Submitted to: Veterinary Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/6/2007
Publication Date: 5/15/2007
Citation: Hill, D.E., Forbes, L., Kramer, M.H., Gajadhar, A., Gamble, H.R. 2007. Parasitological and immunological parameters of long term infection with Trichinella spiralis (Tl) in the horse, Equus caballus. Veterinary Parasitology. 146(1-2):107-116. Interpretive Summary: In the present study, we confirm that T. spiralis can persist for extended periods of time in the musculature of the horse and that host immune reactions to this aberrant host are not sufficient to destroy or even reduce larval numbers. In contrast, stimulation of a detectable, systemic antibody response is lost within the first 3 to 6 months after infection though infective larvae persist in tissues. These data demonstrate that currently available serological tests are not a reliable indicator of infection status in the horse, and are of little value in epidemiological studies. For countries where horsemeat is consumed by humans, care should be taken to alert consumes to the risk of acquiring trichinellosis and the importance of thoroughly cooking meat or obtaining assurance that adequate inspection has been performed using a validated method of artificial digestion.
Technical Abstract: In this study, 35 horses were infected with 1000, 5000, or 10,000 T. spiralis muscle larvae and the course of infection was followed for 1 year. Larval burdens in selected muscles, the condition and infectivity of larvae in tissue, and the serological response of infected horses were assessed. The results of the study demonstrated that T. spiralis establishes infection in horses in a dose dependent manner. Low dose infections may be detected by an increase in parasite-specific serum antibodies despite an inability to recover parasites. Anti-Trichinella IgG antibodies peaked between weeks 6-10 post-inoculation and declined to pre-inoculation levels by weeks 24-26. Viable, infective larvae persist in horse musculature for at least 12 months, and exhibit no reduction in muscle burdens over this period. Given the lack of a detectable serological response by 26 weeks p.i. despite the persistence of infective muscle larvae, direct methods of detection are the only methods suitable for both meat inspection and epidemiological studies of Trichinella infection in the horse.