Tags: Diarrhea


Essentials of Diagnosis Blood flukes: demonstration of eggs in feces, urine, or rectal biopsy Liver flukes: demonstration of eggs in feces Intestinal flukes: demonstration of adult worms or eggs in feces Lung flukes: demonstration of eggs in sputum or feces All trematode species that are parasitic for humans are digenetic. Sexual reproduction in the adult fluke is followed by asexual multiplication in the larval stage. Most species of adult trematodes have an oral and ventral sucker. The life cycles of trematodes that are important human pathogens are similar among all five major species. Eggs are excreted in the feces of the host, hatch in fresh water, and require a primary host […]


Human infections caused by cestodes, or tapeworms, may occur within the lumen of the bowel, where adult cestodes attach themselves to the host intestine (Box 1). Alternatively, human infection may be the result of dissemination of cestodes from the bowel to involve extraintestinal sites, often by larval forms of the parasite. The life cycle of cestodes is determined by definitive hosts, in whom the mature adult worm lives, and intermediate hosts, which harbor the larval forms of the parasite. Humans are a definitive host for six cestodes: Diphyllobothrium latum, Taenia solium, Taenia saginata, Hymenolepis diminuta, Hymenolepis nana, and Dipylidium caninum. In addition, humans may be intermediate hosts for Echinococcus granulosis and […]

Diphyllobothrium Latum Infection

Essentials of Diagnosis Stool examination reveals ovoid, yellow-brown eggs (60-75 um by 40-50 um). Chains of proglottids (up to 50 cm long) may be passed in stool. Proglottids are wider than long (3 by 11 mm). Scolex has no hooklets and two grooves (bothria). Gravid proglottid contains rosette-shaped central uterus. General Considerations D latum is found worldwide, and infection is acquired by ingestion of contaminated raw or improperly cooked freshwater fish. Because of enthusiasm for raw or undercooked fish, Siberia, Europe, Canada, Alaska, and Japan are endemic regions for D latum infection. Once the D latum cyst has been ingested, the worm matures within the human intestine and begins to produce […]


Essentials of Diagnosis Intestinal nematodes: demonstration of characteristic eggs or parasites in stool. Bloodstream nematodes (filariasis): clinical diagnosis can be made; fresh blood smear may be confirmatory. Tissue nematodes: clinical diagnosis can be made; skin snip or other tissue examination may show organism. General Considerations Nematodes (roundworms) are nonsegmented, tapered, bilaterally symmetrical, cylindrical organisms that have complete digestive tracts and reproduce sexually. Although > 500,000 species of nematodes have been described, only a small number are commonly encountered as human parasites. Most nematodes have complex life cycles, sometimes involving several larval forms and intermediate hosts or free-living stages. The pathogenic nematodes may be categorized as primarily intestinal or extraintestinal tissue parasites […]

Intestinal Nematode Infections

ASCARIASIS Worldwide, more than 1 billion people are infested with Ascaris lumbricoides, the causative agent of ascariasis or roundworm. More than 4 million people are estimated to be infected in the United States. Infection occurs predominately in the southeastern states and more commonly in younger children, and it is associated with lower socioeconomic status. The organism is acquired through ingestion of embryonic forms of the worm, which are found in fecally contaminated soil. After ingestion, the embryonic eggs hatch in the small intestine, and the larvae undergo a tissue migration phase. During the migration, the larvae penetrate the intestinal wall and travel intravenously to the pulmonary alveoli. In the lungs, the […]

African Trypanosomiasis

In Africa, a wide variety of trypanosomes infect wild animals but only two cause significant disease in humans: T brucei gambiense and T brucei rhodesiense. Essentials of Diagnosis Epidemiologic factors: living or traveling in an endemic zone; exposure to tsetse fly. History and physical exam: General: periodic fevers, wasting, nutritional deficiencies. Skin: chancre at the site of inoculation, fleeting truncal rash, posterior cervical lymphadenopathy. Neurologic: disturbed sleep patterns (diurnal somnolence, nocturnal insomnia), mental status changes, cerebellar signs. Laboratory: Blood smear with Giemsa stain shows hemoflagellates. Aspiration and stain of chancre (may be positive for visible organisms before parasitemia occurs). Serology: indirect immunofluorescence, ELISA. Card agglutination test against common variant antigens. Cerebrospinal […]


Essentials of Diagnosis Key symptoms include initially profuse and watery diarrhea progressing to foul-smelling and often greasy stools that float. It is the most common pathogen in waterborne diarrheal illness. Patients at highest risk include infants, young children, travelers, and immunocompromised patients. In North America, the Rocky Mountains and mountainous regions of the northwest, northeast, and British Columbia are notorious Giardia reservoirs. Giardiasis is diagnosed either by identification of cysts or trophozoites on wet mounts of fresh stool or duodenal specimens or by antigen detection using enzyme-linked immunosorbent assay or immunofluorescence techniques. General Considerations Giardia, a genus of primitive eukaryotes, is a flagellated enteric protozoan of the class Zoomastigophorea. Giardia lamblia, […]

Giardia: Clinical Syndromes

After ingestion of G lamblia cysts, 5-15% of patients will have asymptomatic cyst passage, and 25-50% of patients will have diarrhea. From 35% to 70% of these patients will have no evidence of infection. The three manifestations of infection include asymptomatic cyst passage, self-limited diarrhea, and chronic diarrhea with associated malabsorption and weight loss. Factors related to each of these manifestations are unknown but are believed to be related to specific host factors, parasite load, and virulence variation among G lamblia isolates. ACUTE GIARDIASIS Clinical Findings Signs and Symptoms After ingestion of cysts, an incubation period of 3-20 days exists before symptom onset. At the time of presentation, patients have generally […]

Cryptosporidium, Cyclospora, & Isospora Species & Microsporidia

Within the last decade, the AIDS epidemic has heightened awareness of several gastrointestinal spore-forming protozoan pathogens. The genera Cryptosporidium, Isospora, and Cyclospora are members of the subclass Coccidia and phylum Apicomplexa; the microsporidia are a group of organisms belonging to the phylum Microspora. The spectrum of disease caused by these protozoans goes beyond gastrointestinal manifestations, and the significance of these protozoan infections is becoming increasingly appreciated in both immunocompromised and immunocompetent hosts. CRYPTOSPORIDIUM Essentials of Diagnosis Key signs and symptoms include dehydration with watery diarrhea of variable quantity. Waterborne transmission is the most common mode of oocyst transmission. Patients at risk for person-to-person transmission include household contacts, sexual contacts, health care […]


Essentials of Diagnosis Most cases of microsporidiosis occur in male patients with HIV infection and CD4 counts of < 100. In HIV-infected patients, microsporidiosis most commonly presents as chronic diarrhea, although cholecystitis, respiratory infection, keratoconjunctivitis, and myositis have also been reported. Infections in non-HIV-infected patients are rare but include central nervous system infection, corneal infection, and myositis. Diagnosis is difficult and depends on identification of 1- to 2-um spores.   General Considerations Epidemiology Microsporidia were first discovered in 1857, but it was not until 1973 that a human case of microsporidiosis was confirmed from a case described in 1959. Awareness of the diversity of microsporidial infections has heightened, especially in light […]