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隐蔽流丝虫寄生。

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“隐蔽”丝虫侵袭猪，并不因丝虫侵袭立即发生流。