Department of Animal Science, Iowa State University, Ames, IA 50011.
Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University College of Veterinary Medicine, Ames, IA 50011.
Avian Dis. 2021 Jun;65(2):310-320. doi: 10.1637/0005-2086-65.2.310.
In April and November of 2018, multiple commercial laying hen flocks within the same company presented with a sharp increase in mortality and drop in egg production that persisted for several days. These flocks showed striking necropsy lesions consistent with systemic infection and responded to antimicrobial treatment in the feed. (SA) was the most frequently isolated organism from multiple tissues including comb and wattle lesions, lungs, liver, ovary, spleen, and bone marrow. Given such an uncommon presentation of SA, which is known as a secondary opportunistic pathogen, a challenge study was conducted to evaluate its role in these disease outbreaks. In the present study, laying hens of two ages (22 and 96 wk) were inoculated with SA via three routes: oral gavage, subcutaneous (SC) injection, and intravenous (IV) injection. Both young and old hens in the IV group showed a significant increase in body temperature and drop in body weight; however, the clinical signs observed in the naturally occurring outbreaks were not present. SA was reisolated at multiple time points postchallenge from all challenge groups except the negative control group. While the SC group showed localized necrosis at the injection site, microscopic changes were different from changes observed in birds from the natural outbreaks. Despite observed initial differences in route and age, the SA challenge strain was not capable of reproducing the disease on its own. The results of this study indicate that SA may have played a role in the increased mortality, clinical signs, and necropsy lesions reported with the naturally occurring outbreaks. However, SA should still be considered as a secondary opportunistic pathogen. Other factors that could have caused the initial insult are stress, immunosuppression, or other primary infectious agents. The results of this study may aid veterinary diagnosticians, clinicians, and all poultry professionals to include SA in their differentials list as a secondary opportunistic pathogen in similar cases. This is an uncommon presentation and further field observations and clinical studies are needed to better elucidate the pathogenesis of this disease, which will in turn help to prevent future outbreaks.
2018 年 4 月和 11 月，同一家公司的多个商品蛋鸡群出现死亡率急剧上升和产蛋量持续下降数天的情况。这些鸡群表现出明显的剖检病变，与全身性感染一致，并对饲料中的抗菌药物治疗有反应。（SA）是从多个组织中分离出的最常见的病原体，包括鸡冠和肉垂病变、肺、肝、卵巢、脾和骨髓。鉴于 SA 如此罕见的表现，它被认为是一种继发性机会性病原体，因此进行了一项挑战性研究，以评估其在这些疾病暴发中的作用。在本研究中，通过口服灌胃、皮下（SC）注射和静脉（IV）注射三种途径对 2 个年龄（22 和 96 周）的蛋鸡进行了 SA 接种。IV 组的所有年轻和年老母鸡的体温均显著升高，体重下降；然而，自然发生的暴发中观察到的临床症状并未出现。除阴性对照组外，所有挑战组均在挑战后多个时间点从所有挑战组中重新分离出 SA。虽然 SC 组在注射部位显示出局部坏死，但显微镜下的变化与自然暴发中观察到的鸟类的变化不同。尽管观察到途径和年龄的最初差异，但 SA 挑战株本身并不能复制疾病。这项研究的结果表明，SA 可能在自然暴发中报告的死亡率增加、临床症状和剖检病变中发挥了作用。然而，SA 仍应被视为继发性机会性病原体。其他可能导致最初损伤的因素包括应激、免疫抑制或其他原发性感染源。本研究的结果可能有助于兽医诊断人员、临床医生和所有家禽专业人员将 SA 纳入他们的鉴别诊断列表中，作为类似病例中的继发性机会性病原体。这是一种罕见的表现，需要进一步的现场观察和临床研究来更好地阐明这种疾病的发病机制，这反过来将有助于防止未来的暴发。
