Canine Parvovirus: A Threat to Pets
Authors -Amit Kr. Verma #, Mahima2 and Amit Kumar3
1 Department of Epidemiology and Veterinary Preventive Medicine, Pandit Deen Dayal Upadhaya Pashu Chikitsa Vigyan Vishwa Vidhyalaya evam Gau Anusandhan Sansthan, Mathura – 281001
2 Veterinary Officer, State Veterinary Hospital, Heempur Deepa, Dist. Bijnor (UP)
3 Assistant Professor, Deptt. of Microbiology and Immunology, Pandit Deen Dayal Upadhaya Pashu Chikitsa Vigyan Vishwa Vidhyalaya evam Gau Anusandhan Sansthan, Mathura – 281001
Canine parvovirus commonly known as Parvo or Canine parvo is a contagious virus affecting dogs of any age, but puppies are usually more severly affected and may collapse in a ‘shock-like’ state and die suddenly without showing any clinical signs, after only a brief period of malaise. The disease is highly contagious and transmission is through direct or indirect contact between dogs with their faeces. CPV2 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. It is more common in overcrowded, breeding colonies, where hygiene is difficult. The virus is a non-enveloped single-stranded DNA virus. There are two types of canine parvovirus CPV1 and 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. The original virus is virtually extinct in domestic dog population. 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.
It has two clinical forms, one is cardiac and other is intestinal. The common signs of the intestinal form are severe vomiting and severe haemmorhagic (bloody) diarrhea. The cardiac form causes respiratory or cardiovascular failure in young puppies. Dogs that develop the disease show signs of the illness within 5 to 10 days. The first sign of CPV is lethargy. Usually the second symptoms would be loss of appetite or diarrhea followed by vomition.The symptoms include depression, abdominal discomfort, vomition, fever, diarrhea (usually bloody), dehydration. Diarrhea and vomiting result in dehydration and secondary infections can develop. Due to dehydration, the dog’s electrolyte balance can become critically affected. 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 endotoxemia. Dogs have a distinctive odor in the later stages of the infection. Copathogens such as parasites, viruses, and certain bacterial species (e.g., Campylobacter spp., Clostridium spp. and Salmonella spp.) hypothesized to exacerbate illness. The white blood cell level falls, further weakening the dog. Any or all of these factors can lead to shock and death.
Diagnosis can be made through detection of virus in the stool or intestinal contents at the onset of disease and for 2-4 days afterward by use of either an EIA or a hemagglutination test, or by electron microscopy. PCR has become available to diagnose CPV2, and can be used later in the disease when potentially less virus is being shed in the feces that may not be detectable by EIA. Parvovirus, however, is more serious and the presence of bloody diarrhea, a low white blood cell count, and necrosis of the intestinal lining also point more towards parvovirus, especially in an unvaccinated dog. The cardiac form is typically easier to diagnose because the symptoms are distinct.
Survival rate depends on how quickly the disease 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. Goals should be to mollify the intestinal tract, restore and maintain fluid and electrolyte balance, and resolve shock, sepsis, and endotoxemia. Treatment ideally consists of crystalloid IV fluids and/or colloids, antinausea injections (antiemetics) such as metoclopramide, ondansetron and prochlorperazine, and antibiotic injections such as cefotaxim, metronidazole or enrofloxacin. IV fluids are administered and antinausea and antibiotic injections are given subcutaneously, intramuscularly, or intravenously. The fluids are typically a mixture of a sterile, balanced electrolyte solution, with an appropriate amount of multivitamins, dextrose and potassium chloride. Analgesic medications such as dicyclomin 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. 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. If more severe, depending on treatment, puppies can remain ill from 5 days up to 2 weeks. However, even with hospitalization, there is no guarantee that the dog will be cured and survive.
No specific antiviral drug is available for treatment of 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. 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.
Prevention and Control
Prevention is the only way to ensure that a puppy or dog remains healthy since the disease is highly contagious and virulent. Maternal antivody interference is most common cause of vaccination failure. Puppies get 10% maternal antibody through transplacental and 90% through transcolostral route. Puppies are generally vaccinated with inactivated vaccines at 2-2.5 months of age and booster after one month then annualy.
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 Sodium hypochlorite and bleach. A dog that successfully recovers from CPV2 sheds virus for a few days. Ongoing infection risk is primarily from fecal contamination of the environment due to the virus’s ability to survive many months in the environment. Isolation of susceptible pups from other dogs. In household, if true isolation is not possible, puppies shoul at least be kept from araeas where dogs congregate such as parks and recreational sites. Neighbours and family members with dogs should be notified of infected animals so that they can ensure that their dogs are vaccinated 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.
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