Zoonotic Diseases

viral | parasites | fungal | bacterial

Introduction: Zoonotic diseases are illnesses that can be shared between a pet and a human. There is only a very slim chance of contracting an illness from a dog. Most people get contagious diseases from other people, not their pets. Disease transmission may be more of a problem for people that are very young, very old, or have illnesses that suppress their immune system. Many of these diseases are not transmitted from the dog to the person, but spread because the dog and person share the same activities and environment, putting them both at risk from the organisms involved.

Transmission: Zoonotic diseases are spread from dogs to people via several routes. Contact with the dog and sharing the dog’s environment are the two most common means of exposure to potential disease. Infectious agents can be in the dog’s saliva, feces, and urine and on the dog’s skin and hair coat. Infectious organisms can also be in the fields, streams, and parks used for recreational purposes with the dog.

Prevention: Common sense and good hygiene can prevent most disease transmission between dogs and people. Dog bites should be thoroughly washed with soap and water and seen by a physician. Dog feces should be disposed of daily. Illnesses in the dog should be treated immediately. Dogs should be kept free of internal and external parasites. Hands should be washed after handling the dog or cleaning up its urine or feces. Children should be taught to keep their hands out of their mouths and to wash their hands before eating.

Treatment: Most zoonotic diseases can be treated with specific therapy appropriate for each individual disease. Some are not treatable.

Important Zoonotic Diseases
These zoonotic diseases are broken down into five major categories: viral, fungal, bacterial, internal or external parasites, and other. Specific diseases and organisms are discussed under each major category.


Viral Diseases

Description: Rabies is the most important viral disease that is shared by humans and dogs. Ninety percent of all rabies cases are found in wild mammals, including foxes, raccoons, skunks, and bats. Feral cats and dogs are also potential carriers, although there have been very few reported cases in dogs.  If an unvaccinated dog contracts rabies from a wild or feral animal, the dog can potentially spread the disease to human beings.

Causative Agent: Rabies is caused by a virus that can infect all warm-blooded animals.

Signs in Dogs: Rabies virus attacks the nervous system, resulting in inflammation of the spinal cord and brain. Affected animals may show no signs for several weeks after the infection. Sick animals show varying degrees of dementia, and signs can vary from extreme depression and quietness to "furious" behavior. The signs can include hiding, loss of appetite, unprovoked aggression, and biting at both living and inanimate objects. As the disease progresses, the animals become paralyzed, lose the ability to swallow, and may have seizures. The animals die within several days of the onset of these symptoms.

Signs in People: The symptoms vary depending on where the virus enters the body, but involve abnormalities of the nervous system. Once the virus enters the spinal cord, the victim suffers from paralysis, which ultimately leads to death by preventing respiration.

Transmission: The primary means of transmission is through a bite from an infected animal. The saliva of an infected animal carries large numbers of the viral agent. Other less common means of transmission include infected saliva coming in contact with an open wound or abrasion. There have been a few cases of disease being spread by the inhalation of aerosolized virus. The most common way for the zoonotic transmission of rabies from dogs to humans is through a bite from an infected dog.

Diagnosis: The only 100% accurate method for diagnosing rabies is to have a diagnostic laboratory perform tests on the brain of a suspected animal. There is no perfect diagnostic test for identifying rabies in humans. If a dog bites a person, the decision to treat the person for rabies is made by examining the circumstances surrounding the bite and the rabies vaccination history of the biting dog.

Treatment: There is no specific treatment for rabies once disease signs are evident. Most cases in animals and people are fatal once the virus replicates and enters the nervous system. Treatment in people is aimed at vaccinating exposed people before the virus replicates and before disease symptoms begin. All circumstances surrounding a dog bite must be examined to decide on a proper course of treatment and vaccinations. In general, if there is any possibility that the biting dog may carry rabies, the person involved must undergo a series of preventive injections. If the dog has a current rabies vaccination and can be found and quarantined, the injections may be avoided. If the dog is a stray, has no record of current vaccination, or cannot be found, the vaccines are given.

Prevention: Avoid contact with wild animals. Maintain current rabies vaccination for all pets in the family. See page A905 for specific vaccination recommendations. Keep dogs away from wild and feral animals. Avoid dog bites and stray or loose dogs. If an owned, vaccinated dog is bitten by another animal, wear gloves when washing the wound and seek veterinary care for the dog. The dog may need a rabies booster and to be quarantined. Unvaccinated animals exposed to rabies may need to be euthanized. Decisions regarding the handling of potentially exposed dogs are usually made by local and state authorities.

