Aspects of Trichinella spiralis in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Studies in Epidemiology at Massey University
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Date
2006
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Massey University
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Abstract
In New Zealand, Trichinella spiralis appears absent from commercial pigs, and is not
a significant cause of zoonotic disease. Surveillance testing at slaughter has not ever
detected T. spiralis in a commercially raised pig in New Zealand, yet many importing
countries still require individual testing of all pig carcases for export. This thesis
comprises four studies designed to evaluate the risk of T. spiralis infection in
commercial pigs in New Zealand.
In the first study, the prevalence of T. spiralis was surveyed in selected populations
of rats, cats, stoats and weasels from landfills, piggeries and Department of
Conservation lands as they are considered potential reservoirs of T. spiralis for domestic
pigs. No positive samples were detected in this survey. The second study investigated
rodent activity and baiting efficacy on three commercial piggeries in the Manawatu
region of New Zealand over 72 weeks. This study found that while baiting and on-farm
sanitation can effectively control rodents, the efficacy of the control depends largely on
staff commitment.
The third study used a mail questionnaire sent to 123 piggeries, to survey current
management practices on commercial piggeries that could pose a risk for Trichinella
transmission. The survey had a 69% response rate and found that risky management
practices occur infrequently in commercial piggeries.
Lastly, a quantitative risk model was developed comparing individual carcass testing
with alternative risk management strategies to assess the annual probability that a
consumer in an importing country will eat a pork product of New Zealand origin
containing at least one larva per gram of T. spiralis. Offals were found to always be
safe. However, the unrestricted risk for fresh pork was over one in a million
(1.87x10-5), which was above the safety threshold and therefore various risk
management options were considered. The strategy of only exporting pigs reared in
certified, confined commercial herds has now been accepted and is in place by the
importing country. This means that individual carcass testing is no longer compulsory
for every exported pig carcass.The overall conclusion from this research established a very low risk of T. spiralis
infection and transmission in New Zealand commercial piggeries. These findings have
directly led to successfully changing export legislation by removing compulsory carcass
testing pre-export, which has advanced New Zealand’s ability to competitively export
high quality pork and pork products.
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Keywords
Trichinella spiralis, Pigs, Pig diseases, Trichinosis