Comparison of three commercial serological tests for the detection of Chlamydia abortus infection in ewes.

BACKGROUND: 20.9% of diagnosable abortions in Ireland in 2015 were caused by Chlamydia abortus infection. Abortion usually occurs in the last 2-3 weeks of gestation, and up to 30% of ewes may be affected in naïve flocks. Serological diagnosis of EAE in flocks using LPS or whole bacteria as antigens is often hindered by cross reactions with C. pecorum. Although the complement fixation test is the official test for diagnosis of EAE, more sensitive and specific ELISA based tests have been developed. This study aimed to compare three commercial ELISA kits to detect C. abortus antibodies in ewes and to determine which of the kits had the highest sensitivity. The IDvet kit utilises a MOMP peptide antigen, the MVD-Enfer kit is based on a POMP90-3 antigen while the LSI kit plates are coated with chlamydial LPS. The study also aimed to examine the potential of these ELISAs to distinguish infected animals that go on to abort compared to those that have live lambs. Ewes were vaccinated with either a commercial live vaccine (n = 10) or Tris-buffer sham inoculation (n = 9) 5 months prior to gestation, these ewes were then challenged with C. abortus (1 × 106 IFU/ml) on day 90 of gestation. Sera were collected at pre-vaccination, 14 days post vaccination, 35 days post vaccination, pre-challenge, 35 days post challenge and 3 weeks post lambing/abortion (~ 70 days post challenge) and tested using the 3 aforementioned ELISAs to determine if one ELISA was more sensitive at detecting circulating anti-chlamydial antibodies. RESULTS: Sensitivity was highest with the LSI test kit at 94.74%, followed by the MVD-Enfer and IDvet kits, at 78.95 and 73.68% respectively. Ewes vaccinated with Enzovax became seropositive at 14 days post vaccination with all kits. Following challenge at day 90 of gestation, antibody titres steadily rose in all groups of ewes. With all ELISA kits, antibody levels were higher in ewes that aborted compared to ewes that had live lambs at 35 days post challenge and three weeks post lambing, and statistically significantly higher antibody levels were recorded in ewes that aborted compared to ewes that had live lambs using the MVD-ENFER ELISA at three weeks post lambing (P = 0.0482). CONCLUSIONS: The LSI assay was the most sensitive out of the three kits tested in this study, when sera were tested at three weeks post lambing. As the LPS used in this kit is cross-reactive with all chlamydia, it is good for identifying flocks infected with any chlamydial species, but it is not considered specific for C. abortus. Furthermore, antibody levels were higher in ewes that aborted compared to ewes that had live lambs, at both 35 days post challenge and at three weeks post lambing. Future work should include evaluation of a larger number of sera at a wider range of time-points as well as an estimation of the specificity of commercially available assays.

Aging with HIV-1 Infection: Motor Functions, Cognition, and Attention--A Comparison with Parkinson's Disease.

Recent advances in highly active anti-retroviral therapy (HAART) in their various combinations have dramatically increased the life expectancies of HIV-infected persons. People diagnosed with HIV are living beyond the age of 50 but are experiencing the cumulative effects of HIV infection and aging on brain function. In HIV-infected aging individuals, the potential synergy between immunosenescence and HIV viral loads increases susceptibility to HIV-related brain injury and functional brain network degradation similar to that seen in Parkinson's disease (PD), the second most common neurodegenerative disorder in the aging population. Although there are clear diagnostic differences in the primary pathology of both diseases, i.e., death of dopamine-generating cells in the substantia nigra in PD and neuroinflammation in HIV, neurotoxicity to dopaminergic terminals in the basal ganglia (BG) has been implied in the pathogenesis of HIV and neuroinflammation in the pathogenesis of PD. Similar to PD, HIV infection affects structures of the BG, which are part of interconnected circuits including mesocorticolimbic pathways linking brainstem nuclei to BG and cortices subserving attention, cognitive control, and motor functions. The present review discusses the combined effects of aging and neuroinflammation in HIV individuals on cognition and motor function in comparison with age-related neurodegenerative processes in PD. Despite the many challenges, some HIV patients manage to age successfully, most likely by redistribution of neural network resources to enhance function, as occurs in healthy elderly; such compensation could be curtailed by emerging PD.