Zoonotic Importance and Human Health Risk: Although most cases of rabies are found in wild animals, wild animals do interact with pet dogs, which in turn interact with people. Behavioral changes in rabid wild-life actually increase their interactions with pet dogs. Sick, inactive, wild animals are easy prey to dogs and aggressive, rabid, wild animals lose their normal behavioral inhibitions and may attack dogs. If these dogs are not vaccinated, they can then contract rabies and expose their owners to infection. Vaccinating all pet dogs maintains a protective barrier between people and wildlife and helps reduce the possibility of a pet spreading rabies if it is bitten.

There are very few cases of rabies in people in the United States, but the disease carries a high human health risk because it is invariably fatal once it enters the nervous system.


Internal and External Parasites (Giardia, worms, ticks, fleas, and mites)

  1. Giardia:

Disease Description: Giardiasis is the most common intestinal parasitic disease in humans in the United States. The organisms live in the intestinal tract of many different species of wild and domestic animals.

Causative Agent: The protozoa Giardia lamblia cause Giardiasis. Protozoans are one-celled organisms. Most are free-living; only a few types of protozoa live in the bodies of mammals and can cause disease.

Signs in Dogs: Many dogs infected with Giardia show no signs of illness. Others may have diarrhea. The diarrhea is characterized as pale, soft, voluminous and especially rancid in odor. The diarrhea may be acute and short-lived, intermittent, or chronic. Animals may lose weight despite a good appetite.

Signs in People: As in dogs, Giardia infection in humans may cause no signs, intermittent signs, or severe disease. Diarrhea, stomach pain, nausea, gas, lethargy, and weight loss have been observed in symptomatic people.

Transmission: Waterborne transmission is the most common. The parasite forms infective cysts that are passed in feces and make their way into fresh water supplies. Aquatic rodents may be responsible for fecal contamination of surface water sources. If water treatment and filtration is inadequate, the organism can enter the drinking water and be spread to thousands of people. Contamination of fresh water sources is also a problem for campers, hikers, and others that use water for recreational purposes.

Direct oral-fecal contamination is a much less common means of transmission. Cysts passed in the feces can contaminate foods and be inadvertently swallowed. At this time transmission from dogs to humans is not considered to be a source of infection.

Diagnosis: This infection can be diagnosed in both humans and dogs by performing specific laboratory tests on feces or finding the parasites during microscopic examination of the feces. Other diagnostic procedures include intestinal endoscopy accompanied by aspiration and biopsy.

Treatment: There are no medications specifically approved and licensed to kill Giardia. The medications that are used in both dogs and humans include specific anthelmintics and antibiotics. Treatments may not be 100% successful and often need to be repeated.

Prevention: Proper filtration of human water sources is the most important tool for prevention. Avoid drinking water directly from lakes, ponds, and streams. Adults and children should be taught to wash their hands before eating. Dogs with giardiasis should be rapidly diagnosed and treated to decrease the shedding of cysts. Proper sanitation should be practiced. Feces should be removed on a continual basis and hands should be washed after handling dogs or feces. A vaccination is available for dogs that can reduce the signs of the disease and reduce the amount and time of cyst shedding in dogs that are subsequently infected with Giardia (see page C276 for information on this vaccine).

Zoonotic Importance and Human Health Risk: Giardiasis is the most common intestinal disease in the United States. It is estimated that 7% of the world’s population carry Giardia. Although both dogs and humans can have giardiasis, dogs are not at this time considered a source of infection for people. Instead, dogs are a signal that Giardia can be found in the environment. Dogs and humans often share water sources and this water may be contaminated with Giardia. So, if a dog has giardiasis, people may also be at risk.

  1. Canine Roundworms:

Disease Description: Canine intestinal worms mature and reproduce in dogs. The adult female worms lay millions of eggs that are passed in the dog’s feces and contaminate the environment. If a person accidentally ingests the eggs, they will hatch in the small intestine and then migrate throughout the body, causing damage to the organs they pass through. This syndrome is called larva migrans.

Causative Agents: Although other worms can cause this illness, the most common cause of larva migrans from dogs is ascarids, commonly called roundworms.

Signs in Dogs: Signs of intestinal worms in dogs can vary depending on the age and severity of infestation. Dogs may have diarrhea, vomiting, a bloated belly, and appear unthrifty. Adult worms may be passed in vomitus or feces. Many adult dogs have no symptoms. All puppies should be assumed to have roundworms even if the mother has been previously de-wormed and no signs of illness are present.

Signs in People: The signs in people vary depending on the location of the migrating worm. Visceral larva migrans occurs when the larvae enter body organs, and is characterized by fever, high white blood cell counts, and wheezing. Ocular larva migrans occurs when the larvae enter the eye and can result in inflammation of the eye and loss of vision.

