Increased Toxoplasma gondii positivity relative to age in 125 Scottish sheep flocks; evidence of frequent acquired infection

Abstract

Toxoplasma gondii seroprevalence was determined in 3333 sheep sera from 125 distinct sheep flocks in Scotland, with the majority of flocks being represented by 27 samples, which were collected between July 2006 and August 2008. The selected farms give a representative sample of 14 400 sheep holdings identified in the Scottish Government census data from 2004. Overall T. gondii seroprevalence, at individual sheep level, was determined to be 56.6%; each flock tested, had at least a single positive animal and in four flocks all ewes tested positive. The seroprevalence of sheep increased from 37.7% in one year old stock to 73.8% in ewes that were older than six years, showing that acquired infections during the life of the animals is frequent and that environmental contamination by T. gondii oocysts must be significant. The median within-flock seroprevalence varied significantly across Scotland, with the lowest seroprevalence of 42.3% in the South and the highest seroprevalence of 69.2% in the far North of Scotland and the Scottish Islands, while the central part of Scotland had a seroprevalence of 57.7%. This distribution disequilibrium may be due to the spread and survival of oocysts on pasture and lambing areas. A questionnaire accompanying sampling of flocks identified farms that used Toxovax®, a commercial vaccine that protects sheep from abortion due to T. gondii infection. Only 24.7% of farmers used the vaccine and the vaccine did not significantly affect the within flock seroprevalence for T. gondii. The implications for food safety and human infection are discussed.

Seropositivity to Toxoplasma infection in sheep samples submitted to Animal and Plant Health Agency laboratories between 2005 and 2012

“…The fact that both studies also showed an increasing seroprevalence with age provides further evidence to suggest that most infections occur in the postnatal period (Hutchinson and others 2011, Katzer and others 2011). Significant regional variation in within-flock seroprevalence to T. gondii infection in sheep has also been identified in some studies.…”

“…For example, since the majority of samples were taken for diagnostic purposes, it is likely that flocks with a recent history of abortion will be over-represented. Furthermore, previous surveys have shown that seroprevalence in sheep tends to increase with age (Halos and others 2010, Hutchinson and others 2011, Katzer and others 2011), and although it is probable that most of the samples used in this study will have been taken from adult breeding female sheep, possible age-related effects could not be accounted for due to lack of data.…”

Technical specifications on harmonised epidemiological indicators for biological hazards to be covered by meat inspection of domestic sheep and goats

“…Elevated T. gondii seroprevalences of up to 65% in small ruminants are frequently reported in the Mediterranean region and in Greece (Tzanidakis et al, 2012). In a recent study conducted in 125 Scottish sheep flocks, the overall T. gondii seroprevalence at individual level was 56.6 % (Katzer et al, 2011). In a study in France conducted in 2007, the proportion of sheep carcases carrying live parasites was 5.4 % (3-7.5 %) and molecular typing mostly revealed genotype II (Halos et al, 2010).…”

“…Some studies have identified other husbandry practices as risk factors, such as large flock size (Klun et al, 2006;Vesco et al, 2007), use of mouse poison and non-timber construction of the sheep house (Skjerve et al, 1998), grazing sheep together with sheep from other farms (Katzer et al, 2011), and cattle kept on the same premises (Hutchinson et al, 2011), but often with large uncertainty. No evidence is available to show whether eliminating these risk factors will have any impact on the presence or prevalence of T. gondii in the flocks or herds.…”

Genotyping of Toxoplasma gondii Isolates from Wild Boars in Peninsular Malaysia

“…It is considered as the most successful parasitic pathogen worldwide [1]. Although all warm blooded animals including marine mammals [2] and birds are susceptible to the infection, only felids are the definitive host of the parasite.…”