Lounas Abdelaziz, Besbaci Mohamed, Akkou Madjid, Tali Oumennoune
Veterinary Sciences Institute, University of Blida 1, Blida, Algeria.
Vet World. 2021 Nov;14(11):3021-3027. doi: 10.14202/vetworld.2021.3021-3027. Epub 2021 Nov 28.
Marek's disease (MD) is a lymphoproliferative disease that occurs in chickens. In the absence of control measures, MD causes devastating losses to commercial poultry flocks. Vaccination has enabled dramatic success in the prevention and control of MD. However, the MD vaccination program has failed frequently, and occasional clinical outbreaks have been reported in the vaccinated flocks as well. The present study aimed to describe the clinical and histopathological characteristics of the field cases of MD in broiler breeder flocks.
A survey on the update of MD occurrence in Algerian broiler breeder flocks was conducted from June 2020 to September 2020. Ten vaccinated broiler breeder flocks located in Central Algeria and having progressive tumors in different visceral organs were evaluated for MD virus infection by conducting a histopathological examination of the birds.
The age of the birds affected with MD ranged from 13 to 22 weeks. The mortality rate varied sensitively from 4% to 10%. The clinical symptoms reported in the affected flocks included locomotor, nervous, digestive, and respiratory symptoms. Necropsy of the dead or euthanized birds revealed visceral lymphomatosis in several organs and macroscopic changes in the peripheral nerves (including loss of longitudinal striation, color change [grayish], and volume increase). The histopathological findings included the infiltration and proliferation of lymphocytes and blast cells (lymphoblasts) in various organs of the birds, which are the typical characteristics of MD and, therefore, confirmed the field infection of MD in these birds.
The present study provided evidence for the high prevalence of MD in the broiler breeder flocks vaccinated with a bivalent vaccine (turkey herpesvirus+Rispens) at the hatchery. The findings of the present study may indicate high-level failure of vaccination in these birds.
马立克氏病（MD）是一种发生于鸡的淋巴增生性疾病。在缺乏防控措施的情况下，MD会给商业家禽群造成毁灭性损失。疫苗接种已在MD的预防和控制方面取得了显著成效。然而，MD疫苗接种计划经常失败，且在接种疫苗的鸡群中也偶尔有临床疫情报告。本研究旨在描述肉种鸡群中MD现场病例的临床和组织病理学特征。
于2020年6月至2020年9月对阿尔及利亚肉种鸡群中MD发生情况的最新信息进行了调查。对位于阿尔及利亚中部的10个接种过疫苗且不同内脏器官出现进行性肿瘤的肉种鸡群，通过对鸡进行组织病理学检查来评估MD病毒感染情况。
感染MD的鸡的年龄在13至22周之间。死亡率在4%至10%之间敏感变化。受影响鸡群报告的临床症状包括运动、神经、消化和呼吸症状。对死亡或安乐死鸡的尸检显示多个器官出现内脏淋巴瘤以及外周神经的宏观变化（包括纵向条纹消失、颜色改变[变灰]和体积增大）。组织病理学发现包括鸡的各个器官中淋巴细胞和成母细胞（淋巴母细胞）的浸润和增殖，这是MD的典型特征，因此证实了这些鸡群中MD的现场感染。
本研究为孵化场接种二价疫苗（火鸡疱疹病毒+Rispens）的肉种鸡群中MD的高流行率提供了证据。本研究结果可能表明这些鸡群中疫苗接种的高水平失败。