Transmission: There is no direct dog to person spread of this illness. The worms and eggs are not transferred by touching and petting dogs. Transmission occurs when people accidentally swallow eggs. Mature worms in the dog lay millions of eggs that are passed in the dog’s feces and contaminate the environment. Humans touching the ground or soil that contains these eggs can then touch their mouths and swallow the eggs. This occurs primarily in children that pick up and eat contaminated dirt. Most cases occur in children because of dirt eating and lack of personal hygiene. Young puppies are also a major source of environmental contamination. These puppies are infected by transfer of the larvae while in the uterus and through the milk after birth. The larvae can mature into egg laying adults by three weeks of age, so young puppies can be passing eggs in their feces within a few weeks of birth. Adults and children that handle the puppies’ litter and bedding can accidentally ingest the eggs.

Diagnosis: The diagnosis of roundworms in dogs is made by checking the feces of the dog for roundworm eggs. Diagnosis in people is made by blood sample testing.

Treatment: Roundworms in dogs can be treated with proper use of medication that kills the worms. See page A622 for more information on internal parasite control. Humans are also treated with appropriate worm killing medication.

Prevention: Proper hygiene and veterinary care are the keys to preventing worm infestations in both humans and dogs. Clean up dog feces on a daily basis to prevent egg contamination of the ground. Avoid allowing the dog to defecate in playgrounds and school yards. If this occurs, clean up the feces immediately. Keep children away from areas that may be heavily contaminated with eggs, such as kennels or the litter areas of young puppies. Adults and children should wash their hands with soap and water after handling dogs and before eating. Adult dogs should be routinely tested and treated for intestinal worms. All newborn puppies should be assumed to have roundworms and treated following the veterinarian’s guidelines. Treatment of puppies can begin by three weeks of age.

Human Health Risk and Zoonotic Importance: There are several thousand suspected cases of larva migrans each year. The risk is greatest in young children. Unrecognized or treated incorrectly, larva migrans can lead to severe illnesses and even blindness.

  1. Canine Hookworms:

Disease Description: Hookworms are another intestinal parasite of dogs that can cause disease in humans if larvae are accidentally ingested or stepped on in the soil. The larva can penetrate the skin and cause a disease known as cutaneous larva migrans. If the larvae penetrate deeper tissues, a visceral larva migrans syndrome can result.

Causative Agent: Ancylostoma and Uncinaria are common intestinal hookworms in dogs. They live in the digestive tract and their eggs are shed in the dog’s feces.

Signs in Dogs: Dogs with hookworm disease can have intestinal symptoms of diarrhea and suffer from anemia. The disease can vary in severity from asymptomatic infection to rapid death due to blood loss, depending on the number of worms and age or condition of the dog. Puppies usually show the most severe symptoms.

Signs in People: Cutaneous larva migrans is also called creeping eruption because it is characterized by a progressive, linear, intensely itchy eruption of the skin. The migrating hookworm larvae create the linear path. If the larvae migrate deeper and penetrate body organs, signs of intestinal problems and other organ disease can occur.

Transmission: Most people contact the hookworm larva when working or walking in areas of heavy hookworm egg concentration. The larvae directly penetrate the skin. Many cases have been traced to the soft, wet sand at beaches and under buildings.

Diagnosis: Hookworm infestation in dogs can be identified by examination of fecal samples by the veterinarian. Puppies should be assumed to be infected with hookworms. Disease symptoms and laboratory tests can identify infection in humans.

Treatment: Hookworms can be controlled in dogs with medication that kills the parasites. See page A622 for information on internal parasite control. People are also treated with medication that kills the parasite.

Prevention: Control hookworm infestation in dogs with routine testing and anthelmintic use. Remove dog feces on a daily basis. Treat puppies for hookworms starting at two weeks of age. Wash hands after handling dogs and cleaning up their feces. Teach children to keep their hands out of their mouths and to wash their hands before eating. Wear shoes in areas contaminated by hookworm eggs. Keep children away from areas potentially contaminated with eggs, such as the litter from young puppies.

Human Health Risk and Zoonotic Importance: This syndrome is not reported to health authorities in the United States, so the number of annual cases is not known. However, the cutaneous larva migrans syndrome is most often diagnosed in the southeastern and Gulf states. Plumbers and workers that crawl beneath raised buildings, people that frequent the beach, and children are the most commonly infected.

  1. Tick Borne Diseases:

Disease Description: Tick borne diseases are illnesses that are transmitted from ticks to people. These include Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis. Although there is no evidence of direct transmission from dogs to people, dogs act as a sentinel species for tick diseases. If ticks are found on a dog, the ticks are in the environment and people are at risk of tick bites. If dogs are found with any of the tick borne diseases, then people are also at risk of these diseases from infected ticks. People can be bitten by ticks that fall off of dogs and by sharing exposure to ticks in the environment.

