Variation in hatching responses of Nematodirus battus eggs to temperature experiences

Abstract

Background Nematodirus battus, unlike most other gastrointestinal nematodes, undergoes maturation to an infective larva within the egg. Historically, eggs were considered to require a period of chilling over winter followed by a period of temperature above 10 °C for synchronous hatching to occur (generally in spring). Anecdotal reports of Nematodirus infection out-with spring in veterinary journals and the farming press suggest that the concentrated pasture abundance of N. battus infective larvae may be changing. In order for control practices to be adapted, and unexpected disease outbreaks to be avoided, it is important to quantify how parasite epidemiology is changing and research the drivers behind it. Method The present study investigated the in vitro hatching response to temperature experiences (with and without a period of chilling) for egg samples of 90 N. battus populations obtained from 73 commercial sheep farms. Six aliquots of larvated eggs were prepared per population, three aliquots were placed at 4 °C for 6 weeks to provide a chill stimulus then incubated at the optimal hatching temperature for the species. The remaining three aliquots of eggs were incubated at the hatching temperature without a prior chill stimulus and the number of hatched larvae was compared between treatments. Results Median hatch rate across all populations with chilling was 45% (95% CI: 42–48%) and without chilling was 4% (95% CI: 2–6%). Inter-population variation in hatching ranged from 0 to 87% of eggs able to hatch in the absence of a chill stimulus, mean non-chill hatching was 13 ± 2% of eggs (mean ± SE). Non-chill hatching rates were greater than chilled hatching rates in seven of the 90 populations tested. Conclusions Clearly, the variation in hatching responses to temperature experience is very large and therefore the seasonality of the parasite may vary not only between regions but also at farm level. In contrast to what previous work has suggested, there was a geographical trend towards higher non-chill hatching in the Northern parts of the UK.

Descriptive analysis of nematode management practices and Nematodirus battus control strategies on UK sheep farms

“…10 Changes in the dynamics, life history traits, timing of infection and pathogenicity of helminth infections have been reported in recent years and such variation has been particularly evident in Nematodirus battus, an economically important parasite which threatens lamb health and sheep farming sustainability in the UK. With apparent changes in epidemiology of N. battus and the emergence of BZ-resistance in this species, [11][12][13][14] it provides an interesting case study to explore variation throughout the country. It is important to understand variation in disease observed on farm, current management practices employed and the rationale behind these control strategies to support the development of optimised control practices in the future.…”

Climate change effects on terrestrial parasitic nematodes: Where are the knowledge gaps?

“…Temperature effects (studied in laboratory) on hatching (n p = 8, n r = 18, ) (Crofton 1965; Melville et al . 2020), development (n p = 14, n r = 29, ) (Ciordia & Bizell 1963; Gyeltshen et al . 2022), and survival (n p = 15, n r = 19, ) (Gardner et al .…”

Changing patterns of Nematodirus battus infection

“…The presence of the nonchilling eggs changes the hatching dynamics and creates a new transmission window. On most UK farms in a recent study, the numbers of hatched eggs hav been shown to be higher with a chilling stimulus, but on some farms, independent of geographic location, non-chilling hatching is the predominant mechanism (Melville et al, 2020). Changes in the hatching patterns of N. battus are probably due to genetic adaptation to factors such as climate change, grazing management and farming practices.…”