Infection is by aerosol and nasal secretions transmission and this can occur even if there is a maternal antibody present in the body. Initial replication occurs in the upper respiratory tract. By 24hrs, coughing is induced once virus has reached bronchi and pulmonary lymph tissue. Cell-associated viremia, with virus predominantly in the [[T cells]] then occurs. Abortion can follow; the virus transfers from leukocytes to placental endothelium, causing [[thrombosis]] and [[Ischaemia|ischemia]]. 95% of abortions are in the last trimester, when chorionic placentomes have created an end-artery system vulnerable to ischemia. Any foals that are born will be weak and virus-positive. | Infection is by aerosol and nasal secretions transmission and this can occur even if there is a maternal antibody present in the body. Initial replication occurs in the upper respiratory tract. By 24hrs, coughing is induced once virus has reached bronchi and pulmonary lymph tissue. Cell-associated viremia, with virus predominantly in the [[T cells]] then occurs. Abortion can follow; the virus transfers from leukocytes to placental endothelium, causing [[thrombosis]] and [[Ischaemia|ischemia]]. 95% of abortions are in the last trimester, when chorionic placentomes have created an end-artery system vulnerable to ischemia. Any foals that are born will be weak and virus-positive. |