Causative Agents: Infective microorganisms carried in the digestive tract of infected ticks cause tick borne diseases. Small bacteria that invade blood cells cause Rocky Mountain spotted fever and ehrlichiosis. A different type of microorganism is responsible for Lyme disease. See page F498 for a complete discussion of Lyme disease in dogs.

Signs in Dogs: Almost any body system can be affected, so signs can vary. Rocky Mountain spotted fever and ehrlichiosis can cause fever, loss of appetite, enlarged lymph nodes, arthritis, coughing, abdominal pain, low platelet count, and bleeding into the skin. Ehrlichiosis can cause a marked decrease in platelets, internal bleeding, and an enlarged spleen. Lyme disease and Rocky Mountain spotted fever can cause a transient rash, arthritis, and problems with the heart and nervous system.

Signs in People: The diseases cause the same types of symptoms in people as they do in dogs. Symptoms of Rocky Mountain spotted fever can include headache, fever, rash, seizures, heart problems, and a variety of other debilitating symptoms. Lyme disease also attacks multiple body systems, so symptoms can include rash, fever, nausea, arthritis, and neurologic, cardiac, and kidney problems. Transient rashes are common in humans affected by both Lyme disease and Rocky Mountain spotted fever.

Transmission: Transmission by feeding ticks requires a minimum of 12-24 hours of attachment. Transmission increases in warm weather when ticks are most active. There is no direct transmission from dogs to people. There is risk of infection during tick removal if the infectious organisms contact broken or abraded skin or mucous membranes.

Diagnosis: These diseases are diagnosed in both dogs and humans by history, disease signs, and specific blood tests looking for antibodies against the disease causing organisms. A veterinarian can collect the blood sample for diagnosis in dogs. Similar blood tests are used for people.

Treatment: These diseases are treated with supportive care and antibiotics. Similar medications are use in people and dogs.

Prevention: The best means of prevention is to avoid tick bites. This is accomplished by avoiding tick infested areas, and wearing long pants, long sleeves, socks, boots, and repellent when traveling in areas that are habitats to ticks. Ticks found on the skin should be removed immediately.

Ticks should be removed daily from dogs. It is important to safely remove embedded ticks. Ticks should not be removed, squeezed, or crushed with bare hands because this can facilitate transfer of the disease organisms. Gloves should be worn when removing and disposing of the ticks. Ticks should be held as close to the embedded mouthparts as possible and removed with constant traction in a straight path away from the point of insertion. There are specific hand tools that can be purchased as aids to tick removal. Tick infestations can be controlled with dips, sprays, collars, and spot-on flea and tick killing preparations.

Human Health Risk and Zoonotic Importance: There are approximately 1,000 cases of Rocky Mountain spotted fever reported each year in the United States. The majority of cases occur in children and young adults. Permanent neurological and organ disease can result. Five to ten percent of those infected die from the disease each year.

Several thousand cases of Lyme disease are reported each year throughout the United States. If not promptly identified and treated, the illness can have life-long debilitating consequences, including arthritis and neurological disease.

  1. Fleas:

Disease Description: Fleas can cause disease by several mechanisms in dogs. A severe flea infestation can lead to anemia from blood loss. Dogs that are allergic to flea saliva can also suffer from fleabite hypersensitivity and allergic dermatitis. Fleas can carry the bacteria responsible for the plague and are intermediate hosts for tapeworms, which are spread to the host animal when an infected flea is swallowed.

Causative Agent: Fleas are wingless insects that feed on the blood of animals, including dogs and people. The adult fleas stay on the host.

Signs in Dogs: Biting fleas can cause a wide range of signs in dogs. Some dogs with only a few fleas show no symptoms. Most dogs infested with fleas show intense itching. Affected dogs may lick, scratch, chew and bite at their skin. Fleas are often concentrated along the back, above the tail and down the back of the rear legs, so biting may be confined to these areas. Discoloration of the hair coat and loss of hair may accompany intense biting and licking. Dogs with fleabite hypersensitivity can be extremely itchy all over their body for many days after exposure to fleas.

Signs in People: People that are bitten by fleas usually have red, irritated, itchy, bumpy lesions on the ankles, and lower legs. The wrists and arms may also be involved. People that are allergic to flea saliva may have intense itchy reactions that can last for days.

Transmission: Adult fleas tend to stay on the host dog unless the flea population on the dog exceeds several hundred, in which case the adult may leave if it finds another host with a lower population. Most flea infestations occur when newly hatched fleas leave the environment for a host that walks or sits near them. Adult fleas can survive for weeks waiting for a mammalian host. The fleas that bite dogs, prefer dogs to people. Humans are usually bitten only when the flea burden on the dog becomes overwhelming or when the dog is absent. Many bites occur when people leave a house unattended for several weeks. When they return, the hungry fleas that had been left behind bite everyone.

