Seroprevalence of Trichinella sp. in Wild Boars (Sus scrofa) from Yanggu-gun, Gangwon-do, Korea

Differences in larval survival and IgG response patterns in long-lasting infections by Trichinella spiralis, Trichinella britovi and Trichinella pseudospiralis in pigs

BACKGROUND

Domesticated and wild swine play an important role as reservoir hosts of Trichinella spp. and a source of infection for humans. Little is known about the survival of Trichinella larvae in muscles and the duration of anti-Trichinella antibodies in pigs with long-lasting infections.

METHODS

Sixty pigs were divided into three groups of 20 animals and infected with 10,000 larvae of Trichinella spiralis, Trichinella britovi or Trichinella pseudospiralis. Four pigs from each group were sacrificed at 2, 6, 12, 18 and 24 months post-infection (p.i.) and the number of larvae per gram (LPG) of muscles was calculated. Serum samples were tested by ELISA and western blot using excretory/secretory (ES) and crude antigens.

RESULTS

Trichinella spiralis showed the highest infectivity and immunogenicity in pigs and larvae survived in pig muscles for up to 2 years p.i. In these pigs, the IgG level significantly increased at 30 days p.i. and reached a peak at about 60 days p.i., remaining stable until the end of the experiment. In T. britovi-infected pigs, LPG was about 70 times lower than for T. spiralis at 2 months p.i. and only very few infecting larvae were detected at 6 months p.i., whereas no larvae were detected at 12, 18 and 24 months p.i. At 6 months p.i., degenerated/calcified larvae and cysts were detected in the muscles by trichinoscopy and histology. The IgG pattern showed by T. britovi-infected pigs was similar to that of T. spiralis-infected pigs, although seroconversion occurred some days later. The larval burden of T. pseudospiralis was slightly greater than for T. britovi at 2 months p.i., but no larvae were detected at 6 and 12 months p.i. In T. pseudospiralis-infected pigs, seroconversion occurred slowly, as in T. britovi-infected pigs. The IgG level showed a significant drop at 6 months p.i. and declining to the cut-off value at 12 months p.i.

CONCLUSIONS

The longer survival of T. spiralis in pigs in comparison with the other two species highlights its exceptional dissemination potential. These results provide an explanation of the controversial data collected by parasitological and serological tools in the course of epidemiological investigations.

Wild Boar: A Reservoir of Foodborne Zoonoses

Wild boar populations around the world have increased dramatically over past decades. Climate change, generating milder winters with less snow, may affect their spread into northern regions. Wild boars can serve as reservoirs for a number of bacteria, viruses, and parasites, which are transmissible to humans and domestic animals through direct interaction with wild boars, through contaminated food or indirectly through contaminated environment. Disease transmission between wild boars, domestic animals, and humans is an increasing threat to human and animal health, especially in areas with high wild boar densities. This article reviews important foodborne zoonoses, including bacterial diseases (brucellosis, salmonellosis, tuberculosis, and yersiniosis), parasitic diseases (toxoplasmosis and trichinellosis), and the viral hepatitis E. The focus is on the prevalence of these diseases and the causative microbes in wild boars. The role of wild boars in transmitting these pathogens to humans and livestock is also briefly discussed.