Prevalence survey of Toxoplasma gondii in hearts from Western Australian sows

Toxoplasma gondii (T. gondii) is a protozoan parasite that infects warm-blooded animals, including humans, with an estimated 30% of the world’s population seropositive for T. gondii (FAO/WHO 2014). Infection in humans can result from the consumption of uncooked or undercooked meat from infected animals. The World Health Organization has classified T. gondii as high priority in a report on the global burden of foodborne hazards based on the potential for serious ongoing pathological conditions (FAO/WHO 2014). Toxoplasma gondii from the meat of small ruminants, pork, beef and game ranked fourth in a global ranking tool of foodborne parasites by ‘importance’ and their primary food vehicle. Congenital toxoplasmosis may cause abortion, fetal death or central nervous system abnormalities, chorioretinitis and encephalitis in neonates.

The aim of this study was to estimate the prevalence of T. gondii in sow meat from Western Australia (WA). The sampling strategy was based on the numbers of sows required for a national baseline survey (a minimum of 300 samples would be required to give 95% confidence in a national prevalence estimate) using a randomised sampling framework and pig numbers proportional to annual production. Western Australia has 12% of the Australian sow population resulting in a total sample of 40 sow hearts from six free range and 14 intensive farms in WA. The sow hearts were collected at slaughter by abattoir employees, frozen to −20°C and transported to the SARDI Food Safety and Innovation laboratory. Heart tissue underwent acid/pepsin digestion (Dubey 1998) followed by DNA extraction using the Wizard Genomic DNA Extraction Kit (Promega Corp., Madison, WI, USA). All DNA extracts were analysed using polymerase chain reaction (PCR) for a mammalian house-keeping gene (Frericks and Esser 2008) and the T. gondii 529 base pair fragment (Opsteegh et al. 2010).

Toxoplasma gondii DNA was detected in two samples from different intensive indoor production herds, resulting in an estimated prevalence of T. gondii in sow hearts from WA of 5% (s.d. ± 1.4%). An earlier pilot study using the same methodology (APL project 2014/506) estimated the prevalence in sow hearts (n = 92 from 62 herds) from south-eastern Australia at 9.8% (s.d. ± 3.1%). Combined, the prevalence of T. gondii in sow hearts is 8.3% (s.d. ± 3.2%) with no statistical significant difference between the prevalence estimates for WA and south-eastern Australia (P = 0.57). It should be noted that this data does not represent the national prevalence of T. gondii in Australian pork due to limited geographic range and numbers sampled. Despite this, the data does indicate that further investigation is warranted to determine the actual prevalence in the Australian herd so that strategies are appropriately implemented to minimise public health risks associated with the consumption of uncooked comminuted fermented meats.