Comprehensive analysis of the impact of endemic Chlamydia pecorum infection in cattle

Abstract

Intracellular Chlamydia (C.) bacteria cause in cattle some acute but rare diseases such as abortion, sporadic bovine encephalomyelitis, kerato-conjunctivitis, pneumonia, enteritis and polyarthritis. More frequent, essentially ubiquitous worldwide, are low-level, asymptomatic chlamydial infections in cattle. In two independent prospective observational studies, we investigated the impact of naturally acquired endemic asymptomatic C. pecorum infections on neonatal health, fertility and milk production in dairy cows. In calves, we analyzed in biweekly sampling the association of blood/plasma markers of health and infection with clinical appearance and growth in dependence of chlamydial infection intensity determined by mucosal chlamydial burden or contemporaneous anti-chlamydial plasma IgM. High chlamydial infection associated with reduction of body weight gains by up to 48% and increased conjunctival reddening (P<10-4). Simultaneously decreased plasma albumin and increased globulin (P<10-4) suggested liver injury by inflammatory mediators as mechanisms for the growth inhibition. This was confirmed by the reduction of plasma insulin like growth factor-1 at high chlamydial infection intensity (P<10-4). High anti-C. pecorum IgM associated eight weeks later with a 66% increase in growth (P=0.027), indicating a potential for immune protection from C. pecorum-mediated growth depression In first lactation dairy cows, we examined the association of cervical chlamydial burden and anti- C. pecorum immune trend (day 100/day 65 anti C. pecorum IgM) at the time of first insemination with reproductive performance and milk production. C. pecorum cervical infection and low plasma luteinizing hormone levels associated highly significantly with reduction of fertility by up to 28% (P=0.007), suggesting that C. pecorum-induced inflammatory endometrial damage and dysregulation of the neuroendocrine axis of reproduction suppress fertility. In contrast, a declining anti-C. pecorum IgM response after first service and low plasma cholesterol and albumin, but not cervical chlamydial burdens, associated with reduction of milk production by up to 7% (P<10-4), suggesting that declining anti-C. pecorum immunity and low liver health suppress milk production. Our findings of very high plasma anti-C. pecorum IgM antibody concentrations in all calves and cows enrolled in the studies, and the simultaneous prevalence of multiple strains of C. pecorum suggest a high, steady-state endemic C. pecorum infection. These studies confirm the enormous economic impact of low-level asymptomatic C. pecorum infection and the need for a protective vaccine against C. pecorum.