Diagnosis: When examining dogs, the history and location of the skin lesions are considered important in a presumptive diagnosis of flea infestation. Identification of tapeworm segments also supports the diagnosis. Definitive diagnosis is based on visualization of the flea eggs, feces, or adult parasites. Diagnosis in people is based on the type and location of lesions, evidence of fleas on the pet or in the house, and resolution of lesions following removal of the biting insects.

Treatment: There are a myriad of flea control medications designed to rid the dog and the environment of biting fleas, eggs, and larvae. See page F770 for specific details on treating fleas in pets.

Treatment in humans typically includes removal of fleas from the environment and topical anti-inflammatory drugs to control itching as the bites heal.

Prevention: Flea control in the environment and on the dog is paramount. Flea control can be modified to meet the needs of the dog owner and can include a variety of topical and environmental treatments. Monthly spot-on solutions that kill fleas meet the needs of most dog owners. Dogs with tapeworm infestations should be treated with the appropriate anthelmintics as well as being examined and treated for fleas.

Zoonotic Importance and Human Health Risk: In most situations, fleas do not bite humans unless the flea population is too high for the pets to adequately support. Most fleabites on humans heal in several days and the bites will stop once the flea population is adequately controlled. Fleas do carry the bacteria responsible for the plague, however dogs are not considered a source of zoonotic spread. Because dogs are resistant to the plague, they do not become sick or pass the illness. However, cats can be infected with the bacteria from fleabites or by eating infected rodents. These cats can then pass the illness to their owners. It is also theoretically possible, though very uncommon, for a person to swallow a flea and develop tapeworm infection. Human health risk from exposure to fleas from dogs is primarily that of fleabites.

  1. Sarcoptic Mange (mites):

Disease Description: Sarcoptic mange, also called scabies is a very itchy, highly contagious skin disease caused by a parasitic mite that burrows into the skin.

Causative Agent: The mite responsible for scabies is Sarcoptes scabei.

Signs in Dogs: Dogs are extremely itchy. A rash may be present on the underline, legs, elbows, hocks, and chest. Loss of hair, scabs, crusts, and scales may be present on the face, body, and edge of the ear. Hair loss, crusts, and itching can spread across the entire body. Scratches and excoriations may be present wherever the dog’s nails can reach the skin. Bacteria can cause secondary skin infections in the damaged areas. In severe cases, the dog may lose its appetite and appear lethargic and ill.

Signs in People: Most people develop a bumpy, pimply, very itchy rash on their bodies wherever clothing directly contacts the body; therefore, the rash may be evident on the waistline, chest, ankles, and wrists. Sarcoptes mites usually do not reproduce on humans. This means that in most cases the rash is self-limiting over 2 to 3 weeks.

Transmission: Mites are transmitted by direct contact between dogs or between dogs and humans. Dogs can be carriers with no signs. Because the mites can live for three weeks off the host, contaminated environmental surfaces, furniture, carpets, grooming tools, and bedding can be a source of mite exposure for humans.

Diagnosis: Presumptive diagnosis in dogs is based on history, skin disease distribution, and lack of response to corticosteroid treatment. Definitive diagnosis, when possible, is based on finding the mites in skin scrapings examined microscopically. Because mites are rarely found on skin scrapings in affected dogs, response to treatment trials may be the only way to diagnose Sarcoptes in dogs. Diagnosis in people is based on history of exposure, and distribution and characteristics of the rash.

Treatment: Dogs are treated with medications that kill the mites. These can be in the form of injections, oral medication, a spot-on solution, dips, and rinses. Secondary bacterial infections are treated with antibiotics. All dogs in the immediate vicinity need to be treated and the environment must be disinfected and treated. Most people do not require extensive treatment because the rash disappears once the dog is mite-free. However, some individuals require dermatological intervention if the rash persists.

Prevention: Identify and treat dogs with scabies as soon as possible. Prevent contact with dogs and wildlife that may be carrying the mites. Have lesions on humans examined and diagnosed as soon as possible.

Zoonotic Importance and Human Health Risk: Adults and children living with or contacting dogs with sarcoptic mange can become infested with the mites. The infestations, although typically self-limiting, can be intensely itchy and bothersome. There are reported cases of sarcoptic mange in humans that are not self-clearing and require months of treatment to control.


