Diseases Transmissible Between Dogs and People
A zoonosis (pl. zoonoses) is a disease occurring primarily in animals (usually mammals), but that can occasionally be transmitted to humans, for example bovine tuberculosis or brucellosis. A wide range of viruses that can cause human diseases survive in nature as infections of other animals; humans are only occasionally infected, and infection of humans is usually unimportant for viral survival. These infections are called zoonoses; many are caused by arboviruses (viruses that are transmitted by arthropod vectors such as ticks) and some are due to direct infection. However, some arbovirus infections, notably dengue and yellow fever, can be maintained indefinitely by human-to-human mosquito transmission, although both have animal reservoir hosts also.
Rickettsial Diseases
Rickettsiae are small, Gram-negative bacilli that have evolved in such close association with arthropod hosts that they are adapted to survive within the host cells. Rickettsioses are zoonoses that, except for Q fever, are usually transmitted to humans by arthropods (tick, mite, flea, louse, or chigger). Therefore, their geographic distribution is determined by that of the infected arthropod, which for most rickettsial species is the reservoir host. Rickettsiae are important causes of human diseases in the United States (Rocky Mountain spotted fever, Q fever, murine typhus, sylvatic typhus, human monocytic ehrlichiosis, human granulocytic ehrlichiosis, and rickettsial pox) and around the world (Q fever, murine typhus, scrub typhus, epidemic typhus, boutonneuse fever, and other spotted fevers).
The tick-borne relapsing fevers and Lyme disease are zoonoses with rodents as the major reservoir; incidence and distribution depend mainly on the biology of the tick vectors. Areas known to harbor infected ticks and lice should be avoided. No vaccines are available. Tetracycline is an effective treatment.
A number of zoonoses are transmitted from dogs to people, which include:
Bordetellosis
Bordetellosis is a zoonotic disease caused by the bacterium Bordetella bronchiseptica. It can be transmitted from infected animals to humans by infected aerosols, probably droplets. In dogs the bacterium causes kennel cough. In humans, illness can range in severity from mild respiratory symptoms to pneumonia; carrier state may exist. B. bronchiseptica is a frequent cause of bronchopneumonia in animals; infected animals may generate infectious aerosols. Fever, abdominal pain, watery or bloody diarrhea, occasionally chronic colitis, and arthritis are seen.
Brucellosis
Brucellosis is a bacterial infection caused by Brucella. It is a true zoonosis in that virtually all human infections are acquired from animals. Human brucellosis is either an acute febrile disease or a persistent disease with a wide variety of symptoms. In the simplest case, the onset is influenza-like illness with fever reaching 101 to 103 degrees F. Limb and back pains are unusually severe, however, and sweating and fatigue are common symptoms. If the disease is not treated, the symptoms may continue for 2 to 4 weeks. True relapses may occur months after the initial episode, even after apparently successful treatment.
Campylobacter enteritis
Campylobacter bacteria are often isolated from dogs that show no signs of the disease (carriers) and those who show signs of the disease. Dogs, especially those recently adopted from shelters, can serve as sources of human infection. Intermittent diarrhea may persists for months. The disease can be detected through tests.
Leptospirosis
Leptospirosis is a disease caused by Leptospira bacteria. It occurs worldwide and can affect humans as well as many wild and domestic animals, including dogs and cats. The bacteria are spread through the urine of infected animals, which can survive in water and soil for weeks to months. Humans and animals can become infected through contact with contaminated body fluids, except saliva, water, or soil. The bacteria penetrate mucus membranes, causing endothelial damage and damage to organs, such as the liver and kidneys. This is a potentially fatal bacterial disease that damages the liver and kidneys of dogs and humans, so get your pet vaccinated against leptospirosis.
Pasteurellosis
Most human infections with Pasteurella multocida occur as localized abscesses of the extremities or face as a result of cat or dog bites. These abscesses require surgical drainage. Disseminated infections, particularly those caused by Pasteurella multocida, can lead to septic shock, meningitis, endocarditis, and other severe illnesses.
Salmonellosis
There are three clinical forms of salmonellosis: (1) gastroenteritis, (2) septicemia, and (3) enteric fevers. The severity of the infection and whether it remains localized in the intestine or disseminates to the bloodstream may depend on the resistance of the patient and the virulence of the Salmonella bacteria. Signs may include fever, loss of appetite, headache, muscle pain, and constipation. Enteric fevers are severe infections and may be fatal if antibiotics are not promptly administered. Gastroenteritis (food poisoning) depends on the dose of bacteria. Symptoms usually begin 6 to 48 hours after ingestion of contaminated food or water and usually take the form of nausea, vomiting, diarrhea, and abdominal pain.
