Modelling the transmission of gastrointestinal nematodes in saiga antelope under changing demography and climate.

  • Ben S Evans

Student thesis: Master's ThesisMaster of Science by Research (MScR)


The saiga antelope, Saiga tatarica, is a critically endangered migratory antelope that exists in the steppe and semi-deserts of Central Asia. Saigas host several gastrointestinal nematode (GIN) species, which can potentially affect their fecundity and fitness. The environment that this host-parasite system inhabits is highly seasonal, with extreme peaks of temperature and low and stochastic precipitation. With a large portion of their life cycle spent outside of the host, different GIN genera have contrasting adaptations to facilitate transmission in these highly variable conditions. To persist, GIN must overcome long periods of migratory host absence and large fluctuations in host demographics.

In this study, a mathematical model was constructed and calibrated to estimate the basic reproductive ratio (R0) of selected GIN species and examine how climatic factors affect their ability to propagate in these challenging conditions. The model was tested using climate and saiga demographic data from 1979 to 2017, and historical and new data on parasite prevalence and diversity in saigas in Kazakhstan, including those collected in the field in 2017 as part of the study.

Results suggest that transmission of Nematodirus and Marshallagia spp. benefit from seasonal aggregation of saigas, which maintains host density despite wide fluctuations in numbers and seasonal distribution, enabling parasite persistence. In contrast, R0 of trichostrongylids (represented by Haemonchus contortus) was frequently below the threshold for persistence due to periods of low host density and unfavourable climatic conditions. These genera are likely to rely on livestock presence within the saiga range to support persistence through spill-over and spill-back events. Host demography was more important in driving parasite persistence than changes in climate over the studied period. Predictions were supported by available data on parasite presence in saigas and fieldwork carried out as part of this study. Implications for conservation of threatened saiga populations are discussed.
Date of Award19 Mar 2019
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorEric R Morgan (Supervisor) & Richard Wall (Supervisor)

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