These pigs had acquired lungworm infestations presumably containing masked influenza virus under natural conditions.

这些猪在自然条件下已受到含有流感病的肺丝。

As a rule the swine infested with the lungworms carrying the "masked virus" did not develop swine influenza immediately upon infestation with the lungworm.

通常，受到携带了“病”的肺丝侵袭的猪，并不因肺丝的侵袭立即发流感。