Antigenic analysis of feline and bovine Chlamydia psittaci with monoclonal antibodies

Chlamydophila felis CF0218 is a novel TMH family protein with potential as a diagnostic antigen for diagnosis of C. felis infection

Chlamydophila felis is a causative agent of acute and chronic conjunctivitis and pneumonia in cats (feline chlamydiosis). Also, C. felis is a suspected zoonotic agent of such diseases as non-Chlamydia trachomatis conjunctivitis in humans, although this is controversial. At present, there is no serodiagnostic system that specifically detects C. felis infection conveniently. Current systems use antigens such as lipopolysaccharide that cross-react with all chlamydia species. In addition, it is difficult to distinguish between cats that are vaccinated with the commercial vaccine against C. felis and cats that are infected with C. felis. Here, we describe a new candidate diagnostic antigen for diagnosis of C. felis infection, CF0218, that was obtained by screening a genomic expression library of C. felis Fe/C-56 with C. felis-immunized serum. CF0218 was a putative transmembrane head (TMH) family protein with bilobed hydrophobic motifs at its N terminus, and orthologues of CF0218 were not found in the Chlamydophila pneumoniae or Chlamydia trachomatis genomes. The recombinant CF0218 was not recognized by antiserum against C. trachomatis, suggesting that CF0218 is C. felis specific. CF0218 transcription during the course of C. felis infection was confirmed by reverse transcription-PCR. By indirect immunofluorescence analysis, CF0218 was colocalized with the C. felis-formed inclusion bodies in the infected cells. The antibody response against CF0218 was elevated following C. felis infection but not by vaccination in experimentally vaccinated and infected cats. These results suggest that CF0218, a novel TMH family protein of C. felis, possesses potential as a C. felis infection-specific diagnostic antigen.

Serological diagnosis of ovine enzootic abortion by comparative inclusion immunofluorescence assay, recombinant lipopolysaccharide enzyme-linked immunosorbent assay, and complement fixation test

Since the 1950s, serological diagnosis of ovine enzootic abortion (OEA), caused by strains of Chlamydia psittaci, has been based mainly on the complement fixation test (CFT), which is neither particularly sensitive nor specific since antibodies to other chlamydial and enterobacterial pathogens may be detected. In this study. a recombinant enzyme-linked immunosorbent assay (rELISA) (medac, Hamburg, Germany), based on a unique chlamydial genus-specific epitope of Chlamydia trachomatis L2 lipopolysaccharide, was evaluated for sensitivity and specificity as a primary screening assay for OEA by comparison with the CFT. A comparative inclusion immunofluorescence assay (IFA), in which antibody titers to C. psittaci and Chlamydia pecorum were examined, was used as the reference test for 573 serum samples from four flocks. Reactivity to C. pecorum was measured since inapparent intestinal infections by C. pecorum are believed to be common in British flocks. In detecting positive sera from an abortion-affected flock, in which a C. pecorum infection was also suggested by IFA, the rELISA outperformed the CFT with significant evidence for increased sensitivity (P = 0.003). In two flocks in which C. pecorum infections alone were suggested by IFA, the rELISA and CFT were prone to detect low levels of false-positive results, but the values were not significant. The rELISA provided results in one flock in which sera that were anticomplementary could not be resolved by the CFT. In another flock in which abortion had not occurred but infection by both chlamydial species was suspected, no significant difference was found between the sensitivities of the rELISA and CFT. The rELISA could not differentiate ovine C. psittaci and C. pecorum infections but was shown to be a more sensitive primary screening test for OEA than was the CFT, particularly where abortion had occurred and even when antibodies due to additional inapparent infection(s) by C. pecorum were present.

Special tests for the diagnosis of infectious causes of reproductive failure in ruminants

The detection of many infectious disease agents, including those of importance in ruminant reproductive failure, increasingly will be achieved through means other than the laborious and time-consuming traditional isolation and culture procedures. New diagnostic methodologies are designed both to enhance the rapidity with which results are obtained and to increase specificity and sensitivity of identification of the causative agent. Immunoenzyme histochemical staining of formalin-fixed paraffin-embedded tissues offers, especially in cases of abortions in which necropsy material routinely is examined histologically, an efficient and timely means of identifying many important pathogens. Antemortem serologic diagnostics will continue to be dominated by ELISA technologies. In the past decade, the specificity of serodiagnosis has been enhanced greatly by the use of monoclonal antibody-based competitive ELISA systems and further improvements in such methods will result from the use of defined antigens derived by recombinant DNA techniques. Although DNA hybridization technology has been applied successfully to detect many important veterinary pathogens and has been shown to have merit for improved diagnosis of some fastidious agents, those methods, because of their technical complexity, in general, have not been shown to be applicable for routine diagnostic uses. In contrast, methods using the PCR for specific gene amplification offer exceptional promise. Although the PCR presently is too technically exacting for routine use, its broad applicability and exquisite sensitivity and specificity suggest that it will play an ever-increasing role in future veterinary diagnostic techniques.

