Evaluation of the protective efficacy of a novel rVCG-based Chlamydia abortus vaccine in a pregnant mouse model

Abstract

Abstract Chlamydia abortus (Cab) is the cause of ovine enzootic abortion (OEA) in small ruminants and poses a zoonotic risk to pregnant women, which may result in spontaneous abortion. Although antibiotics are effective against Cab infection, most infections are asymptomatic, suggesting alternative strategies may be required for controlling these infections. We tested the ability of a recombinant Vibrio cholerae ghost (rVCG)-based Cab subunit vaccine expressing the truncated Cab polymorphic membrane protein 18D (rVCG-Pmp18.3) to protect against Cab-induced abortion in a pregnant mouse model. Thus, groups of female C57bl/6J mice were immunized intranasally (IN) with rVCG-Pmp18.3 and mated with males 3 weeks post immunization. Immunized and control mice were infected IN or transcervically (TC) at day 10 of pregnancy and the number of pups per mouse was enumerated 7 days postpartum. Mice were sacrificed on day 8 and Cab burden in the lungs and spleens was determined. The results showed IN immunization protected mice against abortion and neonatal death while IN infected control mice lost 20% of their litter and 60% of TC infected controls lost their entire litter 7 days post-parturition. Immunized mice completely cleared the infection in the lungs and showed a significant reduction (p ≤0.0001) in bacterial burden in the spleen compared to non-immunized, infected controls. Furthermore, immunized mice were protected from uterine dilation compared to 60% of non-immunized controls that developed tubal pathology. These results demonstrate the ability of rVCG-Pmp18.3 to prevent respiratory/systemic infection and protect against Cab-induced abortion and tubal pathologies in mice, suggesting its potential development as a vaccine for ruminants. Supported by PHS grant R01AI41231 and NIH R01AI26897