Quantitative Risk Assessment of Introduction of Foot and Mouth Virus into the U.S. through Cheese Importation

†H. A. Ahmad, ‡B. Tameru, ‡D. Nganwa, ‡L. Ayanwale, ‡T. Habtemariam, *R. W. Fite

†Department of Biology, Jackson State University,  ‡Center for Computational Epidemiology, Bioinformatics and Risk Analysis, College of Veterinary Medicine, Nursing & Allied Health, Tuskegee University, *United States Department of Agriculture, Animal and Plant Health Inspection Service, Maryland, United States.

ABSTRACT

A quantitative risk assessment was conducted to determine the risk of introduction of foot and mouth disease (FMD) virus into the United States via cheese importation. This risk assessment does not address the consequences of FMD virus introduction, its establishment, spread and the related economic, environmental and epidemiological consequences after introduction. A risk pathway scenario tree was developed to examine the most critical points in cheese production where FMD virus may be introduced or survive. At each node of the scenario tree the FMD viral infectivity was tracked and followed through the next node until the total FMD viral infectivity was determined at the final node. Assuming worst-case scenario that all cheese imported from FMD endemic countries is infected, the total risk of expected FMD infectivity in terms of ID50, in case of all mitigations failure, was determined for six ageing periods of 15, 30, 60, 75, 90, and 120 days. The values for cheese made from pasteurized milk and aged for 15 and 30 days are 363.13 and 8.12 ID50, respectively and for 60, 75, 90, and 120 days the amount is 0 ID50.  For cheese made from un-pasteurized milk the values are 2.13 x 105, 1.41 x 104, 9.25 x 102, 3.85 x 102, 1.88 x 102, and 61 ID50, respectively for the six ageing periods. It is concluded, based upon the number of infected dozes, that the imported cheese, regardless of its origin, kind of milk used, and ageing period, has an extremely low risk of FMD virus introduction into the United States.
Key words: risk assessment, FMD in cheese, pasteurization, pH, ageing.