The domestic dog's health is possibly one of the best-studied areas in veterinary medicine, since the dog has had such a long and close relationship with humans. Infectious diseases are prevalent in dogs and are important not just from a veterinary standpoint but also because of the risk to public health. The most wellknown example of this is rabies. Genetic diseases are common in dogs due to the selective breeding necessary to produce individual dog breeds. Due to the popularity of both commercial and homemade dog foods, nutrition is also a heavily studied subject.
Rabies is a viral disease commonly associated with dogs, although in recent years canine rabies has been practically eliminated in North America and Europe due to extensive and often mandatory vaccination requirements. However it is still a significant problem in Africa, the Middle East, Latin America, and Asia. Dogs are considered to be the main reservoir for rabies in developing countries. Areas that are rabies-free, (usually islands) such as Britain, Ireland, Australia, and the American state of Hawaii have strict quarantine laws to keep their territories rabies-free. These require long periods of isolation and observation of imported animals, which makes them unattractive places to move with a pet unless the pet is quite young. Areas that are not rabies-free usually require that dogs (and often cats) be vaccinated against rabies.
Historically, rabies has long been linked to dogs. The earliest mention of rabies is in the Codex of Eshnunna (ca. 1930 BC) (written prior to the Code of Hammurabi), which dictates that the owner of a dog showing symptoms of rabies should take preventative measure against bites. If a person was bitten by a rabid dog and later died, the owner was fined heavily. The sacred animal of the Babylonian goddess of health Gula or Ninisina was the dog; if a person insulted a dog, Gula caused that dog to bite the person and inflict them with rabies. In the 1800s the infectious nature of rabies was first demonstrated by taking the saliva from a rabid dog and injecting it into another animal.
Rabies in dogs is a fatal disease transmitted by the bite of an infected mammal, such as a cat, raccoon, bat, or another dog. Animals with rabies suffer deterioration of the brain and tend to behave bizarrely and often aggressively, increasing the chances that they will bite another animal or a person and transmit the disease. Three stages of rabies are recognized in dogs and other animals. The first stage is a one to three day period characterized by behavioral changes and is known as the prodromal stage. The second stage is the excitative stage, which lasts three to four days. It is this stage that is often known as furious rabies due to the tendency of the affected dog to be hyperreactive to external stimuli and bite at anything near. The third stage is the paralytic stage and is caused by damage to motor neurons. Incoordination is seen due to rear limb paralysis and drooling and difficulty swallowing is caused by paralysis of facial and throat muscles. Death is usually caused by respiratory arrest.
A person or dog bitten by an unknown dog (or other animal) should always be treated without waiting for symptoms, given the potentially fatal consequences of a rabid biter: there have been very few cases of someone surviving rabies when treatment was not begun until after symptoms appeared. Depending on local laws, dogs that are showing neurological signs at the time of the bite are euthanized in order to have their brain tested for rabies. Unvaccinated healthy dogs need to be confined for ten days from the time of the bite (at home or at a veterinarian depending on local law). If the dog is not showing signs of rabies at the end of ten days, then the bitten person could not have been exposed to rabies. Dogs and cats do not have the rabies virus in their saliva until a few days prior to showing symptoms. Ten day confinement does not apply to other species. A dog or cat bitten by a wild animal in an area known to have rabies should be confined for six months, because it can take that long for symptoms to start. This is an incentive to dog-owners to vaccinate their dogs even if they feel the risk of their dog contracting rabies is low, since vaccination will eliminate the need for their dog to be euthanized or impounded should it bite anyone or be suspected of biting anyone.
Canine parvovirus (caused by canine parvovirus type 2, canine parvovirus type 1 is also known as canine minute virus) causes a highly contagious gastrointestinal infection that is especially severe in puppies. It is spread through contact with infected feces. The virus attacks rapidly dividing cells, notably those in the lymph nodes, intestinal crypts, and the bone marrow. There is depletion of lymphocytes in lymph nodes and necrosis and destruction of the intestinal crypts. Symptoms and signs include vomiting, bloody diarrhea, depression, severe dehydration, fever, and low white blood cell counts. Although there is no specific treatment for the canine parvovirus, aggressive intravenous fluid therapy and antibiotics for dogs with secondary bacterial infections is usually required.
