Cryptosporidium

Julia Richardson, Veterinary Student
David E Anderson, DVM, MS, DACVS

Introduction

Cryptosporidium is a coccidian protozoan parasite that affects a wide range of hosts. Clinical signs it causes are more severe in immunocompromised hosts or neonates. It is usually a self limiting disease but can cause a severe watery diarrhea. If the organism is present in substantial numbers, sites other than the small intestine where it usually inhabits can be infected. Unfortunately, secondary infections can occur simultaneously, worsening symptoms and effects of the disease. One of the most important issues with this parasite comes from its zoonotic potential - e.g. ability to infect people! It is resistant to chlorine and drinking water has been suspected as a means of transmission to humans.

Life cycle

Direct life cycle with both sexual and asexual reproduction

1. Sporozoites within an oocyst is excreted in the feces
2. Oocyst is ingested orally and excystation occurs in the small bowel
3. 4 sporozoites are released and enter the intestinal epithelial cells
4. Asexual intracellular multiplication occurs
5. Differentiation of microgametes and macrogamets occurs
6. Sexual replication and fertilization occurs
7. Oocyst develops followed by formation of new sporozoites

(Image from Kenyon College)

The prepatent period (from infection of the organism to presentation of clinical signs) is approximately 4 days. Each generation can develop and mature in 12 - 14 hours. Due to this and the autoinfection properties of the cycle, the unchallenged organism can quickly escalate into severe disease. The peak age for clinical cryptosporidium in crias is 7 to 14 days old. Although disease has been seen in older crias, this is less likely because the older cria’s immune system is capable to warding off the infection without developing severe clinical signs of disease.

Treatment

There is no safe and effective therapy available to treat Cryptosporidium. Supportive measures, such as fluid therapy and electrolyte replacement can be applied until the hosts immune system fights the disease. Isolation is essential once a diagnosis has been made to protect others in the herd. Limited success has been seen with lasalosid or with paromomycin in treated crias. These drugs can be dangerous and their use should only be attempted with the direct supervision of a veterinarian.

Diagnosis

The cheapest diagnostic tool is direct detection of the oocyst in the feces using an acid-fast stain. IgM, IgG and IgA can be detected using ELISA or IFA but this is not a direct test of the organism. This test is increasingly used because of the difficulty in finding organisms using fecal exam. The newest method which has good sensitivity and specificity is to detect the organisms DNA using PCR. This is however expensive, time consuming and often unpractical. Diagnosis is important for controlling the disease.

Prevention

This is a "disease of domestication" and is strictly hygiene associated. Keeping maternity and nursery areas clean is of paramount importance. Ensuring adequate colostrums ingestion is essential to protection of the neonatal intestine. At this time, no vaccine is available for use.