Abstract
Paridae pox, a novel avipoxvirus infection, has recently been identified as an emerging infectious disease affecting wild tit species in Great Britain. The incursion of Paridae pox to a long-term study site where populations of wild tits have been monitored in detail for several decades provided a unique opportunity to obtain information on the local-scale epidemiological characteristics of this novel infection during a disease outbreak. Using captures of >8000 individual birds, we show that, within two years of initial emergence, Paridae pox had become established within the population of great tits (Parus major) reaching relatively high peak prevalence (10%), but was far less prevalent (<1%) in sympatric populations of several other closely related, abundant Paridae species. Nonlinear smoothing models revealed that the temporal pattern of prevalence among great tits was characterised by within-year fluctuations indicative of seasonal forcing of infection rates, which was likely driven by multiple environmental and demographic factors. There was individual heterogeneity in the course of infection and, although recovery was possible, diseased individuals were far less likely to be recaptured than healthy individuals, suggesting a survival cost of infection. This study demonstrates the value of long-term monitoring for obtaining key epidemiological data necessary to understand disease dynamics, spread and persistence in natural populations.
Highlights
Avian pox is a well-known viral disease of birds caused by dsDNA viruses in the genus Avipoxvirus, with a worldwide distribution and a wide host range [1]
Reports of avipoxvirus infections exist from multiple wild bird families and orders [1] and the disease is considered endemic in Great Britain (GB) in non-Paridae species, avian pox was unknown within the Paridae family in GB prior to the index case observed in Sussex, England, in 2006 [7]
We have shown that there are striking differences in the prevalence of pox infections among closely-related, sympatric Paridae species with very similar ecologies, that temporal variation in pox prevalence among great tits displays regular fluctuations indicative of seasonality in infection rates and, that while recovery is possible, diseased individuals are far less likely to be recaptured than are healthy individuals
Summary
Avian pox is a well-known viral disease of birds caused by dsDNA viruses in the genus Avipoxvirus, with a worldwide distribution and a wide host range [1]. The incubation period and duration of avian poxvirus infection is variable, but affected birds with mild lesions frequently recover and this is considered to be the most common situation in endemic areas [2]. Reports of avipoxvirus infections exist from multiple wild bird families and orders [1] and the disease is considered endemic in GB in non-Paridae species (e.g. common wood-pigeon Columba palumbus, dunnock Prunella modularis), avian pox was unknown within the Paridae family in GB prior to the index case observed in Sussex, England, in 2006 [7]. Spatio-temporal analysis of the nationwide incidence data, coupled with phylogenetic analysis of avian poxvirus core 4b gene sequences, showed that this novel ‘Paridae pox’ originated in south-east England following likely viral incursion from continental Europe and has since spread extensively throughout south and central England and into Wales [7]
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