Isolation of faecal chlamydia from sheep in Britain and their characterization by cultural properties

A Recombinase-Aided Amplification Assay for the Detection of Chlamydia felis

Chlamydia felis is an important zoonotic agent for humans and various animals. A recombinase-aided amplification (RAA) assay was developed for detecting C. felis. RAA can be performed in a closed tube at 39°C within 30 min. The detection limit was 10.6 copies of the C. felis plasmid DNA per reaction. No positive signals for other pathogens were detected. The coincidence rate of RAA and conventional PCR was 95.24% (20/21) and 100% (96/96) for positive and negative samples, respectively. The established RAA assay is a simple, rapid, highly sensitive, and specific method for detecting C. felis.

Chlamydia pecorum Ovine Abortion: Associations between Maternal Infection and Perinatal Mortality

Chlamydia pecorum is a common gastrointestinal inhabitant of livestock but infections can manifest in a broad array of clinical presentations and in a range of host species. While C. pecorum is a known cause of ovine abortion, clinical cases have only recently been described in detail. Here, the prevalence and sequence types (STs) of C. pecorum in ewes from a property experiencing high levels of perinatal mortality (PNM) in New South Wales (NSW), Australia, were investigated using serological and molecular methods. Ewes that were PNM+ were statistically more likely to test seropositive compared to PNM− ewes and displayed higher antibody titres; however, an increase in chlamydial shedding from either the rectum, vagina or conjunctiva of PNM+ ewes was not observed. Multilocus sequence typing (MLST) indicated that C. pecorum ST23 was the major ST shed by ewes in the flock, was the only ST identified from the vaginal site, and was the same ST detected within aborted foetal tissues. Whole genome sequencing of C. pecorum isolated from one abortion case revealed that the C. pecorum plasmid (pCpec) contained a unique deletion in coding sequence 1 (CDS1) that was also present in C. pecorum ST23 shed from the ewes. A further unique deletion was noted in a polymorphic membrane protein gene (pmpG) of the C. pecorum chromosome, which warrants further investigation given the role of PmpG in host cell adherence and tissue tropism.This study describes novel infection parameters in a sheep flock experiencing C. pecorum-associated perinatal mortality, provides the first genomic data from an abortigenic C. pecorum strain, and raises questions about possible links between unique genetic features of this strain and C. pecorum abortion.

Occurrence of Chlamydiaceae and Chlamydia felis pmp9 Typing in Conjunctival and Rectal Samples of Swiss Stray and Pet Cats

Chlamydia (C.) felis primarily replicates in feline conjunctival epithelial cells and is an important cause of conjunctivitis in cats. Data on C. felis infection rates in stray cats in Switzerland has been missing so far. We performed a qPCR-based Chlamydiaceae-screening on 565 conjunctival and 387 rectal samples from 309 stray and 86 pet cats followed by Chlamydia species identification and C. felis typing using the gene pmp9, which encodes a polymorphic membrane protein. Overall, 19.1% of the stray and 11.6% of the pet cats were Chlamydiaceae-positive with significantly higher rates in cats displaying signs of conjunctivitis (37.1%) compared to healthy animals (6.9%). Rectal shedding of Chlamydiaceae occurred in 25.0% of infected cats and was mostly associated with concurrent ocular positivity (87.5%). In 92.2% of positive conjunctival and rectal samples, the Chlamydia species was identified as C. felis and in 2.6% as C. abortus. The C. felis pmp9 gene was very conserved in the sampled population with only one single-nucleotide polymorphism (SNP) in one conjunctival sample. In conclusion, C. felis strains are circulating in Swiss cats, are associated with conjunctivitis, have a low pmp9 genetic variability, and are rectally shed in about 16% of positive cases.

