Infectious Diseases

Diarrheal diseases are an increasing problem in both developed and developing countries. Those diarrheal diseases caused by protozoan species comprise a significant proportion of worldwide diarrheal morbidity and mortality. Giardia lamblia, Entamoeba histolytica, and Cryptosporidium parvum are three of the major causes of protozoa induced diarrhea. A major difficulty in the management of these diseases is the timely and accurate diagnosis of the disease so that appropriate patient treatment can be initiated, whether it be at the level of effective drug therapy or support therapy.

Giardia lamblia is a protozoan parasite that causes the disease giardiasis. The symptoms of giardiasis include diarrhea, nausea, weight loss, malabsorption, abdominal cramps, flatulence and anemia1. Infection with G. lamblia is the most common parasitic infection in the United States and is the causative agent in approximately 100 million infections per year worldwide ranging from mild to severe. The diagnosis of giardiasis is accomplished by numerous invasive and noninvasive methods. Microscopic examination of a fecal specimen is the most common noninvasive method of diagnosis and requires an experienced technologist. Other methods include immunoassays for G. lamblia specific antigens.

Entamoeba histolytica causes amoebic dysentery and amebiasis. E. histolytica is estimated to be responsible for approximately 500 million infections worldwide. The protozoa inhabit the lumen and mucosa of the large intestine. In most cases, amebic dysentery is either asymptomatic or causes nonspecific diarrhea. In more severe cases it may cause ulcerative colitis. In very rare cases the infection can become extraintestinal and can affect any organ or tissue. Young adult men have the highest prevalence. Diagnosis is traditionally made using microscopic examination.

Microscopic examination cannot differentiate E. histolytica from the nonpathogenic species, Entamoeba dispar, which does not normally cause extraintestinal infection. Sensitive and specific methods have been developed using PCR to differentiate the two species in human fecal specimens. Microscopic examination has been shown to be less sensitive and less specific than other methods for the detection of E. histolytica/dispar including culture, immunoassays, and nucleic amplification techniques.

Cryptosporidium parvum is a coccidian parasite that is an important enteric pathogen. The organism causes acute but self-limiting infections in the immunocompetent patient. The incubation period is from one to 12 days with shedding of most oocysts by 21 days. Symptoms are usually mild to severe diarrhea, but may also include nausea, low-grade fever, abdominal cramps, and anorexia. Infection in the immunocompromised patient may be much more severe and possibly even life threatening. Diagnosis is traditionally made using microscopic examination and requires an experienced technician.

G. lamblia, E. histolytica, and C. parvum are all clinically significant parasites that cause mild to severe infections. All are traditionally diagnosed by microscopic examination that requires an experienced technician. The Triage Parasite Panel is an enzyme immunoassay that simultaneously detects specific antigens for G. lamblia (alpha-1-giardin), E. histolytica/dispar (29 kDa surface antigen), and C. parvum (protein disulfide isomerase).