The canine influenza virus (CIV) outbreaks have raised concerns as they pose a threat to the health of dogs. The successful construction of a canine influenza (CI) infection model is essential to study the CIV. Here we investigated the pathogenicity of different infectious doses of H3N2 CIV in Beagle dogs. Thirty-seven healthy Beagle dogs were used in the experiment and were infected with 10³, 10⁴, 10⁵, and 10⁶ 50% egg-infectious doses (EID₅₀). Compared to the dogs in the other three groups, those in the 10⁶ EID₅₀ group presented with obvious clinical symptoms, high virus titer, and typical pathological changes. Considering the ensemble of clinical scores, body temperature, virus shedding, lung lesions, pathological section scores, and visceral virus titers, we determined that 10⁶ EID₅₀ is the minimum infectious dose for the Beagle infection model. The other three infectious doses had almost no clinical symptoms. These results indicate that 10⁶ EID₅₀ is the minimum infectious dose of H3N2 CIV that can cause obvious clinical manifestations and pathological changes associated with CI in Beagle dogs. The theoretical framework developed in this research will guide the establishment of an infection model of CIV for future research.

犬流感病毒（CIV）的爆发引起了人们的关注，因为它们对狗的健康构成了威胁。成功构建犬流感（CI）感染模型对于研究CIV至关重要。在这里，我们调查了不同感染剂量的H3N2 CIV在比格犬中的致病性。三十七个健康只Beagle犬在实验中使用和被感染10 ³，10 ⁴，10 ⁵和10 ⁶ 50％蛋传染性剂量（EID ₅₀）。与其他三组的狗相比，那些10 ⁶ EID ₅₀的狗本组临床症状明显，病毒滴度高，典型病理改变。考虑到临床评分，体温，病毒脱落，肺部病变，病理切片评分和内脏病毒滴度的综合，我们确定10 ⁶ EID ₅₀是Beagle感染模型的最小感染剂量。其他三个感染剂量几乎没有临床症状。这些结果表明，10 ⁶ EID ₅₀是H3N2 CIV的最小感染剂量，可引起比格犬CI的明显临床表现和病理变化。本研究开发的理论框架将指导建立CIV感染模型，以备将来研究之用。