By Ines Di Giacomo DVM
CPV (Canine Parvo Virus) is the main agent of acute gastroenteritis in puppies aged between one and six months. The virus is a serious threat to young dogs due to the severity of clinical signs and the interference with active immunization provided by maternal antibodies that may affect the vaccine program. A disadvantage for disease control is the circulation of field variants (CPV-2a, CPV-2b, CPV-2c), which are antigenically distinct from the original CPV-2 strain, still contained in most commercial vaccines. It is assumed that vaccination can only offerpartial protection, which could then expose the vaccinated puppies to the infection caused by field strains and sometimes the onset of concurrent disease.
A Word About Epidemiology
The original CPV-2 strain, still present in most vaccines, is no longer circulating in the field, while the three antigenic variants are widely distributed throughout the world. North America and South America show a high frequency of CPV-2b/2c and CPV-2a/2c, respectively.
CPV is able to infect domestic dogs, wolves and other wild carnivores. There is no breed sensibility for CPV infection. Large breeds such as German Shepherd, Labrador Retriever, Rottweiler, Alanskan Malamute and Dobermann appear to be at increased risk but this may be due to the fact that maternal antibodies decrease more rapidly in puppies of large breeds that have accelerated growth compared to smaller-sized dogs.
In addition, although CPV infection and disease affect mainly puppies under the age of six months, severe adverse clinical signs, often associated with CPV-2c infection,have been increasingly reported in adult dogs. Feces of infected puppies are the main viral source in the environment; the virus is exceptionally stable and can remain infectious for several weeks or even months. Puppies lacking a specific immune response are infected through the oro-nasal route by direct or indirect contact.
Puppy Parvo Fact: "While puppies are most likely to suffer severe disease and death, any unvaccinated dog, of any age, can become infected with CPV."~Dr. Jyothi Robertson, veterinarian.
Development of Disease
Target tissues for viral replication are intestinal crypts and lymphoid organs, but the virus can spread to all tissues. After penetration into the animal, CPV replicates in the lymphoid tissue associated with oropharynx, thymus, mesenteric lymph nodes and Peyer plaques, causing extensive necrosis that spread to the bloodstream by infected lymphocytes.
Viremia (the presence of viruses in the blood) is lasting and leads to the colonization of small intestine crypts with compromised replacement of the epithelium in the tips of the villi and subsequent diarrhea. The spread of the virus in their feces begin 2-3 days after infection and lasts for up to 45-50 days.
In newborn puppies (up to 2-3 weeks of age), CPV can reproduce in rapid replication myocardial cells causing severe myocarditis, (cardiac parvo) although this is observed sporadically. Compared with the original type 2 antigenic variants, it exhibits greater pathogenicity, shorter incubation period (less than 4-5 days), more severe clinical signs, longer extension and duration of viral diffusion, and fewer viruses needed to infecting dogs.
Puppy Parvo Fact: " All parvoviruses of dogs and cats can remain infectious for at least a year in contaminated cages and kennels, or on rugs, towels, grass or soil etc. Thorough disinfection (e.g. using sodium hypochlorite [bleach] solution; 1 part common household bleach to 30 parts of water) is necessary before new animals are admitted to the premises."~World Small Animal Veterinary Association
Symptoms of Parvo in Puppies
Depending on the age and the immune status of the infected puppy, CPV infection may cause various clinical forms, ranging from subclinical infections to acute gastroenteritis and very rarely to myocarditis.
Parvo virus affects generally puppies with intermediate levels of maternal antibodies that protect against overt disease but not against infection. Different levels in maternal antibodies between puppies of the same litter may explain why some animals may show serious clinical forms while others show limited or nil signs.
Even adult dogs can be infected and show only vague signs such as lethargy and loss of appetite for 2-3 days, along with a leukopenia (overall decrease in the number of leukocytes in the bloodstream). Subclinical infections are of particular importance in animal shelters where the presence of healthy but infected animals can promote the spread of the virus to other puppies.
This is the form most often observed in puppies between one and six months of age. After 3-4 days of incubation, puppies develop anorexia, depression and vomiting, followed by diarrhea, resulting in severe dehydration. Diarrhea is often haemorrhagic, with streaked or dark feces due to blood. Leukopenia (a global decrease in the number of leukocytes in the blood) is a frequent occurrence and its severity is a prognostic factor.
It has been reported that puppies with leukocyte counts lower than 1000 cells/μl are unlikely to survive. Death may occur two days after the onset of clinical signs as a result of disseminated intravascular coagulation (DIC). Mortality rates may vary considerably according to the age and the immunological state of the animals; adult dogs generally show mortality of less than 1%.
The CPV-induced myocarditis can only hit puppies aged less than 3-4 weeks, when the myocardial syncytium is actively replicating and is sensitive to viral replication. Today, however, since most of the dogs was vaccinated (or exposed to the virus), and has therefore developed a strong immune response, almost all puppies receive from their mothers maternal antibodies that protect them from parvovirus infection in the early weeks of life.
