Living with parasites: exploring tolerance of infection to reduce the impact of gastrointestinal nematodes on sheep

Host organisms have two major strategies to mitigate the damaging effects of parasites: resistance, where they reduce the within-host parasite burden, and tolerance, where they limit the health-limiting effects of parasites without necessarily damaging the parasites themselves. Research on important livestock diseases, including gastrointestinal nematodes (GINs) of sheep, have focused mainly on resistance, while largely neglecting tolerance, despite many sources advocating the potential use of tolerance as a disease management strategy. A major obstacle is the lack of understanding of the basic biology of tolerance, its association with immunity, its genetic basis, its response to nutrition, and its effect on animal performance.

This PhD project will aim to address some of these questions using data from a variety of sources. These include data on infection, immune responses and body weight from housed lambs; weight and infection data from different genetic lines; and data from grazing animals monitored on different kinds of pasture from early life on the Moredun Research Institute farm. Data planned for collection on this last project include animal genotype, growth, and parasite burden, but there is considerable opportunity for the studentship to add to the data collected throughout the course of the studentship, enabling the student to choose the direction of their study. Questions that this PhD project could address include:

1. To what extent does tolerance vary among animals?
2. Is there a genetic basis to tolerance of infection?
3. How is tolerance associated with immune-mediated resistance to infection?
4. To what extent is tolerance associated with grazing conditions?
5. To what extent is tolerance of different parasites correlated?
6. How do resistance and tolerance strategies evolve across early life?
7. To what extent does tolerance influence pasture contamination?

The student would have the opportunity to engage in a broad range of research activities, including parasitology, immunology, quantitative genetics, and there will be a strong statistical component. There would also be the opportunity to incorporate mathematical modelling should the student wish to drive the project in that direction.