ARS | Publication request: Viability and infectivity of Trichinella spiralis muscle larvae in frozen horse tissue.

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 4, 2007
Publication Date: May 15, 2007
Citation: Hill, D.E., Forbes, L., Gajadhar, A.A., Gamble, H.R. 2007. Viability and infectivity of Trichinella spiralis muscle larvae in frozen horse tissue. Veterinary Parasitology. 146(1-2):102-106.

Interpretive Summary: Trichinella spiralis can persist for extended periods of time in frozen horsemeat. Though motile larvae can be recovered from these frozen tissues, the infectivity of ML recovered from samples stored at -5 and -18C is low in mice, and this reduced infectivity occurs rapidly (1 day of storage at -18C). Though infectivity of recovered larvae is low in mice, the infectivity of these larvae in humans is currently unknown, as is the ability of this level of infectivity to cause clinical disease in human subjects. These data demonstrate that cold treatment strategies currently utilized for pork cannot be applied to horsemeat as a mitigation strategy for control of Trichinella.

Technical Abstract: The freeze tolerance of T. spiralis in horse meat stored at 5, -5, and -18oC for 1 day to 24 weeks has been assessed. Results demonstrate a steady reduction in the number of live ML recovered from the cold stored meat samples. On Day 1, recovery of larvae had been reduced by 18.6%, 50.1%, and 37.2% , and by 4 weeks, recovery of larvae had been reduced by 65.4%, 66.5%, and 96.2% in samples stored at 5, -5, and -18C, respectively. Infectivity results from mice inoculated with larvae recovered from cold stored meat samples revealed that by day 2 the infectivity of ML recovered from meat samples stored at -18C had been virtually eliminated (RCI 0.9). Infectivity of ML recovered from meat samples stored at 5C remained high for 4 weeks and fell rapidly thereafter. These data demonstrate that T. spiralis, a non-freeze tolerant species, can survive for extended periods in horse tissue, but infectivity in mice is virtually eliminated after 1 day of storage at -18C.