Distribution of lesions in fetal brains following experimental infection of pregnant sheep with Toxoplasma gondii.

Six ovine fetal brains were harvested 33 to 35 days postchallenge from 5 ewes, each of which was given 3000 Toxoplasma gondii oocysts on day 90 of pregnancy. Histopathologic examination of transverse sections taken at 13 levels in the fetal brains revealed the presence of toxoplasmosis-related lesions in all 6 brains. However, lesions were not randomly distributed (P = .007); they were most numerous at the level of the optic tract, the rostral margin of the pons, and 4 mm caudal to the ansate sulcus and were absent in all sections at the level of the caudal cerebellum. Lesion distribution may be due to hemodynamic factors, differences in the expression of endothelial surface receptor molecules at the level of the blood-brain barrier, or the presence of localized permissive/inhibitory factors within the brain. The results have implications for the selection of areas of brain from aborted ovine fetuses to be examined histopathologically for laboratory diagnosis.

Phylogenetic analysis of H and N2 genes of avian influenza viruses detected in Ireland between 2003 and 2007.

Phylogenetic analysis was performed on the haemagglutinin and neuraminidase subtype N2 genes of low-pathogenic avian influenza viruses (LPAIVs) detected in Ireland between 2003 and 2007. Nucleotide sequences were compared to previously published sequences from the National Centre for Biotechnology Information. Sequences from viruses of the same subtype isolated in different years were compared to examine the possibility that LPAIVs may have been maintained in Ireland from year to year. All viruses had closest identity with published sequences of European lineage, supporting the conclusion that LPAIVs had been introduced to Ireland by dabbling ducks that had migrated from Europe. The data suggested that different subtypes of virus had been introduced each year. However, there was evidence that some LPAIVs may have been maintained in the sedentary waterfowl population for consecutive seasons. Furthermore, almost identical H6 and H10 sequences with different N types were found in isolates from the same season, suggesting that reassortment had occurred.

Detection and quantification of leptospires in urine of dogs: a maintenance host for the zoonotic disease leptospirosis.

Leptospirosis is a global zoonotic disease. Pathogenic Leptospira species, the causative agent of leptospirosis, colonize the renal tubules of chronically infected maintenance hosts such as dogs, rats and cattle. Maintenance hosts typically remain clinically asymptomatic and shed leptospires into the environment via urine. In contrast, accidental hosts such as humans can suffer severe acute forms of the disease. Infection results from direct contact with infected urine or indirectly, through contaminated water sources. In this study, a quantitative real-time PCR specific for lipL32 was designed to detect the urinary shedding of leptospires from dogs. The sensitivity and specificity of the assay was evaluated using both a panel of pathogenic Leptospira species and clinical microbial isolates, and samples of urine collected from experimentally infected rats and non-infected controls. The lower limit of detection was approximately 3 genome equivalents per reaction. The assay was applied to canine urine samples collected from local dog sanctuaries and the University Veterinary Hospital (UVH) at University College Dublin. Of 525 canine urine samples assayed, 37 were positive, indicating a prevalence of urinary shedding of leptospires of 7.05%. These results highlight the need to provide effective canine vaccination strategies and raise public health awareness.

Detection of three distinct genetic lineages in methicillin-resistant Staphylococcus aureus (MRSA) isolates from animals and veterinary personnel.

This study involved the phenotypic and molecular characterization of a population of methicillin-resistant Staphylococcus aureus isolates from animals and from veterinary personnel in Ireland. Isolates from 77 animals (dogs, n=44; cats, n=4; horses, n=29) and from 28 veterinary personnel were characterized using their antimicrobial resistance profiles and pulsed-field gel electrophoresis patterns. In addition, a representative number of these isolates (n=52) were further analysed using spa-typing techniques. The results obtained identified the presence of three distinct clonal complexes, CC5, CC8 and CC22, in both animal and human isolates. Two of these clonal complexes, CC8 and CC22, respectively, have been previously described in animals in Ireland but the presence of the third complex CC5 is a novel finding. The significance of this development, in relation to human and animal healthcare, is discussed.

Toxigenic Corynebacterium ulcerans associated with upper respiratory infections in cats and dogs.

