Asynchrony in host and parasite phenology may decrease disease risk in livestock under climate warming: Nematodirus battus in lambs as a case study.

Mismatch in the phenology of trophically linked species as a result of climate warming has been shown to have far-reaching effects on animal communities, but implications for disease have so far received limited attention. This paper presents evidence suggestive of phenological asynchrony in a host-parasite system arising from climate change, with impacts on transmission. Diagnostic laboratory data on outbreaks of infection with the pathogenic nematode Nematodirus battus in sheep flocks in the UK were used to validate region-specific models of the effect of spring temperature on parasite transmission. The hatching of parasite eggs to produce infective larvae is driven by temperature, while the availability of susceptible hosts depends on lambing date, which is relatively insensitive to inter-annual variation in spring temperature. In southern areas and in warmer years, earlier emergence of infective larvae in spring was predicted, with decline through mortality before peak availability of susceptible lambs. Data confirmed model predictions, with fewer outbreaks recorded in those years and regions. Overlap between larval peaks and lamb availability was not reduced in northern areas, which experienced no decreases in the number of reported outbreaks. Results suggest that phenological asynchrony arising from climate warming may affect parasite transmission, with non-linear but predictable impacts on disease burden. Improved understanding of complex responses of host-parasite systems to climate change can contribute to effective adaptation of parasite control strategies.

A survey of the prevalence of Nematodirus spathiger and N. filicollis on farms in the North and South Islands of New Zealand.

AIM: To compare the prevalence of Nematodirus spathiger and N. filicollis on a sample of farms in the lower South Island with the lower and central North Island of New Zealand by way of a presence/absence survey. METHODS: A presence/absence non-random survey was conducted in which pooled faeces from lambs from 50 farms in the lower and central North Island (n=22) and lower South Island (n=28) were cultured, with and without a post-culture period of chilling, to produce third-stage parasitic nematode larvae (L3). After recovery using the Baermann technique, individual L3 were identified to Nematodirus spp. using a PCR assay. This identified the species that were present on each farm that were then used to compare the regions. RESULTS: Nematodirus filicollis was present in 38/50 (76%) samples from which Nematodirus spp. larvae were cultured, compared with 50/50 (100%) in the case of N. spathiger. No regional differences were observed in the prevalence of either species (p=0.74). Of the Nematodirus spp. L3 recovered from the unchilled samples, 415/428 (97%) were N. spathiger and 13/428 (3%) N. filicollis. After chilling 594/695 (85%) of the Nematodirus spp. L3 were N. spathiger and 101/695 (15%) were N. filicollis. CONCLUSION: Despite the non-random nature of the study, the evidence suggests that both these species are likely to occur sympatrically on most sheep farms throughout New Zealand. In general N. filicollis eggs did not hatch without a period of chilling and this has implications for the identification of these larvae using conventional culture methods.