Yersiniosis
Yersinia enterocolitica causes severe diarrhea and local abscesses, and Y. pseudotuberculosis causes severe enterocolitis.
Ehrlichiosis
Canine monocytic ehrlichiosis is caused by the rickettsia Ehrlichia canis, a type of bacteria that live only inside other cells. The bacteria causes fever, enlargement of lymph nodes and spleen, kidney failure, inflammation of the brain, eyes, spinal cord and blood disorders.
Q Fever
Q fever is caused by Coxiella burnetii which infects a wide variety of ticks, domestic livestock, and other wild and domestic mammals and birds throughout the world. The infection rarely causes noticeable signs in animals. Q fever is a highly variable disease, ranging from asymptomatic infection to fatal chronic infective endocarditis. Some patients develop an acute febrile disease that is a nonspecific influenza-like illness or an atypical pneumonia. Other patients are diagnosed after identification of granulomas in their liver or bone marrow. Q fever in humans must be reported to public health officials.
Spotted Fever
Rocky Mountain spotted fever is among the most severe of human infectious diseases, with a mortality of 20 to 25 percent unless treated with an appropriate antibiotic. The severity and mortality are greater for men, elderly persons, and individuals with glucose-6-phosphate dehydrogenase deficiency. The clinical gravity of Rocky Mountain spotted fever is due to severe damage to blood vessels by R. rickettsii. The infection is transmitted by ticks.
Blastomycosis
Blastomycosis is a primary pulmonary infection resulting from inhalation of Blastomyces dermatitidis fungus. The clinical sign of pulmonary blastomycosis is one of chronic pneumonia. The infection may spread most commonly to the skin, bone, and, in males, prostate.
Coccidioidomycosis
Coccidioidomycosis is a noncontagious infection caused by the fungus Coccidioides immitis. Most cases occur as mild infections. However, some patients have progressive pulmonary infection and also may suffer dissemination of the fungus to the brain, bone, and other sites. Coccidioides meningitis is a life-threatening infection requiring lifelong treatment.
Rhinosporidiosis
Rhinosporidiosis is a chronic granulomatous infection of the mucous membranes that usually manifests as polyps that arise from the nasal mucosa or external structures of the eye. The disease is caused by the aquatic parasite Rhinosporidium seeberi. Disease of the skin, ear, genitals, and rectum has also been described. Cases in the United States are rare but are more common in Texas and the Southeast.
Ringworm is a fungal skin infection marked by ring-shaped, red, scaly patches.
Chagas Disease
Chagas disease (American trypanosomiasis) is caused by the Trypanosoma cruzi parasite. Symptoms of acute disease may include fever, inflammation of lymph nodes, increased heart rate, heart enlargement, and myocarditis. The disease is transmitted by cone-nosed bugs and may also be transmitted congenitally and by blood transfusion. Dogs are reservoirs of the infective parasite. Megaesophagus may develop in some cases.
Giardiasis
Giardiasis is a long-lasting, intestinal protozoal infection caused by species of Giardia. The infection can cause a variety of intestinal symptoms, which include diarrhea, gas or flatulence, greasy stools that tend to float, stomach cramps, upset stomach, and nausea.
Leishmaniasis
Leishmaniasis is a disease that is transmitted by sandflies and caused by intracellular protozoa of the genus Leishmania. Human infection is caused by about 21 of 30 species that infect mammals, including dogs. There is no vaccine for this disease, which can rapidly lead to death if no treatment is given. Dogs act as parasite reservoir for humans.
Coenuriasis
Coenurus cerebralis infection has been observed as a common and worldwide problem of small ruminants. Dogs being definitive host of Taenia multiceps play an important role in spreading the disease. Occurrence of coenurosis cysts in brain, spinal cord and in other tissues have been noticed in a wide range of animals such as sheep, goats, cattle, horse, buffalo, camel and yak.
Diphyllobothriasis
Diphyllobothriasis (fish tapeworm infection) is a disease caused by the cestode worm Diphyllobothrium latum, the largest cestode worm of humans measuring 5 to 10 m in length. Signs may include megaloblastic anemia as the parasite competes with the host for vitamin B12, and neurologic disorders. The adult parasite can survive in its host for 35 years.