OBJECTIVES: To describe infection in companion animals with the zoonotic pathogen Corynebacterium ulcerans and to determine its prevalence in clinically-affected and healthy animals. MATERIALS AND METHODS: The clinical presentation and treatment of three cases of C. ulcerans infection is described. Two studies to determine C. ulcerans prevalence rates were undertaken: (a) a prospective study of nasal samples from healthy animals, 479 dogs and 72 cats; (b) a retrospective analysis of records of nasal samples collected over a 10-year period from 189 dogs and 64 cats affected by respiratory signs. RESULTS: Toxigenic C. ulcerans was isolated from four cats with nasal discharge while concurrent C. ulcerans and mecC methicillin-resistant S. aureus infection was detected in a dog suffering from chronic nasal discharge. Clinical features were not distinctive and all cases recovered following antimicrobial treatment. Multilocus sequence typing supported a common source for isolates from the shelter cats. Carriage rates of C. ulcerans in healthy animals were 0.42% (2/479) in dogs and 0.00% (0/72) in cats whereas in animals with signs of upper respiratory tract infection prevalence rates were 0.53% (1/189) in dogs and 6.25% (4/64) in cats. CLINICAL SIGNIFICANCE: Clinicians should be aware that dogs and cats can be infected with (or carriers of) toxigenic C. ulcerans Considering the potential zoonotic risk, assistance from medical and public health colleagues should be sought in confirmed cases.

The ovine placenta and placentitis-A review.

An appreciation of the complexities of placental structure and function is essential to understanding the pathogenesis of infectious placentitis and abortion. This review aims to illustrate aspects of ovine pregnancy and placentation that will assist both the research worker and the diagnostic pathologist. Morphologically, the ovine placenta is classified as being chorioallantoic, villous, cotyledonary and synepitheliochorial. Apposition of foetal and maternal tissues in early pregnancy eventually leads to the formation of the definitive placenta. Physiological features of placentation that are essential to normal pregnancy and foetal development include modulation of immune responses at the placental interface, increasing placental bloodflow to allow for increasing foetal demand and the secretion of hormones for the recognition and maintenance of pregnancy. Descriptions of the morphology of the near-term placenta in a normal pregnancy and of the foetal membranes that are voided during normal parturition provide the proper context for understanding the morphological changes associated with placentitis and how these changes are likely to affect placental function.

High-level gentamicin-resistant and vancomycin-resistant Enterococcus faecium isolated from a wound in a dog.

This report describes the first clinical case, in Europe, of a high-level gentamicin-resistant and vancomycin-resistant Enterococcus faecium infection in a dog. The aim of this report is to alert the veterinary profession to high-level gentamicin-resistant and vancomycin-resistant Enterococcus faecium in companion animal patients. Multi-drug resistant strains of this pathogen are the cause of considerable problems in human hospitals and for community healthcare professionals worldwide. The potential for a similar impact within veterinary medicine is discussed.

Evaluation of protective and immune responses following vaccination with recombinant MIP and CPAF from Chlamydia abortus as novel vaccines for enzootic abortion of ewes.

MIP and CPAF from Chlamydia have been shown to be effective in inducing immune responses important in clearing chlamydial infections. This study evaluates the protection conferred by MIP and CPAF as novel vaccines in pregnant C. abortus challenged ewes. Fifty C. abortus sero-negative sheep were randomly allocated into 5 groups of 10 according to the treatment they were to receive (1) 100 µg of MBP-MIP (2) 100 µg CPAF (3) 50 µg MBP-MIP and 50 µg CPAF (4) Tris-buffer (negative control) (5) Enzovax (positive control). Booster inoculations were administered 3 weeks after primary inoculations. Blood samples were taken pre-vaccination and weekly for 5 weeks. Five months after vaccination the ewes were mated. Pregnant ewes were then challenged on day 90 of gestation. Blood samples taken at four time-points post challenge were analysed for IFNγ levels, TNFα and IL-10 expression and anti-chlamydial antibody levels. Vaginal swabs, placental and foetal tissue and bacterial shedding were analysed using qPCR to quantify levels of C. abortus. Enzovax was 100% effective with no abortions occurring. The MIP/CPAF combined vaccine offered the greatest protection of the novel vaccines with 67% of ewes giving birth to one or more live lambs equating to a 50% vaccine efficacy rate. MIP and CPAF administered singly did not confer protection. Enzovax and MIP/CPAF vaccinated ewes had longer gestations and lambs with higher birth weights than negative control ewes. Aborting ewes shed higher numbers of C. abortus than ewes that had live lambs, all vaccinated ewes demonstrated lower levels of bacterial shedding than negative control ewes with Enzovax ewes shedding significantly fewer bacteria. Ewes that went on to abort had significantly higher levels of IFNγ and IL-10 at day 35 post challenge and significantly higher levels of anti-chlamydial antibodies at 24 h post lambing compared to ewes that had live lambs.

