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

MJ Stear*, K Bairden, GT Innocent, S Mitchell, S Strain, SC Bishop

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

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; h was low when mean infection intensity was low but higher when mean infection intensity was high. As h 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.

Original languageEnglish
Pages (from-to)363-369
Number of pages7
JournalParasitology
Volume129
DOIs
Publication statusPublished - Sep 2004

Keywords

  • Teladorsagia circumcincta
  • density dependence
  • inhibition
  • IgA
  • sheep
  • OSTERTAGIA-CIRCUMCINCTA
  • INHIBITED DEVELOPMENT
  • NEMATODE INFECTIONS
  • IMMUNE-RESPONSES
  • EGG COUNTS
  • LAMBS
  • RESISTANCE
  • POPULATIONS
  • AGGREGATION
  • PARASITES

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