AWWA PATH56555

Cryptosporidium is the most common cause of waterborne outbreaks of gastro-intestinal illness in the UK. Recently, molecular typing has contributed to the understanding of the epidemiology of cryptosporidiosis. Human disease is usually caused by C. parvum, in which two predominant genotypes occur. Genotype 1 is predominantly found in humans and genotype 2 has a broad range of human and animal hosts (Fayer et al., 2000). Thus the detection of genotype 1 indicates a high probability of a human source of infection or contamination and genotype 2 indicates either an animal or a human source. Other Cryptosporidium spp. infect humans and animals but may be indistinguishable from C. parvum by microscopy. In order to investigate the relationship between human, animal and environmental isolates, and further investigate the role of waterborne transmission, a holistic approach was used. In addition to providing support for outbreak investigations (Glaberman et al., 2002), molecular tools are being applied to clinical specimens and prospectively gathered samples from a variety of hosts and the environment in catchment defined areas, particularly catchments in the North West of England. This is complemented by the background provided by the national collection of Cryptosporidium oocysts established since January 2000, containing over 6,000 genomotyped human clinical isolates from England and Wales and by similar work in Scotland. The database supporting the collection contains a minimum data set of demographic and epidemiological information for each isolate, and identifies sample sets (indigenously acquired cases, those reporting foreign travel, those reporting immunocompromise, outbreaks, family clusters and so on) (Chalmers et al., 2002). In the first instance genomotypes are confirmed in faecal specimens using polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP) and PCR-sequencing to detect polymorphisms in the Cryptosporidium oocyst wall protein (Spano et al., 1997) and small subunit rRNA (Xiao et al, 1999; Morgan et al, 1997) genes. Methods are being developed to maximise both the recovery of cryptosporidial oocysts from environmental samples and DNA extraction, and are being investigated for specificity. A variety of molecular tools for further subtyping human, animal and environmental isolates are being evaluated, including single strand conformation polymorphism (Gasser et al., 2001), microsatellite markers (Caccio et al., 2000; Aiello et al., 1999) and sequence analysis of the GP60 gene (Strong et al., 2000) and will be applied to isolates. Data from these analyses will be combined with weather, land use and water quality data in a geographical information system for further analysis and interpretation. This work will further contribute to understanding host/parasite relationships, sources of infection and the significance of Cryptosporidium in the environment for consumer health. Includes 10 references.

Product Details

Edition:

Vol. - No.

Published:

09/22/2002

Number of Pages:

3

File Size:

1 file , 89 KB