Informational Tables

3.5 Parasitic infections: clinical findings in healthy and compromised hosts

Organism(s)

Clinical findings in:

Healthy host

Compromised host^a

Entamoeba histolytica

Asymptomatic to chronic or acute colitis; extraintestinal disease may occur (primary site: right upper lobe of liver)

Diminished immune capacity may lead to extraintestinal disease.

Free-living amebae

Patients tend to have eye infections with Acanthamoeba spp.; linked to poor eye care (primarily contact lens wearers)

Primary amebic meningoencephalitis (seen primarily in immunocompetent patients) caused by Naegleria fowleri, granulomatous amebic encephalitis caused by Acanthamoeba spp. and Balamuthia; severe cutaneous infections in compromised patients (Acanthamoeba spp.)

Giardia duodenalis (G. lamblia, G. intestinalis); often rotating between 2^nd and 3^rd most common organism with Dientamoeba fragilis.

Asymptomatic to malabsorption syndrome

Certain immunodeficiencies tend to predispose an individual to infection.

Dientamoeba fragilis, often rotating between 2nd and 3rd most common organism with Giardia

Asymptomatic to typical GI symptoms (abdominal pain, diarrhea)

Not enough information to tell whether actual differences occur in compromised patients

Blastocystis spp.Most common organism found in human fecal specimens (worldwide) morphology of pathogenic and nonpathogenic subtypes are the same and cannot be differentiated using routine microscopy

Approximately 17 subtypes, half of which are pathogenic. Asymptomatic to symptomatic, often depending on subtypes and number of organisms present

Not enough information to tell whether actual differences occur in compromised patients; infections may be more difficult to eradicate in AIDS patients; infections have been linked to irritable bowel syndrome and urticaria.

Toxoplasma gondii

Approximately 15% of individuals in the U.S. have antibody and organisms in tissue but are asymptomatic.; may be as high as >70% in some areas of Latin America

Disease in compromised host tends to involve CNS, with various neurological symptoms

Cryptosporidium spp.

Self-limiting infection with diarrhea and abdominal pain

Due to autoinfective nature of life cycle, will not be self-limiting, may produce fluid loss of over 10 liters/day, and may show multisystem involvement; no known totally effective therapy

Cyclospora cayetanensis

Self-limiting infection with diarrhea (3–4 days), with relapses common

Diarrhea may persist for 12 wk. or more; biliary disease has also been reported for this group, particularly for those with AIDS.

Cystoisospora belli

Self-limiting infection with mild diarrhea or no symptoms

May lead to severe diarrhea, abdominal pain, and possible death (rare case reports); diagnosis may occasionally be missed due to nonrecognition of oocyst stage; will not be seen when concentrated from PVA fixative

Sarcocystis hominis, S. heydorni (beef) or S. suihominis (pork)

Self-limiting infection with diarrhea or mild symptoms

Symptoms may be more severe and last longer.

Microsporidia (Brachiola, Nosema, Anncaliia, Vittaforma, Encephalitozoon, Enterocytozoon, Pleistophora, Trachipleistophora, Microsporidium spp.)

Less is known about these infections in the healthy host; serological evidence suggests that infections may be more common than recognized.

Can infect various parts of the body; diagnosis often depends on histological examination of tissues; routine examination of clinical specimens (stool, urine, etc.) is becoming more common; eye infections most common in contact lens wearers; NAAT also becoming more important; organisms can cause death

Leishmania spp.

Asymptomatic to severe, destructive, and even life-threatening disease

More serious manifestations of visceral leishmaniasis; some cutaneous species will manifest visceral disease; difficult to treat and manage; definite coinfection with AIDS

Strongyloides stercoralis

Asymptomatic to mild abdominal complaints; can remain latent for many years due to low-level infection maintained by internal autoinfective life cycle

Can result in disseminated disease (hyperinfection syndrome due to autoinfective nature of life cycle); abdominal pain, pneumonitis, sepsis-meningitis with Gram-negative bacilli, eosinophilia

Scabies (Sarcoptes scabiei)

Infections can range from asymptomatic to causing moderate itching.

Severe infection with reduced itching response; hundreds of thousands of mites on body (crusted scabies); infection very easily transferred to others; secondary infection very common