Immunohistochemical Detection of Coxiella Burnetii in Formalin-Fixed Placenta

Coxiella burnetii is a zoonotically transmitted agent in small ruminants that can cause placentitis and subsequent abortion. In humans, Zoonotic transmission results in an acute febrile and sometimes fatal illness. Because domestic animals are the most important agent reservoir, accurate diagnosis is essential for identification of infectious tissue and infected animals. Detection of Coxiella-specific antibodies in complement fixation (CF) or agglutination assays can confirm prior exposure in sheep and goats. However, this does not offer a rapid diagnosis and must be correlated with typical clinical history and microscopic changes to fulfill the criteria for definitive diagnosis. Isolation of Coxiella from milk or placental tissues offers direct detection of the agent but necessitates working with fresh tissue infected with a human pathogen. Historically, the time-consuming method of indirect detection of specific antibodies after 14 or 28 days has been given diagnostic preference to prevent laboratory infections. Although the placental lesions associated with Coxiella infection have been adequately described, the diagnostician would benefit from the ability to definitively identify the organisms in fixed tissue. Immunohistochemical techniques are routinely utilized to diagnose abortion caused by Chlamydia psittaci, another Zoonotic cause of placentitis in small ruminants. To expand capabilities for definitive diagnosis of Coxiella abortion, we developed an avidin-biotin-peroxidase complex immunohistochemistry staining method to demonstrate Coxiella in formalin-fixed paraffin-processed placental tissues. This procedure provides the advantage of a rapid definitive diagnosis without the need to work with tissues containing viable organisms, thus eliminating the source of laboratory infections. Human Coxiella burnetii-negative (A. Louis, 190-91) and Coxiella burnetii-positive (JW261M1-2) antisera, the only known commercially available antisera, were negative for hepatitis B surface antigen, hepatitis C, human immunodeficiency virus (HIV)-1 and HIV-2 (by enzyme-linked immunosorbent assay). Titer against Campylobacter (Vibrio) by microtiter agglutination was < 25 and for Toxoplasma by indirect hemagglutination was < 64. The positive antisera had an indirect immunofluorescence titer against Coxiella burnetii of 1:60-320 for phase 1 and was negative for phase 11.