Children in close and continuous contact with pets are occasionally infected as a result of the accidental ingestion of an infected flea. The infection is usually without any signs and is self-limited. Flea control of pets would largely eliminate the infection from household pets and children.
Echinococcosis
Echinococcosis is a zoonotic infection caused by the larval stage of the tapeworm Echinococcus. Two of the recognised species, E. granulosus and E. multilocularis, are of importance for humans. Infection is acquired through ingestion of parasite eggs released in feces of the host (a carnivore or a rodent) bearing the adult worm in its gut.
Dirofilariasis
Dirofilaria immitis (the dog heartworm) is a worldwide filarial parasite of dogs. Adult worms (up to 30 cm long) usually are located in the dog's heart. In heavy infections, or when adult worms die, the parasites may be carried to the pulmonary vessels where they may produce clogs. Larvae of other Dirofilaria spp. that parasitize lower animals occasionally may be found in the skin or eyes of humans.
Gnathostomiasis
Gnathostoma spinigerum is a nematode that resides in the stomach wall of dogs and cats. Most human infections occur in Thailand and other Asian countries. Infective larvae develop in copepods and are transferred through the food chain. Human infection results from consumption of improperly cooked fish or other food containing infective larvae. The larvae migrate in the tissues and may invade the eyes, brain, and other organs. The larvae may cause eosinophilic meningitis. The immature worm may be recovered from subcutaneous nodules.
Larva Migrans
Cutaneous larva migrans (creeping eruption) is a dermatitis caused by the larvae of Ancylostoma braziliense, the dog and cat hookworm, which penetrate human skin and migrate to the underlying tissue. Ancylostoma caninum and other species of hookworms also can cause this infection.
Strongyloidiasis
Strongyloidiasis is caused by Strongyloides stercoralis worm. Signs include pneumonitis, epigastric pain, and diarrhea. In immunocompromised individuals worms may spread to other organs and cause autoinfection. Infection can range from asymptomatic to multiorgan failure. The mortality rate for patients requiring hospitalization with Strongyloides infection is 16 percent. In disseminated strongyloidiasis, the mortality rate can be as high as 70-90 percent. Infection may most frequently initially occur in childhood, as children are most likely to play outdoors in contaminated soil.
Pentastomid Infection
Pentastomid infection is caused by Linguatula serrata (tongue worms). The infection is transmitted through eggs in feces or nasal discharge from infected dogs which are accidentally ingested by humans. Signs of infection in humans include irritation of throat and nose, accompanied by vomiting, tearing, difficult breathing, and headache. Signs in dogs are excessive nasal discharge and sneezing.
Lymphocytic Choriomeningitis
Lymphocytic choriomeningitis is a flu-like disease which can occur with meningencephalitis or encephalomyelitis. Hidden infection has been found in dogs and humans. The infection can be transmitted to people through bites. The disease has two stages. The first stage is usually characterized by headaches, sneezing, bronchitis, and fever. After a short recovery central nervous system signs may appear. This stage is marked by stiffness of the neck, severe headaches, nausea, and confusion. Meningencephalitis or encephalomyelitis may follow with or without paralysis. Recovery make take weeks.
Nipah Virus Infection
Nipah virus is a newly recognized zoonotic virus that was discovered in 1999. It has caused disease in animals and in humans and is transmitted through contact with infectious animals. The virus is named after the location where it was first detected in Malaysia. It is believed that certain species of fruit bats are the natural hosts of Nipah virus. The onset of the infection is usually with "influenza-like" symptoms, with high fever and muscle pains. The disease may progress to inflammation of the brain (encephalitis) with drowsiness, disorientation, convulsions and coma. Fifty percent of clinically apparent cases die.
Rabies
Rabies virus causes acute infection of the central nervous system. Five general stages are recognized in humans: incubation, prodrome, acute neurologic period, coma, and death. Rabies occurs in nearly all countries. Disease in humans is almost always due to a bite by an infected mammal. Nonbite exposures (e.g., mucosal contact) rarely cause rabies in humans. Early diagnosis is difficult. Rabies should be suspected in human cases of unexplained viral encephalitis with a history of animal bite. Unvaccinated persons are often negative for virus-neutralizing antibodies until late in the course of disease. Virus isolation from saliva, positive immunofluorescent skin biopsies or virus neutralizing antibody (from cerebrospinal fluid, or serum of a non-vaccinated patient), establish a diagnosis.
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