Meticillin-resistant Staphylococcus aureus in animals: a review.

The objectives of this paper are to review published data on the prevalence and epidemiology of meticillin-resistant Staphylococcus aureus (MRSA) infection and colonization in animals and to provide suggestions for preventing and controlling the problem in veterinary practice. MRSA first emerged as a serious pathogen in human medicine during the late 1970s and has been increasingly reported in animals during the past 10 years. The prevalence of MRSA in human infections varies markedly between geographical areas, being as high as 60% in parts of the USA, 40% in southern Europe but <1% in northern Europe. Epidemiological evidence, including phenotypic and molecular typing data, suggests that MRSA isolates from dogs and cats are indistinguishable from human healthcare isolates, whereas strains of MRSA isolated from horses and associated personnel are different. There is evidence that transfer of MRSA strains can occur between animals and humans and vice versa. Guidelines for the control of MRSA in animals have been drawn up by individual institutions based on those available for human MRSA infection. Risk factors for MRSA infection in animals are currently under investigation and such data are essential for the preparation of specific guidelines for control of MRSA in veterinary practice.

Salmonella in breeding pigs: Shedding pattern, transmission of infection and the role of environmental contamination in Irish commercial farrow-to-finish herds.

This study aimed to provide new insights into the epidemiology of Salmonella in pig production, focusing on potential shedding patterns in breeding pigs throughout a full production cycle and the risk of transmission of infection from the sow to her offspring. A longitudinal study was conducted on five farrow-to-finish commercial pig farms. In each herd, shedding of Salmonella in faeces was monitored in breeders through service, gestation and lactation. Swabs of the farrowing room floor and pools of faeces from piglets were collected on two occasions during lactation. Environmental pen swabs were also taken in the weaning and finisher houses. Salmonella isolates were serotyped, tested for antimicrobial resistance (AMR) and typed by Multiple-Locus Variable number tandem repeat Analysis (MLVA). Shedding by breeding pigs was low in all stages of the production cycle; 5% of sows shed at service, the production stage with highest risk of shedding (p < .01), 1.6% shed during gestation and 2.5% after farrowing. Salmonella was detected in 4% of piglet faecal pools in the second week post-farrowing and 5% in the fourth week. Serotyping and AMR profiles of Salmonella isolates revealed that strains in sows and gilts were mostly different from strains isolated in weaner and finisher facilities. MLVA typing confirmed that the source of infection in piglets was in most instances the contaminated environment rather than their dam. Based on the typing results, it appears that sows do not pose a major risk in the maintenance and transmission of Salmonella to their progeny but instead the contaminated pen environment is more significant in the perpetuation of the organism on farm.

Investigation of in-feed organic acids as a low cost strategy to combat Salmonella in grower pigs.

Salmonella carriage in pigs is a significant food safety issue. Dietary supplementation with organic acids has previously been shown to reduce shedding and transmission of Salmonella. Therefore, this study aimed to examine the effect of three commercially available organic acid-based products on Salmonella levels in grower pigs, using a model of experimental infection that closely mimics natural exposure to the organism. Seven week old trial pigs (n=40) with a mean weight of 14.7kg were placed in one of four pens with 10 pigs/pen. Pens had previously been contaminated with Salmonella Typhimurium 4,[5],12;i;- via seeder pigs. Trial pigs received one of four diets for 28days: 1, control diet; 2, sodium butyrate supplemented diet; 3, benzoic acid supplemented diet and 4, formic-citric acid supplemented diet. A further 10 pigs were placed in a Salmonella-free pen receiving the control diet. Pigs were weighed and blood sampled on days 0 and 28. Faeces was collected on day 0, 2, 3, 5, 7, 14, 21 and 28 and examined for Salmonella. On day 28, 5 pigs/group were euthanised and ileocaecal lymph nodes (ILN) and caecal contents sampled for culture. The remaining 5 pigs/pen were then fed the control diet and faeces were collected on days 35 and 42. On day 42 pigs were euthanised and ILN and caecal contents tested for Salmonella levels. The trial was repeated once. Within the first two days of exposure to the contaminated environment, 96% (77/80) of pigs became infected. Most pigs shed Salmonella at levels of between 100-103 CFU/g faeces for at least 7days post-exposure. A significant reduction in Salmonella faecal concentration was observed after supplementation with sodium butyrate (p=0.001) and a formic citric acid blend (p<0.0001). Average daily weight gain (ADWG) was significantly increased in all groups fed the supplemented feed when compared to the positive control group. The use of sodium butyrate or a blend of formic and citric acid in feed could be considered a cost-effective control measure to reduce Salmonella faecal shedding and improve ADWG in Salmonella infected herds.