Chlamydia pecorum-Induced Arthritis in Experimentally and Naturally Infected Sheep

Chlamydia pecorum is an obligate intracellular pathogen with a wide host range including livestock such as sheep, cattle, goats, and pigs as well as wildlife species such as koalas. Chlamydial polyarthritis is an economically important disease resulting in swollen joints, lameness, stiffness, and weight loss in young sheep. In the present study, tissues from sheep experimentally or naturally infected with Chlamydia pecorum were assessed by histopathology and immunohistochemistry. Carpal, hock, and stifle joints as well as spleen, liver, kidney, lymph nodes, lung, and brain of 35 sheep from different inoculation groups were available. Two different C. pecorum strains (IPA and E58), different routes of administration (intraarticular or intravenous), UVA-irradiated IPA strain, and corresponding noninfected control groups were investigated. Similar investigations on tissues from 5 naturally infected sheep were performed. The most obvious inflammatory lesions were observed in synovial tissues and, notably, in the renal pelvis from the experimentally infected group and naturally infected animals. This resulted in chronic or chronic-active arthritis and pyelitis. Intralesional chlamydial inclusions could be demonstrated by immunohistochemistry in both tissues. Immunohistochemical evaluation of the presence and distribution of macrophages, T and B cells in synovial tissues revealed macrophages as the most prevalent inflammatory cell population. Previous observations indicated that C. pecorum isolates can infect circulating monocytes. Together with the finding of the histological lesions in synovial tissues and internal organs alongside the presence of C. pecorum DNA, these observations suggest chlamydial arthritis in lambs is the result of hematogeneous spread of C. pecorum.

Understanding the health and production impacts of endemic Chlamydia pecorum infections in lambs

Lamydia pecorum is a globally recognised livestock pathogen that is capable of causing severe and economically significant diseases such as arthritis in sheep and cattle. Relatively little information is available on the clinical progression of disease and the long-term effects of asymptomatic and symptomatic chlamydiosis in sheep. Recent studies in calves indicate that endemic C. pecorum infections may reduce growth rates. To investigate the clinical health parameters and production impacts of endemic C. pecorum infection in an Australian commercial lamb flock, we performed bimonthly sampling and clinical health assessments on 105 Border Leicester lambs from two to ten months of age. Chlamydial status was investigated via serology and species-specific quantitative PCR. Throughout the study period, conjunctivitis remained a persistent clinical feature while signs of arthritis (e.g. palpable synovial joint effusions) resolved in a subset of lambs while persisting in others. Clinical disease and C. pecorum infection were highest at six months of age (weaning). As previously reported, peak seroconversion tends to occur two months after the onset of clinical symptoms (6 months of age), with lambs clearing chlamydial infection by 10 months of age, despite ongoing disease still being present at this time. Notably, the presence of chlamydial infection did not affect lamb mass or growth rates throughout the study. At necropsy, C. pecorum was not detected within the joints of lambs with chronic arthritis. Molecular analysis of the strains in this flock suggest that the infecting strains circulating in this flock are clonal C. pecorum pathotypes, denoted ST 23, commonly associated with conjunctivitis and polyarthritis in Australian sheep. This study provides a platform for further research in the epidemiology and disease transmission dynamics of C. pecorum infections in sheep.

Clinical, diagnostic and pathologic features of presumptive cases of Chlamydia pecorum-associated arthritis in Australian sheep flocks

Background

Arthritis is an economically significant disease in lambs and is usually the result of a bacterial infection. One of the known agents of this disease is Chlamydia pecorum, a globally recognised livestock pathogen associated with several diseases in sheep, cattle and other hosts. Relatively little published information is available on the clinical, diagnostic and pathologic features of C. pecorum arthritis in sheep, hindering efforts to enhance our understanding of this economically significant disease. In this case series, a combination of standard diagnostic testing used routinely by veterinarians, such as the Chlamydia complement fixation text (CFT), veterinary clinical examinations, and additional screening via C. pecorum specific qPCR was used to describe putative chlamydial infections in five sheep flocks with suspected ovine arthritis.

