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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 online by Cambridge University Press:  23 August 2004

M. J. STEAR ,
K. BAIRDEN ,
G. T. INNOCENT ,
S. MITCHELL ,
S. STRAIN  and
S. C. BISHOP
M. J. STEAR
Affiliation:
Department of Veterinary Clinical Studies, Institute of Comparative Medicine, University of Glasgow Veterinary School, Bearsden Road, Glasgow G61 1QH, Scotland, UK
K. BAIRDEN
Affiliation:
Department of Veterinary Clinical Studies, Institute of Comparative Medicine, University of Glasgow Veterinary School, Bearsden Road, Glasgow G61 1QH, Scotland, UK
G. T. INNOCENT
Affiliation:
Department of Veterinary Clinical Studies, Institute of Comparative Medicine, University of Glasgow Veterinary School, Bearsden Road, Glasgow G61 1QH, Scotland, UK
S. MITCHELL
Affiliation:
Department of Veterinary Clinical Studies, Institute of Comparative Medicine, University of Glasgow Veterinary School, Bearsden Road, Glasgow G61 1QH, Scotland, UK
S. STRAIN
Affiliation:
Department of Veterinary Clinical Studies, Institute of Comparative Medicine, University of Glasgow Veterinary School, Bearsden Road, Glasgow G61 1QH, Scotland, UK
S. C. BISHOP
Affiliation:
Roslin Institute (Edinburgh), Roslin, Midlothian EH25 9PS, Scotland, UK
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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; 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.

Keywords

Teladorsagia circumcinctadensity dependenceinhibitionIgAsheep
Type
Research Article
Information
Parasitology , Volume 129 , Issue 3 , September 2004 , pp. 363 - 369
Copyright
© 2004 Cambridge University Press

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