The response of Cryptosporidium parvum to UV light.

Ultraviolet (UV) light is being considered as a disinfectant by the water industry because it appears to be very effective for controlling potential waterborne pathogens, including Cryptosporidium parvum. However, many organisms have mechanisms such as nucleotide excision repair and photolyase enzymes for repairing UV-induced DNA damage and regaining preirradiation levels of infectivity or population density. Genes encoding UV repair proteins exist in C. parvum, so the parasite should be able to regain infectivity following exposure to UV. Nevertheless, there is an increasing body of evidence that the organism is unable to reactivate following UV irradiation. This paper describes the effective inactivation of C. parvum by UV light, identifies nucleotide excision repair genes in the C. parvum and Cryptosporidium hominis genomes and discusses the inability of UV-exposed oocysts to regain infectivity.

Irreversible UV inactivation of Cryptosporidium spp. despite the presence of UV repair genes.

Ultraviolet light is being considered as a disinfectant by the water industry because it appears to be very effective for inactivating pathogens, including Cryptosporidium parvum. However, many organisms have mechanisms for repairing ultraviolet light-induced DNA damage, which may limit the utility of this disinfection technology. Inactivation of C. parvum was assessed by measuring infectivity in cells of the human ileocecal adenocarcinoma HCT-8 cell line, with an assay targeting a heat shock protein gene and using a reverse transcriptase polymerase chain reaction to detect infections. Oocysts of five different isolates displayed similar sensitivity to ultraviolet light. An average dosage of 7.6 mJ/cm2 resulted in 99.9% inactivation, providing the first evidence that multiple isolates of C. parvum are equally sensitive to ultraviolet disinfection. Irradiated oocysts were unable to regain pre-irradiation levels of infectivity, following exposure to a broad array of potential repair conditions, such as prolonged incubation, pre-infection excystation triggers, and post-ultraviolet holding periods. A combination of data-mining and sequencing was used to identify genes for all of the major components of a nucleotide excision repair complex in C. parvum and Cryptosporidium hominis. The average similarity between the two organisms for the various genes was 96.4% (range, 92-98%). Thus, while Cryptosporidum spp. may have the potential to repair ultraviolet light-induced damage, oocyst reactivation will not occur under the standard conditions used for storage and distribution of treated drinking water.

Evaluation of in vitro and in vivo activity of benzindazole-4,9-quinones against Cryptosporidium parvum.

A series of benzindazole-4,9-quinones was tested for growth-inhibitory effects on Cryptosporidium parvum in vitro and in vivo. Most compounds showed considerable activity at concentrations from 25 to 100 micro M. For instance, at 25 micro M the derivatives 5-hydroxy-8-chloro-N1-methylbenz[f]-indazole-4,9-quinone and 5-chloro-N2-methylbenz[f]indazole-4,9-quinone inhibited growth of C. parvum 78-100%, and at 50 micro M seven of the 23 derivatives inhibited growth > or = 90%. The activity of the former two compounds was confirmed in a T-cell receptor alpha (TCR-alpha)-deficient mouse model of chronic cryptosporidiosis. In these mice, the mean infectivity scores (IS) in the caecum were 0.63-0.20, whereas in sham-treated mice the score was 1.44 (P < 0.05). There were similar differences in IS in the ileum, where the score for treated mice was 1.12-0.20 and that for mice receiving no drug was 1.32. There was no acute or chronic toxicity for any compound tested in vivo.