Tissue Nematode Infections

LYMPHATIC FILARIASIS Lymphatic filariasis is a bloodstream and lymphatic infection caused by the filarial nematodes Wuchereria bancrofti, Brugia malayi, and Brugia timori. The disease is endemic in the tropics and subtropics of both hemispheres. A mosquito serves as an intermediate host and vector; the peak blood parasitemia and optimum time of the day or night for obtaining blood smears differ in various parts of the world, corresponding to the feeding pattern of the local mosquito vectors. After deposition by mosquitoes of infectious microfilariae into humans during a blood meal, 6-12 mo are required before adult worms mature and begin producing numerous circulating microfilariae to continue the life cycle. Symptoms of acute …

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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 …

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Leishmania

Leishmania & Trypanosoma The genera Leishmania and Trypanosoma are members of the family Trypanosomatidae. These protozoans cause diseases with widely varied clinical presentations as well as geographic distributions, including leishmaniasis, American trypanosomiasis (Chagas’ disease), and African trypanosomiasis (sleeping sickness). For example, the endemic zones for African and American trypanosomiasis do not overlap, the diseases are transmitted by different vectors, they involve distinct mechanisms of pathogenesis, and they follow different clinical courses. Nonetheless, the causative agents share important biological features. Each is a hemoflagellate with a kinetoplast containing its own chromosomal DNA with highly conserved and repeated elements, each forms a single flagellum at some point during its life cycle, and each …

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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: 1. General: periodic fevers, wasting, nutritional deficiencies. 2. Skin: chancre at the site of inoculation, fleeting truncal rash, posterior cervical lymphadenopathy. 3. Neurologic: disturbed sleep patterns (diurnal somnolence, nocturnal insomnia), mental status changes, cerebellar signs. • Laboratory: 1. Blood smear with Giemsa stain shows hemoflagellates. 2. Aspiration and stain of chancre (may be positive for visible organisms before parasitemia occurs). 3. Serology: indirect immunofluorescence, …

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American Trypanosomiasis (Chagas’ Disease)

Essentials of Diagnosis • Epidemiologic factors: time spent in an endemic zone; poor housing conditions, eg, mud or thatched housing; exposure to reduviid insect vector • History and physical exam: Romana’s sign (swollen periorbital mucosal tissues after ocular inoculation); chagoma (skin nodule at the site of acute inoculation); in the chronic phase, congestive heart failure, dysphagia or regurgitation, and constipation • Laboratory exam: 1. Acute Chagas’: trypomastigotes revealed by Giemsa smear of blood or buffy coat; culture of affected tissues, ie, the inoculation site; serologic enzyme immunoassay and enzyme-linked immunosorbent assay (ELISA); xenodiagnosis if available 2. Chronic Chagas’: radiological studies show congestive heart failure, megacolon, or megaesophagus; ECG shows right bundle …

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Giardia

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 …

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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. 1. ACUTE GIARDIASIS Clinical Findings A. Signs and Symptoms. After ingestion of cysts, an incubation period of 3-20 days exists before symptom onset. At the time of presentation, patients …

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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 …

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Microsporidia

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 A. 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 …

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Isospora

Essentials of Diagnosis • Patients are usually either travelers to tropical areas with self-limited diarrhea or immunocompromised patients with a protracted diarrheal illness. • Unsporulated oocysts are detected on wet mounts of stool samples by acid-fast staining. General Considerations A. Epidemiology. Isospora infection is endemic in several tropical and subtropical climates in areas of South America, Africa, and southwest Asia. In the United States, Isospora belli infection occurs primarily in patients with AIDS but is still quite rare in this population, accounting for = 0.2% of AIDS-defining illnesses. Isospora infection is more common in patients with AIDS from developing countries in which the prevalence of spore passage is 15% compared with …

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