Genetic characterisation and transmission cycles of cryptosporidium species isolated in New Zealand : a thesis presented in partial fulfilment of the requirements of the degree of Master of Science in Microbiology at Massey University, Palmerston North, New Zealand
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Date
2004
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Massey University
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Abstract
Sixty-nine years separated the first observation of Cryptosporidium by Tyzzer in 1907 from the realisation in 1976 that this enteric protozoan parasite was pathogenic. It is the third major cause of diarrhoeal disease worldwide causing a self-limiting infection in immuno-competent humans and young vertebrates. As yet there is no antimicrobial agent that combats Cryptosporidium so the organism poses a life threatening risk to the immuno-compromised e.g., AIDS patients, patients on immuno-suppressive drugs, chemotherapy or congenital immune deficiencies. By 2000 AD 152 species of mammals had been reported as being infected with Cryptosporidium plus 57 reptilian species and many birds and fish. The advent of AIDS stimulated research into Cryptosporidium resulting in the large amount of information now becoming available, however 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 1613 animal faecal samples and 423 human faecal specimens containing Cryptosporidium oocysts were collected from throughout New Zealand and examined by the polymerase chain reaction - restriction fragment length polymorphism technique (PCR-RFLP). Indeterminant results were resolved by DNA sequence analysis of the small subunit ribosomal DNA (rDNA). Only 2.8% of the animal faecal specimens contained oocysts with the vast majority of these being C. parvum bovine genotype from calves. Two regions supplied the majority of human isolates, one rural and one urban. Overall C. hominis accounted for 47% of all human isolates with the remaining 53% being 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 while 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, that 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.
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Keywords
New Zealand, Cryptosporidium, Genetics, Analysis