Foot-and-mouth disease (FMD) is a severe, highly contagious viral disease of cattle and swine. It also affects sheep, goats, deer, and other cloven-hooved ruminants. FMD is not recognized as a zoonotic disease
This country has been free of FMD since 1929, when the last of nine U.S. outbreaks was eradicated.
The disease is characterized by fever and blisterlike lesions followed by erosions on the tongue and lips, in the mouth, on the teats, and between the hooves. Most affected animals recover, but the disease leaves them debilitated. It causes severe losses in the production of meat and milk.
Since it spreads widely and rapidly and because it has grave economic as well as clinical consequences, FMD is one of the animal diseases that livestock owners dread most.
What Causes It
FMD is caused by a virus. Signs of illness can appear after an incubation period of 1 to 8 days, but often develop within 3 days.
The virus survives in lymph nodes and bone marrow at neutral pH, but is destroyed in muscle when pH is less than 6.0, i.e., after rigor mortis. The virus can persist in contaminated fodder and the environment for up to 1 month, depending on the temperature and pH conditions.
There are seven known types and more than 60 subtypes of the FMD virus. Immunity to one type does not protect an animal against other types.
How It Spreads
FMD viruses can be spread by animals, people, or materials that bring the virus into physical contact with susceptible animals. An outbreak can occur when:
- Animals carrying the virus are introduced into susceptible herds.
- Contaminated facilities are used to hold susceptible animals.
- Contaminated vehicles are used to move susceptible animals.
- Raw or improperly cooked garbage containing infected meat or animal products is fed to susceptible animals.
- People wearing contaminated clothes or footwear, or using contaminated equipment, pass the virus to susceptible animals.
- Susceptible animals are exposed to materials such as hay, feedstuffs, hides, or biologics contaminated with the virus.
- Susceptible animals drink common source contaminated water.
- A susceptible animal is inseminated by semen from an infected animal.
Signs
Vesicles (blisters) followed by erosions in the mouth or on the feet and the resulting excessive salivation or lameness are the best known signs of the disease. Often blisters may not be observed because they easily rupture, leading to erosions.
These signs may appear in affected animals during an FMD outbreak:
- Marked rise in body temperature for 2 to 3 days.
- Vesicles that rupture and discharge clear or cloudy fluid, leaving raw, eroded areas surrounded by ragged fragments of loose tissue.
- Production of sticky, foamy, stringy saliva.
- Reduced consumption of feed due to painful tongue and mouth lesions.
- Lameness with reluctance to move.
- Abortions.
- Low milk production (dairy cows).
- Myocarditis (inflammation of the muscular walls of the heart) and death, especially in newborn animals.
Animals do not normally regain lost weight for many months. Recovered cows seldom produce milk at their former rates, and conception rates may be low.
Confusion With Other Diseases
FMD can be confused with several similar but less harmful diseases, such as vesicular stomatitis, bluetongue, bovine viral diarrhea, foot rot in cattle, and swine vesicular disease. Whenever mouth or feet blisters or other typical signs are observed and reported, laboratory tests must be completed to determine whether the disease causing them is FMD or not.
Where FMD Occurs
While the disease is widespread around the world, North America, Central America, Australia, New Zealand, Japan, Chile, and many countries in Europe are considered free of FMD. Various types of FMD virus have been identified in Africa, South America, Asia, and some parts of Europe.
Prevention and Control
FMD is one of the most difficult animal infections to control. Because the disease occurs in many parts of the world, there is always a chance of its accidental introduction into the United States.
Animals and animal byproducts from areas known to be affected are prohibited entry into this country. Livestock animals in this country are highly susceptible to FMD viruses. If an outbreak occurred in the United States, this disease could spread rapidly to all sections of the country by routine livestock movements unless it was detected early and eradicated immediately.
If FMD were to spread unchecked, the economic impact could reach billions of dollars in the first year. Deer and other susceptible wildlife populations could become infected and potentially serve as a source for reinfection of livestock.
Vaccines for FMD are available, but must be matched to the specific type and subtype of virus causing the outbreak. Vaccination can help contain the disease if it is used strategically to create barriers between FMD-infected zones and disease-free areas.
What You Can Do
You can support U.S. efforts against FMD by:
- Watching for excessive salivation, lameness, and other signs of FMD in your herd; and
- Immediately reporting any unusual or suspicious signs of disease to your veterinarian, to State or Federal animal disease control officials, or to your county agricultural agent.
