Parvovirus, a highly contagious and often lethal virus was first identified in 1978, and is found throughout the world. It is believed that parvo arose as a mutation from wildlife or from the feline parvovirus (feline distemper virus). Parvo also affects coyotes and some other wild canids.
Puppies Are Highest Risk
Parvo affects dogs of any age but puppies are the most susceptible with up to a twenty percent mortality rate even in pups that receive treatment. Puppies stressed from fleas or ticks or from tail docking or ear cropping are at highest risk for severe disease. Rottweilers and Doberman Pinschers seem to be more severely affected by parvovirus than other breeds. The highest incidence of parvo occurs in kennels, pet stores, shelters, and poor-quality breeding facilities.
The virus is shed in the droppings of infected dogs for about two weeks, and the disease is spread by direct contact with this infected material. Dogs are usually infected when they swallow the virus after licking contaminated material. Following exposure, symptoms usually occur in five to eleven days.
Symptoms include depression, usually a fever of 104 to 106 degrees, refusal to eat or drink, and severe vomiting along with diarrhea. Vomiting is often the first sign, with diarrhea usually appearing within 24 to 48 hours. Vomit may be clear, yellow or blood-tinged; diarrhea is often bloody, smells rotten, and may have mucus present. Because these signs are not restricted to parvo, diagnosis is only confirmed by finding the virus in the feces.
The acute form of the disease, however, may result in sudden severe stomach pain and depression, followed by shock and sudden death before any other symptom becomes apparent. A long illness is rare; dogs typically either recover quickly, or they die.
How Parvo Progresses
Parvovirus causes two forms of disease. Myocarditis affects the heart muscles in young puppies four to eight weeks old, and was more common when the disease first appeared. Affected puppies are infected before birth or shortly thereafter and typically stop nursing, gasp for breath and may cry in distress. Retching, convulsions and foaming at the nostrils or mouth may occur. Other times, the disease causes a sudden death syndrome that may occur within hours or a few days of onset. Those pups that survive initial infection may develop congestive heart failure and die weeks to months later. Today, this form is rare because puppies are usually protected by maternal antibodies.
The more common enteric form of parvo affects the intestines. The tonsils are infected first, and from there the virus travels to the lymphatic system which routes it to the bloodstream. Then virus travels throughout the body, ultimately infecting the crypt cells of the intestinal lining.
The small intestine is lined with hill-shaped villi containing tiny hair-like projections called microvilli. It's here the majority of digestive absorption takes place. Crypt cells down in the 'valleys' replace the microvilli every three to four days, and these new microvilli migrate toward the 'hilltops' of the villi. Parvovirus kills the crypt cells that make the nutrient-absorbing microvilli. It takes three to four days for crypt cells to heal, and begin to re-populated the villi. During that time, the puppy's body can’t process food and water.
Sick pups die from dehydration, electrolyte imbalance, shock, or secondary infections. Puppies often collapse and die in as little as twelve hours following the onset of symptoms. Immediate veterinary help is critical.
There is no cure or specific treatment for parvovirus, but early detection and treatment increase chance for survival. Therapy is centered upon good nursing and supportive care. Essentially, a sick dog must be kept alive long enough for his own immune system to suppress and clear the virus from his body. Dogs that survive for three to four days following the onset of vomiting and diarrhea generally recover rapidly, and will become immune to the enteric form of the disease.
Food and water are usually withheld for two to four days to give the digestive system a chance to rest. Fluid therapy helps counter the devastating dehydration and returns electrolyte balance to normal. Antibiotics may be administered to fight secondary infection, along with medications to control vomiting and diarrhea. Once vomiting and diarrhea have subsided, water and a bland food like cottage cheese and rice or veterinary prescribed diet are offered in small amounts several times daily. The normal diet is then reintroduced gradually as the dog recovers over the next several days.
Strict isolation and quarantine helps control the spread of disease. Sick dogs should remain isolated for thirty days after recovery and bathed thoroughly before being brought into contact with other dogs.
Parvo can live in the environment for at least five months and sometimes for years. Direct dog-to-dog contact spreads distemper, for example, isn't necessary to spread parvo. Virus can be picked up simply by walking through a yard contaminated with infected feces, or by contact with kennels or other objects that have been contaminated by an infected pet. You could carry the virus to your puppy on your shoes after you've walked through an infective area.
The virus is resistant to most common disinfectants and household detergents. But thorough cleaning with household bleach will kill the virus. A dilution of one part bleach to thirty parts water is recommended.
Protecting puppies with vaccination reduce the risk of your puppy catching the disease. Be sure your puppy stays away from exposure to other dogs until fully protected.