Meyer Meaghan, Bobeck Elizabeth, Sato Yuko, El-Gazzar Mohamed
Iowa State University Reviewer VDPAM 1809 S Riverside Dr 2430 Lloyd Vet Med Center UNITED STATES Ames Iowa 50011-3619 Iowa State University.
Iowa State University Assistant Professor Veterinary Preventive Medicine 1809 South River Drive UNITED STATES Ames IA 50011 17065403037.
Avian Dis. 2021 Jan 19. doi: 10.1637/aviandiseases-D-20-00118.
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. Staphylococcus aureus (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 is these disease outbreaks. In the present study, laying hens of 2 ages (22 and 96 weeks) were inoculated with SA via 3 routes: oral gavage (OG), subcutaneous injection (SC), and intravenous injection (IV). 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 re-isolated at multiple time points post-challenge 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，同一家公司内的多个商品蛋鸡群出现死亡率急剧上升和产蛋量下降的情况，且持续了数天。这些鸡群在尸检时呈现出与全身感染相符的显著病变，并对饲料中的抗菌治疗有反应。金黄色葡萄球菌（SA）是从包括鸡冠和肉垂病变、肺、肝、卵巢、脾和骨髓在内的多个组织中最常分离出的微生物。鉴于SA这种不常见的表现，它通常被认为是一种继发性机会致病菌，因此进行了一项攻毒试验以评估其在这些疾病暴发中的作用。在本研究中，对2个年龄段（22周和96周）的产蛋鸡通过3种途径接种SA：经口灌胃（OG）、皮下注射（SC）和静脉注射（IV）。IV组的年轻和老龄母鸡均出现体温显著升高和体重下降；然而，未出现自然暴发中观察到的临床症状。除阴性对照组外，在攻毒后的多个时间点，所有攻毒组均再次分离出SA。虽然SC组在注射部位出现局部坏死，但微观变化与自然暴发鸡群中观察到的变化不同。尽管在接种途径和年龄上观察到了初始差异，但SA攻毒株自身无法引发疾病。本研究结果表明，SA可能在自然暴发中报告的死亡率增加、临床症状和尸检病变中起了作用。然而，SA仍应被视为继发性机会致病菌。其他可能导致初始损伤的因素包括应激、免疫抑制或其他原发性感染因子。本研究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在类似病例中将SA作为继发性机会致病菌列入鉴别诊断清单。这是一种不常见的表现，需要进一步的现场观察和临床研究以更好地阐明该疾病的发病机制，这反过来将有助于预防未来的暴发。
