Newcastle Disease Virus (NDV), is a negative-sense single-stranded RNA virus. Transmission occurs by exposure to faecal and other excretions from infected birds, and through contact with contaminated feed, water, equipment and clothing. NDV strains can be categorised as velogenic (highly virulent), mesogenic (intermediate virulence) or lentogenic (nonvirulent). Velogenic strains produce severe nervous and respiratory signs, spread rapidly and cause up to 90% mortality. Mesogenic strains cause coughing, affect egg quality and production and result in up to 10% mortality. Lentogenic strains produce mild signs with negligible mortality.
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鸡新城疫病毒由副粘病毒引起 鸡新城疫
的高度接触性传染病。又称亚洲鸡瘟或伪鸡瘟 。常呈急性败血症状 。主要特征是呼吸困难、便稀、神经紊乱、黏膜和浆膜出血。死亡率高，对养鸡业危害严重。
速发嗜内脏型新城疫(VVND；Doyle，1927)，可致所有年龄的鸡发生最急性或急性、致死性疾病。通常见有消化道出血性病变。 鸡新城疫
速发嗜肺脑型新城疫(VPND；Beach，1942)，可致所有年龄发生急性，通常是致死性疾病，以出现呼吸道和神经症状为特征。
中发型新城疫(MND； Beaudette and Black，1946)，呼吸系统或神经系统疾病的低致病性形式。死亡仅见于幼雏。
缓发型新城疫(LND；Hitchner 和Johnson，1948)，轻度或不显性的呼吸道疾病。
无症状型或缓发嗜肠型新城疫 (LEND；Lancaster，1981)，主要是肠道感染。
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