fThe obligate intracellular bacterium Chlamydia abortus is the causative agent of enzootic abortion of ewes and poses a significant zoonotic risk for pregnant women. Using proteomic analysis and gene expression library screening in a previous project, we identified potential virulence factors and candidates for serodiagnosis, of which nine were scrutinized here with a strip immunoassay. We have shown that aborting sheep exhibited a strong antibody response to surface (MOMP, MIP, Pmp13G) and virulence-associated (CPAF, TARP, SINC) antigens. While the latter disappeared within 18 weeks following abortion in a majority of the animals, antibodies to surface proteins persisted beyond the duration of the study. In contrast, nonaborting experimentally infected sheep developed mainly antibodies to surface antigens (MOMP, MIP, Pmp13G), all of which did not persist. We were also able to detect antibodies to these surface antigens in C. abortus-infected women who had undergone septic abortion, whereas a group of shepherds and veterinarians with occupational exposure to C. abortus-infected sheep revealed only sporadic immune responses to the antigens selected. The most specific antigen for the serodiagnosis of human C. abortus infections was Pmp13G, which showed no cross-reactivity with other chlamydiae infecting humans. We suggest that Pmp13G-based serodiagnosis accomplished by the detection of antibodies to virulence-associated antigens such as CPAF, TARP, and SINC may improve the laboratory diagnosis of human and animal C. abortus infections.
Chlamydia abortus is an obligate intracellularly replicating zoonotic bacterium that shares a characteristic biphasic developmental cycle with all other members of the family Chlamydiaceae (1). Among chlamydiae affecting humans, Chlamydia trachomatis is the most clinically and epidemiologically relevant as a cause of oculogenital infections, including nongonococcal urethritis and cervicitis, lymphogranuloma venereum, and trachoma. Chlamydia pneumoniae is known to be involved in community-acquired pneumonia, pharyngitis, bronchitis, and sinusitis. In addition, the avian pathogen Chlamydia psittaci has well-documented zoonotic potential, causing human psittacosis (ornithosis), which may present as a generalized and life-threatening pneumonia (2).C. abortus typically occurs in ruminants such as sheep and goats and is the leading cause of enzootic abortion of ewes (EAE) worldwide (3). Even in the absence of elevated abortion rates, the agent was shown to be widespread in German sheep flocks, with 50% of flocks testing PCR positive and 94% harboring seropositive animals (4). Afterbirths and fetuses of abortion cases can contain heavy loads of the pathogen and represent the major source of transmission to susceptible humans and naive ewes, as well as environmental contamination (3). Inhalation of infective aerosols by pregnant women poses the risk of severe infection, including spontaneous abortion, stillbirth, and septicemia (3, 5, 6). However, very little is known about the clinical rel...