The distribution of the pathogenic nematode Nematodirus battus in lambs is zero-inflated

TY - JOUR

T1 - The distribution of the pathogenic nematode Nematodirus battus in lambs is zero-inflated

AU - Denwood, Matthew

AU - Stear, M J

AU - Matthews, L

AU - Reid, S W J

AU - Toft, Nils

AU - Innocent, G T

PY - 2008

Y1 - 2008

N2 - Understanding the frequency distribution of parasites and parasite stages among hosts is essential for efficient experimental design and statistical analysis, and is also required for the development of sustainable methods of controlling infection. Nematodirus battus is one of the most important organisms that infect sheep but the distribution of parasites among hosts is unknown. An initial analysis indicated a high frequency of animals without N. battus and with zero egg counts, suggesting the possibility of a zero-inflated distribution. We developed a Bayesian analysis using Markov chain Monte Carlo methods to estimate the parameters of the zero-inflated negative binomial distribution. The analysis of 3000 simulated data sets indicated that this method out-performed the maximum likelihood procedure. Application of this technique to faecal egg counts from lambs in a commercial upland flock indicated that N. battus counts were indeed zero-inflated. Estimating the extent of zero-inflation is important for effective statistical analysis and for the accurate identification of genetically resistant animals.

AB - Understanding the frequency distribution of parasites and parasite stages among hosts is essential for efficient experimental design and statistical analysis, and is also required for the development of sustainable methods of controlling infection. Nematodirus battus is one of the most important organisms that infect sheep but the distribution of parasites among hosts is unknown. An initial analysis indicated a high frequency of animals without N. battus and with zero egg counts, suggesting the possibility of a zero-inflated distribution. We developed a Bayesian analysis using Markov chain Monte Carlo methods to estimate the parameters of the zero-inflated negative binomial distribution. The analysis of 3000 simulated data sets indicated that this method out-performed the maximum likelihood procedure. Application of this technique to faecal egg counts from lambs in a commercial upland flock indicated that N. battus counts were indeed zero-inflated. Estimating the extent of zero-inflation is important for effective statistical analysis and for the accurate identification of genetically resistant animals.

KW - Animals

KW - Bayes Theorem

KW - Female

KW - Male

KW - Markov Chains

KW - Monte Carlo Method

KW - Nematode Infections

KW - Parasite Egg Count

KW - Scotland

KW - Sheep

KW - Sheep Diseases

U2 - 10.1017/S0031182008004708

DO - 10.1017/S0031182008004708

M3 - Journal article

C2 - 18620622

SN - 0031-1820

VL - 135

SP - 1225

EP - 1235

JO - Parasitology

JF - Parasitology

IS - 10

ER -