Tags: Meningitis


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 (Box 1).

Intestinal Nematode Infections

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.

Non-falciparum Malaria (P Vivax, P Ovale, P Malariae)

Patients with nonfalciparum malaria invariably develop fever and chills that may become cyclic. Initially, patients experience chills, which are followed by fever (Box 1). Patients with malaria often manifest many nonspecific symptoms such as weakness, malaise, headache, and myalgias. As the disease progresses, signs of anemia, such as pale conjunctiva, may be seen.

Cryptococcus Neoformans

Cryptococcus neoformans exists as two distinct varieties known as variety neoformans and variety gattii (Table 1). Cryptococcus neoformans variety neoformans exists throughout the world and is found frequently in pigeon droppings that have accumulated over time. The concentrations of these organisms are often quite high in old pigeon droppings found in barns, on window ledges, and around the upper floors of old buildings. Pigeons carrying the organism do not seem to be clinically affected, and wet or fresh droppings rarely contain C neoformans.

Candida Species

Candida organisms are commensal with humans and, in the absence of alterations in host defense mechanisms, usually do not cause disease. Candida exists as normal flora within the oral cavity, throughout the gastrointestinal (GI) tract, in expectorated sputum, in the vagina, and in the bladder of patients with indwelling catheters. There are >150 species within the genus Candida, although the majority are not known to cause disease in humans. C albicans, C krusei, C glabrata, C tropicalis, C pseudotropicalis, C guilliermondii, C parapsilosis, C lusitaniae, and C rugosa are known human pathogens.

Blastomyces Dermatitidis (Blastomycosis)

Blastomyces dermatitidis is an endemic fungus that causes acute and chronic infections in humans and other animals. It is found primarily in the south central, southeastern, and midwestern United States, especially in the states surrounding the Mississippi and Ohio Rivers. Outside the United States, cases have been reported from Canadian provinces bordering the Great Lakes, Africa, India, the Middle East, and Central and South America.

Histoplasma Capsulatum

Histoplasma capsulatum, the etiologic agent of histoplasmosis, is an endemic, dimorphic fungus that causes a wide spectrum of disease in both immunocompetent and immunocompromised individuals. It is found in temperate zones around the world. In the United States, it is endemic within the Ohio and Mississippi River Valleys.