猪在潜伏期期间具有传染力，潜伏期持续4至14天。
Pigs are infectious during the incubation period, which lasts from 4 to 14 days.
第一部分研究了具有一般形式接触率潜伏期有传染力的SEI模型。
In the first section, the SEI epidemic model with a general contact rate and infectious force in the latent period is investigated.
第二部分考虑了永久免疫力因素，研究了一类潜伏期具有传染力的SEIR模型，使模型更具有广泛性。
In the second section, considering the permanent immunity factor, the SEIR epidemic model with infectious force in the latent period which makes the model more universal is investigated.
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