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

这些在自然条件下已受到含有隐蔽流感毒的肺丝虫。

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

常，受到携带了“隐蔽毒”的肺丝虫侵袭的，因肺丝虫的侵袭立即发流感。