Intestinal protozoa Giardia

Giardia intestinalis is the most common cause of parasite-induced diarrhoea in Scandinavia. Lambl described Giardia from humans under the name Cercomonas intestinalis in 1859, and Müller (1889) described the parasite in Sweden the first time. His publication describes flagellates with the characteristic Giardia morphology attached, in several layers, to the mucosa of the small intestine of an executed murderer. The prevalence of Giardia was found to be 6% in Stockholm, Sweden and Helsinki, Finland during the 1930s (Svensson 1935). The most recent survey of the occurrence of intestinal pathogenic protozoa performed in Finland identified G. intestinalis, and the prevalence of Giardia was found to be 1% in healthy adults and in children (Kyrönseppä 1993). Nowadays, the incidence of Giardia infection per 100000 habitants is 3.6 in Sweden. A study of entropathogens in 851 adult patients in Stockholm with diarrhoea identified Giardia in 2% of the cases, whereas none of the 200 healthy controls were positive for Giardia (Svenungsson et al. 2000). Giardia was found in 2% of samples in a Danish study of 109 children with gastrointestinal symptoms (Hjelt et al. 1987) and 1500 cases were reported in Denmark in 1997 (Petersen 1998). The parasite is mainly found in travellers and immigrants: of a total number of 1475 Swedes infected by Giardia during 1998, only 315 were infected in Sweden, and similar figures were obtained in Denmark (Petersen 1998). Giardia was found in 10% of faecal samples during routine screening of refugees into Sweden (Benzeguir et al. 1999). However, the percentage of infected in Sweden has increased during the 1990s, although symptomatic cases are predominantly investigated, which likely underestimates the prevalence rates in the general population. Giardia cysts were recently found in 26% of investigated Swedish raw water samples and similar percentages have been found in Norwegian water supplies (Hansen and Stenström 1998). One of the largest outbreaks of water-borne giardiasis reported in Europe occurred in Sweden in 1986 with more than 1400 cases being diagnosed (Ljungström and Castor 1992), and several other water-borne outbreaks have been reported recently (Hansen and Stenström 1998). The occasional transmission of the parasite among children in day care centres and among institutionalized geriatric patients has also been reported (Svensson 1935; Christenson et al., 1992). Giardia is a potential zoonotic disease and a Danish study revealed that 7.6% of faecal samples from asymptomatic dairy cows and calves contained Giardia cysts (Iburg et al. 1996). Giardia have also been detected in faeces of Swedish dogs (Castor and Lindquist 1990), roe deer, lynx, sheep, and moose (Dan Christensson, personal communication).


Entamoeba histolytica was first described in 1875 by Lösch in Russia in the stool of a dysenteric patient.

It was recently discovered, however, that a morphologically identical parasite E. dispar exists as a separate non-pathogenic species. This makes it possible that not all present and previously reported cases are/were due to E. histolytica as we still lack a simple and highly specific assay system to separate them.

Sievers reported 10 cases of amoebiasis in Finland in 1906; the prevalence was 9% in Helsinki in 1927 (Svensson 1935). The number of reported amoebiasis cases in Sweden has widely varied during the 1990s, mainly due to changes in the number of immigrants. In Sweden 3830 cases of amoebiasis were reported in 1992. The majority of these were

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diagnosed in the faeces of individuals from the former Yugoslavia. In 1998, in Sweden, 445 cases were reported and only 27 of those were infected in Sweden. During a water-borne outbreak in Sweden 106 became infected by E. histolytica (Ljungstrom and Castor 1992). The domestic incidence of amoeba infection during 1999 in gastroenteritis cases was 0.3 per 100000 inhabitants. In a recent survey, 1% of Swedish adults with enteritis had Entamoeba infection while none of the controls was infected (Svenungsson et al. 2000). As a result the number of people infected with E. histolytica is most likely overestimated. Very little data exists regarding the prevalences of Entamoeba in other Scandinavian countries, but Entamoeba was found in 0.3% of investigated travellers in Finland (Kyronseppa 1993) and 300 imported cases were reported from Denmark in 1997 (Petersen 1998).

Other intestinal protozoa

There is a large uncertainty as to the prevalence of other intestinal protozoa since it is not obligatory that they are reported. Microsporidia spp. occur relatively frequently in AIDS patients but only 13 cases were, for example, reported to the Swedish Institute for Infectious Disease Control between 1994 and 1995. Cryptosporidium parvum is yet another parasite which, at the beginning of the 1980s, was believed to only affect immunosuppressed individuals, when serious outbreaks were reported. This is no longer the case. Spread from animals to humans has been reported and outbreaks have occurred at day care centres in Scandinavia (Hjelt et al. 1987). Cryptosporidium was identified in 3% of diarrhoeal cases in three Swedish studies (Atterholm et al. 1987; Svantesson et al. 1988; Svenungsson et al. 2000) and in 6% of faecal samples from neonatal calves (Viring et al. 1993). None of the 519 healthy individuals excreted cryptosporidia. Similar results have been obtained in Denmark (Holten-Andersen et al. 1984). Balantidium coli, the only ciliate known to be pathogenic to humans, was described for the first time by Malmsten in Stockholm in 1856, and Sievers reported 140 cases in Finland in 1906. However, transmission of Balantidium is not known to occur today. Blastocystis hominis and Dientamoebafragilis are frequently detected in faecal samples from children at day care centres in Sweden but their pathogenicity is uncertain (Weiss and Keohane 1997; Marianne Lebbad, personal communication). Entamoeba coli was found in 15% of investigated faecal samples in Finland in 1935 (Svensson 1935) and odd cases of E. coli-associated diarrhoea has been reported to be associated with gastroenteritic symptoms (Wahlgren 1991).

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