Infection by the canine parvovirus (CPV) is an extremely contagious and fairly common disease of domestic dogs. It tends to primarily affect rapidly reproducing cells in puppies, especially the cells lining the digestive tract, causing acute onset of severe gastrointestinal distress.
Causes of Parvoviral Infection in Domestic Dogs
Canine parvovirus is shed in the feces of dogs for several weeks after they become infected. Clinical disease is caused by oral contact with infected fecal matter, which can be present on a dog's fur, feet, crate, bed, owners' shoes, carpet and any number of other objects. This is called infection by the "fecal-oral" route. When a dog licks or ingests anything that is contaminated by parvovirus, it typically will become infected. Young dogs, immunocompromised dogs, highly stressed dogs and dogs with other illnesses are more susceptible to parvoviral infection. The incubation period for clinical parvoviral disease is between 5 and 10 days. However, infected dogs typically start shedding the virus in their feces well before they show any symptoms of sickness.
CPV infection occurs worldwide. It is most common in warm, wet seasons and environments, and in the spring when most puppies are born. The canine parvovirus is very resistant to common household detergents and disinfectants and can survive at room temperature, indoors or outdoors, for several months.
Prevention of Parvoviral Infection
Newborn puppies normally are protected from parvoviral infection by maternal antibodies, which they acquire in utero and through their mothers' milk after they are born. These maternal antibodies naturally decline over time, and puppies become increasingly susceptible to a number of infectious organisms, including canine parvovirus. Infection by CPV is usually preventable by vaccinating young puppies before they reach 8 weeks, and revaccinating every 3 or 4 weeks thereafter until the puppies are 16 weeks old. However, despite appropriate vaccination, there still is a susceptible period, when maternal antibodies are waning and the immune system has not yet fully responded to vaccines, during which puppies are at an increased risk of developing illness from infectious organisms.
Thorough disinfection of areas inhabited or frequented by infected dogs can reduce the risk of infection for other animals. The canine parvovirus is extremely hardy and can survive for months in the environment, despite the presence of household cleaners. The most effective disinfectant for CPV is household bleach, in a 1 to 30 part dilution with water. All surfaces that an infected dog has contacted should be cleansed thoroughly. Dogs known or suspected to be infected with the canine parvovirus should be isolated from all other animals, to limit environmental contamination and to prevent spread of the disease.
Historically, most authorities recommend that healthy puppies be kept away from other dogs, and especially from areas frequented by dogs of unknown vaccination status, until their puppy vaccination series is completed at approximately 16 weeks of age. However, more recent recommendations suggest that the benefits of early socialization with other dogs after the first puppy vaccination may outweigh the risks of becoming infected with parvovirus. Owners should discuss the potential risks and benefits of isolation versus socialization with their veterinarian, their dog's breeder and/or their trainer.
Canine parvovirus is extremely hardy and can survive up to 7 months or more in the environment – and even longer during winter with frozen ground. Owners of dogs that have suffered from this illness need to thoroughly disinfect all indoor surfaces that the affected dog came into contact with, and should remember that outside areas may still contain infectious CPV organisms for a number of months. The incidence of parvoviral infection has decreased markedly with the increase of routine puppy vaccination series. However, outbreaks are still common in animal shelters, high-volume breeding facilities ("puppy mills"), boarding kennels and other places where large numbers of young, immunocompromised and/or unvaccinated dogs congregate.
Canine parvoviral (CPV) infection, commonly called "parvo," is primarily a gastrointestinal disease of puppies under 8 months of age and of unvaccinated adult domestic dogs.
Symptoms of Parvoviral Infection
Most dogs begin to show symptoms of illness following a 5-to-10 day incubation period after exposure to feces from an infected dog. Infected dogs typically start shedding the virus in their own feces before they develop observable symptoms. Owners of dogs in the acute stage of parvoviral disease usually observe one or more of the following clinical signs:
Lethargy (usually appears very suddenly; acute in onset)
Loss of appetite (inappetance; anorexia)
Diarrhea (profuse; often bloody)
Bloody stool (hematochezia)
Mucus in stool (steatorrhea)
Fever (usually fluctuating; can be extremely high)
Elevated heart rate (tachycardia)
Dehydration (tacky gums)
Some people believe that the feces from dogs with CPV infection has a distinctly characteristic, foul odor, while others are convinced that it is impossible to diagnose parvo simply based upon smell.
