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5 Protozoa and Trematodes 5 Protozoa and Trematodes This chapter summarises the evidence for protozoan illnesses acquired through ingestion or inhalation of water or contact with water during water-based recreation. Information on schistosomiasis a disease caused by a parasitic flat worm (trematode) is also presented. The organisms that will be described are: Cryptosporidium parvum; Giardia duodenalis; Microsporidia; Naegleria fowleri and Schistosoma spp. The following information for each organism is presented: general description, health aspects, evidence for association with recreational waters and a conclusion summarising the weight of evidence. © World Health Organization (WHO). Water Recreation and Disease. Plausibility of Associated Infections: Acute Effects, Sequelae and Mortality by Kathy Pond. Published by IWA Publishing, London, UK. ISBN: 1843390663 148 Water Recreation and Disease CRYPTOSPORIDIUM PARVUM Credibility of association with recreational water: Strongly associated I Organism Pathogen Cryptosporidium parvum Taxonomy Cryptosporidium parvum belongs to the phylum Apicomplexa (Sporozoa), class Coccidea and family Cryptosporidiidae. Within the genus Cryptosporidium there are ten recognised species (O’Donoghue 1995). The species of concern to humans is C. parvum, which has been detected in 152 species of mammals. Reservoir C. parvum is an obligate enteric coccidian parasite that infects the gastrointestinal tract of humans and livestock. Oocysts of Cryptosporidium are widespread in the environment including lakes and streams. Cryptosporidium becomes a problem in surface waters in most areas during spring rains which increase run-off, and many neonate animals are present in the environment to amplify oocyst numbers. Many adult animals continue to produce low levels of oocysts on a regular basis, which enhances the environmental load and serves as a source of infection for neonates (Castro-Hermida 2002). Breakdowns or overloading of public water utilities have resulted in community outbreaks of cryptosporidiosis. It is nearly impossible to determine the origin of many individual cases of cryptosporidiosis. There are many anecdotal reports of the parasite being acquired from public water supplies. Many cases may represent cases of cryptosporidiosis transmitted to humans by companion animals such as kittens and puppies, or by contact with other humans (Tzipori and Ward 2002). Distribution Worldwide. Infection and illness caused by Cryptosporidium spp. has been reported in more than 40 countries on six continents. Infection is common in developed regions and nearly universal in impoverished areas (Kosek et al. 2001). Characteristics Oocysts are able to survive for several months in water kept at 4 oC, but at higher temperatures viability decreases more rapidly (Smith and Rose 1990). Protozoa and Trematodes 149 Increased rainfall is associated with increased concentrations of oocysts in receiving waters (Atherholt et al. 1998). Other factors affecting the presence of oocysts in the water environment are the incidence of infection in the animal or human population, the type of animal waste handling and sewage treatment, and the type of disposal of sewage. II Health aspects Primary disease symptoms and sequelae Cryptosporidiosis is generally a mild self-limiting disease in immunocompetent persons but more serious in the immunocompromised. Infection with C. parvum results in severe watery diarrhoea which lasts between several days and two to three weeks in previously healthy persons. Patients may also experience mild abdominal pain and fever. In children from developing countries it has been shown that infection with C. parvum predisposes to substantially increased diarrhoeal illnesses (Guerrant et al. 2002) and shortfalls in linear growth and weight gain (Checkley et al. 1997; Kosek et al. 2001). Chan et al. (1994) emphasise the lasting consequences where children are infected at an early age. Studies have shown a reduced physical fitness four to six years later associated with early childhood diarrhoea and, specifically with cryptosporidial infections in the first two years of life (Guerrant et al. 1999). The fitness deficits alone are comparable with that associated with a 17% reduction in work productivity (Ndamba et al. 1993). Work in Brazil has shown that early childhood diarrhoea is associated with long-term cognitive deficits (Guerrant et al. 1999) and, more recently, educational performance (Lorntz et al. 2000). Severe diarrhoea is associated with weight loss. Malaise and fever are also common with cryptosporidial infections. Non-gastrointestinal illness, such as cholecystitis, hepatitis and respiratory disease may also occur. Disease-parasite development and replication is relatively confined to the terminal jejunum and ileum in immunocompetent patients but in immunocompromised patients the entire gastrointestinal tract as well as biliary and pancreatic ducts may become infected (Current and Garcia 1991). Such patients could experience self-limited infection or an acute dehydrating diarrhoeal syndrome (Kosek et al. 2001). While reactive arthritis has been frequently described in association with bacterial pathogens, arthritis linked to parasitic infection has rarely been documented (Sing et al. 2003). Reactive arthritis complicating cryptosporidial infection is even rarer; Sing et al. (2003) reviews three cases reported by Hay et al. (1987); Shepherd et al. (1989); Cron and Sherry (1995) and Winchester et al. (1987). 