Zero-inflated hierarchical models for faecal egg counts to assess anthelmintic efficacy

Abstract

The prevalence of anthelmintic resistance has increased in recent years, as a result of the extensive use of anthelmintic drugs to reduce the infection of parasitic worms in livestock. In order to detect the resistance, the number of parasite eggs in animal faeces is counted. Typically a subsample of the diluted faeces is examined, and the mean egg counts from both untreated and treated animals are compared. However, the conventional method ignores the variabilities introduced by the counting process and by different infection levels across animals. In addition, there can be extra zero counts, which arise as a result of the unexposed animals in an infected population or animals. In this paper, we propose the zero inflated Bayesian hierarchical models to estimate the reduction in faecal egg counts. The simulation study compares the Bayesian models with the conventional faecal egg count reduction test and other methods such as bootstrap and quasi-Poisson regression. The results show the Bayesian models are more robust and they perform well in terms of both the bias and the coverage. We further illustrate the advantages of our proposed model using a case study about the anthelmintic resistance in Swedish sheep flocks. (C) 2017 The Authors. Published by Elsevier B.V.

Keywords

Bayesian hierarchical model; Faecal egg count reduction test; Anthelmintic resistance; Zero-inflated models; Statistical analysis

Published in

Veterinary Parasitology
2017, volume: 235, pages: 20-28
Publisher: ELSEVIER SCIENCE BV

SLU Authors

• Höglund, Johan

  • Department of Animal Biosciences, Swedish University of Agricultural Sciences
    

Associated SLU-program

AMR: Parasite

UKÄ Subject classification

Pathobiology

Publication identifier

• DOI: https://doi.org/10.1016/j.vetpar.2016.12.007

Permanent link to this page (URI)

https://res.slu.se/id/publ/94206