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Canine Parvovirus

Canine Parvovirus

Compiled by Dr Valmai le Grange BVSc

Overview

Canine parvovirus is a highly contagious viral disease that commonly cause serious illness in dogs in animal shelters, boarding kennels, breeding facilities, and anywhere dogs are concentrated in high numbers. Most kennels and breeding facilities have been affected by outbreaks canine parvo virus in the past or might be affected in the future. Outbreaks can be very costly in terms of resource allocation to manage and eradicate these viruses, animal suffering, and negative public image.

This document provides a basic overview of: 1) the properties of canine parvovirus; 2) incubation times, clinical disease, duration of virus shedding, modes of transmission; 3) diagnosis; and 4) strategies for management and prevention in breeding facilities

Virology 101

Canine parvovirus (CPV-2) emerged in 1978, presumably originating from Feline Parvo Virus through a small number of mutations that allowed the cat virus to replicate in dogs. Although the mutations provided the ability to infect dogs, CPV-2 lost the ability to infect cats. By the mid-1980’s, the original CPV-2 strain was replaced by 2 new genetic variants, CPV-2a and CPV-2b, both of which continue to circulate in dogs today. Despite differences in a few amino acids, CPV-2, CPV-2a, and CPV-2b are still closely related genetically. The most prominent strain in South Africa is CPV-2b, but since it is a genetically unstable virus, it is important to keep monitoring the situation and adapt any vaccines as needed.

In 2000, another genetic variant of CPV-2 was identified in dogs in Italy. This variant, designated as CPV-2c, differs from CPV-2a and CPV-2b by another single amino acid change. Therefore, each of the 3 variants contains a different amino acid at this position in the VP2 protein. However, they are still 99% related genetically. CPV-2c appears to be widespread in Europe, and has been detected in dogs in Asia, South America, and most recently in the U.S.

If you want to know more about CPV-2c

There is no evidence that CPV-2c is a more serious threat to dogs than CPV-2a or CPV-2b. CPV-2c causes the same clinical signs of vomiting, hemorrhagic diarrhea, and leukopenia. Although some believe that CPV-2c causes more severe disease and higher mortality than CPV-2b, others report that there is no difference. There are some reports of vaccinated adult dogs becoming infected with CPV-2c, but the details of the vaccination history with regard to when and how many vaccinations were administered were not provided or fully known.
Recently, a parvo outbreak due to CPV-2c was documented in 11 adult dogs housed in a breeding kennel in Italy. The dogs ranged in age from 6 months to 2.5 years and had received at least 3 CPV vaccines, including boosters at 1 year and 2 years of age, prior to the outbreak. Another recent study evaluated the ability of antibodies from vaccinated dogs to block CPV-2c from infecting tissue culture cells in vitro. Dogs were vaccinated with commercial CPV vaccines containing either CPV-2 or CPV-2b. Antibodies induced by these vaccines were very effective in preventing infection of tissue culture cells by CPV-2a and CPV-2b, but were not as effective in blocking CPV-2c infection of the cells.

These findings have raised concerns about the efficacy of current CPV vaccines in providing protection against infection by CPV-2c. However, recent vaccine trials have demonstrated that currently available commercial CPV vaccines do provide protective immunity to CPV-2c. In one study, 5 beagle puppies that were free of maternal antibodies to CPV received a vaccine containing CPV-2 (Intervet) at 8 weeks and 11 weeks of age. Vaccination induced antibody titers to both the CPV-2 vaccine strain as well as to CPV-2c, but the CPV-2 titers were higher. The vaccinated puppies and non-vaccinated puppies were challenged with CPV-2c administered orally. All of the unvaccinated puppies developed clinical disease within 4 days, shed the CPV-2c virus in feces, and had 50% mortality. In contrast, none of the vaccinated puppies had clinical disease or fecal shedding of virus. In another study, 6 beagle puppies that were free of maternal antibodies to CPV received a vaccine containing CPV-2 (Continuum, Intervet) or CPV-2b (Galaxy, Schering Plough) at 12 weeks of age. The vaccinated puppies and un-vaccinated puppies were challenged 5 weeks later with a combination of CPV-2b and CPV-2c administered orally or intranasally. All of the vaccinated puppies were protected from disease while all of the unvaccinated puppies developed disease with 50% mortality. The unvaccinated puppies also shed high amounts of virus in feces, but only 2 of 18 vaccinated pups shed virus. The most recent study evaluated the efficacy of vaccines containing either CPV-2 or CPV-2b from 5 major manufacturers (Fort Dodge, Intervet, Schering Plough, Pfizer, and Merial) in providing protective immunity against CPV-2c.7 Seronegative puppies were vaccinated with one of the 5 vaccines, then challenged 5 weeks later with CPV-2c. Seropositive adult dogs that had been vaccinated against CPV at least 3 years earlier were also challenged. All of the vaccinated puppies and adults were protected from disease. Collectively, these vaccine trials demonstrate that current commercial vaccines containing CPV-2 or CPV-2b provide protective immunity against CPV-2c, even when dogs were vaccinated 3 or more years prior to challenge.

