Epidemiology of Chlamydiaceae in livestock and emerging Chlamydia psittaci infections in chickens

Chlamydiaceae are a family of obligate intracellular Gram-negative bacteria causing disease in man and animals. C. abortus is a major abortigenic agent in ruminants, causing ovine enzootic abortion (OEA). C. psittaci causes respiratory disease (avian chlamydiosis) in birds and psittacosis or parrot-fever in man. In Chapter I, an overview is given of the epidemiology, prevention, treatment and zoonotic risk of Chlamydiaceae infections in Chinese livestock. Differences in risk-factors, such as bio-security measures, and use of diagnostic tests and veterinary practices applied in China are compared to the West. In Chapter II, we examined the occurrence of C. abortus in Belgian ruminants by serology and molecular diagnosis. Sampling herds at n ≥ 10 revealed a seropositive herd status in 14.3% (6/42), 50% (1/2) and 11.6% (11/95) of sheep, goat and cattle herds, respectively. Seroprevalence in one goat herd was 52.9% (9/17), but prevalence in positive sheep and cattle herds was generally limited to only 1 or 2 seropositive animals on 10 to 20 tested animals per herd. Molecular diagnosis on rectal swabs sampled at 3 cattle farms tested all negative for Chlamydiaceae DNA. In Chapter III, part A, we examined the pathogenicity of the well characterized C. psittaci genotype B (CP3) and D (92/1293) strains in experimentally (aerosol) infected SPF chickens. Both strains caused conjunctivitis, rhinitis and dyspnoea. Pharyngeal and cloacal C. psittaci excretion was observed in all infected animals, indicative for systemic dissemination as proven by immunofluorescence staining of frozen tissue sections. Histopathological lesions were present in all infected chickens. However, differences in pathology were observed as genotype D was more virulent than genotype B, creating mortality and more severe clinical signs and lesions. In Chapter III, part B, sera of 30 Belgian and 10 Northern French chicken farms were tested by a C. psittaci MOMP-based ELISA. Ninety-six percent, 93% and 90% of the Belgian broilers, broiler breeders and layers were seropositive. Ninety-one percent of the French broilers were seropositive. In addition, tissues of 5 Belgian and 5 French broiler farms were examined at slaughter. All French farms ware culture positive while C. psittaci was cultured from the lungs of 80% of examined Belgian farms. Chlamydia psittaci infections are apparently emerging in chickens raised in Belgium and Northern France. We could proof Hill-Evans postulates for chicken-derived C. psittaci genotype B and D strains. In Chapter III, part C, we focused on the histopathological lesions caused in experimentally infected SPF chickens. SPF chickens were experimentally infected with C. psittaci strain 10/423 (genotype B), 10/525 (genotype B) or 10/298 (genotype D), which were all isolated from Belgian or French broilers with pneumonia. All strains induced conjunctivitis, rhinitis, sinusitis, tracheitis, bronchitis, pneumonitis, airosacculitis, splenitis, hepatitis, nephritis and enteritis. Inflammation of the ovaries was only observed in genotype D infected chickens. Overall, the genotype D strain caused more severe histopathological lesions and a high mortality rate (54.5%) early upon infection. In addition, severity of lesions increased more rapidly in genotype D as compared to genotype B infected birds, which suggests faster replication in internal organs

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