Coccidian species

Cryptosporidium parvum

Disease / Pathology

Cryptosporidium parvum infections are usually self limiting and tend to last 1 to 2 weeks in persons with healthy immune systems with watery diarrhea being the most common symptom. Other symptoms can include stomach cramps with or without pain, dehydration from the excessive loss of fluids, vomiting, loss of weight, and fever.

Cryptosporidium parvum infections are usually more serious in those patients that are immunocompromised and was especially problematic prior to the success of anti-retroviral drugs in HIV infected individuals. Infections in these patients were sometimes fatal.

The organism invades the epithelial cells of the small intestine and reproduce on the apical surface of the epithelium thus disrupting the normal function of the cells by inducing moderate levels of apoptosis and altering expression of key epithelial tight function and adherens junctions to disrupt the intestinal barrier integrity. The result is barrier disruption and increased permeability.

Location in the Host

Cryptosporidium parvum infects the epithelial cells of the small intestine.

Geographic Distribution

Cryptosporidium parvum with a worldwide distribution.

Life Cycle

Morphology & Diagnosis

Cryptosporidium parvum are coccidia that are round or oval and very small. They are normally 4um to 6um making them difficult to almost impossible to see under high power microscopy the four sporozoites within each oocyst.

Various methods can be utilized to detect the oocyst in the stool and these include acid fast staining where the oocyst are acid fast positive; DFA where a fluorescently tagged antibody to the oocyst is employed and detection is made using a fluorescent microscope; EIA lateral flow testing can be used; and the probably the best test method in terms of eliminating subjectivity – increasing sensitivity – and ease of use, PCR.

Images

Cryptosporidium oocysts in a stool specimen stained with an acid-fast stain – Photo by W. Vientos

Cyclospora cayetanensis

Disease / Pathology

Cyclospora cayetanensis infections are usually self limiting infections that last about one week. The organism will infect the epithelial cells of the small intestine and causes watery diarrhea that can be at times explosive. Other symptoms include weight loss, loss of appetite, increased gas, nausea, headache, fever, and flu-like symptoms. It is important to note that in some individuals the infection can be asymptomatic.

Infections are acquired by consuming contaminated food or water. The organism is especially prevalent in other countries where sanitary practices are limited.Therefore travelers are at risk for contracting this parasite. An important source of this infection in the United States is the consumption of contaminated fruits and vegetables imported from other countries. Many outbreaks have been traced to imported fruits and/or vegetables. There has been no commercially frozen or canned produce that has been implicated in an outbreak to date.

The infectivity of this organism is dependent on the length of time it has been passed in the stool of an infected individual. It takes about 1-2 weeks before Cyclospora is infectious after fecal passage. Thus the unlikely hood that the organism is passed directly from person to person.
It not treated the symptoms may last for up to a month and relapses are common. The recommended treatment is a combination of two antibiotics (Bactrim , Septra, or Cotrim).

Location in the Host

Cyclospora cayetanensis infects the epithelial cells of the small intestine.

Geographic Distribution

Cyclospora cayetanensis with a worldwide distribution but most common in tropical and subtropical countries.

Life Cycle

Morphology & Diagnosis

Cyclospora cayetanensis are coccidia that are round or oval and very small. They are normally 4um to 6um making them difficult to almost impossible to see under high power microscopy the four sporozoites within each oocyst. They are easily confused with Cryptosporidium parvum. The key differences are that Cyclospora cayetanensis will auto-fluoresce when viewed under an ultraviolet fluorescent microscope while cryptosporidium will not. Cyclospora cayetanensis is also about 8-10u while Cryptosporidium is 4-6u in size. Sporozoites inside the oocyst are difficult to impossible to see just as with Cryptosporidium.

Various methods can be utilized to detect the oocyst in the stool and these include acid fast staining where the oocyst are acid fast positive; EIA lateral flow testing can be used; and the probably the best test method in terms of eliminating subjectivity – increasing sensitivity – and ease of use, PCR.

Cystoisospora belli

Disease / Pathology

Cystoisospora belli infections are usually self limiting and tend to last 1 to 2 weeks in persons with healthy immune systems with watery diarrhea being the most common symptom. Other symptoms can include stomach cramps with or without pain, dehydration from the excessive loss of fluids, vomiting, loss of weight, and fever.

Cystoisospora belli infections are usually more serious in those patients that are immunocompromised and was especially problematic prior to the success of anti-retroviral drugs in HIV infected individuals. Infections in these patients were sometimes fatal.

The organism invades the epithelial cells of the small intestine and reproduce on the apical surface of the epithelium thus disrupting the normal function of the cells by inducing moderate levels of apoptosis and altering expression of key epithelial tight function and adherens junctions to disrupt the intestinal barrier integrity. The result is barrier disruption and increased permeability.

Location in the Host

Cystoisospora belli infects the epithelial cells of the small intestine.

Geographic Distribution

Cystoisospora belli has a worldwide distribution but is most common in tropical and subtropical countries.

Life Cycle

Morphology & Diagnosis

Cystoisospora belli are coccidia that are oval and measure about 30x20u.

The oocyst are usually detected in the stool of infected persons and because of their small size and intermittent shedding, can be difficult to detect. It is best to alert the Microbiologist working in a laboratory that the organism is suspected.

The oocyst may contain one or two sporozoites which can or may not be seen. Though admittedly the sporozoites are most apt to be seen in Cystoisospora belli rather than Cryptosporidium or Cyclospora. In addition the oocyst are significantly larger. But the interior space of the oocyst is clear to see through and can easily blend in with fecal debris making them difficult to detect especially when the shedding is low.