Canine distemper, caused by a paramyxovirus similar to the cause of measles, is a highly contagious disease that affects the respiratory, gastrointestinal, and central nervous systems. It is spread through either direct contact with respiratory excretions, through the air, or on fomites (inanimate objects such as clothing). Symptoms and signs include discharge from the eye or nose, coughing, difficulty breathing, vomiting, diarrhea, depression, seizures, and paralysis. Similar to canine parvovirus, treatment is supportive.
Infectious canine hepatitis is caused by canine adenovirus type 1. The virus is spread in the feces, urine, blood, saliva, and nasal discharge of infected dogs. It causes a liver infection and a bleeding disorder. Signs and symptoms include fever, depression, loss of appetite, coughing, tender abdomen, and spontaneous hemorrhages. Treatment is symptomatic.
Canine herpesvirus is a virus of the family Herpesviridae which most importantly causes a fatal hemorrhagic disease in puppies less than two to three weeks old. It is transmitted to puppies in the birth canal and by contact with infected oral and nasal secretions from the mother or other infected dogs, but it is not spread through the air. Signs and symptoms include depression, nasal discharge, and weakness. The inability of very young puppies to mount a febrile response seems to be a significant contributing factor to the high mortality rate in this age dog - it can reach 80 percent. In adult dogs, canine herpesvirus can cause abortion.
Canine influenza usually refers to infection with equine influenza virus H3N8. This virus was found to infect dogs in 2004, and the disease was very contagious due to the dog's lack of natural immunity. Signs and symptoms include cough and nasal discharge, and in more severe cases fever and pneumonia. Canine influenza has a high morbidity but a low mortality.
Bacterial diseases in dogs are usually not contagious from dog to dog; instead they are usually the result of wound colonization, opportunistic infections secondary to decreased resistance (often the result of viral infections), or secondary to other conditions (pyoderma secondary to skin allergies or pyometra secondary to cystic endometrial hyperplasia). These examples are not considered infectious diseases because they do not satisfy Koch's postulates - for example Staphylococcus intermedius, a commonly isolated bacteria from skin infections in dogs, would not cause pyoderma when introduced to a healthy dog. In all likelihood that type of bacteria is already present on the skin of a healthy dog.
There are some bacteria that are contagious from dog to dog. The most notable of these are Bordetella bronchiseptica, one of the causes of kennel cough, Leptospira sp, which cause leptospirosis, and Brucella canis, cause of brucellosis in dogs. There are also common tick-borne bacterial diseases, including Lyme disease, ehrlichiosis, and Rocky Mountain spotted fever.
Leptospirosis is a zoonotic disease caused by bacteria of the genus Leptospira. Humans and dogs become infected through contact with water, food, or soil containing urine from infected animals. This may happen by swallowing contaminated food or water or through skin contact, especially with mucosal surfaces, such as the eyes or nose, or with broken skin. In dogs, transmission most commonly occurs by drinking puddle, pond, or ditch water contaminated by urine from infected wildlife such as squirrels or raccoons. The liver and kidney are most commonly damaged by leptospirosis. Vasculitis can occur, causing edema and potentially disseminated intravascular coagulation (DIC). Myocarditis, pericarditis, meningitis, and uveitis are also possible sequelae.
Brucellosis in dogs is caused by Brucella canis. It is a sexually transmitted disease, but can also be spread through contact with aborted fetuses. The most common sign is abortion during the last trimester or stillbirth. Other symptoms include inflammation of the intervertebral disc and eye (uveitis), and inflammation of the testicle (orchitis) and prostate (prostatitis) in males.
Tick-borne diseases are common in dogs. Lyme disease, or borreliosis, is caused by Borrelia burgdorferi and spread by Ixodes pacificus on the West coast of the Umited States and by I. scapularis (deer tick) in the rest of the U.S. Signs and symptoms include fever, joint swelling and pain, lameness, and swelling of the lymph nodes. It has been diagnosed in dogs in all 48 states of the continental U.S. Ehrlichia canis, which causes canine ehrlichiosis, and Rickettsia rickettsii, which causes Rocky Mountain spotted fever, are both spread by the American dog tick, Dermacentor variabilis, and the brown dog tick, Rhipicephalus sanguineous.
