by Veterinary Practice News Editors | December 2, 2015 11:46 am
Originally published in the November 2015 issue of Veterinary Practice News. Did you enjoy this article? Then subscribe today!
Despite a widely available parvovirus vaccine, periodic outbreaks of the deadly disease continue. Experts say this is due in large part to animals not being vaccinated fully, or being vaccinated at the wrong time.
Those are the top two reasons that general practitioners still see cases, says Steven L. Marks, BVSc, associate dean and director of veterinary medical services at the North Carolina State University College of Veterinary Medicine.
“There’s probably not a vaccine that’s 100 percent effective guaranteed,” said Dr. Marks, MS, MRCVS, Dipl. ACVIM, a clinical professor of internal and emergency medicine.
While vaccines can sometimes, though rarely, inexplicably fail, Marks finds that many failures occur in young animals that are not fully vaccinated.
Typically these pets are left unprotected because their owners get one vaccine and do not come back for more, believing they are “one and done,” Marks said.
Heather Loenser, DVM, veterinary adviser in professional and public affairs at the American Animal Hospital Association, said that in most cases parvo is seen in unvaccinated puppies or those that did not complete a full vaccine series.
“Providing full protection against this virus requires extensive vaccination for puppies under 16 weeks of age,” Dr. Loenser said.
AAHA’s canine guidelines recommend vaccinating a puppy between ages 6 and 16 weeks every three to four weeks. Puppies completing the initial vaccination series by 16 weeks should receive a single booster vaccination not later than one year after completion of the initial series and should be revaccinated every three years thereafter.
In dogs older than 16 weeks, one dose is considered protective and acceptable, and revaccination is recommended every three years, Loenser said.
Marks warned that failure is possible if a pet is vaccinated too young.
Most animals are vaccinated roughly six to eight weeks after they are weaned. If the mother’s antibodies are still present in the offspring’s system, vaccines can be rendered inactive.
"That’s actually a common reason for failure,” Marks said. “The biggest problem for vets is we never really know when those antibodies are gone.”
Cats may encounter similar problems with vaccines for feline panleukopenia virus—also known as feline parvovirus—said Colleen Currigan, DVM, president-elect of the American Association of Feline Practitioners.
Dr. Currigan, owner of the Cat Hospital of Chicago, said several factors likely contribute to outbreaks despite the wide availability of a “very effective vaccine to prevent this disease.”
The lack of any vaccinations tops Currigan’s list of reasons that cats get feline parvo. These cats are typically unowned, or the owner is unaware of the need for vaccination—and, as with dogs, noncompliance with vaccination recommendations is a major cause of outbreaks, she said.
Kittens that did not receive maternal antibodies can be infected before vaccination.
“Kittens may acquire the virus in utero from an infected—and likely unvaccinated—queen,” Currigan said.
Another similarity between dogs and cats is that both can be vaccinated too early. A kitten can acquire immunity from its mother’s milk that may inactivate the vaccine through 14 to 16 weeks old, she said.
Differences in absorption of the mother’s antibodies among littermates may produce a variable response to the panleukopenia vaccination in kittens, she added.
AAFP’s Feline Vaccination Advisory Panel recommendations for vaccinating cats against panleukopenia state that the onset of protection is considered to be one to three weeks after the second vaccination. Manufacturers recommend revaccination after one to three years.
The panel considers panleukopenia a core vaccination.
“[Maternally derived antibodies] may interfere with immunization when antibody titers are high during the neonatal period, and kittens will be at greatest risk of infection in the period between waning MDA and effective vaccine-induced immunity,” the panel states. “MDA titers generally wane sufficiently to allow immunization by 8 to 12 weeks of age.”
The panel notes a variation between individuals, with some kittens having no or low levels of MDA at 6 weeks and others failing to respond to a final vaccination given at 12 to 14 weeks.
“Because of this variability, the initial series of vaccinations should begin at 6 to 8 weeks of age and be repeated every three to four weeks (or two to three weeks in shelters) until 16 to 20 weeks of age,” the panel states. “Revaccination should take place at 1 year of age after kitten vaccination or one year after the primary course in older cats. Thereafter, cats should be vaccinated no more frequently than once every three years.”
To make a diagnosis, the parvo antigen can be screened for in a dog’s feces using standard tests that often can be performed quickly in the hospital, AAHA’s Loenser said.
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,” Loenser said. “Also, blood tests can support the diagnosis as parvovirus classically causes a very low white blood cell count, predisposing a dog to secondary infections.”
Marks believes that parvo can be treated without a 100 percent guarantee that the disease is present.
“I’m not sure I have to have a definitive diagnosis of parvo to treat it,” Marks said.
He used as an example a dog that presents with vomiting and diarrhea.