Comparison of fetal and maternal inflammatory responses in the ovine placenta after experimental infection with Chlamydophila abortus.

Placentae from 13 pregnant ewes infected intravenously with Chlamydophila abortus, together with placentae from nine uninfected control ewes, were examined at 14, 21 or 28 days post-inoculation (p.i.). Chlamydial inclusions were present in the trophoblast at 14 days p.i. and were widespread by 21 days p.i. Chorioallantoic lesions (oedema, arteritis and thrombosis) were severe at 28 days p.i., the changes being particularly marked in the membrane surrounding placentomes. Lymphocytes constituted only a small proportion of the cellular infiltrate in the chorioallantois; neutrophil infiltration of the chorionic surface was evident where the trophoblast layer had sloughed, whereas macrophages represented the predominant cell type in the deeper stroma. In contrast, on the maternal side of the placenta, chlamydial inclusions were sparse at all timepoints, and even at 28 days p.i., lesions were restricted to focal endometritis at the placentomal limbus and occasional foci of septal necrosis. T lymphocytes were numerous within endometrial and septal lesions, the infiltrate consistently containing more CD8(+) than CD4(+) cells. The fetal response to chlamydial invasion of the placenta was innate in character, whereas the maternal response appeared to represent an acquired, chlamydia-specific immune response.

Methicillin-resistant Staphylococcus aureus isolated from a veterinary surgeon and five dogs in one practice.

Methicillin-resistant Staphylococcus aureus (MRSA) was isolated from five dogs with wound discharges after surgical procedures at a veterinary practice, and MRSA with similar molecular and phenotypic characteristics was isolated from the nares of one veterinary surgeon in the practice. The pulsed-field gel electrophoresis patterns of all the isolates were indistinguishable from each other and from the most common human isolates of MRSA in Ireland.

Antimicrobial Resistance of Faecal Escherichia coli Isolates from Pig Farms with Different Durations of In-feed Antimicrobial Use.

Antimicrobial use and resistance in animal and food production are of concern to public health. The primary aims of this study were to determine the frequency of resistance to 12 antimicrobials in Escherichia coli isolates from 39 pig farms and to identify patterns of antimicrobial use on these farms. Further aims were to determine whether a categorization of farms based on the duration of in-feed antimicrobial use (long-term versus short-term) could predict the occurrence of resistance on these farms and to identify the usage of specific antimicrobial drugs associated with the occurrence of resistance. Escherichia coli were isolated from all production stages on these farms; susceptibility testing was carried out against a panel of antimicrobials. Antimicrobial prescribing data were collected, and farms were categorized as long term or short term based on these. Resistance frequencies and antimicrobial use were tabulated. Logistic regression models of resistance to each antimicrobial were constructed with stage of production, duration of antimicrobial use and the use of 5 antimicrobial classes included as explanatory variables in each model. The greatest frequencies of resistance were observed to tetracycline, trimethoprim/sulphamethoxazole and streptomycin with the highest levels of resistance observed in isolates from first-stage weaned pigs. Differences in the types of antimicrobial drugs used were noted between long-term and short-term use farms. Categorization of farms as long- or short-term use was sufficient to predict the likely occurrence of resistance to 3 antimicrobial classes and could provide an aid in the control of resistance in the food chain. Stage of production was a significant predictor variable in all models of resistance constructed and did not solely reflect antimicrobial use at each stage. Cross-selection and co-selection for resistance was evident in the models constructed, and the use of trimethoprim/sulphonamide drugs in particular was associated with the occurrence of resistance to other antimicrobials.

