Modelling macroparasite aggregation using a nematode-sheep system: the Weibull distribution as an alternative to the...

Area of Science:

• Parasitology
• Statistical Ecology
• Veterinary Epidemiology

Background:

• Macroparasites typically exhibit aggregated distributions within host populations.
• The Negative Binomial Distribution (NBD) is commonly used for modeling parasite aggregation.
• Limitations of NBD include sensitivity to mean parasite load and under-representation of heavily infected hosts.

Purpose of the Study:

• To compare the goodness-of-fit of the NBD with four other distributions for gastrointestinal nematode data in sheep.
• To evaluate the suitability of different statistical distributions for modeling parasite aggregation.
• To assess the impact of sample size on parameter estimation bias.

Main Methods:

• Fitted five probability distributions (including NBD and Weibull) to 11 sheep gastrointestinal nematode datasets.
• Employed maximum likelihood estimation for parameter fitting.
• Utilized Akaike's Information Criterion (AIC) for model selection.
• Conducted simulation studies to evaluate parameter estimation bias.

Main Results:

• The NBD was rarely the best-fitting distribution for the observed gastrointestinal nematode data.
• The Weibull distribution demonstrated superior fit across various aggregation levels.
• Weibull distribution showed greater flexibility in accommodating heavily infected hosts.
• Weibull distribution parameter estimates exhibited less sensitivity to sample size variations.

Conclusions:

• The NBD may not be the most appropriate model for all parasite distribution data.
• The Weibull distribution is a more flexible and robust alternative for modeling gastrointestinal nematode aggregation in sheep.
• Researchers should validate the suitability of the NBD before its application in parasite distribution analyses.