Canine parvovirus

Canine parvovirus (type 2) is a contagious virus mainly affecting dogs. The disease is highly infectious and is spread from dog to dog by direct or indirect contact with their feces. It can be especially severe in puppies that are not protected by maternal antibodies vaccination. It has two distinct presentations, a cardiac and intestinal form. The common signs of the intestinal form are severe vomiting and severe haemorrhagic (bloody) diarrhea. The cardiac form causes respiratory or cardiovascular failure in young puppies. Treatment often involves veterinary hospitalization. Vaccines can prevent this infection, but mortality can reach 91% in untreated cases.

There are two types of canine parvovirus called canine parvovirus type 1 CPV1) and canine parvovirus type 2 (CPV2). CPV2 causes the most serious disease and affects domesticated dogs and wild canids. There are variants of CPV2 called CPV-2a, CPV-2b and CPV-2c. Types 2a and 2b are distinct from the original CPV type 2 in terms of virulence and their ability to infect and cause disease in cats too. CPV-2c is a newly identified variant similar to 2b. The viral protein of 2c contains one amino acid different from CPV-2b but it is believed this could be significant. 2c strains have been identified in parts of Europe, the Americas and in Asia. Emergence of this strain has led to claims of ineffective vaccination of dogs, however studies have shown that the existing CPV vaccines still provide adequate levels of protection against CPV type 2c.

Prevention and decontamination

Prevention is the only way to ensure that a puppy or dog remains healthy since the disease is extremely virulent and contigious. The virus is extremely hardy and has been found to survive in feces and other organic material such as soil for over a year. It survives extremely cold and hot temperatures. The only household disinfectant that kills the virus is bleach.

Weaning puppies can be vaccinated with a modified live virus low passage high titer vaccine at 6 weeks of age, then every 3 to 4 weeks until 15 or 16 weeks. Puppies are initially protected through passive immunity derived from the mother. These maternal antibodies wear off before the puppy's immune system is mature enough to fight off CPV2 infection. Maternal antibodies also interfere with vaccination for CPV2 and can cause vaccine failure. Thus puppies are generally vaccinated in a series of shots, extending from the earliest time that the immunity derived from the mother wears off until after that passive immunity is definitely gone. Older puppies (16 weeks or older) are given 3 vaccinations 3 to 4 weeks apart. The duration of immunity of vaccines for CPV2 has been tested for all major vaccine manufacturers in the United States and has been found to be at least three years after the initial puppy series and a booster 1 year later.

A dog that successfully recovers from CPV2 sheds virus for a few days. Ongoing infection risk is primarily from faecal contamination of the environment due to the virus's ability to survive many months in the environment. Neighbours and family members with dogs should be notified of infected animals so that they can ensure that their dogs are vaccinated or tested for immunity. Vaccine will take up to 2 weeks to reach effective levels of immunity, the contagious individual should remain in quarantine until other animals are protected.

Treatment

Survival rate depends on how quickly CPV is diagnosed, the age of the animal and how aggressive the treatment is. Treatment for severe cases that are not caught early usually involves extensive hospitalization, due to the severe dehydration and damage to the intestines and bone marrow. A CPV test should be given as early as possible if CPV is suspected in order to begin early treatment and increase survival rate if the disease is found.

Treatment ideally consists of crystalloid IV fluids and/or colloids, antinausea injections (antiemetics) such as metoclopramide, dolasetron, ondansentron, and prochlorperazine, and antibiotic injections such as cefoxitin, metronidazole, timentin, or enrofloxacin. IV fluids are administered and antinausea and antibiotic injections are given subcutaneously, intramuscularly, or intravenously. The fluids are typically a mix of a sterile, balanced electrolyte solution, with an appropriate amount of B-complex vitamins, dextrose and potassium chloride. Analgesic medications such as buprenorphine are also used to counteract the intestinal discomfort caused by frequent bouts of diarrhea.

In addition to fluids given to achieve adequate rehydration, each time the puppy vomits or has diarrhea in a significant quantity, an equal amount of fluid is administered intravenously. The fluid requirements of a patient are determined by their body weight, weight changes over time, degree of dehydration at presentation and surface area. The hydration status is originally determined by assessment of clinical factors like tacky mucous membranes, concentration of the urine, sunken eyes, poor skin elasticity and bloodtests.

A blood plasmatransfusion from a donor dog that has already survived CPV is sometimes used to provide passive immunity to the sick dog. Some veterinarians keep these dogs on site, or have frozen serum available. There have been no controlled studies regarding this treatment. Additionally, fresh frozen plasma and human albumin transfusions can help replace the extreme protein losses seen in severe cases and help assure adequate tissue healing.

Once the dog can keep fluids down, the IV fluids are gradually discontinued, and very bland food slowly introduced. Oral antibiotics are administered for a number of days depending on the white blood cell count and the patient's ability to fight off secondary infection. A puppy with minimal symptoms can recover in 2 or 3 days if the IV fluids are begun as soon as symptoms are noticed and the CPV test confirms the diagnosis. However, even with hospitalization, there is no guarantee that the dog will be cured and survive.

Unconventional treatments
There is no specific antiviral treatment for CPV. However, there have been anecdotal reports of oseltamivir (Tamiflu) reducing disease severity and hospitalization time in canine parvovirus infection. The drug may limit the ability of the virus to invade the crypt cells of the small intestine and decrease gastrointestinal bacteria colonization and toxin production. There is also anecdotal evidence suggesting that colloidal silver is effective at treating CPV although currently regulatory authorities are discouraging its use due to potential toxicity issues and lack of demonstrated efficacy. Lastly, recombinant feline interferon omega (rFeIFN-ω), produced in silkworm larvae using a baculovirus vector, has been demonstrated by multiple studies to be an effective treatment.