The Evolution of sheep immunity in response to nematode infection
Date
2019-08
Authors
Cameline, Orlendo
Journal Title
Journal ISSN
Volume Title
Publisher
Strathmore University
Abstract
There is considerable variation in the distribution of the number of parasites amongst
a flock of lambs infected with gastrointestinal nematodes. One hypothesis that could
explain the observed heterogeneity is that hosts evolve immune phenotypes of varying
strengths when infected. The acquired immune response that is mounted by infected
lambs is composed of two components. The IgE immune component which regulates
parasite numbers within a host, and the IgA immune component which lowers adult
parasite fecundity rates, hence decreasing the number of infective agents that are
released by the host back into the communal pasture area. In this study, we use adaptive
dynamics to study the evolution of the IgE and IgA immune phenotypes, and we use
lamb weight as a measure of host fitness. We found that processes affecting the
evolution of the lamb immune phenotypes are: the assumed trade-off relationship
between the IgE and IgA immune responses, variation in immune costs, and the
sensitivity of host maintenance efficiency to the presence of adult nematodes and
seasonality. A key finding is that we can obtain a dimorphic population that emulates
field studies when the presence of adult nematodes severely reduces hosts maintenance
efficiency, and the IgE cost is low while the IgA cost is high. Overall, this study
provides insight on the processes that could lead to variation in immune phenotypes of
lambs infected with nematode parasites.
Description
Paper presented at the 5th Strathmore International Mathematics Conference (SIMC 2019), 12 - 16 August 2019, Strathmore University, Nairobi, Kenya
Keywords
Immunity, Nematode infection, Thade-off