Dogs at Increased Risk
Parvoviral infection can affect dogs of any age, although most cases occur in young puppies between 6 weeks and 6 months of age. Unvaccinated or partially vaccinated animals have a greatly increased risk of developing parvo. Certain breeds are described as being predisposed to CPV infection, including the Doberman Pinscher, Rottweiler, English Springer Spaniel, German Shepherd, American Pit Bull Terrier and Dachshund. These breeds also tend to develop more severe symptoms once they become infected. The reason for reduced resistance to parvoviral infection in these breeds is not known. Also for some unknown reason, Toy Poodles and Cocker Spaniels seem to have a reduced risk of CPV infection. Puppies whose mothers have been routinely vaccinated are also less commonly and less seriously affected, because vaccination of the dam boosts circulating maternal antibody levels in her young puppies.
Parvoviral infection should be suspected in any young, unvaccinated or incompletely vaccinated puppy and in any unvaccinated adult dog with acute signs of gastrointestinal distress.
How Parvoviral Infection is Diagnosed
When presented with a "sick puppy," most veterinarians conduct a thorough physical examination and take a complete history. The initial data base typically includes blood work and a urinalysis, the results of which can guide the attending veterinarian toward or away from a diagnosis of canine parvoviral (CPV) infection. Fecal floatation and microscopic examination of feces on a wet slide preparation can be used to identify the infective organisms, although the results of these tests are not reliable. Abdominal radiographs (X-rays) may be recommended to rule out other causes of gastrointestinal distress, such as intestinal blockage by a foreign body or other forms of intestinal obstruction.
Presently, the best way to diagnose CPV infection is to identify the viral antigens. This can be done by an ELISA test on a fecal sample, which is commercially available in almost any veterinary clinic. Test results may report false negatives during the early course of the disease, before the period of peak viral shedding. False negative results can also occur after approximately 10 to 14 days of infection, when viral shedding rapidly decreases. Dogs that have been recently vaccinated against CPV with a modified live vaccine can have false positive results ELISA results for parvoviral infection.
More advanced and more precise techniques to detect CPV infection include PCR (polymerase chain reaction) testing, electron microscopy, tissue culture and viral isolation. However, the financial considerations of many owners practically prohibit exhaustive diagnostic testing with these advanced techniques. Most owners opt to spend their resources on treating their sick puppy empirically, assuming that it has CPV infection, rather than pursuing advanced diagnostic techniques. This is probably a good approach in most cases, because without treatment the mortality rate for dogs with parvoviral infection is quite high.
Parvoviral infection is especially common in young dogs housed in close quarters with other dogs, such as in animal shelters, humane societies or the facilities of backyard breeders or puppy mills. Vaccination against CPV is almost always effective.
The immediate goals of treating canine parvoviral infection are to reverse the dehydration, electrolyte and metabolic abnormalities caused by the disease and to prevent or eliminate secondary bacterial infections. The overriding goals are to make the dog comfortable and to restore a pain-free, vomit-free and diarrhea-free quality of life.
Dogs clinically infected by the canine parvovirus (CPV) almost universally require hospitalization and intensive medical management. Dehydration and electrolyte imbalances must be corrected as quickly as possible by administration of balanced fluids, either orally, subcutaneously or intravenously. A number of medications are available to help control the severe diarrhea and vomiting that typically accompany CPV infections. Many veterinarians recommend withholding food and water until the dehydration, diarrhea and vomiting are controlled, which can take several days. However, some recent studies suggest that it may be better to encourage early nutritional support with high-protein, high-calorie foods. Affected dogs can be fed through a nasogastric or nasoesophageal tube until they are stabilized, if they are reluctant to eat on their own. Thereafter, a soft, bland diet is usually recommended. In especially severe cases, the dog may require colloid therapy, blood transfusions and/or other types of intensive inpatient care.
Secondary bacterial infections are common adjuncts to parvoviral infection and actually are the most common cause of associated death. The attending veterinarian probably will prescribe a course of broad spectrum antibiotics to help prevent systemic bacterial infection (septicemia) and other bacterial complications that can result from bacterial translocation across the dog's damaged intestinal lining.
The prognosis for dogs infected with parvovirus depends upon a number of factors, including the virulence of the particular viral strain, how quickly the infection is diagnosed, the age and immune status of the dog at the time of infection, and how quickly treatment is begun. Other factors may influence the prognosis as well. If the infection is caught quickly and treated aggressively, most dogs will recover fully and will develop lifelong immunity to the virus. Unfortunately, many young dogs die from this disease, especially those in animal shelters, puppy mills or other crowded, less-than-hygienic living conditions.