October 5, 2010
Leptospirosis is the most common zoonotic disease worldwide, but the U.S. Centers for Disease Control removed it from the reportable human diseases list in the 1990s because of a lull in diagnosed cases.
According to those who research Leptospira interrogans, the bacteria that causes the disease, it now can be considered re-emerging.
Leptospirosis has been diagnosed in more than 150 mammalian species. The leptospira bacteria is shed most commonly through urine and can be contracted through mucous membranes, abrasions and ingestion. Without mandated reporting on the human or animal side, attaching an accurate number to diagnosed cases is difficult, veterinarians say.
But, based on veterinary diagnostic laboratory and practitioner reports, the disease’s prevalence is notable.
“There’s good evidence to support an increase of diagnosed cases of leptospirosis in the U.S.,” says George E. Moore, DVM, Ph.D., Dipl. ACVIM, an associate professor of clinical epidemiology and director of the clinical trials group at Purdue University.
“Wild animals have remained a reservoir for the disease, which then spreads to dogs and potentially people. Lack of predators and increased food supply in suburban areas makes wildlife concentrations eight to 10 times higher per acre than in rural areas.”
Experts attribute the increase of the disease’s incidence in animals to the perception that certain types of dogs are at a lower risk. Dogs considered not at-risk might not be vaccinated, perpetuating a cycle of shedding the bacteria to other dogs and even their owners.
“This isn’t just a disease of large breeds or hunting dogs,” says Richard E. Goldstein, DVM, Dipl. ACVIM, Dipl. ECVIM, an associate professor of small animal medicine at Cornell University. “Small-breed dogs are testing positive for leptospirosis more and more. This is happening because of lack of vaccination and overlap of suburban living and wildlife.”
Maintaining a safe antibody titer against leptospirosis means annual vaccinations. This can pose a concern when many diseases are vaccinated against every three years.
“Killed bacterins tend not to have the duration of a vaccine created against viruses,” says Robert Menardi, DVM, director of marketing of Pet Biologicals for Merial Ltd. of Duluth, Ga. “This is why it’s important for veterinarians to promote annual exams, not only to examine the pet’s health, but to provide annual vaccines as well.”
The American Animal Hospital Association’s canine vaccine guidelines do not list leptospirosis vaccine as core, but many veterinarians have made it so at their practices. The veterinary community’s concern for public and professional recognition of leptospirosis led the American College of Veterinary Internal Medicine to take action.
“ACVIM is in the process of submitting a consensus statement to AAHA about leptospirosis,” says Arne Zislin, VMD, MBA, technical manager of pet marketing for Boehringer Ingelheim Vetmedica Inc. of St. Joseph, Mo.
“It’s really up to veterinarians and technicians to inform the public about the severity of disease. Consider parvovirus—it was a major problem in the ’70s and we never see an upswing of infection because of widespread vaccine protocols. This requirement is necessary with leptospirosis, too.”
Boehringer Ingelheim Vet medica produces Duramune Lyme+LeptoVax 4/C. Pfizer Animal Health of New York markets Vanguard L4, and Merial offers the newest leptospirosis vaccine on the market, Recombitek 4 Lepto.
“There’s really no reason to recommend a two-serovar vaccine when four-serovar vaccines are available,” Dr. Goldstein says. “L. canicola (dog), L. icterohaemorrhagiae (rodents), L. grippotyphosa (raccoon, skunk, opossum, vole) and L. pomona (cattle, swine, skunks, opossum and raccoon) are found with the highest frequency.”
Though all leptospirosis vaccines protect against the same four serovars, each varies.
“Boehringer Ingelheim Vetmedica is the only company that offers a combination vaccine against Lyme and leptospirosis,” says Lorie North, the senior brand manager. “We use subunit technology that uses only immunogins instead of the whole bacteria.”
Pfizer’s vaccine uses microfiltration to remove extraneous protein and purify the leptospirosis fraction. Merial’s four-way vaccine claim says it protects against Leptospira grippotyphosa for 15 months and prevents bacteria shedding.
“The vaccine was 100 percent effective in protecting against leptospirosis and leptospiruria caused by L. icterohaemorrhagiae, L. canicola, and 94.5 percent effective against leptospirosis and leptospiruria caused by L. Pomona,” Dr. Menardi says.
Newer forms of leptospirosis vaccines focus on preventing the disease and its shedding, according to Menardi, while the first productions promised only a reduction of clinical signs.
Leptospirosis’ signs can mimic other diseases and illnesses. Incubation lasts from three to 20 days. The first signs often include depression, loss of appetite, vomiting, weakness and generalized muscle pain, experts say.
“Affected dogs may also suffer from polydipsia and polyuria and have swollen, red and painful eyes,” Dr. Zislin says. “Because these signs are non-specific, owners may try to treat their pets at home, assuming the symptoms will pass. Four forms of leptospirosis infection in dogs are peracute, subacute, acute and chronic.”
The liver and kidney are most commonly damaged by the disease in dogs, but some never show symptoms.
“The disease goes from one extreme to the other in dogs,” Zislin says. “It goes from almost no sign of infection to vasculitis, which causes edema and potentially disseminated intravascular coagulation (DIC). Uveitis, meningitis, myocarditis and pericarditis are also possible conditions.
“When determining the likelihood of getting leptospirosis, the infectious dose amount needs to be considered. If a dog drinks from an infected puddle, it is more likely to become infected due to concentration as opposed to swimming in a lake with leptospira.”
Experts say no one knows why some dogs’ reactions to a leptospirosis infection are worse than others.
“At the June ACVIM meeting, it was stated that it is impossible to determine if or which strain of leptospirosis leads to a more severe infection,” Zislin says. “It’s equally difficult to tell if a certain breed has a higher susceptibility to it.”
While canine patients tend to be the focus in leptospirosis testing, cats also have tested positive for the bacteria but are typically asymptomatic.
“We saw a fairly high incidence of serovars in shelter cats when we first launched the [leptospirosis] vaccine,” Zislin says. “But none of the cats showed symptoms of the disease. They develop an immune response and have kidney and liver inflammation, but their natural antibody response to the organism eventually rids the body of the bacteria.”
The only leptospirosis vaccines on the market are manufactured for canine use.
Some veterinarians believe that current testing options are unreliable, Goldstein says. The lack of a reliable test means some veterinarians forgo testing.
“The Leptospira Microscopic Agglutination Test (L-MAT) is considered the gold standard of current testing despite potential flaws,” Goldstein says. “The PCR test offered by Idexx and some commerical laboratories is becoming more popular,however, and there is a major effort to develop additional testing options.”
Zislin says false positives can occur when a past exposure is detected.
“Testing also requires two tests two to four weeks apart,” he says. “Sometimes getting the client back in the office is an obstacle to this. The problem with a more effective test is that leptospirosis has antigenically similar serovars.”
The leptospira microorganism can be found in blood for the first seven to 10 days after exposure, Dr. Moore says.
“This invokes serologically identifiable reactions and, if not treated, it moves to the kidneys,” he says. “After seven to 10 days the microorganism can also be found in urine, making early detection necessary to avoid shedding the bacteria.”
The first line of treatment for leptospirosis is to provide the dog an antibiotic such as doxycycline or ampicillin. In addition, intravenous and subcutaneous fluids are given as supportive care.
“Treated dogs have a good chance of recovery, especially if treated early,” Moore says. “Veterinarians need to stress the need for vaccination. Urban wildlife is raising the risk to all dogs in their own backyards.”
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