求翻译：近年来猪瘟和口蹄疫的流行和发病特点发生了很大的变化，免疫工作的不到位，使得典型猪瘟逐渐减少，目前多以亚急性、慢性和非典型出现。口蹄疫病毒具有多型性、易变性的特点。根据其血清学特性，现已知有7个血清型，即O、A、C、SAT1、SAT2、SAT3(即南非1、2、3型)以及Asia1(亚洲1型)。是什么意思？

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In recent years classical swine fever and foot-and-mouth disease prevalence and incidence of characteristic was very great changes in immunization work are not in place, making the typical classical swine fever is gradually reduced and is now more to the acute, chronic and non-typical. Foot-and-mout

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Prevalence and characteristics of classical swine fever and foot and mouth disease in recent years great changes have taken place, immunization is not in place, making CHC gradually reduced, now appears as a subacute, chronic and non-typical. Foot and mouth disease virus has the characteristics of p

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