Case presentation

Five separate cases involving multiple lambs (aged six to ten months) of different breeds with suspected C. pecorum arthritis are presented. In two of the five cases, arthritic lambs exhibited marked depression and lethargy. Arthritis with concurrent conjunctivitis was present in four out of five lamb flocks examined. Chlamydia CFT demonstrated medium to high positive antibody titres in all flocks examined. C. pecorum shedding was evident at multiple sites including the conjunctiva, rectum and vagina, as determined via qPCR. Two of the five flocks received antimicrobials and all flocks recovered uneventfully regardless of treatment.

Conclusion

This case series highlights the features a field veterinarian may encounter in cases of suspected ovine chlamydial arthritis. Our analysis suggests a presumptive diagnosis of chlamydial arthritis in lambs can be made when there is evidence of joint stiffness with or without synovial effusion and elevated chlamydia antibody titres. C. pecorum-specific qPCR was found to be a useful ancillary diagnostic tool, detecting Chlamydia positivity in low or negative CFT titre animals. Variables such as symptom duration relative to sampling, sheep breed and farm management practices were all factors recorded that paint a complex epidemiological and diagnostic picture for this disease. These case studies serve to provide a platform for further research to improve diagnostic testing and new treatment and control strategies for C. pecorum infections in sheep.

Chlamydia pecorum infections in sheep and cattle: A common and under-recognised infectious disease with significant impact on animal health

There is a growing recognition that infections of livestock by the obligate intracellular bacterium, Chlamydia pecorum, are more widespread than was previously thought. A range of diseases have been associated with this pathogen, with the most important manifestations including infectious arthritis, infertility, enteritis, reduced growth rates, mastitis, and pneumonia. C. pecorum infections have also been associated with sub-clinical disease, highlighting our lack of knowledge about its true economic impact on livestock producers. Diagnosis of C. pecorum infection is based on clinical findings, serology and histopathology, which are not necessarily implemented in subclinical or early stages of infection, thus potentially contributing to under-diagnosis and under-reporting of infections associated with this bacterium. Recent molecular epidemiology studies have revealed that C. pecorum is genetically diverse and that there may be an association between certain strains and disease in sheep and cattle. Antimicrobial treatment of affected animals has questionable efficacy, justifying development of chlamydia vaccines for livestock. This review summarises current knowledge of the prevalence and impact of C. pecorum infections in sheep and cattle and provides an update on attempts to improve detection, management and treatment of infections by this important obligate intracellular pathogen.

Genetic and antigenic analysis of Chlamydia pecorum strains isolated from calves with diarrhea

Chlamydia pecorum (designated 22-58) was isolated in 2010 in HmLu-1 cells from the jejunum of a calf which died of necrotizing enterocolitis in Yamaguchi Prefecture, Japan. Immunohistochemical staining identified C. pecorum positive reactions in the jejunal villi. C. pecorum, designated 24-100, was isolated from the feces of a calf with diarrhea in another farm in Yamaguchi Prefecture in 2012. A significant increase in neutralizing antibody titers against C. pecorum was confirmed in paired sera. Nucleotide sequence identities of omp1 genes of the 2 isolates were 100%. The isolates were genetically and antigenically more closely related to C. pecorum Bo/Yokohama strain isolated from cattle with enteritis in Japan than to the other prototype strains, Bo/Maeda isolated from cattle with pneumonia and Ov/IPA isolated from sheep with polyarthritis. These results indicate that C. pecorum strains similar to 22-58 and 24-100 might be endemic in Yamaguchi Prefecture and cause enteric disease in cattle.

Detection and genotyping of Chlamydia species responsible for reproductive disorders in Algerian small ruminants

