The risk of introduction of equine infectious anemia virus into USA via cloned horse embryos imported from Canada

摘要

Deriving horse oocytes in the USA is hampered by the lack of abattoirs processing horse carcasses which could provide abundant quantities of ovaries from slaughtered mares. Therefore, several cloning industries in the USA are attempting to import cloned horse embryos from Canada. Like any agricultural commodity, cloned embryos pose a risk of introduction of exotic animal diseases into the importing country. Under such circumstances, risk assessment could provide an objective, transparent, and internationally accepted means for evaluating the risk. This quantitative risk assessment (QRA) was initiated to determine the risk of introduction of Equine infectious anemia virus (EIAV) into USA via cloned horse embryos imported from Canada. In assessing the risk, a structured knowledge base regarding cloning in relation to EIA was first developed. Based on the knowledge base, a scenario tree was developed to determine conditions (with mathematical probabilities) that could lead to the introduction and maintenance of EIAV along the cloning pathway. Parameters for the occurrence of the event at each node were estimated using published literature. Using @RISK software and setting Monte Carlo simulation at 50 000 iterations, the probability of importing an EIAV-infected cloned horse embryo was 1.8×10⁻⁹ (R = 1.5×10⁻¹² to 2.9×10⁻⁸). Taking into account the current protocol for equine cloning and assuming the yield of 5 to 30 clones per year, the possible number of EIAV-infected cloned horse embryos ranged from 2.0×10⁻¹⁰ to 9.1×10⁻⁵ (Mean = 1.4×10⁻⁶) per year. Consequently, it would take up to 1.5×10⁷ (R = 1.6×10⁴ to 5.1×10¹⁰) years for EIAV to be introduced into the USA. Based on the knowledge base and our critical pathway analysis, the biological plausibility of introducing EIAV into USA via cloned horse embryos imported from Canada is extremely low.