Canine Parvovirus Outbreak in Michigan

In August 2022, the Northern Lower Peninsula of Michigan experienced a canine parvovirus outbreak. 

At the time, they knew it looked like parvovirus, but the point-of-care (POC) rapid tests that veterinary clinics and shelters use came back negative. Adding to the mystery is that supposedly some of the dogs were vaccinated against parvovirus. 

Yes; it was necessary to release this message to alert pet caregivers and rescues in order to help protect other dogs. 

Unfortunately, an explosion of panic, anecdotal accounts, speculations on point of origin, and unproven treatment options occurred. 

By August 24, 2022, Michigan State University Veterinary Diagnostic Laboratory (MSU) confirmed the virus was indeed canine parvovirus with PCR testing and necropsies. MSU also noted that the dogs were either unvaccinated or did not have a complete vaccination history against parvovirus.

On September 15, 2022, MSU announced that this was not a novel variant or strain of canine parvovirus. Sequencing determined that the variant was canine parvovirus-2c (CPV-2c), currently the most virulent parvovirus strain circulating in North America. 

You and we have questions about this situation. 

Before we get into questions, we want to clearly state that – at this time – we consider MSU as the lead investigatory unit for this outbreak and will follow only what the laboratory and Michigan Department of Agriculture & Rural Development (MDARD) publicize regarding this outbreak. We would like to thank them for their cautious and guarded approach in releasing accurate information, and for their diligent and precise work behind the scenes. 

Why did the POC rapid tests not detect the virus?

Think about this in terms of COVID-19 testing. The available canine parvovirus POC rapid tests are rapid antigen tests, just like the COVID-19 tests you purchase over-the-counter at a pharmacy, do-at-home, and then find out the results within a few minutes. 

PCR tests are the ones that you drive up to the pharmacy window, swab your nostrils or spit into a cup, and they send it to a diagnostic laboratory.

As we all know from COVID-19 testing, PCR tests are more sensitive and specific. This is the same case with canine parvovirus testing. According to University of Wisconsin Shelter Medicine, “The Idexx SNAP  [point-of-care rapid test] test detected 80%, 78% and 77% of parvovirus 2a, 2b, and 2c respectively.” We are unsure about sensitivity to parvovirus 2d.

According to an emailed communication update sent to licensed veterinarians in the State of Michigan on August 25, 2022, MDARD stated, “most submitted samples tested positive for canine parvovirus by PCR; and in necropsy cases, histopathology was consistent with parvo and IHC was positive.” (IHC is short for immunohistochemistry, which is a diagnostic technique conducted in a laboratory. It involves performing special tests on tissue.)

Bottom line: We do not know why all of the PCR positive cases were POC false negatives. 

This begs another question…

Were all of the POC tests used by shelters and veterinarians in Northern Michigan from the same manufacturer?

MSU investigated this and learned that the POC tests came from different manufacturers or brands. 

If you are reading about the outbreak on social media, many breeders and veterinarians will refer to parvo POC tests as SNAP. This is a colloquialism. (We used a big word to help you remember this.) SNAP is the brand name of Idexx’s canine parvovirus POC test. It’s like calling tissue “Kleenex”, or adhesive bandages “band aids.” There are actually several parvo POC tests available on the market – and various manufacturers were used in Northern Michigan.

Again, no one knows why all of the PCR positive parvovirus tests were POC false negatives. We can all speculate. We have our ideas at Hemopet. However, we will not share them because we fear our speculations might be construed as fact. As we stated, we are only listening to MSU on this current outbreak at this time and ask that you do too. There are too many rumors circulating. 

Speaking of MSU, the September 15, 2022 update stated, “The MSU VDL will continue to test and characterize additional samples to explore ways POC tests may be improved to enhance sensitivity.” 

Why did the PCR detect negative cases of canine parvovirus, but the dogs displayed similar symptoms? 

The MDARD August, 2022 email newsletter stated, “PCR-negative dogs were diagnosed with other common pathogens associated with GI-disease—e.g., giardia, etc.” 

Final question…

Regarding the dogs that did not have a complete history of vaccination against parvovirus but were partially vaccinated, what history is known? 

Our subset of questions would be: when were they vaccinated; how many times they were vaccinated; and, the ages of the dogs at the time of vaccination. Of course, this would be an impossible task and would likely be unreliable due to the unknown pet vaccination history. There are too many variables such as the time of viral exposure compared to timing of vaccination, and accurate recordkeeping. However, if any of the dogs have lived with a companion dog family for a number of years and were adopted from a shelter or purchased from a breeder, we should have a ballpark idea of the vaccinations given. 

Should dogs be vaccinated against parvovirus?


Below is W. Jean Dodds’ latest vaccination protocol. Bear in mind, this could change if new research studies find that additional boosters are necessary or that the timing of vaccinations should change. 

9 – 10 weeks of age
Distemper + Parvovirus, MLV
e.g. Merck Nobivac (Intervet Progard) Puppy DPV

14 – 15 weeks of age
Distemper + Parvovirus, MLV

18 weeks of age
Parvovirus only, MLV
Note: New research states that last puppy parvovirus vaccine should be at 18 weeks old.

20 weeks or older, if allowable by law
Rabies – give 3-4 weeks apart from other vaccines
Thimerosal (mercury)-free = labelled TF)

1 year old
Distemper + Parvovirus, MLV
This is an optional booster or one can measure serum antibody titers instead. If the client prefers not to give this optional booster or plans to retest titers in another three years, giving this optional booster at puberty is wise.

1 year old
Rabies – give 3-4 weeks apart from other vaccines
3-year product if allowable by law; thimerosal (mercury-free; labelled TF)

Perform serum vaccine antibody titers for distemper and parvovirus every three years thereafter, or more often, if desired.

By the way, homeopathic nosodes are not vaccinations and do not provide protection against infection or disease.

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