Genetic evidence substantiates transmission of Trichinella spiralis from one swine farm to another

Ewa Bilska-Zajac,Giuseppe La Rosa,Benjamin M Rosenthal,Tomasz Cencek,Daniele Tonanzi,Edoardo Pozio,Peter C Thompson,Miroslaw Rozycki

doi:10.1186/s13071-021-04861-9

Abstract

BackgroundTrichinella spiralis ranks seventh in the risk posed by foodborne parasites. It causes most human cases of trichinellosis and is the most frequent cause of Trichinella outbreaks on pig farms and in wild boar, worldwide. Veterinary inspectors seek the source of outbreaks in hopes of limiting the spread. Established molecular tools are inadequate for distinguishing among potential T. spiralis infection sources because genetic variability in these zoonotic pathogens is limited in Europe. Microsatellite markers proved successful in tracing an outbreak of T. britovi, a related parasite harboring much more genetic variation. Here, we successfully employed microsatellite markers to determine the genetic structure of T. spiralis isolates from two pig outbreaks, discovering notable uniformity among parasites within each farm and discovering an epidemiological link between these two outbreaks.MethodsThe individual larvae from five isolates of T. spiralis from two pig farms and from ten wild boars were genotyped using nine microsatellite markers to examine their genetic structure.ResultsNotably uniform parasite populations constituted each farm outbreak, and the parasites from the first and second outbreaks resembled each other to a notable degree, indicating an epidemiological link between them. Wild boar harbored more genetically variable larval cohorts, distinguishing them from parasites isolated from domestic pigs.ConclusionsMicrosatellite markers succeeded in distinguishing isolates of the highly homogeneous T. spiralis, aiding efforts to track transmission. Each outbreak was composed of a homogenous group of parasites, suggesting a point source of contamination.Graphical abstract

Highlights

Trichinella spiralis ranks seventh in the risk posed by foodborne parasites
Outbreak backgrounds One Trichinella outbreak occurred at a pig farm located in Mogilno, Kujawsko-Pomorskie Province, Poland
In October 2013, routine diagnostic examinations conducted by Veterinary Inspection Service (VIS) discovered six pigs infected with Trichinella sp. larvae

Summary

Introduction

Trichinella spiralis ranks seventh in the risk posed by foodborne parasites It causes most human cases of trichinellosis and is the most frequent cause of Trichinella outbreaks on pig farms and in wild boar, worldwide. Synanthropic rats complicate epidemiology further, acting as T. spiralis vectors to wild and domesticated animals [18,19,20]. It was most common for only one of a farm’s pigs to be diagnosed with infection by the Polish VIS; since 2013, infections in several of a farm’s pigs have been documented; of late, more detailed epidemiological investigations have documented outbreaks involving several to dozens of pigs on a farm. These clustered outbreaks suggest contamination of shared feed, perhaps by means of illegally added meat [21]

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