Intranasal Infection with Chlamydia abortus Induces Dose-Dependent Latency and Abortion in Sheep |
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| Authors: | David Longbottom Morag Livingstone Stephen Maley Arjan van der Zon Mara Rocchi Kim Wilson Nicholas Wheelhouse Mark Dagleish Kevin Aitchison Sean Wattegedera Mintu Nath Gary Entrican David Buxton |
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| Institution: | 1. Moredun Research Institute, Edinburgh, United Kingdom.; 2. Faculty of Veterinary Medicine, University of Utrecht, Utrecht, The Netherlands.; 3. Biomathematics and Statistics Scotland, Edinburgh, United Kingdom.; University of California San Francisco, University of California, Berkeley, and the Children''s Hospital Oakland Research Institute, United States of America, |
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| Abstract: | BackgroundLatency is a key feature of the animal pathogen Chlamydia abortus, where infection remains inapparent in the non-pregnant animal and only becomes evident during a subsequent pregnancy. Often the first sign that an animal is infected is abortion occurring late in gestation. Despite this, little is understood of the underlying mechanisms that control latency or the recrudescence of infection that occurs during subsequent pregnancy. The aim of this study was to develop an experimental model of latency by mimicking the natural route of infection through the intranasal inoculation of non-pregnant sheep with C. abortus.Methodology/Principal FindingsThree groups of sheep (groups 1, 2 and 3) were experimentally infected with different doses of C. abortus (5×103, 5×105 and 5×107 inclusion forming units (IFU), respectively) prior to mating and monitored over 2 breeding cycles for clinical, microbiological, pathological, immunological and serological outcomes. Two further groups received either negative control inoculum (group 4a,b) or were inoculated subcutaneously on day 70 of gestation with 2×106 IFU C. abortus (group 5). Animals in groups 1, 2 and 5 experienced an abortion rate of 50–67%, while only one animal aborted in group 3 and none in group 4a,b. Pathological, microbiological, immunological and serological analyses support the view that the maternal protective immune response is influenced by initial exposure to the bacterium.Conclusions/SignificanceThe results show that intranasal administration of non-pregnant sheep with a low/medium dose of C. abortus results in a latent infection that leads in a subsequent pregnancy to infection of the placenta and abortion. In contrast a high dose stimulates protective immunity, resulting in a much lower abortion rate. This model will be useful in understanding the mechanisms of infection underlying latency and onset of disease, as well as in the development of novel therapeutics and vaccines for controlling infection. |
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