By Jennifer Coates, DVM
Pet diseases can have many causes, but those that have their origin in bacterial infections are especially important because they can often be successfully treated with antibiotics (if they are diagnosed early enough), and because they may be contagious to other animals and, sometimes, people.
Let’s investigate some of the most important types of bacteria that make dogs and cats sick and what we can do to keep our pets and ourselves healthy.
While the word “plague” may conjure up images of medieval Europe, the disease is still alive and well, particularly in the American West. Plague is caused by infection with Yersinia pestis bacteria, which are usually spread by fleas that feed on infected prairie dogs and sometimes rabbits, squirrels, mice and rats. People and animals can also become sick after coming in contact with blood or tissues from infected animals.
Cats are most frequently diagnosed with the plague due to their inclination to hunt rodents, but dogs and people are not immune. Prevention centers on keeping pets away from rodents and the use of effective flea prevention medications. Antibiotic and supportive therapy is usually effective in curing the plague, so long as a diagnosis can be reached in a timely manner.
Like fleas, ticks can also transmit bacterial infections to pets. One of the most serious of these in dogs (less frequently in cats) is called ehrlichiosis. The disease can develop after a tick carrying Ehrlichia or Anaplasma bacteria bites a susceptible pet. Symptoms include fever, lethargy, enlarged lymph nodes, limping, bruising and bleeding. These clinical signs sometimes develop months after a tick bite, so even if you haven’t seen ticks lately, your pet may still have ehrlichiosis.
Pets treated with certain types of antibiotics (e.g., doxycycline) and sometimes blood transfusions and/or immunosuppressive medications will generally recover from ehrlichiosis. The disease can be prevented through the use of effective tick control products. People can contract ehrlichiosis through the bite of infected ticks but not through contact with a sick pet.
Rocky Mountain Spotted Fever is another bacterial disease that can be transmitted through the bites of ticks, in this case those that carry Rickettsia rickettsii bacteria. Dogs and people (but not cats) typically develop the symptoms of RMSF within a few days to weeks of being bitten by an infected tick. Clinical signs include some combination of fever, lethargy, joint and muscle pain, lymph node enlargement, coughing, difficulty breathing, vomiting, diarrhea, and bruising and bleeding.
Doxycycline and some other antibiotics are quite effective against Rickettsia bacteria, and once treatment begins, infected dogs tend to get better quickly. Many cases of Rocky Mountain Spotted Fever (which is not limited to the Rocky Mountain region) can be prevented through the use of effective tick control products. People cannot contract this disease directly from dogs.
Lyme disease in dogs is caused by infection with Borrelia burgdorferi bacteria, which are transmitted through the bites of eastern and western black-legged ticks (Ixodes scapularis and Ixodes pacificus). Lyme disease is most commonly diagnosed in the northeastern United States, the upper Midwest and Pacific Northwest. People can catch Lyme disease after being bitten by a tick that carries the bacteria, not through exposure to an infected dog. Cats appear to rarely develop clinical Lyme disease.
Common symptoms of Lyme disease in dogs include swollen lymph nodes and painful joints. The kidneys may also be damaged, particularly if treatment is delayed. Dogs who have clinical signs of Lyme disease and have tested positive for exposure to Borrelia burgdorferi should be treated with an appropriate antibiotic like doxycycline. Prevention of Lyme disease involves the use of effective tick control products and vaccination of high risk dogs.
Canine kennel cough can be caused by bacteria like Bordetella bronchiseptica, Streptococcus equi and mycoplasma as well as a number of viruses, either alone or in combination. Whichever microbes are involved, infection results in inflammation and irritation of the upper airways. In severe cases, the infection can progress to pneumonia.
Kennel cough is extremely common. The primary symptom is coughing, but dogs may also have a runny nose, eye discharge, lethargy and a poor appetite. The organisms that cause kennel cough are very contagious to other dogs (and in rare cases, to people and cats) so infected dogs need to isolated to prevent spread of the disease.
Preventive vaccinations are available against Bordetella bronchiseptica and some of the viral causes of kennel cough. Dogs who spend a lot of time indoors around other dogs (think kennels, doggy day cares, shows, etc.) should receive kennel cough vaccines every 6 to 12 months, depending on their particular circumstances.
Infection with any of a number of different types of Leptospira bacteria causes the disease called leptospirosis. Dogs usually develop leptospirosis after contacting urine from an infected animal or by wading or swimming in contaminated bodies of water.
The bacteria enter the bloodstream through small cuts in the skin and then damage the kidneys and sometimes also the liver. People (rarely cats) can also be infected with Leptospira bacteria and contact with a dog suffering from leptospirosis is a potential route of infection. Common symptoms of leptospirosis include fever, lethargy, poor appetite, muscle and joint pain, vomiting, increased thirst and urination, yellow mucous membranes, and bleeding or bruising.
Leptospirosis treatment includes antibiotics, intravenous fluid therapy and sometimes dialysis. Dogs with leptospirosis must be quarantined to protect other animals and people from infection. Vaccines are available that can protect dogs against some but not all of the bacteria that cause leptospirosis.
Of course there are many other types of bacteria that can make dogs and cats sick including Staph infections of the skin, ear infections caused by Pseudomonas, E. coli infections of the urinary tract and Salmonella that can be passed from a pet’s GI tract to people, to name just a few. The best way to protect your pets from bacteria is to stay up to date on appropriate preventative medicine and see a veterinarian at the first sign of illness.