The relationship between IgA activity against 4th-stage larvae and density-dependent effects on the number of 4th-stage larvae of Teladorsagia circumcincta in naturally infected sheep.
The number of Teladorsagia circumcincta 4th-stage larvae in naturally infected lambs from a single farm varied among lambs and among different years. Within each year the distribution of 4th-stage larvae among lambs was similar to that expected from a negative binomial distribution. The ratio of 4th-stage larvae to adult T. circumcincta was low in two years with a low mean intensity of infection but high in two years with a higher mean intensity of infection. The negative binomial distribution is defined by the mean and by k, a parameter that measures dispersion; k was low when mean infection intensity was low but higher when mean infection intensity was high. As k is an inverse index of overdispersion this indicated that the distribution of 4th-stage larvae was more overdispersed at low levels of infection. In a combined analysis, the number of adult T. circumcincta and the plasma IgA activity against 4th-stage larvae were both associated with increased numbers of 4th-stage larvae. There was a statistical interaction between the number of adults and IgA activity that moderated their combined effect.
Stear
M J
MJ
Department of Veterinary Clinical Studies, Institute of Comparative Medicine, University of Glasgow Veterinary School, Glasgow G61 1QH, Scotland, UK. gvma05@udcf.gla.ac.uk
Bairden
K
K
Innocent
G T
GT
Mitchell
S
S
Strain
S
S
Bishop
S C
SC
D000018:Abomasum / Q000469:parasitology; D000818:Animals; D016010:Binomial Distribution; D005260:Female; D007070:Immunoglobulin A / Q000097:blood / Q000276:immunology*; D007421:Intestine, Small / Q000469:parasitology; D007814:Larva / Q000254:growth & development; D016014:Linear Models; D008297:Male; D012044:Regression Analysis; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology* / Q000469:parasitology*; D014251:Trichostrongyloidea / Q000254:growth & development* / Q000276:immunology; D014252:Trichostrongyloidiasis / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*
D007070:Immunoglobulin A