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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.
Diseases and ailments
Some diseases, ailments, and poisons are common to both humans and dogs; others are different.
Transferable diseases
Most diseases that affect dogs or humans are not transferable between the two species. There are some exceptions of zoonoses:
Rabies
Is a usually fatal disease which can be transmitted to dogs or humans by the bite of an infected mammal, possibly a dog's, cat's, raccoon's, or bat's. Although rodents and similar small mammals can be infected with the disease artificially, they are generally not found infected in the wild; the current hypothesis is that they are not likely to survive any attack that would infect them. 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. 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. 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 has been only one case of someone surviving rabies when treatment was not begun until after symptoms appeared. The biter should be apprehended if possible, as only autopsy of the brain can determine if it was rabid. This should be a great 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 and examined in this fashion should it bite anyone or be suspected of biting anyone. This applies to dogs that are showing neurological signs at the time of the bite. Unvaccinated healthy dogs need to be confined for ten days from the time of the bite (at home or at a veterinarian depending on state 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.
Parasites
Particularly intestinal worms such as hookworms, tapeworms and roundworms, can be transmitted in a dog's feces. Some tapeworms have fleas as intermediate hosts: the worm egg must be consumed by a flea to hatch, then the infected flea must be ingested (usually by the dog while grooming itself, but occasionally by a human through various means) for the adult worm to establish itself in the intestines. The worm's eggs then pass through the intestines and adhere to the nether regions of the dog, and the cycle begins again.
Fleas
Ticks of various species can be acquired and brought home by a dog, where they can multiply and attack humans (and vice versa). This is particularly important, now that tick-borne Lyme Disease has become endemic throughout a large area, in addition to other similar diseases such as Rocky Mountain Spotted Fever. Although dogs do not seem to be as susceptible to such diseases as humans, similar rickettsial diseases have been spread by dogs to humans through such mechanisms as a dog killing an infected rabbit, then shaking itself off in the house near enough to its owners to fatally infect most of the family.
Leptospirosis
Bacterial disease that affects humans and animals. It is 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.
Genetic ailments
Genetic conditions are a problem in some dogs, particularly purebreeds:
Hip dysplasia primarily affects larger breeds.
Luxating patellas can be a problem for smaller breeds.
Genes for blindness or deafness seem to be carried by some breeds.
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.
Dangerous foods
Some foods commonly enjoyed by humans are dangerous to dogs:
Dogs love the flavor of chocolate, but chocolate in sufficient doses is lethally toxic to dogs (and horses and possibly cats). Chocolate contains theobromine, a chemical stimulant that, together with caffeine and theophylline, belongs to the group of methylxanthine alkaloids. Dogs are unable to metabolize theobromine effectively. If they eat chocolate, the theobromine can remain in their bloodstreams for up to 20 hours, and these animals may experience fast heart rate, hallucinations, severe diarrhea, epileptic seizures, heart attacks, internal bleeding, and eventually death. A chocolate bar can be sufficient to make a small dog extremely ill or even kill it. Approximately thirty grams of baking chocolate per kilogram (1/2 ounce per pound) of body weight is enough to be poisonous. In case of accidental intake of chocolate by especially a smaller dog, contact a veterinarian or animal poison control immediately; it is commonly recommended to induce vomiting within two hours of ingestion. Large breeds are less susceptible to chocolate poisoning, but still are far less tolerant of the substance than humans are.
Note:Carob treats are often available as dog treats; these are unrelated to chocolate and are safe.
It has recently been confirmed that grapes and raisins can cause acute renal failure in dogs. The exact mechanism is not known, nor any means to determine the susceptibility of an individual dog. While as little as one raisin can be fatal to a susceptible ten pound dog, many other dogs have eaten as much as a pound of grapes or raisins at a time without ill effects. The dog usually vomits a few hours after consumption and begins showing signs of renal failure three to five days later.
Onions and to a significantly lesser extent garlic contain thiosulfate which causes hemolytic anemia in dogs (and cats). Thiosulfate levels are not affected by cooking or processing. Small puppies have died of hemolytic anemia after being fed baby food containing onion powder. Occasional exposure to small amounts is usually not a problem, but continuous exposure to even small amounts can be a serious threat. Garlic is also known to cause diarrhoea and vomiting.
Macadamia nuts can cause stiffness, tremors, hyperthermia, and abdominal pain. The exact mechanism is not known. Most dogs recover with supportive care when the source of exposure is removed.
Alcoholic beverages pose much the same temptation and hazard to dogs as to humans. A drunk dog displays behavior pretty much analogous to that of an intoxicated person. (However, beer presents another problem; see below.)
Hops, the plant used to make common beer, can cause malignant hyperthermia in dogs, usually with fatal results. Certain breeds, such as Greyhounds, seem particularly sensitive to hop toxicity, but hops should be kept away from all dogs. Even small amounts of hops can trigger a potentially deadly reaction, even if the hops are "spent" after use in brewing.
Some dogs have food allergies much as humans do; this is particular to the dog and not characteristic of the species as a whole. An example is a dog vomiting whenever he eats salmon; many humans likewise have seafood allergies.
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