A conservative approach is to provide fluid therapy and control the nausea and vomiting. If the animal has severe or even bloody diarrhea, veterinarians often will prescribe antibiotics to treat secondary infection.
This is also the way parvo would be treated, Marks said.
There’s also the cost to consider. Isolating a dog can be expensive unless a clinic has a built-in isolation area. Without such an area, anyone treating the dog or dealing with the animal must wear gowns and boots and take other time-consuming precautions. This can add considerably to the medical bill, Marks said.
If the treatment doesn’t work, taking this problem-oriented medicine approach may help a practitioner form another diagnosis.
“If you treat conservatively for parvo and a dog has stick in his stomach, then the treatment’s not going to work,” Marks said. “But if you have a young dog with a history of vomiting and being lethargic, and the white count is low, that’s pretty definitive for parvo without the test to confirm.”
Diagnosing feline parvovirus is straightforward in most cases, AAFP’s Currigan said.
“The disease is much more commonly seen in kittens and is diagnosed based on clinical signs along with laboratory testing,” she said.
The symptoms include vomiting, diarrhea, lethargy and poor appetite, and some cats may present with neurological signs such as seizures, Currigan said.
“Cats with this disease usually have a very high fever, although the body temperature may actually be lower than normal later in the course of the disease,” she said. “Sudden or very rapid death is especially common in kittens.”
Currigan listed the primary laboratory tests used to diagnose feline parvo:
. Canine parvovirus test. It has high sensitivity and specificity but will be positive if the patient was recently vaccinated, generally within the past two weeks.
Complete blood count. Most kittens with parvovirus will have a low white blood cell count, often below 1,000/ul. Many may have low platelet counts as well and many are anemic.
Other tests, such as PCR testing, virus isolation, antibody titers and biopsy (most often performed at necropsy).
Treatment of parvo requires intensive care.
“These debilitated puppies often need very aggressive supportive care, which is best performed in a hospital that provides 24-hour veterinary supervision,” AAHA’s Loenser said. “Since they are vomiting, they cannot eat, so they need nutrition, electrolytes and fluid support given through intravenous fluids and trickle feedings of specially formulated food through a nasogastric tube.”
Affected dogs lose body fluids through frequent bouts of bloody diarrhea, so lost fluids need to be constantly replaced to avoid potentially fatal dehydration, she said.
“Also, their immune system is suppressed from the virus due to a low white blood cell count, so antibiotics given IV are helpful in preventing secondary bacterial infections,” Loenser added. “Other medications to treat nausea, painful abdominal cramping, low blood sugar and low protein levels are often added as well.”
Many affected puppies require hospitalization for two to seven days, Loenser said.
Treatment of feline parvo, as with many viruses, is supportive, too, Currigan said.
“All affected cats require aggressive IV fluid therapy to help correct dehydration and maintain normal hydration,” Currigan said.
Additional treatments include anti-emetics, antibiotics and analgesics, and some cats may require a transfusion of whole blood to provide needed white blood cells, she said.
“Plasma infusions, although controversial, have been used by some practitioners who feel that the patients seem to feel better after having had them,” Currigan added.
Because parvo is so contagious, all sources for this article were emphatic about preventing the spread of the disease.
Marks offered a saying: “Prevention is vaccination.”
“It can be spread on water bowls, it can be spread on the floor,” Marks said. “It’s so infectious.”
The key to stopping the spread of parvo “is really, really very fastidious hygiene,” he said.
“I probably wash my hands 50 times a day,” Marks added.
Loenser noted that the virus can exist in the environment for long periods and is resistant to heat, cold, humidity and drying.
“This virus can contaminate most of the surfaces within a home or veterinary hospital, including food bowls, counters, stethoscopes, clothing, leashes,” she said. “Therefore, placing a dog in a single-purpose isolation room away from other patients is imperative. Veterinarians and technicians who care for these dogs should practice excellent personal hygiene and disinfection.”
Wearing gloves, a gown, and shoe covers—or using disinfecting foot baths—and keeping all the equipment and materials inside the isolation room help stop transmission of the virus to other patients, Loenser said.
She advised regularly and thoroughly disinfecting isolation areas, as well as the exam room if a puppy was in the room before being diagnosed.
Feline parvovirus is highly contagious to other cats, and it’s a hardy virus. It can live for a year or more at room temperature, far longer than canine parvovirus does, Currigan said.
“In a veterinary clinic or shelter setting, even one infected kitten can quickly infect multiple animals, resulting in a serious outbreak,” she said. “Strict protocols regarding isolation and treatment of suspected or known feline parvovirus patients is essential to control spread of the virus.”
Cats requiring hospitalization because of suspected parvo should be housed in a dedicated isolation ward or away from other patients, preferably in a place that can be thoroughly cleaned and disinfected, she said.
Currigan recommended these measures to help prevent the spread of the disease:
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