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Zoonotic diseases: Sharing too much

7/27/2005
Keeping your dog's vaccinations up to date will help to protect him from rabies and many other diseases. 

Because of all the publicity about avian flu, mad cow disease and chronic wasting disease, veterinarians frequently receive questions from dog owners about potential zoonotic diseases — diseases that can be spread from animals to man.

Fortunately in the United States, zoonoses are relatively rare, since malnutrition, overcrowding, poor hygiene, and large populations of stray dogs are uncommon. Still, there are a few important diseases that your dog can carry and spread to you. Dog owners should be educated about these conditions since some can have serious or even fatal consequences.

Rabies

Most pet owners are quite aware of the necessity rabies vaccinations to protect their dogs; more importantly, these vaccines also protect the dog owners and their families. Rabies is transmitted through breaks in the skin or by contact of the mucous membranes of the eyes, nose, or mouth with saliva, brain cord, or spinal cord tissue from a rabid animal. Bite wounds are the most common cause of exposure.

In the United States, rabies is primarily carried by raccoons, skunks, bats, and foxes; woodchucks, groundhogs, and other wildlife may also be infected. Raccoon rabies is common along the Eastern seaboard, and skunk rabies is on the increase in Texas, Massachusetts, and Rhode Island. A variety of fox species carry rabies in specific regions of the US — the red fox in western New York, the grey fox in Texas, and the Arctic and red foxes in Alaska.

In the United States, rabies infections in people usually result from exposure to rabid bats; however, dogs are responsible for most of the rabies deaths in the rest of the world.

Infected animals are irritable or excitable and aggressive, and they eventually develop convulsions and die. Pet owners should be wary of any wild or stray animal that attacks them or their pets suddenly and without provocation. If your pet is bitten by a wild animal or if a dead bat is found near your pet, the wild animal's body should be wrapped up (wear gloves!) and taken to a state laboratory that has the facilities to perform rabies testing. If the body cannot be taken immediately, it should be refrigerated until it can be submitted.

Unfortunately, unvaccinated dogs exposed to a rabid animal must either be euthanized immediately or placed in strict isolation for six months and then vaccinated one month before release. Dogs current on their vaccinations that have been exposed to a rabid animal are revaccinated and kept under owner observation for 45 days to make sure they do not develop the disease.

Other diseases

Leptospirosis can also be spread through mucous membranes or through skin abrasions. People usually develop the infection from exposure to water contaminated by infected urine, but they can also get it from contaminated food, soil, or pets.

Some people develop no illness, while others have flu-like signs — fever, headache, chills, muscle aches, vomiting — that can progress to kidney, brain, and spinal cord damage. If caught early, Leptospirosis can be treated with antibiotics. Dogs that develop Leptospirosis can develop signs similar to those in people and may also develop bleeding problems and kidney failure. Dogs that recover from the disease without treatment can still shed the bacteria and therefore should still receive antibiotic treatment. Leptospirosis is prevented by vaccination; because there are several types of Leptospira, veterinarians must choose a vaccine that protects against the Leptospira infection most prevalent in their region.

Campylobacter, E coli and Salmonella, which often cause diarrhea, are common types of bacteria that can be spread from animals to humans. Route of spread is from infected feces or soil, so washing hands and produce and cooking meat thoroughly are important preventative measures. People with poor immune systems — children, elderly, and immuno-compromised persons — are at greater risk for developing these infections and suffering serious side effects.

Feeding "bones and raw food (BARF)" diets greatly increases the risk that dogs will become Salmonella carriers; in fact, Salmonella has been isolated from 80% of BARF diet samples. For those owners providing homemade diets to their dogs, improving sanitation (washing cutting boards) and cooking food will help protect pets and people.

Leishmania, which is transmitted by sand fly bites, is a parasitic disease that causes skin, mucous membrane and internal organ lesions in people and animals. Most reported cases occur in Europe, Asia, and Africa.

Until recently, this disease was thought to be unimportant in the United States until 1999, when Leishmania was detected in a kennel of foxhounds in New York. Since then it has been diagnosed in foxhounds in other areas of North America. Clinical signs in the dogs included dry hair coats; hair loss; itchy, scaly or red skin; and draining wounds or ulcers, although not all dogs that carry the disease have clinical signs. Although some treatments will resolve the clinical signs, there are currently no cures for this infection

Other parasitic zoonoses include mites, ringworm, fleas and ticks. Fortunately, transmission of these can usually be prevented by hand washing, use of flea and tick preventatives and screening and treating new pets for these conditions before adding them to the household.

Surprisingly, people can transmit diseases to their pets as well. For example, infections such as tuberculosis and methicillin-resistant Staphylococcus have been passed to dogs from their owners. See your veterinarian if you have concerns about these or other types of infections.