Concurrent monitoring of Trichinella and Toxoplasma infections in pigs from controlled housing systems

Abstract

Historically, pork was the most prominent food source which contributed towards the transmission of Trichinella spp. and T. gondii infections. To prevent Trichinella transmission via pork an EU regulation specifies that 1) every pig carcass is systematically sampled and examined for Trichinella and infected carcasses are considered unfit for human consumption or alternatively, 2) pigs are kept according the specifications of a controlled housing system (CHS). For T. gondii, no regulation exists which prevents transmission via the consumption of pork. Based on historical information in several pig populations, the T. gondii infection prevalence is higher than that of Trichinella. Trichinella spp. and T. gondii transmission towards pigs run partly via a concurrent route, namely, the consumption of (parts of) an infected animal. Due to the partial mutual infection route of Trichinella and T. gondii to pigs a correlation between the two parasitic infestations in these hosts may be expected. In case a correlation is present and T. gondii prevalence is higher as compared to Trichinella spp., the presence or absence of Trichinella spp. may be correlated to the presence or absence of T. gondii, respectively. As a consequence, given that the T. gondii prevalence is higher than that of Trichinella spp., the absence of T. gondii may predict the absence of Trichinella spp. The subject of this thesis is to test the applicability of a system which predicts Trichinella absence from the absence of T. gondii. The method is intended as an alternative and/or addition to the present EU Trichinella monitoring and control program. Information from our studies indicate that serological tests can be used to indicate the Trichinella and T. gondii infection status of pigs. However, due to their imperfect test accuracy, use of these serological tests will lead to false interpretation of infection status of the individual animal. Alternatively, the infection status can be qualified on population level. In this approach, the level of confidence that an infected population is qualified as infected increases with each additional tested animal. The correlation between the two parasitic infections in pigs was tested in animals from an endemic area. The results show that there is an association between the two parasitic infections in the studied pigs. Because the samples of animals used within this study were preselected from farms with Trichinella cases, the sampling method may have been biased. From the study it remains unclear whether the infections are always correlated. Assuming that in CHS populations the transmission of both parasites are not correlated, the probability of Trichinella absence is equal in T. gondii infected and non‑infected animals. Assuming that the transmission of both parasites are correlated, the probability of Trichinella absence is higher in the T. gondii uninfected animals. Therefore, Trichinella free predicted pork from pig from CHS has a similar to lower Trichinella infection risk for human consumers as compared to the current situation of Trichinella monitoring. Testing the T. gondii infection status generates information on prevalence within that population.