Besides vaccine efficacy, another concern about the new CPV-2c strain is the accuracy of the commonly used ELISA diagnostic tests in detecting CPV-2c antigens in feces. These tests utilize monoclonal antibodies to detect single epitopes of CPV. To date, these tests have been shown to reliably detect CPV-2c in fecal samples from infected dogs. In fact, the only way to determine if dogs are infected with CPV-2a, CPV-2b, or CPV-2c is to perform PCR on feces and DNA sequence analysis of virus isolates. Since vaccine efficacy, diagnostic accuracy, and management strategies for CPV have not changed, there is no real advantage afforded by determining which strain has infected dogs in shelters at this time. Although current vaccines and diagnostic kits work for the newly emerged CPV-2c strain, canine parvovirus is still evolving. It is possible that future genetic variants may be altered enough to escape protection from current vaccines and detection by available diagnostic tests.

Populations at risk

Puppies are the most susceptible to parvoviral infection either due to lack of protective immunity from maternally derived antibodies or from ineffective responses to vaccination (maternal derived immunity suppresses the vaccination respons) Unvaccinated adult dogs are also at risk for infection, but the clinical disease may be in apparent or mild. Older dogs that have spent time outdoors eventually develop immunity by natural exposure to virus in the environment.

Clinical features

The primary route of exposure to parvoviruses is nasal or oral contamination with virus-containing feces. The incubation period from time of exposure to onset of clinical disease ranges from 2 to 14 days, but typically is 5 to 7 days. Apparently healthy animals with parvovirus may be adopted out only to become ill a few days later in their new home.

CPV infect rapidly dividing cells in the intestinal tract, lymphoid tissues, and bone marrow. Resulting clinical signs include a sudden onset of fever, vomiting, diarrhea, dehydration, hypovolemic shock, panleukopenia, and death from shock or sepsis. The clinical signs can be worsened by concurrent infections with internal parasites and protozoa (coccidian/giardia), other viruses, bacteria, and STRESS. The mortality rate can approach 90% in puppies that are not treated aggressively with supportive therapies. Adult dogs may have subclinical infection or mild transient diarrhea.

Parvovirus shedding in feces starts within 4 days of exposure, so that infected dogs in the incubation period are already contagious prior to onset of clinical signs. Virus shedding continues for 14 days, so that animals recovered after a week of illness are still contagious to other animals. Animals with subclinical infection or transient symptoms also shed infectious virus in feces and thus contaminate the environment.

Transmission of parvoviruses occurs by direct contact with an infected animal or feces, by contact with contaminated fomites (cage or kennel surfaces, hands, clothing, food/water bowls, toys, litterboxes), and even by rodents and insects! The infected animal is covered with virus from head to toes, including the fur. Dogs that recover from parvovirus should be bathed before allowed contact with other animals.

Diagnosis

Not all cases of vomiting or diarrhea in juveniles and adults are due to CPV. Therefore, parvovirus infection cannot be diagnosed based on the age of the dog or cat and the clinical signs. Since other diseases mimic parvo, diagnostic testing should be performed on all dogs with compatible clinical signs instead of making a decision on a guess, especially if animals suspected of having parvo are euthanized.

The test kits (IDEXX, Anigen Rapid) for detection of parvovirus antigens in feces are a rapid and cost-effective diagnostic tool for dogs. All animals with compatible clinical signs should be immediately tested in order to start proper containment strategies. False negative results can occur due to intermittent virus shedding very early or late in the course of disease. Test results are most accurate if the test is performed within 5 days of onset of clinical signs. Negative tests should be repeated another day on any dog suspected to have parvo based on clinical presentation.

There has been concern that the new canine parvovirus strain CPV2c may not be detected by currently available fecal antigen tests. A recent study showed that the IDEXX SNAP test was similar in sensitivity for CPV2c as for other strains. However, as with all strains, CPV appears to be shed intermittently and clinically affected animals can test positive on one day and negative on the next day. Thus, clinicians should maintain a high index of suspicion in animals with compatible clinical signs and histories. A PCR test on feces may be helpful cases suggestive of CPV in the face of negative fecal antigen tests. A WBC count can also be performed to build evidence for or against a diagnosis of parvoviral inferction.

Recent vaccination with modified-live parvovirus vaccines sometimes results in transient fecal shedding of vaccine virus that causes false-positive reactions on the parvo tests. Documentation of this phenomenon in dogs is scant. Thus, vaccine interference with parvovirus diagnostic testing is low, especially when the IDEXX SNAP test is used. A strong positive test result in combination with compatible clinical signs or known contact with virus is unlikely to be due to vaccination. Testing of feces by PCR is likely to result in a higher rate of vaccine-induced positive test results due to the high sensitivity of PCR.