There are several fungal diseases that are systemic in nature, meaning they are affecting multiple body systems. Blastomycosis, caused by Blastomyces dermatitidis, is a fungal disease that affects both dogs and humans, although it is only rarely zoonotic. It is found mainly in the United States in the Mississippi River and Great Lakes areas. Signs include weight loss, cough, fever, enlarged lymph nodes, draining skin lesions, blindness, and lameness. Because dogs are ten times more likely to become infected from the environment than humans, they are considered to be sentinels for the disease.
Histoplasmosis, caused by Histoplasma capsulatum, is a disease with a worldwide distribution. In the United States it is mainly found in the Mississippi and Ohio River areas, most commonly in bird and bat feces. Signs include weight loss, cough, fever, enlarged lymph nodes, and gastrointestinal symptoms. Coccidioidomycosis, caused by Coccidioides immitis, is found in arid and semi-arid regions of Central and South America, Mexico, and southwestern United States. Signs include weight loss, fever, cough, enlarged lymph nodes, and lameness.
Genetic conditions are a problem in some dogs, particularly purebreeds. For this reason many of the national kennel clubs require that dogs with certain genetic illnesses or who are deemed to be carriers cannot be registered. Some of the most common conditions include hip dysplasia, seen in large breed dogs, von Willebrand disease, a disease that affects platelets that is inherited in Doberman Pinschers, entropion, a curling in of the eyelid seen in Shar Peis and many other breeds, progressive retinal atrophy, inherited in many breeds, deafness, and epilepsy, known to be inherited in Belgian Shepherd Dogs, German Shepherd Dogs, Cocker Spaniels, and St. Bernards.
Subaortic stenosis, or SAS, is a genetic ailment that causes a narrowing of the passage of blood between the heart and the aorta. This leads to heart problems and sometimes sudden death. It affects larger breeds such as the Newfoundland Dog and the Golden Retriever. In some dogs, such as collies, the blue merle or harlequin coloring is actually the heterozygote of a partially recessive gene preventing proper development of the nervous system; therefore, if two such dogs are mated, on the average one quarter of the puppies will have severe genetic defects in their nervous systems and sensory organs ranging from deafness to fatal flaws.
Skin diseases are very common in dogs. Atopy, a chronic allergic condition, is thought to affect up to 10 percent of dogs. Other skin diseases related to allergies include hot spots and pyoderma, both characterized by secondary bacterial infections, food allergy, ear infections, and flea allergy dermatitis. Canine follicular dysplasia is an inherited disorder of the hair follicles resulting in alopecia (baldness). Mange is an infectious skin disease caused by mites. Endocrine diseases such as hypothyroidism and Cushing's syndrome can also manifest as skin problems like alopecia or recurring bacterial infections.
Hereditary orthopedic diseases are mainly found in purebred dogs. Hip dysplasia is a common problem that primarily affects larger breeds. Hip dysplasia is a defect in the shape of the hip joint which can, depending on the degree of hip luxation, be quite painful to the dog as it ages. Over time it often causes arthritis in the hips. Dysplasia can also occur in the elbow joint. Luxating patellas can be a problem for smaller breeds. It can cause lameness and pain in the hind legs.
Developmental orthopedic diseases include panosteitis and hypertrophic osteodystrophy. Panosteitis occurs in large and giant breed dogs usually between the age of five and fourteen months and manifests as fever, pain, and shifting leg lameness. Hypertrophic osteodystrophy is also seen in young large and giant breed dogs and is characterized by pain, lameness, fever, and swelling of the long bone metaphysis.
Certain breeds are more likely to develop particular tumors, larger ones especially. The Golden Retriever is especially susceptible to lymphoma, with a lifetime risk of 1 in 8. Boxers and Pugs are prone to multiple mast cell tumors. Scottish Terriers have eighteen times the risk of mixed breed dogs to develop transitional cell carcinoma, a type of urinary bladder cancer.
Eye diseases are common in dogs. Cataracts, glaucoma, and entropion are seen in both dogs and humans. Canine-specific eye diseases include progressive retinal atrophy, Collie eye anomaly, sudden acquired retinal degeneration, and cherry eye. Injury to the eye can result in corneal ulcers.
The frequency of bilateral glaucoma with a genetic base in purebred dogs is higher than in any species except humans. Cataracts in dogs either have a genetic base or can also be caused by diabetes. Nuclear sclerosis resembles a cataract but is actually a normal age-related change.