Fungal Infections

  1. Ringworm:

Disease Description: The term dermatophytosis refers to infections of the hair, claws, and skin caused by unique fungi that have adapted to living on animals. In humans, the infection is commonly known as ringworm, due to the typically raised and circular shape of the lesion on the skin. There is no worm involved.

Causative Agent: Ringworm is caused by several species of fungal organisms. The most common species in dogs are in the genus Microsporum and Trichophyton.

Signs in Dogs: Signs in dogs can vary tremendously. Some animals show no disease signs, while others have patches of hair loss and scaling. Few animals show the classic ring with central healing and peripheral crusting. Most dogs are not itchy. Some dogs develop secondary bacterial skin infections.

Signs in People: People tend to develop skin lesions in distinct, raised circular patterns. The periphery of the circle may have redness, crusting, and scaling. The ring gets larger as the disease progresses. The number of rings can vary.

Transmission: Dogs contact the ringworm organisms in several ways. They can get the fungi directly from other animals, including rodents, cats, dogs, and humans, or from the soil. They can also be exposed to the infectious agents found on environmental surfaces, such as brushes and bedding. Similarly, ringworm in people is transmitted by contact with fungi found in the soil or by exposure to ringworm infected animals and contaminated objects such as hair, skin flakes, bedding, brushes, cages, and air vents.

Diagnosis: An exact diagnosis is made on dogs by skin scrapings, and fungal cultures. Diagnosis in people is made by observing the characteristic circular skin lesion, skin scraping, and fungal culture.

Treatment: There are a variety of anti-fungal creams, lotions, shampoos, and oral medications available for both dogs and people.

Prevention: Keep the dog’s skin healthy. Routine brushing will help identify skin lesions early and begin treatment as soon as possible. Do not allow the dog’s skin to remain damp and dirty, because these conditions encourage fungal growth. Follow the veterinarian’s instructions when treating ringworm. If ringworm is identified on the dog, all bedding, combs, brushes, and cages must be thoroughly cleaned and disinfected. A 1:10 dilution of household bleach can be used. The fungal spores remain viable for up to 18 months, so remove as many as possible by vacuuming floors, walls, all surfaces, and vents. Steam cleaning carpets may help.

Human Health Risk and Zoonotic Importance: Although humans can get ringworm from dogs, dogs are not a major source of infection for humans. Most zoonotic transmission is from cats. Humans that contract ringworm from a dog will typically find the lesions on points of the body that contact the animal. So the forearms and chest are often involved.

  1. Systemic Fungi:

Disease Description: There are thousands of species of fungi in the environment. A few of these can cause disease in man and animals. These diseases are called mycoses. Ringworm, a superficial fungal infection, is discussed above. Systemic mycoses are those fungal infections that can invade internal organs and potentially cause serious illness. These types of infections are usually not contagious from dogs to people. They occur in both species because both people and dogs share the same environment and are exposed to the fungi living in the soil or vegetation. If a dog becomes sick with systemic fungi, then people are also at risk of infection from the organism in the environment.

Causative Agent: The four major systemic mycotic agents are Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, and Cryptococcus neoformans. These organisms can live in the soil or decaying vegetation and are typically found in areas of the country that fit the needs of the specific organism. Coccidioides is found primarily in the sandy, dry areas of the southwestern United States. Blastomyces thrives in sandy soil near water and is found the Mid-Atlantic States in an area that includes the Mississippi, Missouri, Ohio, and St. Lawrence River Valleys. Histoplasma likes moist, humid areas and is found in soil rich with nitrogen from bat and bird droppings. It is usually found in the center of the country throughout the Ohio, Missouri, and Mississippi River Valleys. Cryptococcus can be found throughout the country and is frequently associated with the droppings in pigeon roosts.

Signs in Dogs: Systemic mycoses are rare, even in areas where the fungi are concentrated in the soil and organic debris. Many animals carry the organisms without signs of disease. Dogs that are exposed to large numbers of infective organisms or have a suppressed immune system may get ill. Those that get blastomycosis, coccidiomycosis, or histoplasmosis may show loss of appetite, weight loss, fever, coughing, difficulty breathing, eye problems, lameness, and skin disease. Cryptococcosis usually causes disease of the nervous system, eyes, and skin.

Signs in People: The systemic mycoses produce similar signs in people as in dogs. The signs can be limited to the respiratory tract and include coughing, difficulty breathing, and fever. These mycotic agents can spread to other organs and cause a loss of appetite and weight loss. Cryptococcosis in humans is also associated with nervous system disease, including encephalitis and meningitis.

Transmission: Dogs and people usually contract these mycoses by inhaling infectious particles from the environment. Dogs that hunt and use their noses to explore vegetation can easily inhale spores or fragments of the fungi. There have been isolated reports of direct transmission of Blastomyces to the skin of humans from dogs that carried the organism in their respiratory tracts. In these cases the dogs bit the affected people and transferred the organism into their skin, resulting in a cutaneous infection, not systemic disease.

