Vol. 20, No. 48
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, November 27, 2001

A. Provided by Karen Fujii, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

2 outbreaks were reported to DHMH during MMWR week 47 (November 18 - November 24):

1 outbreak of acute febrile respiratory disease at a head start program (Queen Anne's Co.)

1 outbreak of foodborne gastroenteritis at a private home (Prince George's Co.)

B. The Johns Hopkins Hospital, Department of Pathology. Information provided by Rob Law, M.D.

A 19 year old woman status post cadaveric renal allograft was transferred from an outside hospital for evaluation of diarrhea. She reports a 3-4 week history of watery diarrhea, up to 10 stools per day. She denies any other symptoms. Her water source is from a well located near livestock, she recently consumed venison, and her boyfriend also reports a brief episode of diarrhea one month ago. Her labs are significant for a sodium of 127, creatinine 10.0, WBC 6.1; her hematocrit fell from 43% to 35% following hydration. Stool studies for ova and parasites were performed, revealing numerous Cryptosporidium organisms.

Organism: Cryptosporidium is a member of the protozoan phylum Apicomplexa, class Sporozoasida, subclass Coccidiasina. Other coccidians include Babesia, Sarcocystis, Plasmodium and Toxoplasma. Closely related coccidians include Isospora, Eimeria, Microsporidium, and Cyclospora which also develop in the gastrointestinal and respiratory epithelium. Approximately twenty species of Cryptosporidium have been named based on morphologic features.
 
 

The life cycle of Cryptosporidium begins with ingestion of oocysts, transmitted from fecally contaminated material from infected humans or animals. Excystation occurs after exposure to reducing agents such as bile salts and digestive enzymes. Four banana-shaped sporozoites are released and attach to the epithelial cell wall of the gastrointestinal tract. Later development occurs within a vacuole composed of host cell and parasite derived membranes, making Cryptosporidium intracellular but extracytoplasmic. Sporozoites mature asexually into meronts, which release merozoites into the intestinal lumen. Some merozoites will reinvade the host cell and begin a powerful autoinfectious cycle while others begin sexual maturation leading to zygote formation. The oocysts containing four new sporozoites are excreted in a fully infectious form. The presence of merozoites and oocysts may lead to an autoinfectious cycle, which may explain why ingestion of only a few oocysts may lead to disease, and why immunodeficient patients develop persistent infections.
 
 

Clinical features. After an incubation period of 7-10 days, the patient develops and enteritis characterized by watery diarrhea with or without abdominal cramping and a low-grade fever. Patients with AIDS can have voluminous diarrhea (up to 17 L/day). Biliary infection in patients with AIDS is associated with right upper quadrant pain, nausea, and vomiting.

Diagnosis. Stool microscopy with modified acid-fast staining displays red-stained round oocysts against a blue background. Leukocytes should not be seen in the stool in cryptosporidiosis. Stool culture should be performed to rule out other enteric pathogens.

Management. Supportive care with hydration and nutritional supplementation are the mainstays of treatment; as is symptomatic therapy with antidiarrheal agents (loperaminde, diphenoxylate). Results of antibiotic treatment with paromomycin (an oral nonabsorbed aminoglycoside) have been disappointing. In immunosuppressed individuals, careful adjustment of immunosuppressive agents is recommended. The use of HAART in the HIV population has greatly reduced the incidence of cryptosporidiosis.

References:

1. Koneman et. al. Color Atlas and Textbook of Diagnostic Microbiology, 5^th Edition, Lippincott-Raven, Philadelphia, 1997.

2. Current, WL. Garcia, LS. Cryptosporidiosis. Clinics in Laboratory Medicine. 1994; 11(4) 873-97

3. Mandell, GL, Bennet, JE, and Dolin R: Principle and Practice of Inf. Dis. Fifth Edition (1999), Churchill Livingstone Inc., PA. 2903-15.