- When traveling outside the United States, ensuring that you do not bring back prohibited animal products or other at-risk materials (see APHIS Factsheet on Protecting America from FMD).
External Factors
One of the most important external factors is the time of year, the number of cases being greater in winter than in summer. Wet weather conditions are also conducive to maintaining high bacterial levels. Lameness in grazing cattle tends to increase about three weeks after heavy rainfall.
Farm Factors
Farm factors associated with lameness include herd size: veterinary practitioners saw proportionally fewer cases of foul-in-the-foot but more cases of sole ulcer in larger than in smaller herds. Overcrowding, especially of first calved heifers, leads to reduced lying times and increased lameness.
Stockmanship is important, as farmers who know more about lameness or who have been trained tend to have lower overall prevalence of lameness in their herds than untrained herdsmen. Housing is a very important factor. The overall incidence of lesions is lower in strawyards (0.71 cases/100 cows/ month) than in cubicles with yards (0.93 cases/100 cows/ month). The difference is thought to be due largely to longer lying times in strawyards. Cattle at pasture tend to lie down for longer periods than those in cubicles. This is thought to be beneficial. Straw yards also reduce the exposure to bacteria causing digital dermatitis.
The floor surface is another important factor. A two-year survey of 37 farms showed that only 25% of floor surfaces were satisfactory in the first winter and 34% in the second winter. 55% and 33% were considered smooth or very smooth and 20% and 33% were rough or very rough in the two periods. There is no doubt that feed input has an important role to play in lameness associated with lesions of hoof horn and laminitis.
Animal Factors
Found differences between breeds in claw score traits for certain foot conditions. Ayrshires and Jerseys had better scores than other breeds. The Brown Swiss had the worst scores for corkscrew claws, laminitis and sole ulcers. White line score was worst in Guernseys and heel erosion and digital dermatitis were worst in Friesians. There is evidence that Jerseys tend have harder feet and less lameness. It has also been suggested that heavier cows are more prone to clinical lameness. Claw colour has also been implicated in lameness, with cattle with less pigmented feet being more prone to lameness. The heritability of clinical lameness in dairy cows from 24 herds was estimated as 0.10 and 0.22 using linear and threshold model analysis respectively reported that a cow with a sole ulcer in one lactation was more likely to have one in a subsequent lactation.
Age is also important with regard to lameness. An initial peak in lameness occurs in young first calving heifers. There appears to be a marked reduction in horn growth in late-pregnant heifers, making them more prone to bruising and haemorrhages when housed on concrete floors. The reduced growth leads to softer horn formation, causing a weakening and possible separation at the white line and predisposing to mechanical bruising of the underlying sensitive corium. Older cows are mainly affected between five and eight years old found that the risk for six different foot disease traits increased with age.
There is evidence that low dominance-ranked cows spend less time lying down than high-ranking animals, leading to higher lameness risks. Many foot lesions are also related to the early post-calving period.
Lameness lesions
Over 90% of lameness involves the foot, with leg injuries being far less common. Lameness lesions can be classified into four main categories: horn, skin, joint and leg problems:
Horn Diseases:
Laminitis
Laminitis is an acute or chronic inflammation of the laminae, which lie immediately below the outer horny wall of the foot. The disease may cause lameness in its own right, often in all four feet, but usually it is a predisposing cause or risk factor for other types of lameness lesions, such as sole ulcer and white line abscesses.
Factors causing laminitis include housing systems and management factors that decrease lying times and increase stress on the feet, such as:
- cubicle design and overall cow comfort;
- competition for cubicle space;
- cubicle bedding material;
- sudden changes in calving, especially at calving.
Nutritional factors have also been implicated in predisposing laminitis. These factors include:
- diets high in starch and low in fibre, leading to ruminal acidosis;
- possibly, diets high in crude protein content;
- sudden, major changes of diet at calving, especially from low to high concentrate diets;
- Excessive cow condition at calving, where overfat cows have a lower appetite for forage and hence are more prone to ruminal acidosis;
- The way food is offered – large amounts of concentrates at one time can produce acidosis.
Sole ulcer
Sole ulcers are the most common disease of the foot and most typically occur in the outer claw of the hind foot. Events such as laminitis may cause the pedal bone to drop and damage the underlying horn of the sole. As a result, an ulcer appears in the typical position – the centre of the sole towards the heel. The ulcer sometimes appears as a haemorrhage, with a softening and yellowing of the horn, progressing to necrotic tissue and often infection. Lumps of proud flesh – granulation tissue – may protrude from the ulcer area.