Chlamydiosis in small ruminants is a zoonotic disease mainly related to Chlamydia abortus. This bacterium is responsible for abortions and reproductive disorders in sheep and goats. Stillbirth and infertility, leading to important economic losses, are also associated with this pathology. In Algeria, abortion cases are frequently reported by veterinarians but, except for brucellosis which is a notifiable disease in this country, abortive diseases are in general poorly studied. In order to detect and genotype Chlamydia species in small ruminants in different areas of Algeria, a study was conducted on samples collected from females (164 blood samples and 199 vaginal swabs) between October 2011 and March 2013. Serum samples were tested with a C. abortus-specific indirect ELISA test. Fourteen samples (8.5 %), from six farms (6/20, 30 %) were tested positive. Vaginal swabs were analysed with a real-time PCR targeting all Chlamydiaceae spp. Thirty samples (15 %) were diagnosed positive in 16 farms (16/25, 64 %). Positive samples were all re-tested with a C. abortus- and a C. pecorum-specific real-time PCR. Finally, 13/30 (43.3 %) and 6/30 (20 %) were identified as C. abortus and C. pecorum, respectively. Enough concentrated C. abortus samples were genotyped by multi-loci variable number of tandem repeat (VNTR) analysis (MLVA), and all were related to the genotype [2] group which mainly includes French C. abortus isolates. C. pecorum-positive samples were genotyped by multi-locus sequence typing (MLST). Interestingly, two of them were successfully genotyped and showed identical MLST sequences to VB2, AB10, E58 and SBE, a group which includes C. pecorum isolates considered as highly pathogenic. These findings suggest a possible role of C. abortus and C. pecorum strains in the aetiology of abortion in Algerian small ruminants.

Evaluation of the relationship between Chlamydia pecorum sequence types and disease using a species-specific multi-locus sequence typing scheme (MLST)

Chlamydia pecorum is globally associated with several ovine diseases including keratoconjunctivitis and polyarthritis. The exact relationship between the variety of C. pecorum strains reported and the diseases described in sheep remains unclear, challenging efforts to accurately diagnose and manage infected flocks. In the present study, we applied C. pecorum multi-locus sequence typing (MLST) to C. pecorum positive samples collected from sympatric flocks of Australian sheep presenting with conjunctivitis, conjunctivitis with polyarthritis, or polyarthritis only and with no clinical disease (NCD) in order to elucidate the exact relationships between the infecting strains and the range of diseases. Using Bayesian phylogenetic and cluster analyses on 62 C. pecorum positive ocular, vaginal and rectal swab samples from sheep presenting with a range of diseases and in a comparison to C. pecorum sequence types (STs) from other hosts, one ST (ST 23) was recognised as a globally distributed strain associated with ovine and bovine diseases such as polyarthritis and encephalomyelitis. A second ST (ST 69) presently only described in Australian animals, was detected in association with ovine as well as koala chlamydial infections. The majority of vaginal and rectal C. pecorum STs from animals with NCD and/or anatomical sites with no clinical signs of disease in diseased animals, clustered together in a separate group, by both analyses. Furthermore, 8/13 detected STs were novel. This study provides a platform for strain selection for further research into the pathogenic potential of C. pecorum in animals and highlights targets for potential strain-specific diagnostic test development.

The evolution of infectious agents in relation to sex in animals and humans: brief discussions of some individual organisms

The following series of concise summaries addresses the evolution of infectious agents in relation to sex in animals and humans from the perspective of three specific questions: (1) what have we learned about the likely origin and phylogeny, up to the establishment of the infectious agent in the genital econiche, including the relative frequency of its sexual transmission; (2) what further research is needed to provide additional knowledge on some of these evolutionary aspects; and (3) what evolutionary considerations might aid in providing novel approaches to the more practical clinical and public health issues facing us currently and in the future?

High frequency of chlamydial co-infections in clinically healthy sheep flocks

Background

The epidemiological situation of ovine chlamydial infections in continental Europe, especially Germany is poorly characterised. Using the German state of Thuringia as a model example, the chlamydial sero- and antigen prevalence was estimated in thirty-two randomly selected sheep flocks with an average abortion rate lower than 1%. Seven vaccinated flocks were reviewed separately.

