犬腺病毒2型（CANINE ADENOVIRUS TYPE 2）
[1T"aH2E%U0Canine adenovirus type 2(CAV一2)determines unapparent to mild infection of the respiratory tract and is regarded as one of the causes of the common widespread ITB．CAV一2 has also been implicated in episodes of enterifs and has been detected in the brain of dogs with neutological signs． The virus was first detected in l 96 1，in Canada， from dogs affected by laryngotracheitis．The isolate，strain Toronto A26／6 1，was characterized as an adenovirus，and was initially considered to be an attenuated strain of canine adenovirus type 1 (CAV一1)． Subsequently，structural and antigentic differences were observed and strain A26／6 1 was proposed as the prototype of a distinct canine adenovirus，designated as type 2 (CAV一2)．CAV一1 and CAV-2 were found to be genetically different by restriction endonuclease analysis and by DNA hybridization．The complete sequence analysis of both the CAV一1 and CAV一 2 9enome has revealed about 75％nucleotide identity．Although CAV一1 and CAV-2 are related genetically and antigenically，they have different tissue tropism．Vascular endothelial cells and hepatic and renal parenchymal cells are the main targents of CAV一1，while the respiratory tract epithelium and，to a limited degree，the intestinal epithelium，are the targets of CAV一2．In addition，the two types display different hemagglutination patterns． Infection with CAV——2 appears to be widespread in dogs that are not immune to CAV——l or CAV一2．CAV一2 was isolated from 34 0ut of 22 1 throat swabs of pups with and without respiratory signs that were taken to a veterinarian for vaccination．Likewise，pups in pet shops and in laboratory animal colonies were found to carry CAV一2 in the respiratory tract．By converse， CAV——2 was not detectable in dogs vaccinated in a rehoming center． The host range of CAV-2 includes a broad number of mammalian species．Wild—life animals may be a source infection for domestic dogs．The overall prevalence of antibodies to canine adenoviruses in European red foxes in Australia was 23．2％with marked geographical．seasonal and age differences，while the prevalence of antibodies was 97％in Island foxes in the Channel Island． California．Antibodies to CAV一2 were also detected in free——ranging terrestrial carnivores and in marine mammals in Alaska and Canada， including black bears，fishers，polar bears，wolves， walruses and Steller sea lions． The route of infection of CAV-2 is oronasal．The virus replicates in non-ciliated bronchiolar epithelial cells，in surface cells of the nasal mucosa， pharynx，tonsillar crypts，mucous cells in the trachea and bronchi in peribronchial glands and type 2 alveolar epithelial cells．In addition to these tissues，the virus can be isolated from retropharyngeal and bronchial lymph nodes as well as from the stomach and the intestine．The peak of replication is reached by 3——6 days post infection． Subsequently， virus loads rapidly中国宠物医师网9L:A
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5pe J#q%F:IEPl.OiG0decline， in relation to the production of antibodies，and CAV一2 usually can not be isolated by 9 days post infection．Respiratory signs are consistent with damage of bronchial epithelial cells．There may be evidence of narcotizing bronchitis or bronchiolitis and of bronchiolitis obliterans．Infection of type 2 alveolar cells is associated with interstitial pneumonia． Dogs exposed to CAV——2 alone rarely show spontaneous disease signs，although lung lesions can be extensive．