Evaluating the influence of epidemiological parameters and host ecology on the spread of phocine distemper virus through populations of harbour seals.

Catriona M Harris,Justin M J Travis,John Harwood,Matthew Baylis

doi:10.1371/journal.pone.0002710

Catriona M Harris, Justin M J Travis + Show 2 more

Open Access

https://doi.org/10.1371/journal.pone.0002710

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Journal: PloS one	Publication Date: Jul 16, 2008
Citations: 39	License type: CC BY 4.0

Affiliation: University of Aberdeen, University of St Andrews

Abstract

BackgroundOutbreaks of phocine distemper virus (PDV) in Europe during 1988 and 2002 were responsible for the death of around 23,000 and 30,000 harbour seals, respectively. These epidemics, particularly the one in 2002, provided an unusual opportunity to estimate epidemic parameters for a wildlife disease. There were marked regional differences in the values of some parameters both within and between epidemics.Methodology and Principal FindingsWe used an individual-based model of seal movement that allowed us to incorporate realistic representations of space, time and animal behaviour into a traditional epidemiological modelling framework. We explored the potential influence of a range of ecological (foraging trip duration, time of epidemic onset, population size) and epidemiological (length of infectious period, contact rate between infectious and susceptible individuals, case mortality) parameters on four readily-measurable epidemic characteristics (number of dead individuals, duration of epidemic, peak mortality date and prevalence) and on the probability that an epidemic would occur in a particular region. We analysed the outputs as if they were the results of a series of virtual experiments, using Generalised Linear Modelling. All six variables had a significant effect on the probability that an epidemic would be recognised as an unusual mortality event by human observers.ConclusionsRegional and temporal variation in contact rate was the most likely cause of the observed differences between the two epidemics. This variation could be a consequence of differences in the way individuals divide their time between land and sea at different times of the year.

Highlights

Phocine distemper virus (PDV) was first identified in 1988 when it killed more than 23,000 harbour seals around Europe [1,2,3,4]
These data can be used to determine the number of individuals that came into contact with the disease, the contact rate and the case mortality for each local population [11]
The number of dead individuals, prevalence and the proportion of replicates where a detectable epidemic occurred all increased with increasing contact rate, whereas DOE and PMD decreased with increasing contact rate

Summary

Introduction

Phocine distemper virus (PDV) was first identified in 1988 when it killed more than 23,000 harbour seals around Europe [1,2,3,4]. An estimated 30,000 harbour seals died in the 2002 epidemic, again within a 9 month period [5] In both epidemics, intensive effort was made to ensure that the numbers of dead animals washed ashore were recorded, together with additional information on their species, sex and age [4,7,8]. Intensive effort was made to ensure that the numbers of dead animals washed ashore were recorded, together with additional information on their species, sex and age [4,7,8] These data have been used to estimate basic epidemiological parameters for both years on a regional basis. There were marked regional differences in the values of some parameters both within and between epidemics

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Conclusion