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

• Published in: Parasitology 2004-09, Vol.129 (3), p.363-369
• Main Authors: STEAR, M. J., BAIRDEN, K., INNOCENT, G. T., MITCHELL, S., STRAIN, S., BISHOP, S. C.
• Format: Article
• Language: English
• Subjects: Abomasum - parasitology; adult worms; Adults; Animals; antibody formation; Armor; Binomial Distribution; Biological and medical sciences; biological development; Confidence intervals; density dependence; disease severity; Female; frequency distribution; Fundamental and applied biological sciences. Psychology; General aspects; General aspects and techniques. Study of several systematic groups. Models; Generalized linear models; host-parasite relationships; humoral immunity; IgA; immunoglobulin A; Immunoglobulin A - blood; Immunoglobulin A - immunology; Infections; inhibited development; inhibition; Intestine, Small - parasitology; Invertebrates; lambs; Larva - growth & development; Larvae; larval inhibition; Linear Models; Male; nematode infections; nematode larvae; Nematodes; Parasites; Plasma; population density; Regression Analysis; Sheep; Sheep Diseases - immunology; Sheep Diseases - parasitology; Studies; Teladorsagia circumcincta; Trichostrongyloidea - growth & development; Trichostrongyloidea - immunology; Trichostrongyloidiasis - immunology; Trichostrongyloidiasis - parasitology; Trichostrongyloidiasis - veterinary
• ISSN: 0031-1820; 1469-8161
• DOI: 10.1017/S0031182004005736

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.