When additional bacterial or viral agents are involved，the ITB complex can be observed． Antibodies to CAV——2 antigens have been demonstrated by hemagglutination—inhibition， agar gel diffusion，virus precipitation，complement fixation and by neutralization．Protection appears to correlate with the neutralizaing antibody level． Nasal or throat swabs appear to be suitable for virus isolation．Primary dog kidney ceUs have been used successfully for isolation and cultivation of CAV一2．However，a variety of cell lines are similarly susceptible to CAV一2 and to CAV一1． Demonstration of CAV——2 antigen by immunofluorescence in acetone——fixed lung sections or tissue imprints is used for diagnosis of CAV一2．A polymerease chain reaction(PCR) assay has been developed to detect canine adenoviruses to distinguish between CAV——l and CAV一2． Modified live CAV——2 vaccines proved to be highly effective in reducing the circulation of CAV一2 in canine populations．Dogs vaccinated with CAV——2 develop imnmnity to both CAV——l and CAV一2．In a similar fashion，dogs vaccinated with CAV——l develop immunity to both CAV——l and CAV一2．However，the use of CAV一2 for immunization of pups against both canine adenovirus types has eliminated safety side——effects encountered with CAV一1 vaccines，i．e．the occurrence of ocular lesions．Maternally—derived antibodies in pups may prevent active immunization after vaccine administration up．to the age of l 2—1 6 weeks．Vaccine administration by the intranasal route has been proposed to overcome the interference of maternal antibodies． but products for intranasal vaccination are not marketedN9LL"Y;M OF0l-tYl0
中国宠物医师网 T2DP lX~,E U
犬腺病毒2型(CAV一2)导致呼吸道隐性或 者轻微感染，视为常见的世界范围内流行的 ITB的病原之一。CAV一2还与肠炎的发病有 关，在出现神经症状的患犬脑中曾发现过该病 毒。中国宠物医师网 S,`O Dx,p*P~
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1961年，该病毒首次在加拿大发现于喉气 管炎的患犬中。分离株，即多伦多A26／61株，被 归为腺病毒，开始认为是犬腺病毒1型(CAV一 1)的致弱株。后来发现病毒的结构和抗原性都 存在差异，A26／61株被列为不同的犬腺病毒原 型，命名为cAv一2。通过限制性内切酶和DNA 杂交试验证明，CAV一1和CAV一2的基因型不 通。对CAv一1和cAv一2进行全序列分析后， 提示两者存在75％核苷酸一致性。虽然CAV一1 和CAV一2的基因型和抗原性相关，但是两者的 组织亲嗜性却不同。CAV一1主要的亲嗜靶位为 血管内皮细胞和肝脏及。肾脏实质细胞，而 CAV一2的亲嗜靶位为呼吸道上皮以及很少的 肠上皮。此外，cAv一1和CAV一2呈现出不同的 血细胞凝集类型。(OUJqmdyE0
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对CAV一1或CAV一2没有免疫力的犬中感 染CAV一2看似较为普遍。在出现呼吸症状及前 来进行免疫的无呼吸症状的221只幼犬的咽拭 子中，有34例都分离出CAV一2。同样的，宠物 店以及试验动物房的幼犬中也发现在其呼吸道 中携带CAV一2。但是，在领养中心的犬中没有 发现CAV一2。U/S F}e/t0
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CAV一2的宿主包括大量的哺乳动物。野生 动物可能是家养犬的感染源。在澳大利亚的欧 洲红狐中，犬腺病毒抗体的整体阳性率为 23．2％，并且有明显的地域性、季节性和年龄性； 然而，在加利福尼亚州的海峡岛上，狐狸的抗体 的整体阳性率为97％。自由出没的食肉动物及 其阿拉斯加州和加拿大的海洋动物，包括黑熊、 食鱼动物、极地熊、狼、海象和北海狮，在这些动 物身上都能发现CAV一2抗体。中国宠物医师网,Vn
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CAV一2通过口、鼻感染，病毒在无纤毛的细 支气管上皮细胞，鼻粘膜、咽和扁桃体隐窝的表 面细胞，支气管周腺体中气管和支气管的粘膜 细胞以及肺泡2型上皮细胞中进行复制。除了 这些组织之外，在咽后淋巴结和支气管淋巴结、 胃和肠中都能分离到病毒。感染后3～6大，病毒 复制达到高峰。之后，病毒载量迅速下降，这和 抗体生成相关。在感染9天之后，通常就无法分 离到CAV一2。呼吸症状的严重程度与支气管上 皮细胞的损伤程度一致，可能出现坏死性支气 管炎或细支气管炎和闭塞性细支气管炎。肺泡2 型细胞感染可以导致间质性肺炎。P7N@#Nu(TY|L0
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犬仅接触CAV一2时，很少表现出自然疾病 症状，但是会出现广泛性的肺脏损伤。当继发感 染细菌或病毒时，就能观察到ITB综合征。通过 血凝抑制试验、琼脂扩散试验、病毒沉淀试验、 补体结合试验和中和试验都能检测到CAV一2 抗体。机体的保护力和中和抗体水平相关。中国宠物医师网m(~6JZ3gqt,W
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鼻拭子或咽拭子适用于病毒的分离。原代狗 肾细胞曾成功分离和培养CAV一2。然而，多种 细胞系都同样对CAV一2和CAV一1易感。通过 免疫荧光试验检测丙酮固定的肺切片或组纱：[=1] 片中的CAV一2可以进行CAV一2的诊断。聚合 ’酶链式反应(PCR)已经用来检测犬腺病毒以区 分CAV一1和CAv一2。{4]'TCj0xR-TB0
P y |3QB7G f;I-C0改良的CAV一2活疫苗证明可以有效减少 犬群中CAV一2的流行。接种过CAV一2疫苗的 犬对CAV一1和CAV一2都有免疫力。同样的， 接种过CAV一1疫苗的犬对CAV一1和CAV-2 也具有免疫力。然而，当幼犬应用CAV一2疫苗 以获得对腺病毒的各型都具备抵抗力，在遇到 CAV一1疫苗时安全性降低，比如发生眼睛损 伤。幼犬体内的母源抗体可能在出生后的l2～16 周内都会干扰免疫力的建立。鼻腔免疫被认为 可以克服母源抗体的干扰，但是适用于鼻腔免 疫的产品目前还没有上市。(B
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