GENOTYPING OF HUMAN CRYPTOSPORIDIUM INFECTIONS IN AUSTRALIA

Abstract

Cryptosporidium parvum is now recognised as being responsible for around 2% of gastroenteritis cases in the immunocompetent population in developed nations, as well as being a significant cause of morbidity in immunocompromised hosts with depressed T-cell function. The resistance of Cryptosporidium oocysts to chlorine-based disinfectants creates particular concerns for drinking water supplies, and numerous outbreaks of cryptosporidiosis have been recorded from both drinking water and recreational water sources in parts of Europe and North America. In Australia, there have been a number of swimming pool-associated outbreaks of cryptosporidiosis, and only one drinking water outbreak from a small private water supply has been documented. Two genotypes of Cryptosporidium parvum have been identified as the major cause of infections in immunocompetent humans. Genotype 1 (or H), appears to infect humans specifically, whereas genotype 2 (or C) may infect humans and a range of other mammals (including cattle, sheep and goats). Species other than C. parvum have been reported to be responsible for up to 20% of infections in immunocompromised hosts, and there is emerging evidence that such species are also responsible for a minority of infections in the immunocompetent human population. We carried out case-control studies of cryptosporidiosis in Melbourne (with high quality source water treated by chlorination only) and Adelaide (with poor quality source water treated by conventional flocculation, sedimentation, filtration and chlorination). The results indicated that drinking tap water was not a significant risk factor for cryptosporidiosis in either city, but that person-to-person transmission and public swimming pools were the main sources of public health risk. Cryptosporidium isolates from participants in the Adelaide case-control study were characterised genetically using single strand conformation polymorphism analysis of the small subunit gene (pSSU; ∼300bp) and second internal transcribed spacer (pITS-2; 230bp) of nuclear ribosomal DNA. Of 26 isolates characterised to date, 15 (58%) were identified as C. parvum genotype 1, 9 (35%) were C. parvum genotype 2 and 2 (7.5%) were C. meleagridis. Neither of the people infected with C. meleagridis had reported any illness or condition affecting the immune system when interviewed for the case-control study. These results support observations from Europe that a small proportion of Cryptosporidium infections in immunocompetent people are caused by species other than C. parvum, in particular C. meleagridis. Acknowledgment: This work was funded by the CRC for Water Quality and Treatment, the Water Services Association of Australia, Melbourne Water Corporation, City West Water Ltd, South East Water Ltd and Yarra Valley Water Ltd.