Chronological analysis of gross and histological lesions induced by field strains of fowl adenovirus serotypes 1, 8b and 11 in one-day-old chickens

Fowl adenoviruses (FAdVs) cause diseases in domestic chickens, including inclusion body hepatitis (IBH), with immunosuppression believed to play a role in their pathogenesis. To gain a better understanding of the pathogenesis and chronology of disease caused by FAdVs, the gross pathology, histopathology and dissemination of virus were examined at several different time points, after inoculation of one-day-old specific pathogen-free chickens with FAdV-1, FAdV-8b or FAdV-11 via the ocular route. FAdV-8b had a slightly greater virulence than FAdV-11, but both were primary pathogens. The presence and severity of hepatic lesions were used to define the three stages of the disease: incubation (1–3 days post-inoculation, PI), degeneration (4–7 days PI) and convalescence (14 days PI). Both viruses were detected in the liver, kidney, bursa, thymus and gizzard of most birds during the degenerative stage, and persisted in the gizzard into convalescence. The FAdV-1 isolate was found to be apathogenic, but virus was detected in the bursa and/or gizzard of several birds between 2 and 7 days PI. This is the first study examining the chronology of gross and microscopic lesions of pathogenic and apathogenic FAdVs in association with viral presence in multiple tissues. It was concluded that both FAdV-8b and FAdV-11 are primary pathogens, and that these strains may play a role in immunosuppression.

禽腺病毒（Fowl adenoviruses, FAdVs）可感染家鸡并引发多种疾病，其中包括包涵体肝炎（inclusion body hepatitis, IBH），学界普遍认为免疫抑制在其发病机制中发挥关键作用。为更深入解析禽腺病毒感染的发病机制与疾病时序进程，本研究对1日龄无特定病原体（specific pathogen-free, SPF）鸡经眼部（ocular route）接种途径接种FAdV-1、FAdV-8b或FAdV-11后，于多个不同时间点开展了大体病理学（gross pathology）、组织病理学（histopathology）检测以及病毒播散（dissemination of virus）情况分析。实验结果显示，FAdV-8b的毒力（virulence）略强于FAdV-11，但二者均为原发性病原（primary pathogens）。研究团队以肝脏病变（hepatic lesions）的存在与否与严重程度为依据，将该疾病划分为三个阶段：潜伏期（接种后1~3天，post-inoculation, PI）、变性期（接种后4~7天，PI）与恢复期（接种后14天，PI）。在变性期，两种病毒均可在多数受试鸡的肝脏、肾脏、法氏囊、胸腺及肌胃中被检出，且病毒可在肌胃中持续存留至恢复期。值得注意的是，FAdV-1分离株被证实为无致病性（apathogenic）毒株，但在接种后2~7天期间，可在部分受试鸡的法氏囊和/或肌胃中检测到该病毒。本研究首次针对致病性与无致病性禽腺病毒，结合其在多种组织内的病毒分布情况，系统探究了其大体与微观病变的时序变化。最终研究结论指出，FAdV-8b与FAdV-11均为原发性病原，且这两株病毒可能与免疫抑制过程存在关联。