Outbreak Management

The most effective management strategy for limiting transmission of CPV is the prompt removal of sick dogs with positive test results. These animals should be housed in an isolation room. Since sick animals shed infectious virus before onset of clinical disease, all others exposed to the sick animals either by direct contact or fomite contact should be quarantined from the general population for 14 days with twice daily monitoring for appearance of clinical signs. If clinical signs occur, the animal should be immediately tested and removed if positive to help reduce the infectious dose of virus in the environment. Staff caring for the quarantined population should wear protective wear (hair cover, gown, gloves, booties). Use of footbaths in lieu of disposable foot covering is not as effective because the entire shoe could be contaminated, not just the soles. Handling of dogs in quarantine should be minimized. Staff should always care for healthy animals first, and then quarantined animals, then sick animals in isolation.

In some situations, the numbers of exposed but asymptomatic dogs in quarantine may comprise almost the entire population. One option is to quarantine all exposed dogs for at least 14 days after the last diseased dog is removed from the population. An alternative to holding all the animals for 14 days is to test them for protective antibody titers to parvovirus.

The virus is very stable in the environment and able to withstand wide pH ranges and high temperatures. It is resistant to a number of common disinfectants and may survive for several years in contaminated areas. A few disinfectants kill parvoviruses – eg bleach and quaternary ammonium( F10 at the correct concentration). For optimum killing activity, environmental surfaces contaminated with feces, urine, vomit, blood, and other organic material must first be cleaned with a detergent before applying the bleach or F10 solution. The minimum required contact time is 10 minutes. Air drying is preferred if possible, but if the animal needs to be returned to the same run or cage, the area should be rinsed after the 10 min contact time, then dried using a squeegee or towel. Moisture favors the survival of pathogens.

A 5% solution of household bleach should be prepared fresh daily and stored in an opaque container since light exposure inactivates it. F10 solution should be prepared according to manufacturer instructions - it is not inactivated by light and is less corrosive to metal and skin than bleach. For both disinfectants, more is not better! The more concentrated the solutions, the more irritating and damaging to skin, eyes, and the respiratory tract of animals and staff.

Cleaning followed by disinfection with bleach or F10 should be performed not just during CPV outbreaks, but on a daily basis for all animal housing areas, food and water bowls, animal transport vehicles, transport cages, and hallways to reduce the risk for environmental transmission of any infectious disease. In addition, they should be made of stainless steel instead of plastic because scratched plastic is difficult to fully disinfect.

Mop buckets should not be used for cleaning and disinfection of kennel runs. High pressure hoses and power washers should also not be used in kennels unless all dogs are removed, because the force sprays feces on all surfaces and can even aerosolize fecal matter. Cleaning and disinfection supplies should be dedicated to each room and not removed for use in other areas in order to minimize cross contamination.

Prevention

Vaccination of all dogs is the cornerstone for prevention of parvoviral transmission. All dogs 4weeks of age should receive a vaccine containing modified-live parvovirus All puppies should be re-vaccinated every 3 weeks until they are at least 4 months old.

Vaccines containing modified-live parvovirus for dogs or cats are one of the most effective vaccines for reliably inducing protective immunity very quickly. Vaccine trials have proven many times that canine modified-live parvovirus vaccines induce protective immunity within 3 days if there is no interference by maternally derived immunity. The potential for maternally derived antibodies to interfere with vaccination in puppies and kittens

Another strategy to reduce risk for parvoviral outbreaks is to segregate juvenile animals from adults. Puppies should not be housed with adults.

In combination with vaccination and segregation of age groups, another key strategy is the daily cleaning of all areas followed by disinfection with bleach or F10. Puppies and kittens should be cared for before adult animals, and healthy animals should be cared for before sick or exposed animals.

A couple of pointers for breeding facilities

  • Educate staff on the importance of the transition of any disease. Why should they dilute it like this and wash it like that if they do not understand it. A F10 consultant has many training modules for workers that they can assist you with when you use their product.
  • Have spray bottles with F10 or bleach as well as disposable booties handy at the entrance of all puppy runs. Everybody must spray and don booties before entering. Preferably dedicate one worker to the care of the puppies and only the puppies while there are puppies.
  • Limit the exposure of the puppies to strangers
  • When prospective owners visit, let them spray their hands and bring the puppies to them. When they want to sit down and play with the puppies, offer towels to throw over their laps.
  • Be aware of possible contamination of your gear at shows and training facilities.
  • Do not visit your own puppies after a show/training before you have donned clean clothing.
  • Do not forget to keep the bitches’ vaccinations up to date.
  • All of the above is also applicable during an outbreak of kennel cough or (heaven forbid) a distemper virus outbreak.

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