Canine Parvovirus –Life Threatening Disease in Dogs
Canine parvo-viral enteritis is a relatively new disease that appeared in the late 1970s. It was first recognized in 1978 and spread worldwide in one to two years. Although the vaccination is being carried out the disease is present throughout the India causing ill health and mortalities in puppies. The disease Canine parvo-viral enteritis, caused by the canine parvovirus, is a highly contagious disease in dogs that affects their digestive system. CPV is a non-enveloped single-stranded DNA virus. CPV continues to evolve, and the success of new strains seems to depend on extending the range of hosts affected and improved binding to its receptor, the canine transferrin receptor. Canine parvovirus affects dogs, wolves, foxes, and other canids.
It is now known that the disease is transmitted via the oral/fecal route. Huge numbers of virus are shed in the stools of infected dogs for up to two weeks after infection. Since the virus is extremely hardy, it can survive and remain infectious for months in the environment and is extremely difficult to kill with disinfectants.
There are two forms of CPV: Intestinal and Cardiac. Puppies are most susceptible. Most dogs that are infected, however, (more than 80 percent) will show no symptoms. With severe disease, dogs can die within 48 to 72 hours with no treatment. In the more common, less severe form, mortality is about 10 percent. Certain breeds, such as Rottweiler, Doberman Pinschers, Labrador Retrievers, and Pit bull terriers as well as other black and tan colored dogs may also be more susceptible to CPV. Along with age and breed, factors such as a stressful environment, as well as concurrent infections with bacteria, parasites, and canine corona virus increase a dog’s risk of severe infection.
Following ingestion, the virus replicates in the lymphoid tissue in the throat, and then spreads to the bloodstream. From there, the virus attacks rapidly dividing cells, notably those in the lymph nodes, intestinal crypts, and the bone marrow. There is depletion of lymphocytes in lymph nodes and necrosis and destruction of the intestinal crypts. Bacteria that normally live in the intestines then cross into the bloodstream and cause sepsis. Dogs with CPV are also at risk for intussusceptions, a condition where part of the intestine prolapses into another part. Three to four days following infection, the virus is shed in the feces for up to three weeks, and the dog may remain an asymptomatic carrier and shed the virus periodically.
This form is less common and affects puppies infected in-utero or shortly after birth until about 8 weeks of age. The virus attacks the heart muscle and the puppy often dies suddenly or after a brief period of breathing difficulty. On the microscopic level, there are many points of necrosis of the heart muscle that goes alongside mononuclear cellular infiltrate. The formation of excess fibrous tissue (fibrosis) is often evident in surviving dogs. Myofibers are the site of viral replication within cells. The disease may or may not be accompanied with the signs and symptoms of the intestinal form.
Dogs that develop the disease show symptoms of the illness within 3 to 10 days. The symptoms include lethargy, vomiting, fever, and diarrhea (usually bloody). Diarrhea and vomiting result in dehydration and secondary infections can set in. Due to dehydration, the dog’s electrolyte balance can become critically unbalanced. Because the normal intestinal lining is also compromised, blood and protein leak into the intestines leading to anemia and loss of protein, and endotoxins escaping into the bloodstream, causing endotoxaemia. There is a distinct odor that the dogs produce, which is in the later stages of the infestation. The white blood cell level drops, further weakening the dog. Any or all of these factors can lead to shock and death.
Tentative Diagnosis is based on an appropriate history and clinical signs and confirmed by a positive fecal ELISA or hemagglutination test or through microscopy. Now a days the PCR based diagnosis is available but as there is no treatment to viral diseases it can’t help much.
Dogs with parvo-viral enteritis typically have vomiting and diarrhoea which typically is severe but may be mild. Lymph nodes may be enlarged and the dog may have a fever. Other diseases may mimic parvo, so a clinical diagnosis made without the aid of diagnostic testing is not precise.
CBC (complete blood count)
Dogs with parvo typically have very few white blood cells. If the normal lower limit for white blood cell counts on the CBC is 6000 cells/micro liter, a dog with parvo may have less than 1000. Although this also does not confirm parvo, it is strong evidence and a dog with some other disease and such a low white cell count requires aggressive treatment or euthanasia regardless.
Survival rate depends on how quickly CPV is diagnosed 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.
Home treatment using IV fluids is sometimes an effective option, but hospitalization may be required. Treatment ideally consists of IV fluids and colloids, antinausea injections (antiemetics) such as metoclopramide, dolasteron, ondansetron and prochlorpromazine, and antibiotic injections such as cefoxitin, metronidazole, timentin, or enrofloxacin. IV fluids are administered and anti-nausea 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 information gathered in blood work.
A blood plasma transfusion 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 survive.
Prevention and Decontamination
Since the virus is so tough and can survive in the environment for such a long time, it is almost impossible to prevent exposure. Vaccination is the only truly effective way of preventing and controlling this disease. It is extremely important to in your puppies and adult dogs against CPV. Weaning puppies should receive initial vaccination of a modified live virus low passage high titer vaccine by a licensed veterinarian at 8 weeks of age, then every 3 to 4 weeks until 15 or 16 weeks. Puppies are initially protected through passive immunity from nursing. These maternal antibodies wear off before the puppy’s immune system is mature enough to fight off CPV infection. Maternal antibodies also interfere with vaccination for CPV 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) should receive 3 vaccinations 3 to 4 weeks apart. A dog that successfully recovers from CPV is still contagious for up to 2 months, so the dog must be kept away from other dogs and puppies. Neighbors and family members with dogs should be notified of infected animals so that they can ensure that their dogs are vaccinated and tested.