Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
Department of Bacteriology and Epidemiology, Wageningen Bioveterinary Research, Lelystad, the Netherlands.
Transbound Emerg Dis. 2021 Jan;68(1):88-97. doi: 10.1111/tbed.13597. Epub 2020 May 17.
In recent years, different subtypes of highly pathogenic avian influenza (HPAI) viruses caused outbreaks in several poultry types worldwide. Early detection of HPAI virus infection is crucial to reduce virus spread. Previously, the use of a mortality ratio threshold to expedite notification of suspicion in layer farms was proposed. The purpose of this study was to describe the clinical signs reported in the early stages of HPAI H5N8 and H5N6 outbreaks on chicken and Pekin duck farms between 2014 and 2018 in the Netherlands and compare them with the onset of an increased mortality ratio (MR). Data on daily mortality and clinical signs from nine egg-producing chicken farms and seven Pekin duck farms infected with HPAI H5N8 (2014 and 2016) and H5N6 (2017-2018) in the Netherlands were analysed. In 12 out of 15 outbreaks for which a MR was available, MR increase preceded or coincided with the first observation of clinical signs by the farmer. In one chicken and two Pekin duck outbreaks, clinical signs were observed prior to MR increase. On all farms, veterinarians observed clinical signs of general disease. Nervous or locomotor signs were reported in all Pekin duck outbreaks, but only in two chicken outbreaks. Other clinical signs were observed less frequently in both chickens and Pekin ducks. Compared to veterinarians, farmers observed and reported clinical signs, especially respiratory and gastrointestinal signs, less frequently. This case series suggests that a MR with a set threshold could be an objective parameter to detect HPAI infection on chicken and Pekin duck farms at an early stage. Observation of clinical signs may provide additional indication for farmers and veterinarians for notifying a clinical suspicion of HPAI infection. Further assessment and validation of a MR threshold in Pekin ducks are important as it could serve as an important tool in HPAI surveillance programs.
近年来，不同亚型的高致病性禽流感（HPAI）病毒在世界范围内导致了多种家禽类型的爆发。早期检测 HPAI 病毒感染对于减少病毒传播至关重要。此前，曾提出使用死亡率比值阈值来加速对蛋鸡养殖场疑似感染的通知。本研究的目的是描述 2014 年至 2018 年期间在荷兰发生的 HPAI H5N8 和 H5N6 暴发期间在肉鸡和北京鸭养殖场早期报告的临床症状，并将其与死亡率比值（MR）的升高进行比较。对荷兰九家蛋鸡养殖场和七家北京鸭养殖场感染 HPAI H5N8（2014 年和 2016 年）和 H5N6（2017 年至 2018 年）的数据进行了分析，这些数据包括每日死亡率和临床症状。在可获得 12 次 MR 增加的 15 次暴发中，MR 增加先于或与农民首次观察到临床症状同时发生。在一次鸡和两次北京鸭暴发中，观察到临床症状早于 MR 增加。在所有农场，兽医都观察到了一般性疾病的临床症状。所有北京鸭暴发均报告有神经或运动症状，但仅在两次鸡暴发中报告有神经或运动症状。在肉鸡和北京鸭中，其他临床症状的观察频率较低。与兽医相比，农民观察和报告临床症状（尤其是呼吸道和胃肠道症状）的频率较低。本病例系列表明，具有设定阈值的 MR 可以作为在肉鸡和北京鸭养殖场早期检测 HPAI 感染的客观参数。临床症状的观察可能为农民和兽医提供额外的指示，以通知 HPAI 感染的临床疑似病例。进一步评估和验证北京鸭的 MR 阈值非常重要，因为它可以作为 HPAI 监测计划中的重要工具。