Results

A wide range of samples from 32 flocks were examined. Assumption of a seroprevalence of 10% (CI 95%) at flock level, revealed that 94% of the tested flocks were serologically positive with ongoing infection (i.e. animals with seroconversion) in nearly half (47%) of the flocks. On the basis of an estimated 25% antigen prevalence (CI 95%), PCR and DNA microarray testing, together with sequencing revealed the presence of chlamydiae in 78% of the flocks. The species most frequently found was Chlamydophila (C.) abortus (50%) followed by C. pecorum (47%) and C. psittaci genotype A (25%). Mixed infections occurred in 25% of the tested flocks. Samples obtained from the vaccinated flocks revealed the presence of C. abortus field samples in 4/7 flocks. C. pecorum was isolated from 2/7 flocks and the presence of seroconversion was determined in 3/7 flocks.

Conclusions

The results imply that chlamydial infections occur frequently in German sheep flocks, even in the absence of elevated abortion rates. The fact that C. pecorum and the potentially zoonotic C. psittaci were found alongside the classical abortifacient agent C. abortus, raise questions about the significance of this reservoir for animal and human health and underline the necessity for regular monitoring. Further studies are needed to identify the possible role of C. psittaci infections in sheep.

Monitoring clinical outcomes, pathological changes and shedding of Chlamydophila abortus following experimental challenge of periparturient ewes utilizing the natural route of infection

Enzootic abortion of ewes (EAE) caused by Chlamydophila abortus is an important disease resulting in significant lamb loss in most sheep producing countries. Ewes are considered to be naturally infected with C. abortus via the oral-nasal route and may become persistent carriers, shedding during subsequent oestrous cycles and at lambing. The aim of this study was to monitor the clinical outcomes, pathological changes and shedding of C. abortus in 18 periparturient orally infected sheep for two breeding seasons. In the first season, C. abortus was detected by real-time PCR (rt-PCR) in 13/18 conjunctival swabs at oestrus. Three out of the 15 pregnant ewes gave birth to 1 live and 1 dead lamb, and 2 of them aborted. Following parturition/abortion, C. abortus was detected in 12/15 vaginal swabs and in all the collected foetal membranes. However, only those membranes containing high copy numbers of the bacterium displayed the EAE typical lesions. In the second season, none of the 13 pregnant ewes aborted, and 5 of them gave birth to dead or weak lambs. C. abortus was not detected in conjunctival or vaginal swabs at oestrus or parturition. The bacterium was detected at low levels in 36% of the foetal membranes, but with no evidence of histopathological lesions. These results indicate that C. abortus can be detected in a large proportion of animals during the first pregnancy after oral infection. However, this proportion is reduced at the subsequent breeding season, confirming the occurrence of a chronic low level persistent infection in post-abortion/lambing ewes.

Recent advances in the understanding of Chlamydophila pecorum infections, sixteen years after it was named as the fourth species of the Chlamydiaceae family

Chlamydophila pecorum found in the intestine and vaginal mucus of asymptomatic ruminants has also been associated with different pathological conditions in ruminants, swine and koalas. Some endangered species such as water buffalos and bandicoots have also been found to be infected by C. pecorum. The persistence of C. pecorum strains in the intestine and vaginal mucus of ruminants could cause long-term sub-clinical infection affecting the animal’s health. C. pecorum strains present many genetic and antigenic variations, but coding tandem repeats have recently been found in some C. pecorum genes, allowing C. pecorum strains isolated from sick animals to be differentiated from those isolated from asymptomatic animals. This review provides an update on C. pecorum infections in different animal hosts and the implications for animal health. The taxonomy, typing and genetic aspects of C. pecorum are also reviewed.

Efficacy of live Chlamydophila abortus vaccine 1B in protecting mice placentas and foetuses against strains of Chlamydophila pecorum isolated from cases of abortion

The efficacy of Chlamydophila abortus vaccine strain 1B in protecting against two selected Chlamydophila pecorum strains, isolated from an aborted goat (M14) in Morocco and a ewe (AB10) in France, was investigated in a mouse model, by comparing the reduction in number of bacteria in the placentas of vaccinated mice challenged intraperitoneally at 11 days of pregnancy with the reference C. abortus (AB7) and C. pecorum (M14, or AB10) strains, to those of unvaccinated mice. Vaccine 1B was shown to provide effective protection against the field strains of C. pecorum, since it significantly reduced the placental Chlamydophila colonisation. The two C. pecorum strains were not sufficiently abortifacient in mice to use reduction in abortion as a criterion of protection.

