Epidemiology of nematode infections of Soay sheep (Ovis ariesL.) on St Kilda

Abstract

The epidemiology of nematode infections of Soay sheep on the island of St Kilda over a period of 2 years (August 1988-August 1990) spanning a host population crash is described. Infective larvae (L3) levels on pasture were high (2422 +/- 365 L3/kg D.M. grass in midsummer 1988) when host population density was high, decreasing after the sheep population declined by 70% in early 1989 (601 +/- 14 L3/kg D.M. in midsummer 1989). The availability of infective larvae to sheep increased during the winter of 1988-1989, probably as a result of concentration of existing larvae on grass as vegetation was destroyed by bad weather and overgrazing. Increased availability of pre-parasitic stages was accompanied by a marked increased in faecal egg counts from sheep of all ages and both sexes. Prevalence and intensity of infection (faecal egg counts) were higher in males than females throughout the 2-year study (chi 2 = 208.3, P < 0.005 and F1, 2000 = 304, P < 0.001 respectively), except during the lambing periods, and decreased with age in both sexes. Changes in prevalence and intensity of strongyle infections were associated with changes in host population density. Prevalence and intensity of Dictyocaulus filaria larvae in faeces increased during the host population crash. Infection intensity decreased with age (F1, 203 = 44.02, P < 0.001) and was higher in males than females (F1, 203 = 13.45, P < 0.001).

Response to Teladorsagia circumcincta infection in Scottish Blackface lambs with divergent phenotypes for nematode resistance

“…This may also account for the very low FEC values observed over the course of infection. Female lambs also have a stronger immune response than males, who are less resistant to the establishment of infection (Barger, 1993;Gulland and Fox, 1992).…”

Cellular and humoral immunity in a wild mammal: Variation with age & sex and association with overwinter survival

“…The population exhibits a distinctive, unstable dynamic characterized by low and rising sheep numbers followed by high mortality (“crash”) winters in which more than half of the population may perish (Clutton‐Brock & Pemberton, 2004). High mortality winters are associated with strong selection on a range of phenotypic traits and are thought to result from a combination of low food availability due to competition, harsh winter climate conditions, and parasite pressure, predominantly from Strongyle gastrointestinal nematodes (GINs) (Coulson, 2001; Gulland, 1992; Gulland & Fox, 1992). Age‐related variation is well understood in this population, with differences evident between lambs, yearlings, prime age adults (2–6 years), and geriatrics (>6 years) in demographic rates and phenotypic traits both within and among the sexes (Coulson, 2001).…”

“…Upon capture, each individual was weighed and measured and then blood and fecal samples were collected. Fecal samples were used to measure Strongyle and Strongyloides parasite fecal egg counts (FEC), using a modification of the McMaster technique (Gulland & Fox, 1992; Ministry of Agriculture Fisheries and Food 1971). Two 9‐ml Li‐heparin Vacutainer tubes of whole blood were taken from each individual and stored at 4°C until processing.…”

Prevalence of gastrointestinal helminths of sheep in Sherpur, Bangladesh

“…Factually, females are more vulnerable to parasitic infections during parturient and peri-parturient period due to stress and reduced immune status (Urquhart et al, 1996). Mostly, all males were grazed more compared to females as the latter did not graze during parturient period, so that, infection is chiefly found in male than female (Gulland and Fox, 1992 …”