zoonoses and communicable diseases common to ... - PAHO/WHO

LISTERIOSIS 173A study carried out in 1970–1971 in Victoria (Australia) (Dennis, 1975) showedthat listeriosis is an important cause of perinatal mortality in sheep. In 94 flocks,fetuses and lambs that died during the neonatal period were examined, and L. monocytogeneswas found in 25%. The disease caused by this agent occurs mostly in winter.It has been estimated that the rate of abortion in flocks affected by listeriosis inVictoria varies from 2% to 20%.L. ivanovii, which differs from L. monocytogenes on the basis of several phenotypiccharacteristics, was associated in several countries with abortions in sheep and,occasionally, in cows (Alexander et al., 1992).OTHER MAMMALS: Listeriosis is rare in swine; when it does occur in the first fewweeks of life, it usually takes the septicemic form. Few cases are known in dogs, inwhich the disease may be confused with rabies. In other domestic and wild species,the disease generally appears as isolated cases and in the septicemic form.Outbreaks have been described in rabbit and guinea pig breeding colonies.FOWL: Young birds are the most affected. Outbreaks are infrequent and mortalitymay range from the loss of a few birds on one farm to a high rate of losses onother farms. The septicemic form is the most common, with degenerative lesions ofthe myocardium, pericarditis, and focal hepatic necrosis. On rare occasions, themeningoencephalitic form is found, with marked torticollis. Since the generalizeduse of antibiotics in poultry feed began, few cases of listeriosis in this species havebeen reported.Source of Infection and Mode of Transmission: The causal agent is widely distributedin animals and man, as well as in the environment. L. monocytogenes hasbeen isolated from different mammalian and avian species and from the soil, plants,mud, pasture, wastewater, and streams. The presence of virulent and avirulent (formice) strains in animals and in the environment complicates clarification of the epidemiology,but serotyping can be of considerable help. Cattle, sheep, and manyother animal species eliminate the agent in their feces. L. monocytogenes has alsobeen isolated from the feces of patients and their contacts, as well as from a smallpercentage of the general human population. However, it has been isolated from thestools of some 20% to 30% of pregnant women, and has also been found in thefemale genital tract. In addition to untypeable strains, potentially pathogenicserotype 1 and serovar 4b have been isolated (Kampelmacher and van NoorleJansen, 1980). Consequently, the natural reservoir is wide and the number of hostsis large. Despite this, few people contract the disease. Many women from whosestools the agent has been isolated give birth to healthy children. Concurrent conditions,such as stress and other predisposing causes (particularly diseases or treatmentsthat depress the immune system), come into play in initiating the disease.Another predisposing cause is the decline in the immune system that occurs withaging, as well as endocrine changes during pregnancy and deficiencies inimmunoregulation at the placental level.The source of infection for the fetus and newborn is evidently the infected motherherself. It is believed that the almost inapparent disease course manifested by themother is caused by a mild bacteremia. Airborne infection might play a role, as suggestedby the influenza-like symptoms exhibited by the mother. The mother’s genitaltract is probably infected via the fecal route, while the fetus is infected via the