As a future large animal veterinarian, it is especially important to be well-versed in reportable diseases and foreign animal diseases, particularly Foot and Mouth Disease Virus (FMDV), which spreads very quickly and has the potential to devastate livestock populations in the United States. Classic clinical signs of FMDV in ruminants include oral ulceration and lameness. However, in many discussions of FMDV, effects on pigs are given less emphasis. There are several differences between the signs of FMDV in pigs versus ruminants that should be acknowledged.
Pigs are often infected by FMDV-contaminated products or by direct contact with another infected animal. Unlike ruminants, pigs are significantly less susceptible to aerosolized infection, requiring a nearly 600 times higher infective dose than cattle or sheep. Pigs also produce less aerosolized virus than ruminants. Many pigs become infected via oral transmission and the necessary infectious dose of virus is considerably lower if the pig has existing abrasions in or around the mouth. In contrast to ruminants, pigs do not become carriers of the virus following recovery from FMDV infection.
Pigs can develop subclinical or mild disease when exposed to low doses of virus and may show no appreciable clinical signs. Sub-clinically affected animals may not transmit the infection to other individuals, as the disease progresses quickly and viral levels in the blood are very low or undetectable. This can be problematic for veterinarians attempting to survey for and identify clinical signs of FMDV infection.
Fortunately, the most consistent clinical finding in pigs affected by FMDV are lesions around the coronary bands (immediately above the hooves) which are readily observable. Tongue lesions may also appear but at a later time than the signs on the feet. However, tongue vesicles can also be difficult to observe as they often occur far back on the tongue or as very tiny lesions on the tip of the tongue. As a result, diagnosis of FMDV in pigs is based initially on clinical signs and can easily be confused with other vesicular diseases such as vesicular stomatitis or vesicular exanthema virus infection. Therefore, it is crucial to remain aware of different disease manifestations across species as a veterinary professional and a steward of animal health and disease prevention.