Chlamydia gallinacea is a recently discovered and widespread obligate intracellular bacterium in chickens. In chickens, infections appear to be asymptomatic, but can result in reduced weight gain in broilers. Molecular typing revealed C. gallinacea is genetically diverse which might lead to differences in pathogenic potential between strains. However, studies about the pathogenesis of different C. gallinacea strains are still limited. In this study, the pathogenesis of C. gallinacea strain NL_G47 was investigated in three consecutive animal experiments. The first experiment served as a pilot in which a maximum culturable dose was administered orally to 13 chickens. Excretion of chlamydial DNA in cloacal swabs was measured during 11 days post infection, but no clinical signs were observed. The second and third experiment were a repetition of the first experiment, but now chickens were sacrificed at consecutive time points to investigate tissue dissemination of C. gallinacea. Again excretion of chlamydial DNA in cloacal swabs was detected and no clinical signs were observed in line with the results of the first experiment. PCR and immunohistochemistry of tissue samples revealed C. gallinacea infected the epithelium of the jejunum, ileum and caecum. Furthermore, C. gallinacea could be detected in macrophages in the lamina propria and in follicular dendritic cells (FDCs) of the B cell follicles in the caecal tonsil. Results of serology showed a systemic antibody response from day seven or eight and onward in all three experiments. The experiments with strain NL_G47 confirmed observations from field studies that C. gallinacea infection does not result in acute clinical disease and mainly resides in the epithelium of the gut. Whether the presence of C. gallinacea results in chronic persistent infections with long term and less obvious health effects in line with observations on other infections caused by Chlamydiae, needs further investigation.

Chlamydia gallinacea是最近在鸡中发现并广泛存在的专性细胞内细菌。在鸡中，感染似乎是无症状的，但会导致肉鸡增重减少。分子分型显示C. gallinacea具有遗传多样性，这可能导致菌株之间致病潜力的差异。然而，关于不同鸡冠菌菌株发病机制的研究仍然有限。在本研究中，鸡冠菌的发病机制在三个连续的动物实验中研究了菌株 NL_G47。第一个实验作为试点，其中向 13 只鸡口服最大可培养剂量。在感染后 11 天内测量泄殖腔拭子中衣原体 DNA 的排泄量，但未观察到临床症状。第二个和第三个实验是第一个实验的重复，但现在在连续的时间点处死鸡以研究鸡冠菌的组织传播。再次检测到泄殖腔拭子中衣原体 DNA 的排泄，并且没有观察到与第一次实验结果一致的临床症状。组织样本的 PCR 和免疫组织化学显示，鸡冠菌感染了空肠、回肠和盲肠的上皮。此外，C. gallinacea可以在固有层的巨噬细胞和盲肠扁桃体中 B 细胞滤泡的滤泡树突细胞 (FDC) 中检测到。血清学结果显示，在所有三个实验中，从第 7 天或第 8 天开始出现全身抗体反应。与应变NL_G47的实验证实，从实地研究的意见，即C. gallinacea感染不会导致急性临床疾病，主要存在于肠道的上皮细胞。C. gallinacea的存在是否会导致慢性持续性感染，其对健康的影响与对衣原体引起的其他感染的观察结果一致，其长期和不太明显的健康影响，需要进一步调查。