For Foot-and-Mouth Disease Virus, which animal group tends to be the indicator hosts?

• A. Pigs
• B. Beef cows
• C. Sheep
• D. Dairy cows

Answer: (D)

Indicator hosts are the species in which infection is most readily detected and thus provides an early signal of the virus circulating in a region. For Foot-and-Mouth Disease Virus, dairy cattle fit this role well because they are kept in large, densely managed herds where clinical signs—especially oral and hoof lesions that affect milk production—are quickly noticed. The frequent handling of dairy cattle for milking and veterinary checks also makes surveillance and sample collection more practical, allowing rapid detection of outbreaks through clinical observation or milk testing.

In contrast, other groups tend to be less reliable as indicators. Pigs are highly susceptible and can amplify the virus, but outbreaks may be more localized to certain herds or production systems and may not provide as broad an early signal for regions with mixed livestock. Sheep often show milder signs, which can be easily overlooked, and beef cattle are typically more dispersed and less routinely monitored than dairy herds. Therefore, dairy cows are considered the best practical indicator hosts for surveillance purposes in many settings.