Unraveling Canine Health Problems
Biologist and breeder Margaret Pough discusses the genetic, environmental, and infectious causes of disease.
Photo by Isabel Francais for AKC
Any dog of any breed can have health problems. Dogs can become infected by viral and bacterial diseases, and internal and external parasites, and be exposed to environmental toxins. Is a problem seen in a puppy or an adult dog the result of an inherited trait or due to external factors such as toxins or an infectious disease?
Each individual dog in the world carries some “bad” genes that can be expressed at different times during the development of the fetus, in the growing puppy, or later in life. We breeders have a profound influence through our breeding programs. The environment in which the dog lives can influence the expression of some genes, as can nutrition and husbandry.
In many cases breeders just say, “Oh, the pups died” or “The dog died.” As a biologist I want to know why. As breeders and owners, we need to know why. Follow-up testing may help us differentiate between genetic, environmental, and infectious causes of disease.
Congenital, Developmental, and/or Inherited
A congenital disorder is one that is present at birth. But that does not mean it is inherited. Exposure to toxins, viruses, and bacteria may cause congenital and developmental defects. Congenital defects as the result of an insult during the early development of the fetus may cause a severely deformed puppy or a litter where many puppies have severe problems. Breeders must be aware of the frequency of developmental defects that occur in their breed or in their bloodlines. A defect that is widespread in occurrence in a breed is probably heritable, but that does not mean it is inherited in every breed, or in the same manner in every breed.
Cleft palates are congenital defects (present at birth) that can occur in any breed, but are more common in chondroplastic breeds, probably related to the general conformation that occurs with achondroplasia.
But not all cleft palates are inherited; exposure to toxins during pregnancy may also cause cleft palates.
One breeder had cleft palates pop up in multiple litters in one of her breeds. When a cleft palate appeared in her other breed, she felt that these were probably congenital defects caused by an outside insult, rather than inherited. She decided to change from the locally produced food to a name brand, and the incidence of cleft palates dropped to zero. She suspects there may have been a problem in the food, though she also ruled out water and did research to make sure the new house was not on a toxic-waste dump.
Progressive retinal atrophy is a developmental disorder that is inherited, but there are at least seven different genes responsible for the expression we call PRA. Different genes are present in different breeds, and the mode of inheritance is not always the same.
In addition, retinal degeneration may have nonheritable causes. In some breeds there are genetic tests for the specific type of PRA present in that breed. But yearly examinations by board-certified ophthalmologists are still the only way to ensure that individuals of other breeds are not affected.
Hip dysplasia has a complex mode of inheritance, and the expression is strongly affected by the “environment” in which the puppy grows, including growth rate, adult weight, footing, and many other factors. We still need to select against hip dysplasia genes, but we also need to raise puppies in a manner that will not contribute to its expression.
Breeders need to keep careful records and not assume that a disorder is inherited, or dismiss it as a congenital accident. Inherited disorders may have a simple or complex mode of inheritance, in both cases risk factors must be assessed in breeding decisions. Breeding decisions must include the mode of inheritance if known, tests available (Is there a genetic test, or only phenotypic tests?), as well as the size of the breeding pool, and the severity of the disorder to the health of the dog. Imported breeding stock should have the same health clearances you would require if buying a dog here.
Dogs are traveling abroad to shows and on vacation with their owners. They may be exposed to exotic parasites and different infectious diseases. We must be aware that our dogs may become infected with “exotic” diseases even when we travel within the U.S.A. A dog may contract an infection that is seldom seen where we live. There are fungal diseases that are present in regional areas.
It is important to take your dog to your veterinarian if your dog gets ill after traveling or attending a show. And is important to tell your veterinarian where you have been. Although we do not think of rabies as a disease of dogs in this country, in 2005 an imported rescue puppy was diagnosed with rabies.
We often jump to conclusions when a dog exhibits clinical signs similar to those seen with a common disease. When dogs are ill, pursuing diagnostics help us differentiate between different infectious diseases, environmental causes, and inherited traits. Virus isolation identified distemper, parvovirus, and the newly emerged canine influenza virus. However, respiratory disease has many causes, and a rescue dog in transit that was presumed to have canine influenza actually had distemper. Most cases of respiratory disease in dogs are caused by the common “kennel cough” pathogens, adenoviruses, Mycoplasma, Bordetella, or a combination infection of two or more of these pathogens.
Canine brucellosis is common in puppy mills, and in free-roaming dogs in many parts of the South; all dogs coming into rescue should be tested. Neutering will prevent shedding of the bacteria in bitches, but infected males may still harbor organisms in their prostate gland even after neutering, and may be potential shedders for extended periods of time. Antibiotics may mask infection and blood cultures a month after the end of treatment are required to determine infection status.
Dogs from subtropical countries may harbor intestinal and blood-borne parasites, as well as viral and bacterial diseases. Leishmaniasis, a protozoan parasitic organism, was predominantly found in returning military dogs. The vector is the sand flea. As importations from Mediterranean countries and subtropical regions become more common, more cases of Leishmania have surfaced. Only through proper diagnostic testing can we identify and work to prevent exotic diseases from entering our canine populations.
Viruses, bacteria, or protozoa may cause gastrointestinal illness. The common assumption I hear is that there is a “new parvo.” If a dog dies, it is very important to have a necropsy performed to help us determine if we are dealing with an emerging disease, or a different variant of a known infectious entity.
Diagnostics empower us and help us produce healthy dogs. Do not assume. Persuade your veterinarian that you need to know. Be willing to pay for necropsies on dogs that die. Get in touch with veterinary colleges or universities for help in diagnostics for infectious, environmental, andand inherited diseases.
[This article is an update from one that originally appeared in the AKC Delegate Perspectives newsletter.]
- Work with your veterinarian
- Share information
- Pursue diagnostics
- Be willing to have necropsies performed
- Knowledge is power
Margaret Pough is AKC Delegate from the Finger Lakes Kennel Club and a member of the Delegate Canine Health Committee.