animal handlers such as farmers, standing water, and uncooked food scraps and feed supplements containing infected animal products can harbor the virus, as well. Cows can also catch FMD from the semen of infected bulls. Control measures include quarantine and destruction of both infected and healthy (uninfected) livestock, and export bans for meat and other animal products to countries not infected with the disease. There is significant variation in both susceptibility to infection and ability to spread disease between different species, virus strains, and transmission routes. For example, cattle are far more vulnerable than pigs to infection with aerosolized virus, and infected pigs produce 30 times the amount of aerosolized virus compared to infected cattle and sheep. Also, pigs are particularly vulnerable to infection through the oral route. It has been demonstrated experimentally that FMD can be spread to pigs when they eat commercial feed products contaminated by the FMD virus. Also, the virus can remain active for extended periods of time in certain feed ingredients, especially soybean meal. Feed biosecurity practices have become an important area of study since a 2013 outbreak of Porcine Epidemic Diarrhea Virus (PEDV) in the US, thought to be introduced through contaminated feed. Just as humans may spread the disease by carrying the virus on their clothes and bodies, animals that are not susceptible to the disease may still aid in spreading it. This was the case in Canada in 1952, when an outbreak flared up again after dogs had carried off bones from dead animals. Wolves are thought to play a similar role in the former Soviet Union. Daniel Rossouw Kannemeyer (1843–1925) published a note in the Transactions of the South African Philosophical Society volume 8 part 1 in which he links saliva-covered locusts with the spread of the disease. Transmission of the FMD virus is possible before an animal has apparent signs of disease, a factor that increases the risk that significant spread of the virus has occurred before an outbreak is detected. A 2011 experiment measured transmission timing in cattle infected with serotype O virus by exposing susceptible cattle in 24-hour increments. It estimated the infectious period of the infected cattle to be 1.7 days, but showed the cattle were only infectious for a few hours before they developed fevers or classic FMD lesions. The authors also showed that the infectious period would have been estimated to be much higher (4.2