The incubation period of FMD in pigs varies with the strain of<br>infecting virus, the dose of virus, the route of infection,<br>individual susceptibility and the environment under which the<br>animals are kept. When exposed to a low dose of virus, animals<br>may only develop sub-clinical or, rarely in pigs, mild disease.<br>Sub-clinical infection is characterised by no detectable clinical<br>signs or lesions, a short, very low level or undetectable viraemia<br>and a low-level, transient antibody response. Such animals may<br>not transmit infection or may do so inefficiently. Consequently,<br>the initial incubation period, especially from premise to<br>premise, is likely to be longer while the virus levels are low,<br>followed by a much shorter animal to animal incubation period<br>from the time the disease first appears on a farm. The Cathay<br>topotype of serotype O, including the Taiwan 1997 outbreak<br>strain (20), is adapted to and highly virulent in pigs but<br>attenuated in cattle. For these strains, clinical signs can be<br>observed within 18 h in pigs after being placed in a heavily<br>contaminated pen. For other strains, the incubation period may<br>be as short as 24 h for pigs kept in intense direct contact. More<br>frequently, the incubation period is two or more days,<br>depending on the type of exposure – the two pigs that<br>developed clinical signs following aerosol exposure in the<br>thí nghiệm của Alexandersen et al. (1, 2, 3, 4) đã làm như vậy vào những ngày <br>4 và 5, tương ứng
đang được dịch, vui lòng đợi..