150 Water Recreation and Disease In immunocompetent patients, symptoms and oocyst shedding usually resolve themselves in less than 14 days and need only symptomatic treatment. In the cases reported in the literature treatment resulted in either spontaneous recovery or disappearance of gastrointestinal symptoms with prolonged presentation of arthritis. In contrast to other forms of reactive arthritis, mainly small joints seem to be affected with cryptosporidia-associated reactive arthritis. Although cryptosporidia was typically excreted for a long period of time (over a year), patients did not suffer any gastrointestinal complaints except for a two- day history of mild diarrhoea starting two weeks before the onset of arthritis. Normally, gastrointestinal cryptosporidiosis is self-limiting within two weeks in immunocompetent individuals. Exposure/mechanisms of infection The main route of infection is person-to-person contact (WHO 2004a). The transmission of Cryptosporidium spp. through water consumption has been well documented (see Fayer et al. 2000 for a review). Initially, the oocyst is ingested and passes through the stomach where four motile sporozoites are released and attach to the epithelial cell wall where they are taken into superficial parasitophorous vacuoles. The sporozoite here matures into a trophozoite and then divides and releases merozoites. Merozoites infect other epithelial cells, perpetuating the infection. Eventually some merozoites form microgametes and macrogametes which fertilise and become zygotes. These zygotes mature into an oocyst which is the infective stage and is passed in the faeces. Disease incidence During the past two decades, Cryptosporidium has become recognised as one of the most common causes of waterborne disease (drinking and recreational) in humans in the United States. In 2000, the annual incidence was estimated as 1.17 in 100,000 people (Groseclose et al. 2002). In many other countries, particularly developing nations, records tend to be sporadic or based on particular studies. In the South-East Asia Region and Western Pacific Region the annual incidence of infection has been reported to range from 2% to 20% and in India from 4% to 13% (Nath et al. 1999). Incubation surveys of stools carried out in developed countries have shown the prevalence of infection to be between <1% and 4.5%, and many infections are subclinical (Benenson 1995). In the United States roughly 20% of young adults have measurable serum IgG antibody to cryptosporidium. In rural China 75% of 11–13-year-old children are seropositive and in a Brazilian shantytown over 90% of children become seropositive by the age of 1 year (Zu et al. 1994). Protozoa and Trematodes 151 Incubation period The incubation period is normally between seven and ten days (range 4 to 28 days) (Hunter 1998). Infectivity The infective dose of oocysts for humans is unknown but probably small – less than 10 oocysts (Dillingham et al. 2002). Cryptosporidium oocysts discharged by ill individuals are usually observed at densities of between 106 and 107 per gram of faeces (Hunter 1998). Sensitive groups Individuals infected with Cryptosporidium spp. usually develop self-limiting diarrheal illness with enteric symptoms. However, Cryptosporidium also has been associated with more persistent symptoms and serious illness in immunocompromised persons, especially those with HIV, primary immunodeficiency, X-linked hyper-IgM syndrome, severe combined immunodeficiency, and selective IgA deficiency; those undergoing solid-organ transplantation; and children who are undernourished (Huang et al. 2004). Illness can last for several months or until death. Cryptosporidiosis is considered incurable in immunocompromised patients (Ferreira and Borges 2002) although for persons with AIDS, anti-retroviral therapy that improves immune status will decrease or eliminate symptoms of cryptosporidiosis. However, even if symptoms disappear, they may return if the immune status worsens (Anonymous 2004; Morales Gomez 2004). Biliary cryptosporidiosis in AIDS patients results
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