Cryptosporidiosis: Infection and transmission

Cryptosporidiosis is a disease caused by Cryptosporidium spp, an obligate intracellular protozoan parasite. Cryptosporidium muris was first described by Tyzzer in 1910 and Cryptosporidium parvum was described two years later. However, it was not until the 1970s that Cryptosporidium was determined to be a significant cause of gastrointestinal disease in humans.

It is a frequent cause of diarrheal disease in humans, and several groups of humans are particularly susceptible to cryptosporidiosis. In developing countries, Cryptosporidium infections occur mostly in children younger than 5 years.

In immunocompromised persons such as human immunodeficiency virus-positive (HIV) patients, the incidence and severity of cryptosporidiosis increases as the CD4 lymphocyte cell count falls.

The persistent diarrhea and malabsorption can become life-threatening, particularly in acquired immunodeficiency syndrome (AIDS) patients.

Cryptosporidium is a small protozoan parasite that infects the microvillous region of epithelial cells in the digestive and respiratory tract of vertebrates. It is an obligate intracellular parasite of man and other mammals, birds, reptiles and fish. It requires its host to multiply.

When the oocysts enter the gastrointestinal tract, the invasive Cryptosporidium causes damage to the small intestinal epithelium. It disrupts the barrier function and absorption capability that leads to mild-to-severe diarrhea and other abdominal symptoms.

Cryptosporidiosis is an opportunistic parasitosis. It is characterized by self-limiting gastroenteritis in otherwise healthy people, while it is more severe in immunocompromised subjects in HIV-infected patients and constitutes a serious threat leading to chronic or fulminant disease, wasting and death.

The infection is spread in a number of ways: from person to person, from animals, via food, and by water. Cryptosporidiosis is now the most common cause of waterborne disease in the world.

Cryptosporidium oocysts transmission can occur following direct or indirect contact with an infected host usually via the fecal–oral route. Person to-person contact, zoonosis, and the consumption of contaminated food or water are well known mechanisms for fecal–oral transmission.

The largest cryptosporidiosis outbreak reported to date in the USA occurred in Milwaukee, Wisconsin in 1993 when over 403,000 individuals were sickened out of a potentially exposed population of 1.6 million.
Cryptosporidiosis: Infection and transmission 

What are the symptoms of cryptosporidiosis?

Long term sequelae resulting from infection can be common and van cause non-intestinal symptoms. The first signs and symptoms of cryptosporidium infection usually appear within a week after infection and may include:
*Watery diarrhea
*Dehydration
*Lack of appetite
*Weight loss
*Abdominal pain
*Mild Fever
*Nausea
*Anorexia
*Vomiting
*Respiratory problems

As might be expected, many individuals experienced multiple symptoms. In people with a profound immunodeficiency, there can be symptoms that are different and more prolonged, and disease can result in an earlier death than would be the case of the patient had not been infected.

Symptomatic diarrhea may be marked by stool volumes that exceed 6 liters per day. Intestinal infections may extend from the small intestine into then colon, stomach, and esophagus and may involved a variety of extra-intestinal organs and tissues.
What are the symptoms of cryptosporidiosis?

Cryptosporidiosis: History, definition, outbreak

Cryptosporidiosis
The protozoan Cryptosporidium parvum was first described in 1907 in asymmetric mice, and for decades now it has been known to be a pathogen of at least 40 mammals and varying numbers of reptiles and birds.

Although the first documented human case was not recorded until 1976, this disease has a worldwide prevalence of 1-4% among patients with diarrhea, and it appears to be increasing.

It is estimated to cause infections in from 7 to 38% of AIDS patients in some hospitals.

The prevalence of C. parvum is diarrheal stools is similar to that of Giardia lamblia.

In human disease is self limiting in immunocompetent individuals, but it is a serious infection in the immunocompromised, such as AIDS patients.

The protozoan is known to be present in at least some bodies of water and this exist the potential for food transmission.

The fecal-oral route of transmission is the most important, but indirect transmission by food and milk is known occur.

C. parvum is an obligate intracellular coccidian parasite that carries out its life cycle in one host. Following ingestion of the thick-walled oocystsm, they excyst in the small intestine and free sporozoites and penetrate the microvillous region of host enterocytes, where sexual reproduction leads to the development of zygotes.

They invade host cells by disrupting their own membrane as well as that of their host.

Host cell acting polymerization at the interface between the parasite and the host cell cytoplasm has been found to be necessary for infection.

The first demonstrated waterborne outbreak of cryptosporidiosis occurred in Braun Station, Texas, in 1984 following the consumption of artesian well water.

There were actually two outbreaks – one in May and the other in July, with 79 victims. A second outbreaks with 13,000 victims occurred in Carrolton, Georgia in 1987 and oocysts were found in the tools of 58 of 147 victims.

The clinical course of cryptosporidiosis in human depends on the immune state, with the most severe cases occurring in the immunocompromised.

In immunocompetent individuals, the organism primarily parasitizes the intestinal epithelium and causes diarrhea.

The disease is it self-limiting, with an incubation period of 6-14 days and symptoms typically last 9-23 days.

In the immunocompromised diarrhea is profuse and watery with as many as 71 stools per day and up to 171 per day reported.

Diarrhea is sometimes accompanied by mucus but rarely blood.
Cryptosporidiosis: History, definition, outbreak