Parasitology



Tick-borne Great Island Virus: (II) Impact of age-related acquired immunity on transmission in a natural seabird host


M. A. NUNN a1c1, T. R. BARTON a2p1, S. WANLESS a2, R. S. HAILS a1, M. P. HARRIS a2 and P. A. NUTTALL a1
a1 NERC Centre for Ecology and Hydrology, Mansfield Road, Oxford OX1 3SR
a2 NERC Centre for Ecology and Hydrology, Hill of Brathens, Banchory, Kincardineshire, AB31 4BW

Article author query
nunn ma   [PubMed][Google Scholar] 
barton tr   [PubMed][Google Scholar] 
wanless s   [PubMed][Google Scholar] 
hails rs   [PubMed][Google Scholar] 
harris mp   [PubMed][Google Scholar] 
nuttall pa   [PubMed][Google Scholar] 

Abstract

Tick-borne pathogen transmission is dependent upon tick number per host and the physical and temporal distribution of each feeding stage. Age-related acquired immunity to tick and pathogen may also be important but has received less attention. In this study we evaluate which of these parameters has the greatest impact on Great Island Virus (GIV) transmission between Ixodes uriae ticks and common guillemots (Uria aalge). The study system is well suited to investigate age-related effects because the guillemot population is naturally divided into 2 groups, older breeding and younger pre-breeding adult birds. The physical distribution and timing of adult and nymphal tick feeding was similar for both guillemot age groups. However, breeding birds were parasitized by significantly more ticks (mainly nymphs). Calculations based on tick number predict virus prevalence should be higher in ticks that have fed on breeding rather than pre-breeding birds. However, empirical evidence indicates the reverse. Protective acquired immunity to GIV infection may be the reason why GIV prevalence is actually significantly lower in ticks that have fed on breeders. Far more breeding (74%) than pre-breeding (12%) guillemots had antibodies that neutralized 1 or more GIV strains. Estimates of the force of infection support the view that pre-breeding birds experience higher rates of virus infection than breeding birds. The results indicate age-related acquired immunity is a key factor in GIV transmission and highlight the need to consider age-related effects and host immunity when undertaking quantitative studies of tick-borne pathogen transmission.

(Received May 26 2005)
(Revised August 1 2005)
(Accepted August 3 2005)
(October 3 2005)


Key Words: age-related immunity; arbovirus; Uria aalge; virus transmission; tick; Ixodes uriae.

Correspondence:
c1 NERC Centre for Ecology and Hydrology, Mansfield Road, Oxford OX1 3SR. Tel: +44 (0)1865 281630. Fax: +44 (0)1865 281696. E-mail: amn@ceh.ac.uk
p1 Present address: University of Aberdeen, Lighthouse Field Station, George Street, Cromarty, Ross-Shire, IV11 8YJ


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