Cryptosporidiosis is a GI illness caused by protozoa of the genus Cryptosporidium. Cryptosporidium was first associated with human GI disease in 1976. It was first identified in stomachs of mice in 1907, and the name Cryptosporidium was proposed in 1912. Prior to 1982, few incidents of human infection were reported. In early 1980, with the advent of the acquired immunodeficiency syndrome (AIDS) epidemic, Cryptosporidium infections became increasingly recognized as a cause of diarrheal illness. The disease is transmitted via the fecal-oral route from infected humans or animals. Infection usually occurs following ingestion of contaminated water, but can transmission can also occur through food and person-to-person. Extensive waterborne outbreaks have occurred from contamination of municipal water and recreational waters (eg, swimming pools, ponds, lakes). 1, 2 Although less common, transmission through certain sexual practices involving oro-anal contact has been documented.
The parasite the genus Cryptosporidium consists of a group of protozoan parasites within the protist subphylum Apicomplexa (including Plasmodium species). There are 10 recognized Cryptosporidium species based on host specificity, morphology, and molecular biology studies. Besides humans, the parasite can infect many different species of animals (eg, mammals, birds, reptiles) and is pathogenic to immunocompetent and immunocompromised hosts.
Two species mainly infect humans: Cryptosporidium hominis (previously Cryptosporidium parvum genotype
- which infects only humans, and C parvum (previously C parvum genotype
- which infects humans and animals. Cryptosporidium canis (genotype) infects dogs and humans. Cryptosporidium (genotype4) can complete its life cycle within a single host, including both asexual (merogony) and sexual (sporogony) reproductive cycles. Infection is initiated by ingestion of oocysts, which are activated in the stomach and upper intestines and release 4 infective sporozoites. These motile sporozoites bind to the receptors on the surface of the intestinal epithelial cells. Two morphologic forms of the oocysts have been described: Thin-walled oocysts (asexual stage) excyst within the same host (causing self-infection), whereas the thick-walled oocysts (sexual stage) are shed into the environment.
Cryptosporidium has emerged as the most frequently recognized cause of recreational water associated outbreaks of gastroenteritis, particularly in treated (disinfected) venues. The infectious dose is low, and ingestion of as few as 10-30 oocysts can cause infection in healthy persons. Cryptosporidium does not multiply outside of the host. The oocyst stage can resist disinfections, including chlorination, and can survive for a prolonged period in the environment, thus facilitating waterborne transmission. Because the oocysts are infectious when shed, the parasites are readily transmitted person-to-person. Some genotypes have animal reservoirs, and, thus, animal contact can be associated with transmission.
Host immune response limits the duration and severity of infection. 5, 6, 7 Persons at increased risk for infection include
- individuals who have had contact with infected animals,
- individuals who have ingested contaminated recreational water (eg, lake, river, pool, hot tub) or drinking water, close contacts of infected persons (eg, those in the same family or household or in daycare settings), and
- travelers to disease-endemic areas. Cryptosporidium parasites are ubiquitous, except in Antarctica, and infection is more common in warm, moist months. In the United States, incidence peaks from July through September. Wastewater sources, such as raw sewage and runoff from dairies and grazing fields, contaminate the water sources. Outbreaks in daycare centers with incidence rates of 30-60% have been reported. Cryptosporidium species also cause traveler's diarrhea.
In 1993, more than 400,000 cases of diarrheal illness due to Cryptosporidium infection was reported in Milwaukee, Wisconsin. 8 As of July 24, 2007, a total of 18 cryptosporidiosis outbreaks have been reported to the Centers for Disease Control and Prevention. 9 Cryptosporidiosis is a notifiable disease at the European Union level, and surveillance data are collected through the European Basic Surveillance Network. 10, 11 The disease distribution in Europe for 2005 included 7,960 cryptosporidiosis cases reported among 16 countries. The crude incidence rate was 1.9 cases per 100,000 population, although considerable differences in the rates of cryptosporidiosis between countries were observed.
The blue green algae or cyanobacteria represent a diverse group of organisms that produce potent natural toxins. There have been case reports of severe morbidity and mortality in domestic animals through drinking water contaminated by these toxins. Microcystins, in particular, have been associated with acute liver damage and possibly liver cancer in laboratory animals. Although, there has been little epidemiological research on toxin effects in humans, a study by Yu (1995) found an association between primary liver cancer and surface water. Surface water drinking supplies are particularly vulnerable to the growth of these organisms; current US drinking water treatment practices do not monitor or actively treat for blue green algal toxins including the microcystins.
A pronounced seasonal peak was observed in the autumn season, with 59% of cases reported between August and November. However, Ireland and Spain experienced a peak in spring and summer, respectively. Routine cryptosporidiosis surveillance in Northwest England over 17 years revealed that the cases predominantly occurred in spring and autumn. Pathophysiology Organisms of the genus Cryptosporidium are able to infect and reproduce in the epithelial cell lining of the GI and respiratory tracts without causing cytopathic effects. C parvum causes most human infections. In immunocompetent individuals, the organism is primarily localized to the distal small intestines and proximal colon, whereas in immunocompromised hosts, the parasites have been identified throughout the gut, biliary tract, and respiratory tract.
Children with persistent cryptosporidiosis may have villous atrophy; in children with heavier infections, crypt hyperplasia and lymphocyte infiltration is also seen. 4 Cryptosporidiosis is characteristically associated with voluminous watery diarrhea that resembles toxin-mediated illnesses. Damage to intestinal microvilli may cause secondary malabsorption and steatorrhea. Altered intestinal permeability results in decreased absorption of fluids and electrolytes, as well as solute fluxes into the gut. Infected persons have been reported to shed 108-109 oocysts in a single bowel movement and to excrete oocysts for as long as 50 days after cessation of diarrhea.
In the end, there are many other of cryptosporidium. Foods such as unwashed fruits and vegetables especially from foreign countries, swimming pools, recreational water, day-care centers, and nursing homes are common sources. About one-third of the world population has been exposed to Cryptosporidium, indicating that there are many possible sources of exposure. The common factor for all Cryptosporidium exposure is contamination from stools of infected humans or animals.