Methicillin-resistant Staphylococcus aureus (MRSA) isolated from animals and veterinary personnel in Ireland.

Reports of methicillin-resistant Staphylococcus aureus (MRSA) in animals have become more frequent in recent years. This paper documents the recovery of MRSA from animals with respiratory, urinary tract or wound infection and from animals subjected to surgical procedures following treatment in one veterinary hospital and 16 private veterinary clinics in different geographical locations throughout Ireland. MRSA was recovered from 25 animals comprising 14 dogs, eight horses, one cat, one rabbit and a seal, and also from 10 attendant veterinary personnel. Clinical susceptibility testing suggested that the 35 isolates fell into two different groups. One group of isolates (Group 1) was resistant to one or more of the following classes of antimicrobials: macrolides, lincosamines, tetracyclines and/or fluoroquinolones. The second group (Group 2) was resistant to macrolides, aminoglycosides, tetracyclines and trimethoprim/sulphamethoxazole and variably resistant to fluoroquinolones, lincosamines and rifampicin. One isolate in Group 2 was susceptible to trimethoprim. Epidemiological typing by antibiogram-resistogram (AR) typing, biotyping and by chromosomal DNA restriction fragment length polymorphism analysis using SmaI digestion followed by pulsed field gel electrophoresis (PFGE), confirmed these two major clusters. PFGE analysis showed that most isolates from non-equine animals were indistinguishable from each other and from the isolates from personnel caring for these animals. MRSA was isolated from eight horses which attended six different veterinary practices before referral to an equine veterinary hospital. Isolates from the eight horses and from their attendant personnel had PFGE patterns that were indistinguishable and were unlike the patterns obtained from the other isolates. Comparison of PFGE patterns of isolates from veterinary sources with patterns from MRSA recovered in human hospitals showed that the most frequently occurring pattern of MRSA from non-equine animals was indistinguishable from the predominant pattern obtained from the most prevalent MRSA strain in the human population in Ireland. However, the patterns of the isolates from horses were unlike any patterns previously reported in Irish studies of human isolates. This study shows that transmission of two strains of MRSA is occurring in veterinary practices in Ireland and that one strain may have arisen from human hospitals. The source of the second strain remains to be determined.

New transtracheal bronchoalveolar lavage technique for the diagnosis of respiratory disease in sheep.

A new transtracheal bronchoalveolar lavage technique for the diagnosis of respiratory disease in sheep under field conditions was tested in 76 sheep. The sheep were divided into three groups, normal sheep, sheep with clinical signs of respiratory disease and housed sheep, on the basis of their respiratory disease history and husbandry conditions. The detection of Mannheimia haemolytica and Mycoplasma ovipneumoniae or parainfluenza virus type 3 and bovine respiratory syncytial virus antigen in the lavage samples was closely correlated with clinical disease. The sheep with clinical respiratory disease had a higher mean percentage of neutrophils in the lavage fluid than the sheep in the other two groups.

Persistence of Mycoplasma bovis infection in the mammary glands of lactating cows inoculated experimentally.

To study the course of clinical mycoplasma mastitis and investigate its potential for persistence, 10(8) colony-forming units (cfu) of an Irish isolate of Mycoplasma bovis was inoculated aseptically into the right fore teat canal of three lactating cows. M bovis rapidly colonised the infected quarters and grew exponentially to more than 10(10) cfu/ml within the first three days, and spread to other quarters of each of the three cows within five to 10 days. After periods of between 24 and 72 hours the infected quarters became distended and sensitive to touch, and their secretions changed from containing visible particles, to a seropurulent exudate, to an aqueous suspension of fine particles which formed a sediment after a sample was collected. M bovis-specific antibody levels increased to varying degrees in all three cows. Subsequently, the concentrations of mycoplasma decreased to less than 10(7) cfu/ml in two of the cows, but remained at more than 10(8) cfu/ml to the end of the lactation of the other cow. Apparently normal milk was secreted by one of the cows within a month of the challenge, and by the other two cows at the start of their next lactation. However, in two of the cows subclinical M bovis infection persisted through the dry periods and into their next lactations.

Rechallenge of previously-infected pregnant ewes with Chlamydophila abortus.

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.