Cox Sherri L, Campbell G Douglas, Nemeth Nicole M
a Office of the Vice President of Research , University of Guelph , Guelph , ON , Canada.
Avian Pathol. 2015;44(2):135-41. doi: 10.1080/03079457.2015.1011604.
The detrimental effects of West Nile virus (WNV) have been well characterized in several taxonomic groups of North American birds, such as corvids and raptors. Relatively less is known about the virus' effects in waterfowl species, many of which are abundant in North America and occupy habitats, for example wetlands and marshes, likely to harbour dense mosquito populations. In two successive years, outbreaks of WNV-associated disease were observed in waterfowl at a rehabilitation centre. In the present report, clinical and pathological findings are provided for seven mallards (Anas platyrhynchos) and one Canada goose (Branta canadensis) that developed acute disease and either died or were killed humanely. The most severe and consistent microscopic lesion in mallards was myocardial degeneration and coagulative necrosis consistent with acute heart failure. The Canada goose had necrotizing myocarditis. Other lesions included pulmonary perivascular oedema, lymphoplasmacytic hepatitis, and splenic and bursal lymphoid depletion. WNV infection was confirmed using reverse transcriptase-polymerase chain reaction and immunohistochemical staining. Myofibres within all cardiac muscle layers had positive immunohistochemical staining, as did blood vessel walls in the heart and spleen. These results suggest that juvenile mallards are highly susceptible to fatal WNV-associated cardiac failure, and confirm that adult Canada geese are susceptible to fatal WNV-associated disease. The synchronous timing of clinical disease and death in these waterfowl are consistent with WNV mosquito-borne infections within a WNV transmission focus during the summer (July and August) of 2012 and 2013.
西尼罗河病毒（WNV）对北美鸟类的几个分类群，如鸦科鸟类和猛禽的有害影响已得到充分描述。关于该病毒对水禽物种的影响相对了解较少，其中许多水禽在北美数量众多，栖息于可能有密集蚊虫种群的湿地和沼泽等栖息地。在连续两年中，一家康复中心的水禽出现了与WNV相关的疾病暴发。在本报告中，提供了7只绿头鸭（Anas platyrhynchos）和1只加拿大鹅（Branta canadensis）的临床和病理结果，它们患上急性疾病后死亡或被人道处死。绿头鸭中最严重且一致的微观病变是心肌变性和凝固性坏死，符合急性心力衰竭。加拿大鹅患有坏死性心肌炎。其他病变包括肺血管周围水肿、淋巴细胞性肝炎以及脾脏和法氏囊淋巴组织耗竭。通过逆转录聚合酶链反应和免疫组织化学染色确诊了WNV感染。所有心肌层内的肌纤维以及心脏和脾脏的血管壁免疫组织化学染色均呈阳性。这些结果表明，幼年绿头鸭对致命的WNV相关心力衰竭高度易感，并证实成年加拿大鹅易患致命的WNV相关疾病。这些水禽临床疾病和死亡的同步时间与2012年和2013年夏季（7月和8月）WNV传播疫源地内WNV通过蚊子传播的感染情况一致。
