Smileband health topics

Parasitic Infections

I. Problem/Condition

Medical parasitology is primarily concerned with organisms that infect the human host and may cause symptomatic or asymptomatic diseases. Three main classes of parasites cause disease in humans: protozoa - microscopic organisms that live in the blood or stool, helminths-multi-cellular organisms that can either cause systemic tissue invasive infection or establish infection in the gut, and ectoparasites that burrow in the skin causing prolonged infections (weeks to months).

Although the prevalence of parasitic infections in the US is not as widespread of a problem as the rest of the world, there are pockets of infection in the Mississippi Delta, disadvantaged urban areas, near the US-Mexico borderlands, and Appalachia where these infections cluster with poverty and presumably poor sanitation. Moreover, these infections can remain underdiagnosed if the clinician does not think of parasitic diseases in immigrants/travellers from areas of the world which are endemic for these infections.

US health professionals should be aware of the five "neglected parasitic infections" - Chagas disease, toxocariasis, cysticercosis, toxoplasmosis, and trichomoniasis that have been targeted by as public health priorities based on the large number of people affected, the severe morbidity caused and the availability of treatment and prevention.

Lastly, physicians should be cognizant of "delusional parasitosis" characterized by the fixed belief of being infested with parasites against all medical evidence to prevent unnecessary medical work-up for parasitic infection. Details of this disorder are beyond the scope of this chapter, but have been summarized in several excellent reviews.

II. Diagnostic Approach

Consideration of parasitic infection and further work-up is determined primarily by whether the patient is an immigrant from, or has recently travelled to a region endemic for parasites. The differential diagnosis in these patients vs. someone who has never travelled outside the US is broader. A good clinical history and focused physical examination can narrow the diagnosis and prevent unnecessary testing.

Common symptoms warranting consideration of specific parasitic infections in the immigrant/returning traveller are presented first. A distinction should be made between parasitic infections that can present as severe acute illness and those that cause more chronic disease. Important geographical considerations to keep in mind are:

• Chloroquine resistant falciparum malaria should be assumed in a patient suspected of having malaria unless the patient is from Central America west of the Panama Canal, Haiti, the Dominican Republic, and most of the Middle East.
• Chagas disease has not been reported to occur in Africa or Asia.
• Of the filarial infections, onchocerciasis has been eliminated in most of Latin America except Venezuela and Brazil.
• Loasis (eye worm infection) is not reported in Latin America.

Symptomatic presentations of diseases endemic to the US are presented separately.

a. The immigrant/traveller with exposure to a parasite endemic region

Fever

Fever is probably the most common nonspecific complaint and the most important infection to assess and rule out in this population is malaria. Since malaria caused by Plasmodium falciparum can be severe and cause complications, prompt workup and assessment of parasite burden in the blood is warranted. Important information is patient's country of origin/travel, duration of symptoms (Plasmodium vivax and Plasmodium ovale can relapse after months to years if not treated with radical cure).