Genetic characterization and transmission cycles of Cryptosporidium species isolated from humans in New Zealand

Abstract

Little is known about the genetic characteristics, distribution, and transmission cycles of Cryptosporidium species that cause human disease in New Zealand. To address these questions, 423 fecal specimens containing Cryptosporidium oocysts and obtained from different regions were examined by the PCR-restriction fragment length polymorphism technique. Indeterminant results were resolved by DNA sequence analysis. Two regions supplied the majority of isolates: one rural and one urban. Overall, Cryptosporidium hominis accounted for 47% of the isolates, with the remaining 53% being the C. parvum bovine genotype. A difference, however, was observed between the Cryptosporidium species from rural and urban isolates, with C. hominis dominant in the urban region, whereas the C. parvum bovine genotype was prevalent in rural New Zealand. A shift in transmission cycles was detected between seasons, with an anthroponotic cycle in autumn and a zoonotic cycle in spring. A novel Cryptosporidium sp., which on DNA sequence analysis showed a close relationship with C. canis, was detected in two unrelated children from different regions, illustrating the genetic diversity within this genus.

FIG. 1.

DNA sequence alignment through the variable region of the Cryptosporidium 18S rDNA, including the novel isolates 2683 and 2893 and the rabbit isolate. Nucleotide position is based on the 734-bp length of aligned sequence and, depending on gaps in the individual sequences, the actual positions are an approximation.

FIG. 2.

Neighbor-joining tree analysis of Cryptosporidium 18S rDNA showing the phylogenetic relationship of two novel isolates to others in the genus. Analysis was based on genetic distances calculated by the general time-reversible model. C. serpentis was used as an outgroup with 1,000 bootstrap pseudoreplications.

FIG.3.

Seasonal shift in transmission route between C. parvum and C. hominis human infections.

FIG.4.

National monthly number of human cryptosporidiosis cases since the disease became notifiable in July 1996.