Swine influenza A viruses (SIV) infection is among the leading causes of respiratory diseases in a number of animal species and human, and has been reported to cause substantial losses to pig industry. Previous reports of serological, molecular, and surveillance studies in commercial piggeries in Nigeria indicated the presence of SIV subtypes H1N1 and H3N2 in infected pigs; hitherto, there exists lack of studies on the pulmonary pathology and pathogenicity of SIV in Nigeria. This study investigates the presence of SIV subtype H1N1 antigen in the formalin-fixed paraffin-embedded lung sections obtained from apparently healthy pigs slaughtered at abattoirs located in Lagos, Ogun, and Oyo States, Southwest Nigeria using a streptavidin-biotin (ABC) immunoperoxidase (IP) staining. Two hundred four lungs consisting of 144 grossly pneumonic lungs and 60 apparently normal lungs were randomly collected, fixed in 10% neutral-buffered formalin, embedded in paraffin wax, and processed for histopathological examination and immunohistochemistry. The main gross lesions were marked pulmonary edema and mild bilateral consolidation of cranial lobes. Histopathology revealed suppurative bronchitis, and bronchiolitis with or without concurrent widespread degeneration and necrosis of epithelial cells (52.08%) and thickening of alveolar septa due to cellular infiltration consisting predominantly of neutrophils and mononuclear cells (macrophages and plasma cells) (39.58%). The lumina of most airways contained exudate consisting of neutrophils, desquamated epithelia cells, and necrotic debris. SIV antigen was immunohistochemically detected in 7/204 (3.43%) samples using SIV-specific (H1N1) monoclonal antibody. Positive cells exhibited a typical dark-brown reaction in the infected cells. A strong positive immunohistochemical staining was detected mainly in the alveolar macrophages and bronchial submucosal glandular epithelial cells while less intense staining was observed in the bronchiolar epithelial cells. The present study describes the distribution and localization of SIV subtype H1N1 antigens in the lung tissues of the infected pigs and provides public awareness on the presence of the virus in pig population in Nigeria and the risk factors associated with the infection. Therefore, people working in pig farms should maintain high level of biosafety and personal hygiene. This is the first report of immunohistochemical detection of SIV subtype H1N1 antigen in naturally infected pigs in Nigeria and may indicate rapid dissemination of the virus in susceptible pigs in the study area. A further molecular epidemiological study to investigate other SIV subtypes circulating in Nigerian pig population is warranted.

中文翻译：

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自然感染猪的福尔马林固定石蜡包埋肺组织中猪流感A病毒亚型H1N1抗原的定位和免疫组织化学检测

猪流感 A 病毒 (SIV) 感染是许多动物物种和人类呼吸道疾病的主要原因之一，据报道，它对养猪业造成了重大损失。尼日利亚商业猪场血清学、分子和监测研究的先前报告表明，受感染的猪中存在 SIV 亚型 H1N1 和 H3N2；迄今为止，尼日利亚缺乏对SIV肺部病理学和致病性的研究。本研究使用链霉亲和素-生物素 (ABC) 免疫过氧化物酶，调查了在位于尼日利亚西南部拉各斯、奥贡和奥约州的屠宰场屠宰的表面健康猪的福尔马林固定石蜡包埋肺切片中是否存在 SIV 亚型 H1N1 抗原。 IP) 染色。随机收集 204 个肺，其中包括 144 个严重肺炎和 60 个明显正常的肺，固定在 10% 中性缓冲福尔马林中，包埋在石蜡中，并进行组织病理学检查和免疫组织化学处理。主要的肉眼病变是明显的肺水肿和颅叶轻度双侧实变。组织病理学显示化脓性支气管炎和细支气管炎，伴有或不伴有广泛的上皮细胞变性和坏死（52.08%），以及由于主要由中性粒细胞和单核细胞（巨噬细胞和浆细胞）（39.58%）组成的细胞浸润导致的肺泡隔增厚。大多数气道的管腔含有由中性粒细胞、脱落的上皮细胞和坏死碎片组成的渗出液。使用 SIV 特异性 (H1N1) 单克隆抗体对 7/204 (3.43%) 个样本进行免疫组化检测 SIV 抗原。阳性细胞在感染细胞中表现出典型的深褐色反应。主要在肺泡巨噬细胞和支气管粘膜下腺上皮细胞中检测到强阳性免疫组织化学染色，而在细支气管上皮细胞中观察到的染色强度较低。本研究描述了 SIV 亚型 H1N1 抗原在受感染猪的肺组织中的分布和定位，并提高了公众对该病毒在尼日利亚猪群中的存在以及与感染相关的风险因素的认识。因此，在养猪场工作的人应保持高水平的生物安全和个人卫生。这是尼日利亚首次对自然感染猪的 SIV 亚型 H1N1 抗原进行免疫组织化学检测的报告，可能表明该病毒在研究区的易感猪中迅速传播。有必要进行进一步的分子流行病学研究，以调查在尼日利亚猪群中传播的其他 SIV 亚型。