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Oocysts of Cryptosporidium parvum stained by the acid-fast method. This image shows that the staining can be variable. In particular, infections that are resolving can be accompanied by increasing numbers of non acid-fast oocysts “ghosts”.

Cryptosporidium - is a small parasite, measuring about 3-5 µm. Members of the genus Cryptosporidium are parasites of the intestinal tracts of fishes, reptiles, birds, and mammals. A number of researchers believe that to date 23 species of cryptosporidium have been named based on host occurrence. It seems however, that members of this genus do not display a high degree of host specificity, so the number of species in this genus remains a matter of some discussion. Cryptosporidium isolated from humans is now referred to as C. parvum. Cryptosporidium infections have been reported from a variety of wild and domesticated animals, and in the last six or seven years literally hundreds of human infections have been reported, including epidemics in several major urban areas in the United States. Cryptosporidiosis is now recognized as an important opportunistic infection, especially in immunocompromised hosts.

In birds C. baileyi and C. meleagridis as well as c.parvum have been reported. This does not mean that other species of cryptosporidium can not effect birds. It simply means that this occurrence has not been shown and it is not yet clear if other species of cryptosporidium effect birds.

The trachea of a turkey "lined" with numerous Cryptosporidium. (From: Gardiner et al., 1988, An Atlas of Protozoan Parasites in Animal Tissues, USDA Agriculture Handbook No. 651.)

It lives on (or just under) the surface of the cells lining the small intestine, reproduces asexually, and oocysts are passed in the feces (view diagram of the life cycle). Transmission of the infection occurs via the oocysts.

Many human infections have been traced to the contamination of drinking water with oocysts from agricultural "run-off" (i.e., drainage from pastures), so it is considered a zoonosis. Most mammals, birds, reptiles and fish are susceptible to Cryptosporidium.


Crypto lives in the intestine of infected humans, birds, fish reptile and other animals. Millions of Crypto can be released in a single bowel movement from an infected specimen. Infections occur after oral consumption of the parasite. Crypto may be found in soil, food, water, or surfaces that have been contaminated with the feces from infected humans or animals. Crypto is not spread by contact with blood.

Life cycle (stages)

• Thick-walled oocysts with 4 sporozoites passed in feces; thin-walled oocysts remain in gut, excysting and releasing merozoites (= autoinfection)

• Thick-walled oocysts usually appear at 1 to 2 weeks postpartum; are ingested by DH and excyst

• Sporozoites enter microvillous brush border (therefore extracytoplasmic) of enterocytes

• Trophozoites rapidly form schizonts with 4-8 merozoites; 1 to 2 generations
First generation schizont has 6 to 8 zoites
Second generation schizont has 4 zoites

•Gametogony to oocyst production
80% of the oocysts produced are thick-walled and are passed in the feces
20% of the oocysts produced are thin-walled and cause autoinfection

•Prepatent period - 3 days

In most patients infected with Cryptosporidium the infection causes ashort term, mild diarrhea. Since such symptoms are associated with a number of ailments, infected individuals may not seek medical treatment, and the infection may subside on its own. Thus, it is difficult to say how many Crypto infections occur. On the other hand, individuals with with compromised immune systems can develop pronounced, chronic diarrhea; that may go on for weeks or months. Needless to say, such an infection, if not fatal unto itself, can exacerbate other opportunistic infections common in immunocompromised hosts.

In birds Symptoms most associated with a crypto infections are diarrhea, and strong smelling fecal material. Birds can also develop respiratory signs. In snakes and other reptiles, the most striking clinical manifestation in chronic infections is swelling of the stomach.

Prevention: Practice good hygiene. Avoid water that might be contaminated. Avoid food that might be contaminated.
Treatment: No therapeutic agent has been clearly identified as effective however, some encouraging results following use of paromomycin (an aminoglycoside antibiotic) have been reported. Azithromycin and Lactobin-R (bovine colostrum immunoglobulin concentrate) have had some experimental success. If diarrhea persists, provide plenty of fluids to prevent dehydration. Rapid loss of fluids because of diarrhea can be life-threatening. Individuals in poor health or who have a weakened immune system are at higher risk for more severe and more prolonged illness.

For persons with AIDS, anti-retroviral therapy that improves immune status will also decrease or eliminate symptoms of Crypto. However, in many cases the infection is not cured and may come back if the immune status worsens.


A: Agarose gel (2%) analysis of a PCR diagnostic test for detection of Cryptosporidium parvum DNA. PCR was performed using standard ABI protocol.
Lane S: Molecular base pair standard (100-bp ladder). Black arrows show the size of standard bands.

Lane 1: C. parvum positive fecal specimen. The red arrow shows the diagnostic band for Cryptosporidium parvum zoonotic genotype (size: 435 bp).


For PCR testing, samples from suspected birds are collected with fresh cloacal and fecal samples. Swabs must be sterile and transported in a correct medium. Multiple specimens collected over period of time are required for best results.

Environmental samples can also be submitted to help evaluate the environment.
Handling: Prior to shipping samples should be stored at 4 C. (refrigerator). Samples must be shipped in a padded envelope or box. Samples may be sent by regular mail, but overnight is recommended.

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