Ovine toxoplasmosis

Abstract

Congenital infection with Toxoplasma gondii is an important cause of abortion in sheep worldwide. The cat is the definitive host of the parasite, and infected cats may shed millions of oocysts in their faeces resulting in extensive environmental contamination and an important source of infection for grazing herbivorous animals. Studies looking at development of specific antibodies in sheep, as an indicator of exposure to T. gondii, have shown that there is an increase in seroprevalence associated with age indicating that most infections in sheep occur following birth. The stage of gestation when transplacental transmission of T. gondii to the developing foetus occurs is critical in determining the clinical outcome. The importance of endogenous transplacental transmission in persistently infected ewes and its clinical importance is a subject of current debate. Ewes infected prior to mating develop immune responses that help protect against disease in a subsequent pregnancy and also against experimental challenge administered during pregnancy. Both innate and adaptive immune responses are activated following T. gondii infection and experiments involving the chronic cannulation of peripheral lymph nodes in sheep have allowed the dynamics of the immune responses to be analysed in real time. A live vaccine, Toxovax is the only commercially available vaccine worldwide to protect against congenital toxoplasmosis.

First report of seroprevalence of <i>Toxoplasma gondii</i> infection in sheep in Pomerania, northern Poland

“…In 1987, Blewett and Trees [6] suggested that the T. gondii parasite may be responsible for 1-2% of neonatal losses annually. Thus, these losses may translate to over 1.5 million lambs lost in Europe per year, representing a significant loss to producers and national economies [7]. In addition, the tissue cysts of T. gondii in meat of infected sheep are an important source of infection for humans [1].…”

Outbreak of ovine congenital toxoplasmosis in Iran, confirmed by different diagnostic methods

“…Infection at mid-gestation can result in birth of a stillborn or weak lamb which may have an accompanying small mummified fetus, whereas infection in later gestation may result in birth of a live, clinically normal, but infected lamb (Buxton 1990;Innes et al 2009). We proposed that the occurrence of the disease (exposure to T. gondii), which took place in October 2010, was the reason of the death of the lambs 4-5 days after birth.…”

“…It was first described by Hartley et al (1954) which even today is known as one of the major causes of sheep abortion world wide (Buxton 1991). Another characteristic of vertical transmission of T. gondii is that this kind of transmission can occur more frequently than what was previously thought (Duncanson et al 2001;Morely et al 2005Morely et al , 2007Hide et al 2009;Innes et al 2009;Dubey 2009). …”

Outbreak of caprine abortion by Toxoplasma gondii in Midwest Brazil

“…Although in Brazil it is difϐicult to accurately deϐine the incidence of toxoplasmosis as the cause of abortion and stillbirth in goats, a study made in the UK suggested that the disease was responsible for 1-2% of neonatal losses per year (Blewett & Tress 1987) and if this incidence was extrapolated throughout Europe, this would mean a loss of around 1.5-2 million animals, suggesting that T. gondii is an important cause of reproductive losses (Innes et al 2009). …”

“…In toxoplasmosis the severity of disease is a function of the stage of gestation when infection occurs (Innes et al 2009). In our study, the age of the fetuses was between 110 and 140 days, but it was not possible to know the time when infection was established.…”