Available vaccines have controlled the transmission of parvovirus infection, but sometimes, even vaccinated dogs get infected and die due to this disease. Better understanding of the disease and sources of the virus by pet parents can prevent and reduce the spread of this disease and untimely loss of their altruistic companions.
Canine parvovirus (CPV) infection is one of the most common problems in dogs, causing massive mortality in puppies. The disease is highly infectious, depicted by diarrhoea which is frequently haemorrhagic. This virus affects dogs of all ages, but puppies are most commonly affected. CPV infection is manifested in two forms: the intestinal form and the cardiac form. Cardiac form is fatal and affects young puppies.
Who can get affected?
- Young (6 week to 6 months), unvaccinated or incompletely vaccinated dogs are most vulnerable.
- Breeding kennels and dog shelters that house a large number of inadequately vaccinated puppies are particularly hazardous places to acquire infection.
- Sufficient colostrum ingestion by puppies born to a dam with CPV antibodies is protected from infection for the first few weeks of life; however, susceptibility to infection increases as maternally acquired antibodies fade.
- Improper vaccination protocol and vaccination failure can also lead to a CPV infection.
- Immunosuppressive diseases or drugs also increase the likelihood of infection.
- Certain breeds of dogs like Rottweiler, Doberman Pinschers, Pit Bulls, Labrador Retrievers, German Shepherds, English Springer Spaniels, and Alaskan sled dogs, are particularly vulnerable to the disease.
- Male dogs more than six month old are more susceptible than female dogs for this infection.
How CPV affects dogs?
The virus affects in two ways:
1. Diarrhoea and vomiting, resulting in extreme fluid loss and dehydration, leading to shock and death.
2. Loss of the intestinal barrier allows bacterial invasion of potentially the entire body resulting in septicemia and death.
There are three main manifestations of Parvovirus infection. The onset of clinical signs is usually sudden, often 12 hours or less. The incubation period varies from 3 to 10 days.
1. Asymptomatic- No clinical signs expressed and animal shed virus in his excretion. This carrier form is common in vaccinated and adult dogs.
2. Intestinal- The virus has affinity towards rapidly dividing cells, such as those lining the gastrointestinal tract and causes extreme damage and sloughing of the intestinal tract lining. This can leave the patient open to secondary bacterial infection and death rate of 16-35 percent has been reported. Most of the affected dogs are less than one year old and between 6-20 weeks old.
3. Cardiac – This form is much common than the intestinal form due to extensive vaccination. Severe inflammation and necrosis of the heart muscle causes breathing difficulty and death in very young puppies. Older dogs who survive this form have scarring in the heart muscle.
Parvovirus infected dogs show variable symptoms with varying severity. The most common form of the disease is the gastroenteritis form. Clinical signs of enteritis usually develop within 3-7 days post infection. Severe and bloody diarrhoea, vomiting, anorexia, severe weight loss, lethargy characterises parvovirus enteritis with lowered WBC counts. Eyes and mouth may become evidently red and the heart may beat too swiftly. Infected dogs are depressed, feverish, dehydrated or may also have a low body temperature. Physical examination of dog may reveal dilated fluid filled intestinal loops. Abdominal pain necessitates further investigation to rule out the possible complication of intussusceptions. Acute parvovirus gastroenteritis can occur in dogs irrespective of age, breed or sex. The disease progresses at a very fast pace and death can occur as early as two days after the onset of the disease. A less common form of the disease causes myocarditis. This form is more common in puppies less than eight weeks of age and is characterised by breathing difficulties leading to death.
How CPV spreads?
Canine parvovirus is resistant to many common disinfectants and can persist indoors at room temperature for up to two months and outdoors for up to five months, if protected from sunlight and desiccation. CPV can spread through following ways:
- In acutely infected dogs, the virus is shed in extremely large amounts in faeces within 4-5 days of exposure, throughout the period of illness and for approximately 10 days after clinical recovery.
