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有蔽流感病的肺丝虫。

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“蔽病”的肺丝虫侵袭的猪，并不因肺丝虫的侵袭立即发流感。