Since the 1980s, cetacean morbillivirus (CeMV) has caused mass mortality events worldwide. However, no epizootics had been recorded in the South Atlantic, until an unusual mortality event (UME) linked to Guiana dolphin cetacean morbillivirus (GD-CeMV) began in Ilha Grande Bay, southeastern Brazil, in November 2017. In a five-month period, the UME spread to neighboring Sepetiba Bay and accounted for the death of at least 277 Guiana dolphins (Sotalia guianensis). Prevalence of morbillivirus positive dolphins, as estimated from RT-PCR diagnostics, was 92.3% (24/26) in Ilha Grande Bay and 91.9% (57/62) in Sepetiba Bay. Females had higher mortality rates during the UME (1.5:1), in contrast with historical mortality data from both bays that showed a 2:1 male to female death ratio. Calf mortality rates also increased in both bays. These results suggest that females and calves were more vulnerable to morbilliviral infection. Herein, we discuss possible explanations for such sex-biased death pattern during the UME and their implication for the conservation of endangered Guiana dolphins. We also speculate about the origin and spread of morbillivirus in the South Atlantic Ocean.

中文翻译：

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第一次与南大西洋鲸类麻疹病毒相关的异常死亡事件的流行病学特征（巴西，2017-2018 年）

自 1980 年代以来，鲸类麻疹病毒 (CeMV) 已在全世界造成大规模死亡事件。然而，直到 2017 年 11 月在巴西东南部的格兰德湾开始发生与圭亚那海豚鲸目动物麻疹病毒 (GD-CeMV) 相关的异常死亡事件 (UME) 之前，南大西洋没有记录到流行病。 在五个月的时间里，UME 蔓延到邻近的 Sepetiba 湾并导致至少 277 只圭亚那海豚 ( Sotalia guianensis)死亡）。根据 RT-PCR 诊断估计，麻疹病毒阳性海豚的流行率在 Ilha Grande 湾为 92.3% (24/26)，在 Sepetiba 湾为 91.9% (57/62)。女性在 UME 期间的死亡率较高（1.5:1），而这两个海湾的历史死亡率数据显示男性与女性的死亡率为 2:1。两个海湾的小牛死亡率也有所增加。这些结果表明雌性和小牛更容易受到麻疹病毒感染。在这里，我们讨论了 UME 期间这种性别偏见死亡模式的可能解释及其对保护濒临灭绝的圭亚那海豚的影响。我们还推测了麻疹病毒在南大西洋的起源和传播。