- Veterinary hospital and clinics are also likely places to pickup the virus due to contamination of premises by excretions
of infected animals coming for treatment.
- Contaminated feed and water is another major route of disease transmission.
- Dogs can also pickup virus through contact inanimate belongings of infected dogs.
- Mechanical transmission by insects and rodents may also occur.
Parvovirus infection should be differentially diagnosed with other enteric viruses such as coronavirus, adenovirus, rotavirus, morbillivirus, reovirus and norovirus which also express similar type of clinical manifestations. The most efficient way to diagnose parvovirus infection is to identify either the virus or virus antigens in stools by enzyme-linked immunosorbent assay (ELISA) antigen test. A complete physical examination, abdominal radiographs and abdominal ultrasounds aids in determining the severity of the disease. A chemical blood profile and a complete blood cells count may also be performed. Low WBC levels in association with bloody stools are indicative of CPV infection. Serum biochemical tests and urine analysis may reveal elevated liver enzymes and electrolyte imbalances.
Radiography helps rule out other likely causes for vomiting and diarrhoea, while an abdominal ultrasound may reveal enlarged lymph nodes in the groin, or throughout the body, and fluid-filled intestinal segments. Alternative methods of detecting CPV in faeces include virus isolation in cell culture, identification using electron microscopy and viral nucleic acid detection by PCR. Sero-diagnosis of CPV infection requires demonstration of a 4-fold increase in serum IgG titer over a 14-day period or detection of IgM antibodies in the absence of recent (within four weeks) vaccination.
Diseased dogs require intensive veterinary management. Fluid therapy for replacing fluids loss through vomiting and diarrhoea is unarguably the most efficient treatment. Intravenous fluids and medications to control vomiting and diarrhoea are often required, but in less severe cases, subcutaneous or oral fluids may be given. In severe cases, a blood plasma transfusion can be done. Puppies and dogs should be given intravenous fluid support during vomiting and never be permitted to eat or drink until the vomiting has stopped. To check secondary bacterial infections antibiotic therapy is generally prescribed.
Dogs must be monitored for development of hypokalemia and hypoglycemia. If electrolytes and serum blood glucose concentration cannot be routinely monitored, empirical supplementation of intravenous fluids with potassium (potassium chloride 20-40 mEq/L) and dextrose (2.5-5 percent) is suitable. If GI protein loss is severe, colloid therapy should be considered. The outcome depends upon the virulence of the specific strain of parvovirus, the age and immune status of the dog, and how quickly the treatment is started. Most pups that are under good veterinary care recover without complications. In dogs with severe symptoms, antiserum against endotoxins is recommended. Corticosteroids may be given if the animal is in shock. After the intestinal symptoms begin to subside, a broad-spectrum deworming agent is often used.
Prevention and control…
- To limit environmental contamination and further spreads to other susceptible animals, dogs with confirmed or suspected CPV enteritis must be kept in strict isolation.
- All infected or suspected surfaces should be cleaned with a solution of dilute bleach in a 1:32 dilution and must be left on the contaminated surface for 20 minutes before being rinsed. The same dilution bleach solutions can be used as footbaths. The bleach solution should be used on bedding, dishes, kennel floors and other impervious materials suspected for contamination.
- Clean and disinfect the quarters of infected animal thoroughly.
- Isolate young puppies as much as possible from other dogs and from potential sources of infection until they complete the vaccination.
- The canine parvovirus vaccine is considered a core vaccine i.e. all dogs should receive this vaccine. Vaccinate puppies against parvovirus by subcutaneous injection at 6-8 weeks of age, and revaccinating every three weeks until the puppy is 16-20 weeks of age. A booster is given at one year of age and every 1-3 year afterwards.
(Dr Vinod Kumar Singh, Department of Veterinary Microbiology and Immunology and Dr Rahul Kumar, Department of Veterinary Pathology, belong to College of Veterinary Science and Animal Husbandry, DUVASU, Mathura.)