Tags: Complex


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 […]

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 […]


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 […]

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 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 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 5% in industrialized […]


Essentials of Diagnosis Patients present with watery diarrhea, which is usually self-limited in immunocompetent patients but may be prolonged in the immunocompromised patient. A history of travel to areas such as Nepal, Haiti, and Peru, a history of berry consumption, or community outbreak of diarrhea may increase suspicion of diagnosis. Acid-fast stain of stool specimens reveals abundant oocysts. General Considerations Cyclospora is a coccidian that had been described as a "large cryptosporidium" or "cyanobacterium-like body" before being confirmed as a member of the phylum Apicomplexa in 1993. The life cycle in humans has not been fully detailed. The organism has been shown to infect jejunal enterocytes. Similar to Isospora, the oocysts […]

Toxoplasma Gondii

General Considerations Epidemiology Toxoplasma gondii infection, or toxoplasmosis, is a zoonosis (the definitive hosts are members of the cat family). The two most common routes of infection in humans are by oral ingestion of the parasite and by transplacental (congenital) transmission to the fetus. Ingestion of undercooked or raw meat that contains cysts or of water or food contaminated with oocysts results in acute infection. In humans, the prevalence of toxoplasmosis increases with age. There are also considerable geographic differences in prevalence rates (eg, 10% in Palo Alto, CA; 15% in Boston, MA; 30% in Birmingham, AL; 70% in France; = 90% in El Salvador). Differences in the epidemiology of T […]

Malaria and Babesia

PLASMODIUM SPP. Exposure history, such as travel, recent transfusion, or living in close proximity to an international airport. Nonfalciparum malaria: chills and fever spikes, followed by defervescence and fatigue; symptoms may be cyclic every 48-72 h. Falciparum malaria: fever spikes and chills, often noncyclic and associated with rapidly progressive systemic symptoms. Detection and identification of a Plasmodium species in a thick and thin blood smear, respectively. Molecular detection of P falciparum's histidine-rich protein by enzyme-linked immunosorbent assay (ELISA) or Plasmodium DNA by polymerase chain reaction (PCR) followed speciation by probe hybridization or DNA sequencing. General Considerations Epidemiology Malaria, a disease of antiquity, was recognized by Hippocrates and described possibly as early […]