Persistence thresholds for phocine distemper virus infection in harbour seal Phoca vitulina metapopulations

Abstract

Summary 0[ This paper explores the concept of the critical community size for persistence of infection in wildlife populations[ We use as a case study the 0877 epidemic of phocine distemper virus in the North Sea population of harbour seals\ Phoca vitulina[ 1[ We summarize the available data on this epidemic and use it to parameterize a stochastic compartmental model for an infection spreading through a spatial array of patches coupled by nearest!neighbour mixing\ with replacement of susceptibles occurring as a discrete annual event[ 2[ A combination of analytical and simulation techniques is used to show that the high levels of transmission between di}erent seal subpopulations\ combined with the small annual birth cohort\ act to make persistence of infection impossible in this harbour seal population at realistic population levels[ The well known mechanisms by which metapopulation structures may act to promote persistence can be seen to have an e}ect only at weaker levels of spatial coupling\ and higher levels of host recruitment\ than those empirically observed[ We ask which of the variables of this critical meta! Reviewing that mass mortality\ Hall "0884# com! population distribution are central in determining per! mented that {if PDV behaves like other morbilliviruses sistence] for example\ is it more important to know it should have been eliminated from the North Sea\ patch population sizes\ the number of patches\ the because the surviving population of susceptible ani! level of interpatch mixing or the total population size< mals is too small to allow the disease to persist or to Metapopulation theory has been used to estimate the permit the establishment of a new epidemic|[ This minimum amount of suitable habitat Ð MASH "Han! concept of a threshold susceptible population has been ski\ Moilanen + Gyllenberg 0885# Ð necessary for a a central one in ecological epidemiology since the population to persist[ On the other hand\ conservation work of Bartlett on measles 39 years ago "Bartlett biologists have attempted to estimate the minimum size necessary for a population to have a particular 0845# and much theoretical work has been concerned to establish that persistence properties can be strongly probability of persisting for a certain length of time "the minimum viable population\ MVP "Soule 0876dependent on mixing structure[ In this paper we use the PDV example to study how the mixing that arises Bjo Ârge\ Steen + Stenseth 0883##[ The fact that the theoretical relationship between patch size and local from a patchy host population a}ects persistence[ A common theoretical approach to this problem is to extinction is well understood in an epidemiological setting has enabled us to investigate the way in which interpret the host patches as habitat patches of a pathogen metapopulation "Hanski + Gilpin 0880#[ local and total population size interact in determining

Long-term monitoring of classical swine fever in wild boar (Sus scrofa sp.) using serological data

“…Contact between wild boars and domestic pigs are assumed to favour CSF persistence in Nuoro [24,25,30]. In our present case, conditions favourable to persistence could be a high host density, a high host birth rate or an optimal contact structure between the host social groups [33,36,37]. Additionally, we propose that infection persistence may be a dynamic phenomenon.…”

“…Consequently, we also supposed that we overestimated incidence in yearlings in 1993. Since juveniles constitute the most susceptible class, we interpreted the absence of seropositive juveniles in 2001 as a break in the chain of transmission from 2000 to 2001 [36]. These findings highlight the reliability of serological compared to virological diagnoses: CSF transmission could be detected using observations of seropositive juveniles until 2000, Table IV.…”

Evidence of Psittacine Beak and Feather Disease Virus Spillover Into Wild Critically Endangered Orange-Bellied Parrots (Neophema Chrysogaster)

“…The threshold susceptible population size required to maintain BFDV endemically in psittacine populations is unknown but, with less than 50 individuals, the wild population of Orange-bellied Parrots is almost certainly too small to maintain one, let alone two, BFDV genotypes on its own (Raidal et al, 1993(Raidal et al, , 1998Swinton et al, 1998). Nevertheless, the three wild birds we investigated represent more than 6% of the wild population of this species.…”

Spatially Explicit Conditions for Waterborne Pathogen Invasion

“…Similarly, susceptible individuals can be infected by pathogens far from their home sites when traveling or commuting. While metapopulation dynamics was incorporated into traditional SI or SIR models many years ago (Bolker and Grenfell 1995;Swinton et al 1998;Gog et al 2002;Arino et al 2005), the addition of human mobility to spatial models of waterborne diseases is more recent. This has been accomplished via either diffusion-based or gravity-like models Chao et al 2011;Tuite et al 2011;Gatto et al 2012;Mari et al 2012aMari et al , 2012bRinaldo et al 2012).…”