Listeriosis is a disease caused by the bacterium Listeria monocytogenes. This disease can cause serious disease in the unborn or newborn child. The disease may be transmitted by contact with infected animals or ingestion of contaminated food.
Infection in pregnancy generally presents as a mild flu-like illness, but may cause miscarriage or premature birth. Infection in utero or during delivery may lead to septicaemia and meningitis with a 50-100% mortality. Subsequent pregnancies are not at risk. Mother to foetus transmission occurs in utero, or during birth, or via person-to-person spread between infants shortly after delivery. Infection in the newborn may take the form of disseminated disease, involving many organs including the respiratory tract, eyes and nervous system.
There are on average 20-30 cases of listeriosis in pregnancy reported annually in the UK, but it is not known how many of these, if any, are associated with contact with sheep.
Infection is acquired by ingestion and most cases are probably the result of consumption of infected food. If contact with ewes at lambing time is unavoidable, washing of the hands after handling animals should prevent any possibility of infection.
The diagnosis may be made by isolating the organism from samples of blood, faeces or other body fluid. Listeria monocytogenes is susceptible to a number of antibiotics. There is no vaccine.
Listeria infection accounts for only 1-2% of sheep abortion incidents reported and diagnosed in Great Britain each year. In 2012 there were 139 diagnoses in sheep and goats in the UK (not all these cases were associated with abortion), compared to 111 diagnoses in 2011.
Animal infections include septicaemia, and abortion can occur from 12 weeks of pregnancy onwards. There may be occasional deaths in ewes. Encephalitis due to listeria infection may also be seen in sheep, but is not generally associated with abortions. Gastro-intestinal listeriosis in sheep has recently been recognised.
Last reviewed: 3 January 2014