CPV myocarditis is characterized by the sudden death of infected puppies. Puppies that recover after myocarditis by CPV develop myocardial fibrosis. Dogs that die because of myocardial shape are often in good condition and sometimes the only visible post-mortem finding is pulmonary edema.
Puppy Parvo Fact: "Most deaths from parvovirus occur within 48 to 72 hours following the onset of clinical signs. If your puppy or dog shows any of these signs, you should contact your veterinarian immediately."~American Veterinary Medical Association
At the Vet's Office
The diagnosis of CPV infection is often based on the mere presence of a malodorous and bloody diarrhea, but other pathogens can also induce similar findings. Therefore, a laboratory diagnosis is always needed to confirm or exclude CPV infection.
The presence of vomiting and haemorrhagic diarrhea, associated with acute leucopenia, is indicative of a CPV infection. However, differential diagnoses (other possible conditions causing similar clinical signs) include canine distemper, canine infectious hepatitis, intestinal parasites and other eating disorders.
Serologic tests have no diagnostic value; but are still useful in evaluating the immunological status of a dog in relation to the CPV before and after vaccination. In addition, by identifying the decline of maternal antibodies, the assay may help to calculate when the puppy can be vaccinated without interference from maternal antibodies.
Puppy Parvo Fact: "The most common test is an enzyme-linked immunoabsorbent assay (ELISA). “These tests can have false negative results if the dog is not yet shedding the virus, so additional testing including PCR (polymerase chain reaction), serum antibody titers and response to supportive care can also be used."~Heather Loenser, veterinarian.
Treatment of Puppy Parvo
The primary goal of therapy for the CPV-induced enteritis is to restore the balance of fluids and electrolytes and prevent the concomitant infection by opportunistic bacteria. A fluid intravenous therapy with Ringer's solution, supplemented with glucose and potassium is given to correct hypoglycemia and hypokalaemia.
Parenteral antiemetic drugs can help reduce fluid loss and patient discomfort by facilitating enteral nutrition. A combination of penicillin and aminoglycoside antibiotics is the best approach to controlling bacterial infections that often complicate canine parvovirosis.
If vomiting has stopped for 12 to 24 hours, it is recommended not to keep the puppies fasting, in fact it has been proven that recovery is faster when animals are fed with easily digestible food. No specific drug has proven to be really effective against CPV infection.
Puppy Parvo Fact: "Early enteral nutrition, such as with CliniCare (Abbott Laboratories), Purina Pro Plan Veterinary Diets CN Critical Nutrition (Nestlé Purina PetCare), or Emeraid (Emeraid), has been proven to make a difference in patients with parvovirus. In one study, it resulted in shortening hospitalization by one day."~Medora Pashmakova, veterinarian
Prevention of Disease
The exceptional resistance of the virus makes it difficult to eradicate from the environment. Strict isolation of affected puppies accompanied by extensive disinfection is mandatory. The fecal material should be removed as soon as possible. The most common disinfectants fail to inactivate the CPV, but 5-10% sodium hypochlorite solutions are effective. All resistant surfaces should be exposed for at least 10 minutes to diluted bleach. Non-resistant bleach surfaces must be steam-cleaned.
The main problem in vaccination against CPV is that maternal antibodies protect puppies from infection caused by field strains, but interfere with active immunization. The titers of maternal antibodies depend on the level of serum antibodies of the mother and the amount of colostrum ingested by puppies, as a result, the puppies of the same dog may have different levels of maternal antibodies and be susceptible to CPV in different ages.
Vaccination of puppies with high levels of maternal antibodies may result in lack of seroconversion due to the destruction of the vaccine virus from the colostrum antibodies. To avoid interference with active immunization, vaccines should be administered to puppies only after the disappearance of maternal antibodies. In fact, there is a period of 2-3 weeks "sensitivity window" in which puppies cannot be vaccinated but can be infected and develop the disease. This is because they still have maternal antibodies, but not enough to be considered protective.
The World Small Animal Veterinary Association's guidelines claim that the first vaccination cycle against CPV is not completed before 14 to 16 weeks of age so to ensure protection also in puppies with maternal antibodies of long duration.
Puppy Parvo Fact: "Clients should be taught about the window of susceptibility for their puppy to develop parvovirus, and the importance of keeping them isolated from potential exposure during this vulnerable time. "Dr. Kate KuKanich, board-certified veterinarian.
- Decaro N. (2016) “Parvovirus canino” Veterinary Focus, 26 (1), 39-44
About the Author
Ines Di Giacomo DVM graduated from the Faculty of Veterinary of the University of Teramo, in Abruzzo Italy. She's interested in ultrasound diagnostics so decided to follow a specialist so to learn more about this topic.
In the meanwhile, she has been attending a veterinary clinic to put into practice what she has learned during her years of study. Since her graduation, Ines has attended numerous seminars to improve her knowledge in different areas of veterinary medicine such as radiology, ultrasound, reproduction, dermatology.
Ines would love to expand her knowledge in parasitology, anethesiology, and surgery but the road is still long. She says "Although the university is over, you never stop learning!"