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.
Department of Veterinary Clinical Studies, Institute of Comparative Medicine, University of Glasgow Veterinary School, Glasgow G61 1QH, Scotland, UK. gvma05@udcf.gla.ac.uk
M J
MJ
Stear
K
K
Bairden
G T
GT
Innocent
S
S
Mitchell
S
S
Strain
S C
SC
Bishop
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