Mike Tildesley, an expert in infectious disease modeling at the University of Warwick, told CNN it's not the slaughter that dramatically heightens the risk of infection but the "significant movement of animals in the lead up to the festivals."

"We see this in Turkey -- there is a festival every year (where FMD is endemic) called Kurban which also involves the slaughter of significant numbers of livestock, preceded by vast movement of livestock around the country and a rise in FMD reported cases is typically observed when this occurs," he told CNN in an email.

"It is also possible for transmission to occur as a result of contact with carcasses, particularly in the first few hours after slaughter and that's why disposal of potentially infected carcasses has to be handled with great care," he said.

By July 7, Indonesia's outbreak had spread to more than 330,000 animals in 21 provinces, according to the Agriculture Ministry. Thousands more doses of vaccine had arrived from France, and more than 350,000 animals had been immunized.

Mike Tildesley, an expert in infectious disease modeling at the University of Warwick, told CNN it's not the slaughter that dramatically heightens the risk of infection but the "significant movement of animals in the lead up to the festivals."

"We see this in Turkey -- there is a festival every year (where FMD is endemic) called Kurban which also involves the slaughter of significant numbers of livestock, preceded by vast movement of livestock around the country and a rise in FMD reported cases is typically observed when this occurs," he told CNN in an email.

"It is also possible for transmission to occur as a result of contact with carcasses, particularly in the first few hours after slaughter and that's why disposal of potentially infected carcasses has to be handled with great care," he said.

By July 7, Indonesia's outbreak had spread to more than 330,000 animals in 21 provinces, according to the Agriculture Ministry. Thousands more doses of vaccine had arrived from France, and more than 350,000 animals had been immunized.