|dc.description.abstract||This thesis studies aspects of the epidemiology of Nematodirus spathiger and
Nematodirus filicollis, both are common and potentially pathogenic parasites of lambs
in New Zealand. Three studies were undertaken; the first a presence/absence survey to
determine the distribution of the two species on farms, the second examined the
prevalence of benzimidazole (BZ) resistance in the two species and the third experiment
investigated the requirements for chilling for N. filicollis eggs to hatch.
The first two studies utilised faecal samples from routine faecal egg counts and/or
routine faecal egg count reduction testing on farms. To identify the Nematodirus species
involved, eggs from these samples were chilled and then incubated to facilitate hatching
of N. filicollis, before larvae were recovered. The identity of the larvae was determined
using PCR of the ITS-2 region of rDNA. The third experiment used a bulk collection of
N. filicollis from naturally infected lambs. Extracted eggs were incubated at
temperatures between 2.7°C - 9.9°C, for up to 224 days. The proportion of eggs
hatching was assessed against chill units. Chill units (degree-day) were calculated by
subtracting the culture temperature from a constant threshold of 11°C and multiplying
by the number of days for which the sample was cultured.
In Study 1, N. spathiger was present on all farms tested, while N. filicollis was found on
76% of farms. Both species were distributed throughout New Zealand, with no regional
differences. In Study 2, the BZ-resistance study, efficacies below 95% were recorded
for N. spathiger and N. filicollis on 95% (20/21) and 40% (4/10) respectively of farms
tested. In Study 3, the chilling experiment, the overall hatching of N. filicollis eggs was
low, but increased with chill accumulation to plateau at about 11%, with 800-1000 chill
units required for maximum hatching.
In conclusion the two species of Nematodirus were commonly found on most New
Zealand farms. The prevalence of BZ-resistance in N. filicollis was lower than that in N.
spathiger. N. filicollis required a considerable period of chilling to enable hatching to
occur and this will influence their epidemiology.||en_US