Intranasal Infection with Chlamydia abortus Induces Dose-Dependent Latency and Abortion in Sheep

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.

Improving the molecular diagnosis of Chlamydia psittaci and Chlamydia abortus infection with a species-specific duplex real-time PCR

“…No amplification was obtained with sample 1088D that was negative for both C. abortus and C. psittaci according to our collaborator gold standard (Longbottom et al, 2013). In contrast, we obtained amplification with PCR1, but not with PCR2, revealing the presence of C. abortus DNA in samples 1086D, 1092D, 723P and 572P.…”

“…The sample corresponding to a bird spleen positive for C. psittaci (case study 2) was also identified as C. psittaci with our new duplex PCR. The 27 ovine placental samples positive for C. abortus (Longbottom et al, 2013) were all correctly identified by our duplex PCR.…”

Analysis of Humoral Immune Responses to Surface and Virulence-Associated Chlamydiaabortus Proteins in Ovine and Human Abortions by Use of a Newly Developed Line Immunoassay

“…The human and animal serum samples used in this study were taken from already existing serum collections of previous studies (4,5,7,10,13,14). Human serum samples were anonymized, and their use was approved by the local ethics committee of the University of Ulm (96/09) and the local ethics committee of the University Hospital Jena (2525-04/09).…”

“…(i) Experimentally infected sheep. Serum samples were obtained from three different groups of experimentally infected sheep as described in a previously published experimental model of latency (7). In that study, animals received different intranasally administered doses of infectious C. abortus elementary bodies (EBs) 8 weeks before mating and were monitored and bled over several months during pregnancy.…”

“…Recently, it was shown that relatively small doses of intranasally inoculated C. abortus organisms induced latent infection in nonpregnant ewes (7). When latently infected ewes became pregnant, this resulted in placental infection and consequent abortion, whereas animals infected with large doses were better protected and showed a much lower abortion rate.…”