Digital Dermatitis

Also known as

Strawberry foot rot, Mortellaro’s disease, Italian foot rot, hairy heel warts, papillomatous digital dermatitis

Description

Digital dermatitis is a highly contagious, erosive infection usually affecting skin on the bulbs of the heel but can also be found between the digits and sometimes at the coronary band.

Often considered to be a dairy problem, this infection also occurs in beef cattle, especially when confined. It’s rare in a pasture situation.

Digital dermatitis is present on many dairy farms. It is very infectious and hard to get rid of. Several different types of bacteria can affect the skin in the interdigital space but lameness is generally caused by Treponema, a type of spirochete bacteria. This is the organism most commonly found in these lesions.

The infection is characterized by red, hairless and very painful lesions. Due to their appearance, the lesions are often referred to as “strawberry like” and most frequently seen at the back of the foot in the interdigital space between the two heels. The lesions sometimes become inactive, after which they either heal or become re-activated. Affected animals are severely lame and may hold that foot off the ground.

Digital dermatitis can affect any breed or age, although young animals with poor immune response are most susceptible. It spreads rapidly from newly acquired animals, or may be introduced by contaminated objects or tools, such as boots or hoof trimming instruments.

The causative bacteria are normal inhabitants of cattle digestive tracts. In the outside environment they thrive best in wet, muddy conditions. Large concentrations of bacteria in wet conditions (which weaken natural defenses of the feet by softening and abrading the skin) allow the infection to start.

The bacteria might be there in the environment, but need wet conditions and mud for the infection to get started. In a confined area, more animals become infected after the first one. If an infected animal comes into a feedlot, dairy or backgrounding yard, the disease may spread through many animals.

The affected foot is painful, like typical foot rot, but this lameness is a little different. Foot rot usually appears as swelling between the toes, with some necrotic tissue. By contrast, digital dermatitis infection occurs more frequently in the back cleft between the heel bulbs-- often on the backside of the heels.

It appears as a reddened, roughened, ulcerated and irritated area and eventually looks granular (like a strawberry) and is very painful. The animal stands with weight on the toe, with heel up, trying to not put weight on the sore heels. In later stages the affected area may have long hair-like structures that grow out from the heel.

This type of foot infection is more common in dairy than in beef cattle, but may appear in beef animals in a contaminated environment. It is rare in young calves, but there have been outbreaks in feed yard cattle (backgrounded calves, or feedlots) and in bulls grouped in wet pens or housed in barns.

In backgrounding calves or in a feedlot, pen checkers may pull lame cattle and treat them for foot rot, if they are not familiar with what digital dermatitis looks like, but the animals do not respond to antibiotics like a typical foot rot case does. Digital dermatitis is diagnosed with a biopsy of the lesion; the bacteria can be seen under a microscope.

Two types of lesions are seen; one is erosive, the other is proliferative or wart-like. Both forms cause varying degrees of discomfort and may cause severe lameness. Sometimes, one form predominates in a herd, but both forms can be seen in the same animal. The two forms may represent different stages of the disease.

Signs

• Rough, reddened, painful area at the heels
• Weight is placed on the toe with heels up
• Walks on toes
• Hairy structures growing out from the heels
• Lesions vary from a few matted hairs to loss of hair and skin damage
• White keratin plugs on skin and scabs
• Foot shaking
• Shifting weight from one foot to another

Causes

Contact with manure/slurry often leads to development of digital dermatitis. The disease is more prevalent in housed herds with poor hygiene and wet conditions.

The condition was first seen in European countries, but eventually spread across dairy-producing areas of the U.S. and into some beef herds. Incidence is highest in housed herds in dirty conditions. Prevalence is highest in fall and winter and lowest if animals are pastured.

Cattle tend to harbor this bacterium in the digestive tract, but once it has an opportunity to enter the foot via a scrape, crack or scratch--in a moist environment—the infection gets going and can amplify. There’s increased concentration of bacteria after the infection starts, and more animals may develop the problem.

Once there is inflammation, swelling and discharge, more pathogens are shed into the environment (into mud and manure) which can lead to further cases. If a lame animal—especially one in confinement--has a lesion between the toes or heel bulbs and it looks like foot rot but is not responding to antibiotics, a closer look may reveal its true nature.

Prevention

There are vaccines for digital dermatitis. These are sometimes used in dairy cattle or bulls that are housed in preparation for sales, but haven’t been greatly effective for prevention. Best prevention is to keep cattle out of wet and dirty areas.

Once an area is contaminated—such as a pen or confinement lot—it stays contaminated.  If the ground has a chance to dry out thoroughly, however, you may not see the disease again in that pen the next wet season, especially if you scrape the pen and clean up all mud and manure. Getting rid of most of the organic matter, then let it dry out, generally helps.

Liming the pen after cleaning it may be counter-productive since creating an alkaline environment may be more desirable for the Treponema bacteria. Don’t put cattle into that pen again until it has been cleaned and dried out.

Digital dermatitis thrives best in damp dirty conditions, so keeping passageways clean and minimizing cow contact with slurry reduces risk of infection.

New cattle coming onto the farm can be treated by antibiotic spray or antibiotic footbath and kept separated from the herd for two weeks. Then they can be given another footbath and put with the existing herd.

All possible hygiene measures should be taken to ensure against contamination with foot trimmers and other tools used on more than one animal.

Treatment

Treatment is different than for foot rot. Digital dermatitis does not respond as well to systemic antibiotics and they are not labeled for bovine digital dermatitis. Systemic antibiotics labeled for foot rot, even when given in large volume, will not halt this infection, so local treatment is recommended.

Footbaths containing antibiotics can be used. For optimal effect, the heels should be washed thoroughly before cows enter the footbath. Non-antibiotic treatments include footbaths containing copper sulfate, zinc sulfate, or formalin--thoroughly rinsing the feet in an intensive program to try to halt infection and limit spread.

Topical oxytetracycline spray or powder can also be used, along with drying the foot. Moisture allows these bacteria to keep going.

Repeat treatments may be needed after four to six weeks, depending on the extent of environmental challenge (how muddy and dirty the pens are).

Affected animals must be recognized early and isolated in a treatment pen--treated daily for a few days. Continue to keep them isolated from the rest of the cattle as they start to recover.

In advanced cases, individual treatment may be needed. The foot, especially the interdigital area, should be thoroughly cleaned to remove the prolific population of spirochetes. A single dressing of caustic mix can be applied carefully to the infected tissue and protected by a waterproof bandage.

The affected foot can be wrapped and bandaged after topical treatment with antibiotic. This not only helps dry it out, but keeps it from continuing to contaminate the pen. The bandage should be kept dry for a couple days, and removed/replaced if it becomes wet. 

You want to make sure the “bug” doesn’t get spread around, and this means being careful not to move affected animals to other pens.

As the animal starts to recover, the ulcerated red, seeping area starts to dry up and get a proliferative hairy-looking surface. By the time this starts to scar and scab over, looking crusty, you know it’s healing. The animal becomes more comfortable, placing more weight on the affected foot.