A new mathematical model from researchers at North Carolina State University reveals the high risk of cross-species disease spread on farms with more than one type of livestock. According to the model, biosecurity efforts focused on the top 3% of farms in a particular contact network may significantly cut back cross-species disease dissemination.
“Most disease-prevention programs focus control and prevention measures on one species; however, it is well known that cross-species transmissions occur,” says Gustavo Machado, assistant professor of population health and pathobiology at NC State and corresponding author of a paper describing the work. “For example, foot-and-mouth disease can be transmitted among all ungulate species. And all of these farms are connected – they sell and share animals all the time.”
Machado and postdoctoral researcher Nicolas Cardenas created a stochastic mathematical model that described the “connectedness” of farms in one area of Southern Brazil. The model included three years’ worth of data for a population of 90 million animals and traced over 1.6 million animal movements between farms, such as animal sales and grow-finishing movements.
The model simulated disease outbreaks that began in cattle, swine, and small ruminants (i.e., sheep or goats), respectively, in order to determine the likelihood of cross-species contamination in each case. They ran 1,000 distinct simulations 100 times each to identify all possible outbreak routes.