lentogenic

len·to·gen·ic

(len'tō-jen'ik), Denoting the virulence of a virus capable of inducing lethal infection in embryonic hosts after a long incubation period and an inapparent infection in immature and adult hosts; the term is used in characterizing Newcastle disease virus, particularly strains used as vaccines administered in water or as sprays, that is, mild or avirulent strains. [L. lentus, sluggish, inactive, + G. -gen, producing]