Cardiomyopathy, or disease of the heart muscle, is also seen in dogs and is associated with large breeds (the exception being Cocker Spaniels, a medium-sized breed). Dilated cardiomyopathy is seen in Great Danes, Irish Wolfhounds, St. Bernards, Dobermanns, Boxers, and other large breeds. Dobermanns, in addition to heart muscle failure, are prone to ventricular arrhythmias. Boxers often present with weakness and fainting due solely to arrhythmias - there is no heart muscle failure at the time of diagnosis. They do, however, eventually develop congestive heart failure, if they do not die suddenly due to an arrhythmia.
Contact your veterinarian or the ASPCA Animal Poison Control Center in case of possible exposure.
Most diseases that affect dogs or humans are not transferable between the two species. There are some exceptions of zoonoses. The most well known zoonosis is rabies, a viral infection transmitted through a bite. A common bacterial zoonosis is leptospirosis, transmitted through urine. Some of the most important zoonoses are parasitic. Zoonotic intestinal parasites transmitted through contact with feces include Toxocara canis (the canine roundworm), which causes toxocariasis, visceral larva migrans, and ocular larva migrans, and hookworms, which can cause cutaneous larva migrans. Zoonotic skin parasites include scabies, caused by the mite Sarcoptes scabiei. The most common zoonotic fungal disease is ringworm, caused in this case by Microsporum canis.
Feeding table scraps to a dog is generally not recommended, at least in excess. Dogs get ample correct nutrition from their natural, normal diet. Otherwise, just as in humans, their diet must consist of the appropriate mix of nutrients, carbohydrates, and proteins, with the appropriate mix to provide all of the minerals and vitamins that they need. A human diet is not ideal for a dog: the concept of a "balanced" diet for a facultative carnivore like a dog is not the same as in an omnivorous human. Wild and feral dogs can usually get all the nutrients needed from a diet of whole prey and raw meat. In addition, the scraps often consist of fat rather than meat protein, which in excess is no better for dogs than it is for humans. While not all human delicacies are acutely toxic to dogs (see above), many have the same chronically unfortunate results as they do for humans. Lastly, many people overfeed their dogs by giving them table scraps and human food such as ice cream. Dogs will usually eat all the scraps and treats they are fed, which is more than often too much food.. The result of too much food is obesity, an increasingly common problem in dogs in Western countries, which can cause numerous health problems just as it does in humans, although dogs are much less susceptible to the common cardiac and arterial consequences of obesity than humans are.
Additionally, the feeding of table scraps directly from the table (as opposed to taking scraps after the meal, and giving them in the dog's food dish as a treat) can lead to trained begging behavior on the part of the dog, or even encourage the dog to reach up and take food directly from the table (another trained response). These are normally seen as undesirable behavioral traits in a dog.
Obesity can be a sign of other serious ailments such as Cushing's Disease which is characterized by weight gain, appetite increase and lethargy in primarily older dogs.
A modern trend in canine diets is raw feeding of whole meats, bones and little filler material.
Animal control agencies in the United States and the ASPCA advise that dogs not intended for further breeding should be spayed or neutered so that they do not have undesired puppies.
Because of the overpopulation of dogs in some countries, puppies born to strays or as the result of accidental breedings often end up being killed in animal shelters. Spaying and neutering can also decrease the risk of hormone-driven diseases such as mammary cancer, as well as undesired hormone-driven behaviors. However, certain medical problems are more likely after neutering, such as urinary incontinence in females and prostate cancer in males. The hormonal changes involved with sterilization are likely to somewhat change the animal's personality, however, and some object to spaying and neutering as the sterilization could be carried out without the excision of organs.
It is not essential for a female dog to either experience a heat cycle or have puppies before spaying, and likewise, a male dog does not need the experience of mating before neutering.
Female cats and dogs are seven times more likely to develop mammary tumors if they are not spayed before their first heat cycle. The high dietary estrogen content of the average commercial pet food as well as the estrogenic activity of topical pesticides may be contributing factors in the development of mammary cancer, especially when these exogenous sources are added to those normal estrogens produced by the body. Dog food containing soybeans or soybean fractions have been found to contain phytoestrogens in levels that could have biological effects when ingested longterm.