Infection with microbes of the genus Listeria. Although listeriosis is primarily known as a disease of animals, particularly ruminants (e.g. cattle), low-grade infections in man may be commoner than is generally suspected and, in pregnant women, may lead to death of the foetus. Perinatal infection accounted for almost 75% of all cases reported in humans; meningitis or meningo-encephalitis accounted for most of the remainder. Other manifestations of listeric infection are conjunctivitis, endocarditis and urethritis.