Novartis Animal Health recently acquired a provisional United States
licence for a vaccine against heel warts. Approval to distribute the
vaccine in Canada will be sought after the product is fully licensed in
the U.S.
Though the first case of heel warts was described in Italy in 1974, it
wasn’t recognized in the U.S. until 1980. Financial losses caused by
heel warts are significant. A British study estimated the loss at $200
per dairy cow per year.
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A 1996 survey showed that 47 percent of all U.S. dairy herds were
infected with heel warts. In herds with more than 200 cows, the
incidence was up to 82 percent.
Heel warts, caused by the bacterium Treponema, are also known as hairy
foot warts, strawberry heel warts and digital dermatitis.
Infected dairy cows are lame. Their feet are so painful that it reduces
milk production and reproductive efficiency.
Treponema is usually introduced to a farm by replacement cow carrying
the bacteria. Once established, the infection spreads among adult cows.
Within one year, most herd members become infected. Heel warts are
especially prevalent in first and second lactation cows, just after
they join the milking string. These young animals suffer the most
debilitating lameness.
Heel warts can be confused with foot rot. While both diseases are
caused by bacteria that require specific conditions to spread, they
differ markedly in other respects.
Foot rot is triggered by an injury that allows the foot rot bacteria to
invade. Heel warts strike feet that are exposed to high moisture and
manure containing Treponema bacteria. Herds kept in areas with moist
contaminated soil, especially around troughs and unscraped alleys, are
at high risk for heel wart epidemics. Cattle on pasture are rarely
affected.
A foot rot infection will spread into the deep tissues of the foot,
causing swelling and severe pain. The bacterium often spreads up the
leg. The heel wart bacterium is confined to the surface layer of the
skin and it is also limited to the area below the dewclaws and above
the hoof. Both foot rot and heel warts cause cattle to limp, but foot
rot causes more severe lameness.
Injectable antibiotics are a good treatment for foot rot. Once therapy
is started, the swelling goes down quickly. Heel warts are treated with
topical antibiotics. Though therapy quickly reduces the pain, the
lesions on the foot are slow to shrink.
Foot baths may be a enough to treat heel warts if there are only a few
infected cattle on the farm.
Preventive measures for foot rot and heel warts also differ. For foot
rot, the focus must be on preventing physical damage to the animal’s
feet. Heel warts are prevented by housing cattle in dry areas.
If no management changes are made, Treponema infections will occur
repeatedly, usually in the same animals.
Once the disease is in a herd, it is difficult to eliminate it, even
with the appropriate changes in housing. Only one small university herd
has ever documented eradication of Treponema.
Jeff Grognet is a veterinarian and writer practising in Qualicum Beach,
B.C.