Serological diagnosis of ovine enzootic abortion by enzyme-linked immunosorbent assay with a recombinant protein fragment of the polymorphic outer membrane protein POMP90 of Chlamydophila abortus

Ovine enzootic abortion (OEA) resulting from infection of sheep and goats with Chlamydophila abortus is of major economic importance worldwide. Over the last 50 years the serological diagnosis of infection has been based mainly on the complement fixation test (CFT), which lacks both sensitivity and specificity because of cross-reactive antibodies to other gram-negative bacteria, including another common chlamydial pathogen of sheep, Chlamydophila pecorum. In the present study, a series of overlapping recombinant antigens representing the polymorphic outer membrane protein POMP90 of C. abortus was assessed by enzyme-linked immunosorbent assay (ELISA) with a panel of 143 serum samples from sheep experimentally infected with C. abortus, from sheep clinically free of OEA, and from specific-pathogen-free lambs experimentally infected with different subtypes of C. pecorum. The results were compared to those obtained by CFT and another recently described test, an indirect ELISA (iELISA) with the recombinant OMP91B (rOMP91B) fragment (rOMP91B iELISA) (D. Longbottom, E. Psarrou, M. Livingstone, and E. Vretou, FEMS Microbiol. Lett. 195:157-161, 2001). The rOMP90-3 and rOMP90-4 ELISAs were identified as being more sensitive and specific than CFT. Assays with both fragments were evaluated further with a panel of 294 field serum samples from flocks with documented histories of abortion, from flocks with no clinical histories of abortion but which had a high proportion of samples seropositive by CFT, and from animals with no histories of abortion but from which various C. pecorum subtypes had been isolated. ELISAs with both POMP90 fragments outperformed CFT with serum samples from C. pecorum-infected animals, producing no false-positive results. However, the ELISA with the rOMP90-4 fragment appeared to be more sensitive than the one with rOMP90-3, as it identified more of the OEA-positive samples. The ELISA with the rOMP90-4 fragment was also able to identify apparently healthy animals that were infected with an enteric strain of C. abortus in flocks that were probably infected with both enteric C. abortus and C. pecorum strains. The identification of animals infected with enteric C. abortus is extremely important in controlling the spread of OEA. Overall, the new rOMP90-4 ELISA was found to be a more sensitive and specific test than CFT for differentiating animals infected with C. abortus from those infected with C. pecorum.

Chlamydia and Chlamydiales: more than meets the eye

This review summarizes the dramatic changes that have occurred in the taxonomy of bacteria known as Chlamydia. Best known for the diseases they cause in humans, these intracellular bacteria also comprise many species that are responsible for a wide variety of clinically and economically important diseases in livestock and companion animals. The old taxonomy grouped most of these species into C. psittaci because systematic methods for routinely distinguishing them were not available. DNA-based testing methods are now available that distinguish different chlamydial families, genera, and species. This summary reviews these tests and a number of oligonucleotide primers that distinguish these groups using PCR and PCR-RFLP. DNA-based methods are also being used to discover new families of chlamydia-like bacteria, at least one of which is responsible for abortion in cattle (Waddlia chondrophila). This review summarizes the pathogenic roles of the Chlamydiaceae, new families, and individual species within the order Chlamydiales. These discoveries create opportunities for veterinarians to carry out epidemiological studies of chlamydiae that previously were not possible.

Experimental infection of pregnant ewes with Chlamydia pecorum

Pregnant ewes were infected in midpregnancy with three isolates of Chlamydia pecorum derived from the feces of healthy lambs from three different farms. Oral infection, alone or together with Fasciola hepatica, did not result in tissue invasion, since all placental and fecal samples were negative for chlamydiae. Intravenous infection resulted in placental infection in 16 of 18 ewes in that chlamydiae were cultured from placentas or vaginal swabs. Two ewes bore dead lambs after a shortened gestation time. The chlamydiae isolated were all C. pecorum. There were no significant differences between the weights of the lambs from the infected groups and those from uninfected control ewes. Most ewes showed no serological evidence of infection by the complement fixation test; therefore, it is unlikely that the enteric subtype of C. pecorum is responsible for the cross-reactions sometimes seen in flocks being tested for C. psittaci infection.

