticosteroids and surgery

Schistosomiasis

• Blood fluke infection acquired from larva in water with snail host
• Skin penetration, then into bloodstream, to lungs and liver, then to veins of abdominal cavity
• Fever, malaise, abdominal pain, rash
• Renal failure (obstructive uropathy)
• Colic, abdominal pain, bloody diarrhea
• Hepatomegaly, ascites, hematemesis
• Diagnosis: See eggs in stool, urine or biopsy specimens
• Treatment: Praziquantel

Cryptosporidiosis

• Person-to-person spread; think of AIDS
• Diarrhea, nausea, cramps
• Duration: 12 to 14 days
• No treatment except fluid replacement

Ascaris lumbricoides

• Oral ingestion followed by intestinal penetration, then to lungs and up trachea, then swallowed again and eggs are excreted in stool
• May be asymptomatic
• Cough, eosinophilia, CXR infiltrates (Loeffler's Syndrome)
• Abdominal pain and distention
• Bowel or biliary obstruction
• Diagnosis:  Eggs in stool (O&P x 3)
• Treatment: Mebendazole or Pyrantel pamoate, then repeat stool for O&P in three weeks.  Treat families as a group; recurrences are common.
• Prevention:  Sanitary disposal of human feces

Enterobius vermicularis (pinworm)

• Ingest eggs which hatch in the stomach, then larvae migrate to cecum; female worms migrate to perianal area at night to lay eggs.
• Nocturnal anal pruritis; vaginitis/salpingitis
• Diagnosis: Press tape against anus in morning and examine for worms and eggs
• Treatment: Pyrantel pamoate or mebendazole in single dose which is repeated in two weeks.

Ancyclostoma duodena & Necator americanus (hookworm)

• Intense pruritis in feet
• Anemia (from GI blood loss -- stools do not have gross blood but may have occult blood).  Worms attach to the intestinal mucosa and secrete anticoagulant.
• Diagnosis: Eggs in stool
• Treatment: Mebendazole or pyrantel pamoate.  Treat anemia with iron supplement.

Clonorchis sinensis (Chinese liver fluke)

• Raw or undercooked freshwater fish containing larvae; larvae migrate to bile ducts and then adult worms develop in the biliary radicles
• Anorexia, diarrhea, sensation of abdominal pressure
• Fever, chills, hepatomegaly
• Jaundice, cirrhosis, ascites, edema
• May become chronic
• Diagnosis: Eggs in stool
• Treatment: Praziquantel

Hymenolepsis nana (dwarf tapeworm)

• Person-to-person spread
• May be asymptomatic
• Enteritis with or without diarrhea
• Diagnosis: Eggs in stool
• Treatment: Praziquantel; hygiene; treat constipation

Strongyloides stercoralis (roundworm)

• May reinfect self without a soil phase
• Pruritic papule at site of penetration (usually feet)
• Pneumonitis (coughing with blood streaked sputum)
• Abdominal pain, distention, vomiting, diarrhea
• Diagnosis: Eggs in stool
• Treatment: Thiabendazole (but not until Ascaris is treated because thiabendazole causes Ascaris to migrate); reexamine stools after treatment

Trichuris trichiura (whipworm)

• Ingestion of eggs from soil; large intestine disease
• Usually asymptomatic
• Abdominal pain, tenesmus, rectal prolapse
• Diarrhea (with blood and mucous)
• Iron deficiency anemia
• Diagnosis: Eggs in stool or worms in colon on sigmoidoscopy
• Treatment: Mebendazole

References

Acknowledgment