Rechallenge of previously-infected pregnant ewes with Chlamydophila abortus

Abstract

In an attempt to ascertain the means whereby previous exposure to Chlamydophila (C.) abortus can protect against the re-occurrence of enzootic abortion of ewes (EAE), ten previously-exposed ewes were intravenously rechallenged with a large infective dose of C. abortus during pregnancy. The patterns of development of chlamydial placentitis and its sequelae closely resembled that observed following first-time challenge of previously-naïve ewes, although placentitis appeared to develop more slowly following rechallenge infection and none of the rechallenged ewes aborted. Chorioallantoic and foetal pathology and foetal immune responses were qualitatively similar whilst the local maternal response to C. abortus infection of the endometrium did not appear to differ in rechallenged and first-time challenged sheep. This demonstrates that if C. abortus reaches the foetal side of the placenta, a stereotypical response is elicited, regardless of the status of maternal immunity. Therefore it appears that in natural circumstances, acquired immunity of the dam protects against the re-occurrence of EAE by preventing the causative agent from reaching the susceptible foetal trophoblast.

Effect of Preventive Chlamydia abortus Vaccination in Offspring Development in Sheep Challenged Experimentally

“…In fact, in the present study, 10 ewes (8 vaccinated and 2 control) with different reproductive outcome (2 reproductive failures, 7 normal parturitions and the sheep from group C died during delivery, of which 3 were positive in the PCR) never seroconverted during the study, demonstrating that serological responses do not always correlate with C. abortus previous contact, reproductive failure, or vaccine efficacy, in agreement with previous findings (11, 18, 40, 44, 51, 56, 58). However, negative results in these animals (known to be exposed to C. abortus through vaccination and/or challenge) could also be due to a lack of sensitivity of the ELISA used, based on the detection of antibodies against major outer membrane proteins (MOMPs), considered to be less sensitive than tests based in polymorphic outer membrane proteins (POMPs) (9, 36, 44, 45).…”

“…This finding could be explained at least in part by several factors. First, the moment of the experimental infection during the pregnancy has been demonstrated to impact the ability of the ewe to control it (11, 53, 54); here, the challenge was performed at approximately 85 ± 8 days of pregnancy in contrast with previous reports in which it took place between 60 and 75 days of pregnancy, considered the most susceptible period (2, 7, 42, 44, 46, 55). A challenge performed later during pregnancy could lead to a lower degree of colonization of the placenta and a milder infection and, ultimately, a lower level of excretion (thus being more difficult to detect by PCR) and a lower proportion of abortions (9, 12) as supported by results based on a late (90–105 days post-mating) challenge (4, 23, 39).…”

“…Susceptible animals can become easily infected by the ingestion of contaminated material (9) or the inhalation of aerosols (10). EAE-affected ewes will develop an effective post-infection immune response preventing future C. abortus -induced abortions (11), but may still shed the bacteria in the following estrus, contributing to the maintenance of the infection in the flock. The reproductive failure rate in a newly infected naive sheep flock is around 30% (up to 60% in goat herds), whereas in endemically infected flocks, prevalence is around 10% (12).…”

Identification of Immunologically Relevant Proteins ofChlamydophila abortusUsing Sera from Experimentally Infected Pregnant Ewes

“…No fetal antibodies specific for EB were detected at 30 dpi. The failure of the fetuses to respond serologically to C. abortus until day 35 is consistent with the time required for the organism to spread from the infected trophoblast to the fetal tissues and the development of lesions of multifocal necrosis in the major fetal organs (37). The 26-to 32-kDa antigens were clearly detected on 2-D immunoblots with both ewe and fetal sera.…”

Protective adaptive immunity to Chlamydophila abortus infection and control of ovine enzootic abortion (OEA)

“…These haematomatas may allow C. abortus to invade the placenta from maternal blood in persistently-infected ewes. The pathogenesis of OEA has been linked to the ability of the ewe to control the levels of infectious EBs in blood, suggesting that both timing and dose of placental infection are important factors (Sammin et al, 2005;2006). Thus, it may be simply be a case of opportunistic infection of trophoblast by C. abortus when fetal cells come in direct contact with maternal blood.…”