Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2012
Publication Date: 9/14/2012
Citation: Poudel, A., Elsasser, T.H., Rahman, S., Chowdhury, E.U., Kaltenboeck, B. 2012. Asymptomatic natural Chlamydia pecorum infection reduces growth rates in calves by up to 48 percent. In: PLoS One 7:1-12, 2012. Interpretive Summary: Bacterial disease costs animal producers as well as consumers billions of dollars yearly when the animals that become infected grow poorly or die. A worst case scenario occurs where the presence of the infecting bacteria largely goes undiagnosed because of subclinical presence in mildly affected animals who continue to shed the organism into the environment only to have more susceptible animals succumb to acquired active disease. Data herein document that the world-wide presence of Chlamydia infection in livestock can be looked at as 2 rather different infections according to the pathogenicity of the infecting organism strain, or, in other world, how severe the infection from a given bacteria type is. The data suggest that even though some strains of Chlamydia are tremendously potent in causing disease, they are also very sensitive to preventive antibiotic treatment. Based on the measured impact of these infections in cattle, the presence of the disease could account for as much as a 48% decrease in growth rate in young animals. The data support early testing for intracellular bacteria like Chlamydia and are consistent with the need to use appropriate antibiotic intervention to limit the spread of this disease.
Technical 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. Much more frequent, essentially ubiquitous worldwide, are low-level, asymptomatic chlamydial infections in cattle. We investigated the impact of these naturally acquired infections in a cohort of 51 female Holstein and Jersey calves from birth to 15 weeks of age. In biweekly sampling, we measured blood/plasma markers of health and infection and analyzed their association with clinical appearance and growth in dependence of chlamydial infection intensity as determined by mucosal chlamydial burden or contemporaneous anti-chlamydial plasma IgM. Only the low pathotype 66P130 of C. pecorum was found by real-time PCR in conjunctival and vaginal swab specimens, and all calves acquired the infection but remained clinically asymptomatic. 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 66% increased growth (P=0.027), indicating a potential for immune protection from C. pecorum-mediated growth depression. The worldwide prevalence of chlamydiae in livestock and their high susceptibility to common feed-additive antibiotics suggest that the growth promoting effect of such antibiotics may be based to a large extent on suppression of chlamydial infections.