Abstract
To improve understanding of the aetiology and epidemiology of human cryptosporidiosis, over 8,000 Cryptosporidium isolates were submitted for typing to the species level over a four year period. The majority were either Cryptosporidium parvum (45.9%) or Cryptosporidium hominis (49.2%). Dual infection occurred in 40 (0.5%) cases and six other known Cryptosporidium species or genotypes were found in 67 (0.9%) cases. These were Cryptosporidium meleagridis, Cryptosporidium felis, Cryptosporidium canis, and the Cryptosporidium cervine, horse and skunk genotypes. The remaining 3.5% were not typable. Epidemiology differed between infecting species. C. parvum cases were younger, although C. hominis was more prevalent in infants under one year and in females aged 15 to 44 years. Spring peaks in cases reported to national surveillance were due to C. parvum, while C. hominis was more prevalent during the late summer and early autumn as well as in patients reporting recent foreign travel. Temporal and geographical differences were observed and a decline in C. parvum cases persisted from 2001. Typing of isolates allowed outbreaks to be more clearly delineated, and demonstrated anthroponotic spread of C. parvum as well as C. hominis. Our findings suggest that national surveillance for Cryptosporidium should be conducted at the species level.
Highlights
The aetiological agent of the diarrhoeal disease cryptosporidiosis in humans has been traditionally ascribed to the protozoan parasite Cryptosporidium parvum, on the basis of microscopical identification of oocysts or detection of oocyst wall antigens in faeces, and the assumption that all oocysts detected were monospecific [1]
Between January 2000 and December 2003, faecal samples in which Cryptosporidium was detected during routine diagnosis of diarrhoeal disease in publicly funded laboratories through out England and Wales were referred to the Cryptosporidium Reference Unit (CRU) in Swansea for typing to the species level
In this paper, long term, Cryptosporidium species-specific epidemiological analysis is described for the first time at a national level, demonstrating that aetiological identification of a large proportion of cryptosporidiosis cases is possible, and enhances the surveillance data provided by routine genus-level reporting
Summary
The aetiological agent of the diarrhoeal disease cryptosporidiosis in humans has been traditionally ascribed to the protozoan parasite Cryptosporidium parvum, on the basis of microscopical identification of oocysts or detection of oocyst wall antigens in faeces, and the assumption that all oocysts detected were monospecific [1]. C. parvum variants, recognised initially phenotypically (designated human or H and cattle or C types) and latterly through genomic studies, segregate into two genotypes (1 and 2), of which genotype 1 is host-adapted for humans [2]. This is assigned species status and called Cryptosporidium hominis and genotype 2 remains C. parvum [3]. These are the most commonly found species in human cryptosporidiosis worldwide, the distribution varies temporally and geographically [1]. The site-specific occurrence and pathogenicity of these unusual Cryptosporidium species/genotypes in humans appears to depend on a combination of endemnicity, exposure and parasiterelated factors rather than host immune status [7]
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