Foot-and-mouth disease (also called hoof-and-mouth disease) produces fluid-filled blisters on the mouth, tongue, lips, and feet of infected livestock. These blisters rupture within a day or two, leaving behind raw, eroded patches of tissue that are often the most recognizable sign of the disease. The condition affects cattle, sheep, goats, and pigs, and it looks slightly different in each species.
What the Blisters Look Like
The hallmark of foot-and-mouth disease is vesicles: raised, fluid-filled blisters that develop on soft tissue. In cattle, these blisters appear on the tongue, lips, and inside the mouth. They can also form on the feet around the hooves and occasionally on the udder or teats. The fluid inside ranges from clear to cloudy.
When the blisters pop, they discharge that fluid and leave behind raw, eroded areas surrounded by ragged fragments of loose tissue. These open sores are painful and often easier to spot than the intact blisters, which can rupture quickly. In the mouth, the erosions may look like irregular, reddish ulcers against the pink tissue of the tongue or gums.
How It Looks in Different Animals
Cattle tend to show the most prominent mouth lesions. You’ll see blisters and erosions on the tongue and lips, heavy drooling, and strings of saliva hanging from the mouth. Affected cattle are often reluctant to eat because of the pain. Foot lesions cause visible lameness, and young calves can die suddenly from heart damage without ever showing obvious blisters.
Pigs develop the most severe hoof lesions. Blisters form along the coronary band, the strip of tissue where the hoof meets the skin, and in the space between the toes. When these blisters rupture, they can undermine the heel or create deep clefts along the coronary band. In severe cases, the entire hoof claw can separate and slough off. Pigs also develop vesicles on the snout, though their oral lesions tend to be less dramatic than in cattle.
Sheep and goats often show milder, subtler signs. Their blisters may be small and easy to miss, especially in the mouth. Lameness from foot lesions is sometimes the only visible clue.
Behavioral Signs You Can See
Beyond the blisters themselves, infected animals show visible changes in behavior that often raise the first alarm. Cattle drool excessively and may smack their lips or chew gingerly. They stop eating or eat very slowly. Lameness is common across all species because blisters on the feet make walking painful, so animals may shift their weight, stand reluctantly, or refuse to move at all.
A sudden drop in milk production in dairy cattle, combined with drooling and lameness in the same herd, is a classic early warning pattern. Fever precedes the blisters by a day or two, so animals may appear dull and lethargic before any visible lesions develop.
Diseases That Look Nearly Identical
One of the biggest challenges with foot-and-mouth disease is that several other livestock diseases produce blisters that look almost exactly the same. Vesicular stomatitis, swine vesicular disease, vesicular exanthema, and Senecavirus A all cause similar mouth and foot lesions. According to the Center for Food Security and Public Health at Iowa State University, these five vesicular diseases are “clinically indistinguishable from each other, particularly in swine.” Only laboratory testing can confirm which virus is involved.
One useful field clue: horses can get vesicular stomatitis but are not affected by foot-and-mouth disease. So if horses on the same property also have mouth blisters, that points away from FMD. But this rule only helps when horses are present.
This Is Not Hand, Foot, and Mouth Disease
People frequently confuse foot-and-mouth disease with hand, foot, and mouth disease (HFMD), the childhood illness that causes a rash and mouth sores in kids. These are completely different diseases caused by different virus families. HFMD is caused by enteroviruses and only affects humans. Foot-and-mouth disease is caused by an aphthovirus and only affects cloven-hoofed animals like cattle, pigs, sheep, and goats. Humans do not get the animal disease, and animals do not get the human disease.
The visual differences are clear: HFMD in children produces small, flat or slightly raised red spots on the palms, soles of the feet, and inside the mouth, sometimes with blisters at their base. These heal within 7 to 10 days. Foot-and-mouth disease in livestock produces larger, more destructive blisters concentrated on the tongue, lips, and hooves, with tissue erosion that can take weeks to fully heal.
Where This Disease Occurs
Foot-and-mouth disease is endemic throughout much of Africa, the Middle East, Asia, and parts of South America. Many countries in North America, Europe, and Oceania have maintained FMD-free status, which is why an outbreak in these regions triggers an aggressive emergency response. If you’re raising livestock in an FMD-free country and notice blisters on your animals’ mouths or feet, reporting it to your state or national veterinary authority immediately is critical. Any vesicular disease in livestock is treated as a potential FMD case until proven otherwise.