Diagnosis of Canine Parvovirus - Mar Vista Animal Medical Center

	This is Page 6 of 8 Pages in the Canine Parvovirus Information Center
	Basic Virology A Preface	Canine Parvovirus: What Is It?	The Virus in the Environment: Disinfection	How Infection Happens
(original graphic by marvistavet.com)	The Physical Illness and It's Treatment	Diagnosis of Canine Parvovirus	Caring for the Recovered Dog	Vaccination Options /Prevention

Diagnosis of Canine Parvovirus

A puppy with a bloody diarrhea could have a parasite problem, a virus other than parvovirus, a stress colitis, an intestinal foreign body, or may simply have eaten something that disagreed with him. It is important to confirm the diagnosis of parvovirus before embarking on what could be the wrong treatment.

TESTS THAT ARE ESPECIALLY USEFUL

THE FECAL PARVO ELISA TEST

Snap Parvo Test Kit and Box mvamc

The IDEXX snap test kit for parvo, one
of the most popular ELISA kits
(original graphic by marvistavet.com)

The ELISA test has become the most common test for parvovirus in puppies. ELISA stands for Enzyme Linked ImmunoSorbant Assay. This is sounds complicated and high tech but is actually the same type of technology that home pregnancy test kits use. The parvo ELISA test is available as a kit and is performed in the vet’s office in about 15 minutes or less. There are many different brands and testing is very sensitive in its ability to detect the actual presence of the virus in stool. If a puppy is shedding parvovirus in his or her stool, that would indicate an active infection.

The test has some limitations that are important to realize. Recent vaccination with a live vaccine (the type of vaccine that is most effective) may interfere with the test results. This means that the test may detect the live virus from the vaccine and show a positive reading when, in fact, the puppy does not have a parvo infection. Classically, this interference occurs 5-12 days after vaccination so if a positive fecal ELISA test is obtained within this period after vaccination, additional tests may be recommended.

A false negative result is possible. The puppy could be infected but no longer shedding virus in its stool or only shedding virus intermittently. Alternatively, the virus particles may be so thoroughly coated with antibodies that they cannot react with the chemicals of the test. Any test will have some potential for false negatives as well as false positives but if the puppy's clinical presentation fits and the ELISA test is positive, treatment for parvo infection should be pursued.

THE DROP IN WHITE CELL COUNT

Recall that one of the first actions of the canine parvovirus is to inhibit white blood cell division in the bone marrow. The virus essentially turns the immune system off before making its deadly way to the GI tract. This is a feature of parvovirus infection in all species which means that a characteristic drop in white blood cell count is seen on a blood panel when the infection is active and real. If there is any question about the veracity of an ELISA test result, the presence or absence of a white cell count drop can be used to clarify the situation but it should be mentioned that the positive ELISA test often precedes the white cell drop by a couple of days. White blood cell count is commonly monitored through the treatment of infection. The white blood cell numbers bottom out during the brunt of infection and recovery of the white blood cell numbers heralds recovery.

Doctor in lab

(Photocredit: CDC Public Health Image Library)

TESTS THAT ARE HARD TO INTERPRET AND RARELY USED

(BUT YOU MIGHT HEAR ABOUT THEM SO WE'LL EXPLAIN THEM)

PCR TESTING

PCR ("Polymerase Chain Reaction") testing is probably the newest method of testing for parvo. A fecal sample must be submitted to a reference laboratory for PCR testing; this is not the sort of test that can be done while you wait. The DNA of the parvovirus is recognized and amplified so as to be able to detect even small amounts of it. PCR testing is generally too sensitive to be clinically helpful yet canine parvovirus is commonly included on PCR panels that test for multiple intestinal virus organisms. The problem with PCR testing is that, because it amplifies DNA, very small amounts of virus can be detected which means that positive results will turn up on dogs that are vaccinated or who are passing insignificant amounts of virus. PCR testing is very helpful for many infections but often clouds the issue for parvovirus.

ANTIBODY TITERS

Vials

(Photo credit: CDC Public Health Image Library)

There are two types of antibody titer that can be run: IgG and IgM. With the advent of ELISA testing, titers are not frequently used in making this diagnosis any more. The IgG titer is a more long lasting antibody level. A high IgG titer would probably indicate active infection in a puppy that is old enough to generate antibodies and who has not yet received any vaccinations. Most of the time, the IgG titer simply reflects antibodies generated by vaccination. The IgM titer reflects recent antibody production so if a vaccinated puppy had not been vaccinated recently, a high IgM titer might indicate active infection.

Because parvovirus infected puppies have frequently received vaccinations in their recent past and are frequently too young to generate their own antibodies (which is how vaccinated puppies get infected in the first place), these test results are difficult to interpret. It is easy to see why the ELISA test that directly detects presence of the virus has become so popular.

Titering is mostly used nowadays to determine if a dog has adequate protection against parvo, either through vaccination or prior exposure. In a shelter setting, a dog of unknown vaccination status can be tested to determine if he or she is considered protected from infection or not. In the pet setting, a dog can be tested to determine if a vaccine is needed or not. Certain antibody levels are associated with protection; however, because of other contributing branches of the immune system, an inadequate titer does not necessarily mean a dog is vulnerable.

BIOPSY

Parvovirus lesions in the GI tract are of a classical appearance. There is no mistaking them under the microscope. Unfortunately, tissue samples of the GI tract are not readily available and most infected puppies are not good surgical candidates. Still, if a puppy has died and the cause is unclear, submitting samples of the GI tract can generally confirm or rule out a parvovirus diagnosis provided the tissue has not degenerated.

It is also important to realize that puppies with parvovirus infection may have
concurrent intestinal parasites or even swallowed foreign bodies
and additional diagnostics are needed to discover such complicating factors.

There will be complicating conditions that must be monitored. This means that other tests will be required during the management of the parvo patient. The above tests are simply those that can be used to confirm the parvovirus diagnosis.

Page last updated: 5/6/2022