Diagnosis: Diagnosis in both dog and humans is based on a history that includes exposure to fungal contaminated areas. Diagnosis in dogs is usually made by finding the organisms in a tissue sample. This can be done by biopsy or by examination of fluid or cells microscopically. Blood tests are often used in humans to make the diagnosis, but are used less frequently in veterinary medicine.

Treatment: Both dogs and humans are treated with antifungal medications. These can be given by injection or orally. Treatment can take months.

Prevention: The only way to prevent mycoses is to avoid exposure to the fungi that cause disease. This can only be accomplished by avoiding places that contain large numbers of organisms. Certain activities increase exposure to these fungi. These include hunting, farming, gardening, recreational hobbies involving water, cave exploring, moving earth, and cleaning out bird and bat roosting areas.

Zoonotic Importance and Human Health Risk: Most people that are exposed to these mycotic organisms do not get ill. The human health risk is greatest in those that have suppression of the immune system. In addition, laboratory and hospital workers have greater exposure and greater risk than the general public.

Dog to person transmission is almost nonexistent, except for veterinary personnel exposed to contaminated wounds and the few reported cases of transmission by dog bite. The most important human health consideration is the knowledge that dogs and humans share environmental exposure to these disease-causing organisms. If a dog contracts a systemic mycosis, it is a warning to those that share its environment.


Bacterial Diseases

  1. Streptococcus Group A:

Disease Description: One of the most common bacterial diseases of childhood is a throat infection called "strep throat." This is a highly contagious disease easily passed from person to person.

Causative Agent: Strep throat is caused by bacteria called Streptococcus. There are several groups of Streptococcus. Group A is responsible for this particular disease syndrome. People are the principal natural host for Streptococcus Group A.

Signs in Dogs: Streptococcus Group A is not a normal inhabitant of the dog. If found in the dog, the bacteria can live in the throat and nasal areas for several weeks without causing any signs of illness.

Signs in People: Fever, chills, red or white plaques in the throat, headache, and enlarged lymph nodes in the region of the neck characterize strep throat in people.

Transmission: Dogs do not naturally get the streptococcus bacteria that cause strep throat. People typically spread it to each other through contaminated airborne droplets. It is possible for an infected person to spread the bacteria to his or her dog. The bacteria can colonize and survive in the dog’s throat for several weeks. The dog may be able to transmit the bacteria back to the person.

Diagnosis: Diagnosis in people is made by throat culture. Diagnosis in dogs is difficult and may require sedation to get an appropriate throat culture specimen.

Treatment: People with streptococcal pharyngitis are treated with the appropriate antibiotics. Dogs carrying the bacteria may also be treated with antibiotics.

Prevention: Human cases of strep throat should be promptly identified and treated. Antibiotics should be used following the doctor’s instructions and finished completely. If recurrent infections occur, antibiotic treatment may be considered for the dog so that any bacteria living in the dog’s throat can be eliminated.

Human Health Risk and Zoonotic Importance: Streptococcus Group A infections in humans can have severe health consequences if not identified and treated promptly. Recurrent infections typically appear due to failure to continue treatment as prescribed by the physician or exposure to other people carrying the bacteria. There have been some reports of infected people passing the bacteria to their dogs. The bacteria can then be passed back to members of the household. This is not of major zoonotic importance, but should be considered in dog owning families that get recurrent "strep throat" infections.

  1. Leptospirosis:

Disease Description: Leptospirosis is a bacterial disease that can infect many species of animals and people. The bacteria lives in wet areas, including stagnant pools of water, marshes, and ponds. Wildlife that frequent these water sources can spread the disease to dogs and people.

Causative Agent: Bacteria called Leptospira cause this disease. There are many strains of Leptospira. Traditionally, Leptospira canicola and Leptospira icterohaemorrhagiae have caused disease in dogs. New strains are now appearing that cause disease in dogs and people.

Signs in Dogs: Signs in dogs vary depending on the age and health of the animal and the strain of leptospirosis involved. Signs can include fever, chills, severe muscle pain, dehydration, vomiting, jaundice, and shortness of breath. Dogs may die if this infection is not properly identified and treated.

Signs in People: Signs in people also vary and can include severe muscle pain, nausea, flu-like symptoms, fever, joint pain, and jaundice. People can die if this infection is not properly identified and treated.

Transmission: The bacteria are spread in body fluids and secretions of infected animals. It can be spread in urine, uterine and vaginal secretions, milk, and through other body tissues. Water contaminated by urine containing the bacteria is a very common cause of infection in dogs and humans. Wildlife such as deer and rodents that carry Leptospira can urinate in water sources. Dogs and people that use these water sources for recreational or work purposes can be infected.