Sole ulcers can cause severe losses and reduced fertility, especially when occurring 70-120 days after calving. Many sole ulcers never fully heal and cows may suffer from chronic lameness for the rest of their productive lives. Solar ulcers may also predispose other conditions, such as septic arthritis.
White line abscess
The white line is the site at which the horn of the wall of the hoof joins that of the sole. It is a naturally weak area in the horn and cracks can allow dirt and bacteria to enter, causing abscess formation, pain and lameness. The initial weakness in the white line may be a result of laminitis, abnormal conformation and possibly dietary effects. The abscess most commonly occurs on the outside of the outer claw of the hind foot.
This type of lameness is the most common form of lameness in yarded cattle, especially on slats. Excessive activity on poor underfoot surfaces can lead to a high incidence of the condition. Restrictions of trough space in yarded cattle may also predispose the condition.
Slurry heel
Slurry heel is also known as heel erosion and is very common. Almost all older cattle which are housed show some degree of irregular loss of the bulbar horn. The problem may occur in all four feet, but often it may only affect the hind feet. The lateral digit is most commonly involved. It is thought the bacterium Dichelobacter (Bacteroides) nodosus, an obligate anaerobic bacterium producing keratolytic enzymes that are able to erode the horn, is involved. As a result, the hoof might rotate backwards and the toe may no longer be weight-bearing, the pedal bone rotates and leads to an increased risk of lameness. The predisposing factors include moist conditions, which soften the horn, unhygienic conditions allowing bacterial proliferation, and overgrown feet and chronic laminitis, which produce poor quality horn.
Skin Diseases:
Digital dermatitis
Digital dermatitis is the most common skin disease of the foot, often associated with housing. It is a contagious inflammation of the epidermis. Classically, it occurs between the bulbs of the heels, but more recently it has also affected the interdigital space. There is a severe form that attacks the horn/skin junction at the coronary band.
Digital dermatitis is likely to be caused by an infection. Spirochaetes (a type of bacteria) are most probably involved. They have a predilection for keratinised cells and produce a toxin which is keratolytic. It can produce two types of lesion: erosive (strawberry-like) or proliferative (wart-like). The erosive form is most commonly found in the United Kingdom. It is very painful and has a pungent smell. The wart-like lesion occurs when the infection is not treated and is due to a chronic irritation reaction of the skin.
Foul-in-the-foot
Foul-in-the-foot is caused by an infection with Fusobacterium necrophorum, usually following damage to the interdigital skin by a foreign body. The infection results in sudden lameness, often in one limb. Body temperature is raised. There is swelling of the coronary band area, forcing the claws apart, and a split in the interdigital skin often associated with pus and dead tissue. The degenerated skin causes a ‘foul’ odour. At certain times of the year (wet, muddy and often warm at grazing) there can be herd outbreaks.
‘Super foul’ is an aggressive form of the disease that has become more common in recent years. It produces severe interdigital necrosis with rapid extension deep into the surrounding structures.
Joint Diseases:
Septic Arthritis
Septic arthritis usually involves the pedal joint between the pedal bone and the second phalangeal bone. It results from the direct extension of infection from a foot lesion (e.g. sole ulcer or white line infection) into the surrounding tissues and eventually involving the structures such as the joint itself. It is associated with swelling of the joints, acute pain, reduced appetite, weight loss and longer periods of recumbency.
Joint-Ill
Joint-ill is a disease of newborn calves and results from any form of septicemia that spreads to the joints of the limbs. The most common causative bacteria involved are E. coli and Streptococcus, which are found in great numbers in damp, dirty bedding. It causes severe lameness, usually in one or two joints.
Leg Injuries:
Hock Damage and Carpal Hygromas
Hock damage, such as hygroma and traumatic arthritis, primarily results from chronic mechanical irritation due to rough floors with little or no bedding, poor cubicle or building design, and poor hygienic conditions. A hygroma is a swelling on the outside face of the hock joint and is produced by changes in the skin and underlying structures. The skin is often hairless, thickened and flaky. The underlying tissues are thickened and swollen, mainly with fibrous tissue. A cavity may develop, containing blood clots and serum, but infection often produces an abscess, which will eventually burst and drain. A fibrous lump will remain.