Serological diagnosis of chlamydial abortion in sheep and goats: comparison of the complement fixation test and an enzyme-linked immunosorbent assay employing solubilised proteins as antigen

A new ELISA for antibodies against chlamydial abortion of ewes which uses detergent solubilised proteins (dsp) of Chlamydia psittaci as antigen (Anderson, I.E., Herring, A.J., Jones, G.E., Low, J.C., Greig, A., 1995. Development and evaluation of an indirect ELISA to detect antibodies to abortion strains of Chlamydia psittaci in sheep sera. Vet. Microbiol., 43, pp. 1-12] was compared with the complement fixation test (CFT) in screening 1000 ovine and caprine sera obtained from selected flocks/herds ('flocks') and submitted to a veterinary diagnostic laboratory. Fifteen of the 17 'flocks' had a history of abortion while the remaining two did not and were classified as 'negative flocks'. Infection with Chlamydia was confirmed during the study period in five 'flocks' using direct immunofluorescence and the modified Ziehl Neelsen stain on pathological material. The dspELISA and CFT identified 37 and 45 positive sera on 158 samples tested from these 'flocks'. Chlamydia antibodies were not detected in one of the two negative flocks, in two other flocks where the cause of abortion was undetermined and in three flocks in which the causes of abortion were diagnosed as Listeriosis and/or Salmonellosis. One of the 'negative flocks' yielded two positive reactors by CFT and five by dspELISA, suggesting infection with a cross-reactive subtype of C. pecorum. Of the five 'flocks' in which a definitive diagnosis from pathological material was not possible, four were positive by both serological tests, suggesting that the abortions were due to Chlamydia. The fifth flock, though negative by dspELISA and marginally positive in two samples by CFT, had experienced confirmed chlamydial abortions in previous lambing seasons, but culling and tetracycline treatment have prevented further abortions in the study period. Overall, the proportions of samples positive by CFT and dspELISA were similar (9.1% and 8.8%). These studies confirmed the value of the dspELISA as a screening test for chlamydial abortion. Furthermore, the dspELISA compared to the CFT is easier to perform, does not require reagent titration at each testing and uses automated assessment of results.

Comparison of five tests for the detection of antibodies against chlamydial (enzootic) abortion of ewes

Five tests for antibodies against chlamydial (enzootic) abortion of ewes were compared using 255 sera from experimentally (group 1) or naturally (group 2) infected animals, flocks free of the disease (group 3) and individual animals testing positively by the complement fixation test but from flocks with no evidence of chlamydial abortion (group 4). Sera from five specific pathogen-free lambs vaccinated with two different subtypes of Chlamydia pecorum were also included (group 5). All tests used some form of processed culture of C psitiaci as antigen. Specificities, established with group 3 and 4 sera, ranged between 96 per cent (ELISA using lipopolysaccharide antigen) and 59 per cent (Immunocomb). Reactions with group 5 sera suggested that the cause of false positive results in the field might be cross-reactive antibodies against the arthritogenic subtype of C pecorum. Sensitivities, established with groups 1 and 2 sera, ranged between 81 per cent (Immunocomb) and 51 per cent (ELISA using solubilised protein antigen). The minimum sample sizes required to be 95 per cent certain of detecting at least five seropositives in two infected flocks (combined data) were 15 to 48, dependent on the test applied. The Western blot test, applied to a proportion of samples, yielded no false positives with group 3 sera but 31.7 per cent with group 4 sera. Thus, none of the tests in this comparison emerged as sufficiently satisfactory in all respects, suggesting that further improvements in chlamydial serology must come through the use of non-native antigens or in the form of a competitive ELISA.