Primary pathogenicity of an European isolate of Chlamydia psittaci from turkey poults

Chlamydia psittaci was isolated as the sole pathogenic agent from a severe outbreak of respiratory disease in a commercial broiler turkey farm in the Netherlands. The mortality rate in the flocks was 65%. Clinical signs included conjunctivitis, swelling of the sinus infraorbitalis and sneezing. Cloacal excretion of chlamydia was demonstrated in twelve out of fifteen birds examined by a direct immunofluorescence test. In all the fifteen birds antibodies against Chlamydia psittaci were detected in the sera by a competitive ELISA. At necropsy sinusitis, rhinitis, airsacculitis, pneumonia, pericarditis and enlargement of the liver and spleen were found. Chlamydiae were demonstrated in the sinus material of all and in conjunctival smears of eight of the fifteen examined birds. Chlamydiae were isolated from all the examined birds after one to three passages on Buffalo Green Monkey (BGM) cell cultures using samples taken from lung, liver and spleen. No other pathogens were isolated. The chlamydia isolate was typed using a panel of serovar-specific monoclonal antibodies in a micro-immunofluorescence test. The isolate belonged to the avian Chlamydia psittaci serovar D. Experimental inoculation with this isolate of 7-day-old specific pathogen free (SPF) turkeys resulted in severe clinical signs, with mortality and extensive pathological lesions, similar to those seen in turkeys from the examined broiler turkey farm. From the data it was concluded that this Chlamydia psittaci isolate can cause severe disease in turkeys.

Typing Chlamydia psittaci--a review of methods and recent findings

When the present chlamydial classification was established it was recognized that a wide variety of types were contained within the arbitrary designation Chlamydia psittaci. Early workers relied mostly on observations of growth characteristics to differentiate the types of C. psittaci isolated from a wide range of different hosts. The differences between isolates were confirmed serologically using a variety of tests of which the most sensitive was the micro-immunofluorescence (MIF) test which was able to recognize nine immunotypes among the mammalian isolates alone. This approach has recently been improved by the use of monoclonal antibodies in the MIF test which has confirmed most of the mammalian immunotypes and divided the avian strains into four groups. Studies on the nucleic acid of C. psittaci isolates show clear differences in the size distribution of DNA fragments produced by restriction endonuclease digestion of the genomes of the various types. Most importantly, studies of DNA/DNA homologies showed that at least four of the types identified by biological, serological and restriction endonuclease tests were sufficiently different to be considered separate species. Most recently, attention has been focused on DNA sequence comparisons of C. psittaci genes amplified by the polymerase chain reaction (PCR). The usual target has been the major outer membrane protein gene for which much sequence information is now available. The combination of PCR and MIF with monoclonals has provided a set of practical techniques with which all chlamydial isolates can be detected and typed with relative ease. It is likely that these developments will lead to the reclassification of the genus and, hopefully, a rapid increase of our understanding of the diseases caused by C. psittaci.

Serotyping of European isolates of Chlamydia psittaci from poultry and other birds

A panel of five serovar-specific monoclonal antibodies which distinguish the five known avian serovars of Chlamydia psittaci was used to serotype 45 European avian Chlamydia psittaci isolates. Chlamydial antigen was grown in Buffalo green monkey (BGM) cells or in embryonated chicken eggs and was then inoculated into BGM cells. Serotyping was performed in an indirect immunofluorescence test. The 45 European isolates included 22 isolates from the order Psittaciformes, 9 isolates from the order Columbiformes, 6 isolates from the order Galliformes, 5 isolates from the order Passeriformes, and 3 isolates from the order Anseriformes. All of these were successfully serotyped. No additional serovars were found. One isolate from a duck and two isolates from psittacine birds gave positive immunofluorescences with two monoclonal antibodies considered to be specific for two different serovars. These three isolates were cloned by an agar overlay method. Serotyping of the clones demonstrated that the duck and one psittacine bird each were infected with two different serovars. After cloning, one isolate from a psittacine bird reacted only with serovar A. From these results it was concluded that this serotyping system allows the classification of all isolates tested so far. The results show that similar serovars are prevalent in avian species in Europe and the United States. The results also indicate that birds from a certain order are more susceptible to a distinct serovar. The use of a panel of serovar-specific monoclonal antibodies in the immunofluorescence test provides a reliable method for serotyping avian isolates. Monoclonal antibodies to new avian isolate serovars can easily be added to the panel, which makes the system useful for epidemiological studies.