RESUMEN
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.
Asunto(s)
Aborto Veterinario/diagnóstico , Pruebas Serológicas/veterinaria , Enfermedades de las Ovejas/diagnóstico , Aborto Veterinario/inmunología , Animales , Anticuerpos Antibacterianos/sangre , Chlamydophila psittaci/inmunología , Chlamydophila psittaci/patogenicidad , Pruebas de Fijación del Complemento/métodos , Pruebas de Fijación del Complemento/estadística & datos numéricos , Pruebas de Fijación del Complemento/veterinaria , Ensayo de Inmunoadsorción Enzimática/métodos , Ensayo de Inmunoadsorción Enzimática/estadística & datos numéricos , Ensayo de Inmunoadsorción Enzimática/veterinaria , Estudios de Evaluación como Asunto , Femenino , Técnica del Anticuerpo Fluorescente Indirecta/métodos , Técnica del Anticuerpo Fluorescente Indirecta/estadística & datos numéricos , Técnica del Anticuerpo Fluorescente Indirecta/veterinaria , Lipopolisacáridos , Embarazo , Sensibilidad y Especificidad , Pruebas Serológicas/métodos , Pruebas Serológicas/estadística & datos numéricos , Ovinos , Enfermedades de las Ovejas/inmunologíaRESUMEN
A chlamydial agent was recovered from the placental cotyledons of an aborting cow from a 100-cow dairy herd in Cumbria. Immunoblotting analysis of purified elementary bodies of the isolate revealed a reactivity pattern typical of serotype I Chlamydia psittaci strains. Nucleotide sequencing of the major outer membrane protein (MOMP) gene further confirmed the isolate, BA1, as a serotype I strain. The sequence was identical to that of the type strain of ovine enzootic abortion, B577. In both the antigenic and MOMP sequencing analyses BA1 was distinguishable from serotype II C. pecorum strains. A sequential series of sera obtained from the aborting cow, from which BA1 was recovered, was analysed by immunoblotting against the homologous isolate, and demonstrated reactivity to major chlamydial antigens over a 110-day period. Close contact between ruminant species on the farm suggested that the C. psittaci strain may have been transmitted to cattle from infected sheep.