Review articleAll about Toxoplasma gondii infections in pigs: 2009–2020
Introduction
The protozoan Toxoplasma gondii infects virtually all warm-blooded animals, including humans, livestock, and marine mammals (Dubey, 2010). Approximately one-third of humanity is infected with T. gondii worldwide although this varies markedly between populations (Dubey, 2010; Robert-Gangneux and Dardé, 2012). Most infections appear to be asymptomatic in immunocompetent persons; however, the parasite can cause serious disease in humans, especially neonates, and immunocompromised people, who can die of toxoplasmosis (Peyron et al., 2016). In many animal host species, the infection is also typically subclinical; however, toxoplasmosis can be fatal in many hosts (Dubey, 2010).
The ingestion of food or water contaminated with oocysts excreted by infected cats or ingesting uncooked or undercooked meat containing tissue cysts of T. gondii are the 2 major modes of transmission of T. gondii. The proportion of the human population that acquires infection by ingestion of oocysts in the environment or by eating contaminated meat is not generally known and varies with cultural habits and the environment (Boyer et al., 2011; Hill et al., 2011).
Serological surveys have indicated that up to 30% of domestic pigs have been exposed to T. gondii worldwide (Limon et al., 2017; Rostami et al., 2017; Foroutan et al., 2019) and viable T. gondii has been isolated from pork tissues obtained at slaughter (Dubey, 2010). Recently, there has been numerous articles on T. gondii infection in pigs from China, especially on association of outbreaks of clinical toxoplasmosis in pigs with a unique genotype of T. gondii (ToxoDB genotype #9) (reviewed in Dong et al., 2018; Zhang et al., 2019).
The European Food Safety Authority (EFSA) recognized T. gondii as one of the public health hazards in swine to be assessed during meat inspection (see van Asseldonk et al., 2017). A research program was initiated in The Netherlands, to study cost effectiveness of the control programs for reducing T. gondii infection in pigs (van Asseldonk et al., 2017). In the past decade, demonstration of T. gondii DNA in processed pork or in cured pork products (Bayarri et al., 2010; Herrero et al., 2017; Costa et al., 2018) has raised questions of the safety of these products with respect to T. gondii transmission. There are conflicting reports concerning the survival of T. gondii in cured pork products.
Here, we review prevalence of anti-T. gondii antibodies, viable T. gondii, and T. gondii DNA in porcine tissues, epidemiology, risk factors, clinical disease, safety of processed and cured pork products for the past decade.
Section snippets
Methods of review
Papers published since 2009 and cited in PubMed, in review papers (Rostami et al., 2017; Dong et al., 2018; Olsen et al., 2019; Foroutan et al., 2019; Zhang et al., 2019; Abbas et al., 2020; Kolören and Dubey, 2020) and in the collection by one of us (J.P.D.) were consulted without any limits with respect to language. Additionally, help of international collaborators was sought to make the review inclusive of all papers published. This review is divided in two parts, domestic pigs and wild
Serologic prevalence
Surveys based on the presence of antibodies in blood sera have reported a worldwide distribution of T. gondii (Table 1). Most of these studies were based on convenience samples collected from slaughtered pigs. Prevalence of T. gondii varied dramatically among the classes of pigs surveyed (market pigs versus sows, indoor pigs from biosecure housing systems versus free-range or organic pigs). In the USA, the pigs sold for fresh pork consumption (feeder pigs, market pigs) are mostly raised indoors
Seroprevalence
Seroprevalences are summarized in Table 8. Seroprevalence varied a great deal and was dependent on several factors, include age, geography, management, and sampling. Most data were from hunted wild swine. The prevalence was generally low in a few samples from farmed boars in China (9.9%, Bai et al., 2017), Denmark (28.0%, Laforet et al., 2019), Finland (33.0%, Jokelainen et al., 2012), Latvia (20.3%, Deksne and Kirjusina, 2013), and Ukraine (6.6%, Galat et al., 2018). These pigs are probably
Genetic types of T. gondii in pigs
Pigs are important in the transmission of T. gondii in many countries. The genotypes of T. gondii in pigs in Brazil, China, France, and the USA are summarized in Table 11. Contrasting results are apparent. The highest genetic diversity is in Brazil with almost all strains as atypical or nonclonal. The T. gondii strains from Brazil are phenotypically different than strains elsewhere; most of the strains are virulent for outbred mice. However, little is known of their association with clinical
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was supported in part by an appointment of Camila K. Cerqueira-Cézar and Fernando H. A. Murata to the Agricultural Research Service (ARS) Research Participation Program administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy (DOE) and the U.S. Department of Agriculture (USDA). ORISE is managed by ORAU under DOE contract number DE-SC 0014664. All opinions expressed in this paper are the
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2023, International Journal for ParasitologyCitation Excerpt :In addition, ocular toxoplasmosis was described both in immunocompetent and immunocompromised patients after congenital and post-natal infections, and is considered the most common form of infectious posterior uveitis, which can lead to blindness (Maenz et al., 2014). In pigs, T. gondii infections are mostly asymptomatic (Stelzer et al., 2019; Dubey et al., 2020). Nevertheless, T. gondii has been reported to be a cause of reproductive failure in sows (Basso et al., 2015) and occasionally of severe illness with respiratory, digestive and/or neurological signs and even death in different age categories (Dubey, 2009; Klein et al., 2010; Li et al., 2010; Olinda et al., 2016; Stelzer et al., 2019; Dubey et al., 2020).
Risk factors associated with Toxoplasma gondii seroprevalence in domestic pig farms in Argentina
2022, Veterinary Parasitology: Regional Studies and Reports
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