Diagnosis: Diagnosis in both dog and humans is based on a history of possible exposure of the bacteria, signs of disease, and laboratory testing of blood samples. Blood samples can be tested for antibodies against the bacteria that cause leptospirosis.

Treatment: Treatment in dogs and people involves supportive care and antibiotics that eliminate the bacteria.

Prevention: Dogs that live in areas where leptospirosis is prevalent should be vaccinated against the disease. Because the urine of infected dogs can carry the organism, care should be taken to avoid areas where dogs congregate and urinate. Access to swampy, wet areas such as ditches, polluted waterways, and stagnant pools should be limited. Rodent control and kennel cleanliness should be priorities. Dogs showing signs of illness should be promptly diagnosed and treated. Protective goggles and latex gloves should be used when handling dogs suspected of infection. The same precautions apply when cleaning their urine, and disinfecting runs, kennels, and cages.

Human Health Risk and Zoonotic Importance: Leptospirosis has not received much attention in the United States for many years. The incidence in dogs was considered very low and most cases in humans were attributed to large animal or wildlife involvement. However, in the last few years, there has been a dramatic increase in the number of disease cases identified in dogs and the emergence of new strains of the bacteria. Although new vaccines are now on the market, they still do not protect dogs from all strains of Leptospira. The increase in the number of ill dogs means that more bacteria are being spread through the environment, which increases the risk of infection in both dogs and humans.

Because leptospirosis is a relatively uncommon disease, it may be left out of the list of possible causes of illness in a person. If it is not diagnosed and treated correctly, death can result.



Dog Bites:
Disease Description:
There are an estimated 4.7 million dog bites per year. Most dog bites are not severe, but depending on the location of the bite and the severity of the wound, dog bites can result in infection, loss of use of a limb, disfigurement, damage to bones and soft tissues, and death.

Causative Agent: The damage inflicted by dog bites is a function of both the physical trauma associated with the wound and the bacteria that spread from the dog’s mouth into the wound. Dogs' mouths contain over 60 species of bacteria, several of which can cause disease if inoculated into a wound. One common isolate of infected dog bites is Pasteurella multicida, a bacteria that can cause infection.

Sign in Dogs: Dog bites inflicted by other dogs are not considered zoonotic diseases.

Signs in People: Most bites from familiar dogs occur on the arms and hands. Most bites from stray dogs occur on the legs. Most facial bites are inflicted on children. The majority of dog bites result in small wounds with minimal bruising, bleeding, and tissue damage. However, severe injury can result, depending on the location and type of wounds inflicted. Physical damage results from injury to the soft tissue and bony structures involved in the bite. Additional signs will result if infection occurs secondary to transmission of bacteria from the dog’s mouth. Signs of infection can include pain, swelling, redness, and drainage from the wound. Septic arthritis, abscesses, and even fatal systemic infections can occur if treatment is not begun promptly.

Transmission: Dog bites are not a traditional zoonotic disease. There is no passive spread of a contagious agent from dog to person. Instead, disease spread is the result of an improper physical interaction between a person and a dog. Aside from people that handle dogs routinely, such as veterinarians, most dog bites occur in children under the age of 12.

Diagnosis: Diagnosis is based on the report of the victim and observation of the wounds.

Treatment: All dog bites should be vigorously cleaned with copious amounts of water and soap and then rinsed thoroughly. A physician should see all bite victims. Irrigation should be performed to flush out contaminants. Removing severely damaged or contaminated tissue (debridement), suturing, and/or referral to a specialist may be needed. Many people are treated with antibiotics to prevent infection. Surgery may be required depending on the severity of the wound.

Prevention: Dog bites can be avoided by taking measures to prevent the interactions that lead to bites. The vast majority of bites are not caused by one or two "killer breeds," but inflicted by family pets or dogs that are known to the victims. Education and owner responsibility are the keys to the prevention of dog bites. Owners should learn proper methods of obedience training and behavior modification. Children should be taught to avoid loose dogs, how to properly handle and interact with all dogs, and the necessary safety tips to avoid bites. Young children should always be supervised when playing with dogs; no child should ever be alone with a dog. Dogs should be properly trained, socialized, supervised, and confined. Aggressive behaviors in a family dog should be identified and modified with appropriate therapy and training. Only professionals trained in appropriate confinement techniques should handle stray dogs.

Zoonotic Importance and Human Health Risk: Every year there are millions of dog bites in the United States and 10 to 20 fatalities. Most bites involve children. Bite victims can suffer from long term negative physical and emotional effects.