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PCR Testing: Why Is It So Important?

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Let's talk about PCR testing and why it’s so important

PCR stands for Polymerase Chain Reaction. The PCR amplifies DNA so that one copy becomes millions of copies in a matter of hours. This is a useful tool to detect and identify DNA where small amounts are present. For example, in a fecal sample, blood sample, or swab sample from a pet’s eye, nose, or mouth. Every living thing has unique genetic material, and that means finding a viral, bacterial, or protozoal cause of a kitten or cat’s symptoms can be as easy as collecting fluid or tissue samples and sending them off to a lab like Idexx to be analyzed.

Ethical and responsible breeders will perform all proper health screening and make hard decisions to remove kings or queens from their program that pose a risk to future generations. With pedigree pets, this should include not just genetic, cardiac, and orthopedic screening required for the breed, but properly testing and treating breeding cats for bacterial, viral, fungal, or protozoal illnesses that pop up too.

How does a PCR test work?

Collecting samples for PCR testing is best done prior to beginning treatment for a suspected illness, and at least a few weeks after any modified live vaccinations are given. That’s because sometimes, being on a recent course of antibiotics can actually cause a PCR test to come back negative before diagnosis, and having certain types of vaccinations may cause a “false” positive (i.e.: the PCR sample will be positive for the modified live version of the very thing you are testing for, making it unclear if the pet is actually positive for the disease).

A positive PCR test indicates your pet is positive for the bacteria, virus, fungus, or protozoa that was tested for. Some tests will even indicate how much was present in the sample and if the amount present is clinically significant or not.

A negative test means that the sample tested did not have any of the organism being tested for. This does not always mean the pet is in the clear. Depending on the clinical symptoms (if any) and what you are testing for, it could also mean that the particular sample had too small an amount of the DNA present for the PCR to detect, a chronic carrier state, or the occurrence of a new strain.

What kind of PCR testing should a breeder be doing?

There are two PCR panels that breeders should be doing any time they bring a new kitten or cat into their cattery, or any time a kitten or cat shows signs of fecal or upper respiratory related illness. If the kitten or cat lives in a multi-cat household, PCR samples are best collected while they are in quarantine, and the animal should not be released from quarantine or introduced to other pets until the tests come back negative for all clinically concerning organisms.

PCR Fecal Profile (Feline Diarrhea Panel)

  • HOOKWORM ANTIGEN

  • WHIPWORM ANTIGEN

  • ROUNDWORM ANTIGEN

  • TRITRICHOMONAS FOETUS PCR

  • CRYPTOSPORIDIUM by RealPCR

  • GIARDIA SP

  • SALMONELLA PCR

  • TOXOPLASMA GONDII

  • FELINE CORONA VIRUS

  • PFELINE PANLEUKOPENIA VIRUS

  • CAMPYLOBACTER JEJUNI PCR

  • CAMPYLOBACTERCOLI PCR

  • C. PERF ALPHA TOXIN GENE

  • C PERF ENTEROTOXIN GENE

PCR Upper Respiratory Disease (URD) Profile

  • CHLAMYDOPHILA FELIS PCR

  • FELINE CALICIVIRUS PCR (FCV)

  • HERPESVIRUS 1 PCR (FHV-1)

  • BORDETELLA PCR

  • MYCOPLASMA FELIS PCR

  • H7N2 INFLUENZA PCR FE

  • INFLUENZA A PCR

Things to consider when PCR testing

Depending on the lab, PCR assays can be offered as individual tests or in panels.

Real-time PCR can be more sensitive than conventional PCR for some organisms.

The predictive value of a positive test, or PPV, is the probability that a test positive animal is diseased; the predictive value of a negative test, or NPV, is the probability that a negative animal is normal. 

When the organism being tested for commonly infects the background population of healthy pets, interpretation of results for a single animal can be difficult. For example, healthy cats commonly carry FCoV, FCV, and FHV-1 and modified live vaccine strains colonize cats; therefore, although PCR is a sensitive way to document infection, its PPV is actually very low.

Furthermore, in one study of cats with and without conjunctivitis, more FHV-1 positive tests were detected in the healthy control group than the group with conjunctivitis. The same problems exist with feline calicivirus. The available RT-PCR assays can’t distinguish between regular calicivirus, vaccine strains of calicivirus and virulent systemic calicivirus. These realities need to be considered when interpreting test results.

Advice for the future pet buyer

When you decide you are ready to purchase a pedigree Maine Coon (or any breed for that matter), it’s so very important to first and foremost research the breed. Learn about their personality type, their energy levels, their nutrition and exercise requirements, and any health related issues they may be predisposed to.

Next, it’s important to research what health screening tests are available and routinely performed by ethical and responsible breeders. For the Maine Coon, that means confirming negative health screening results for HCM, SMA, and HD at the very least, and preferably for PKD, PKdef, Factor VII, and Factor XII as well. And, as discussed in this article, it’s important to ask about Fecal and Upper Respiratory PCR lab work too.

Kittens and cats are living, breathing beings, and at one time or another, just like kids, they are bound to get sick. A breeder that claims they’ve never had an issue in their cattery is likely either fibbing, or simply inexperienced.

Researching and interviewing breeders can be a daunting task. At the end of the day, no one is perfect, but the way a breeder chooses to respond when a health concern is brought to their attention is what differentiates a good breeder from the less than reputable ones.

If and when you are serious about purchasing a pedigree pet, don’t be afraid to ask lots of questions! Ethical and responsible breeders will be fully transparent about their process, and will not hesitate to be fully forthcoming with the aforementioned health screening results.

Call to action for breeders

I don’t claim to have all the answers, but my hope is that in researching and writing on topics like this, I can give myself and others who are reading along a chance to pause and think: Are we doing everything in our power to diagnose, prevent, and treat health issues in our Cattery?

If you are a new breeder, or an established breeder that is not currently doing all the proper health screening for your breed, including Fecal and Upper Respiratory PCR lab work as needed, I implore you, please reconsider.

We can do better.

Our kittens, our cats, and our pet buyers deserve more.

The future of our breed is depending on us to get this right.

SOURCES:

  • https://vcahospitals.com/know-your-pet/recognizing-signs-of-illness-in-cats

  • https://www.gopetplan.com/blog/posts/polymerase-chain-reaction-testing

  • http://csu-cvmbs.colostate.edu/Documents/vdl-lablines-volume-15-issue-01.pdf

REFERENCES:

  1. Burgesser KM, et al. Comparison of PCR, virus isolation, and indirect fluorescent antibody staining in the detection of naturally occurring feline herpesvirus infections. J Vet Diagn Invest. 1999 Mar;11(2):122-6.

  2. Low HC, et al. Prevalence of feline herpesvirus 1, Chlamydophila felis, and Mycoplasma spp DNA in conjunctival cells collected from cats with and without conjunctivitis. Am J Vet Res. 2007 Jun;68(6):643-8.

  3. Maggs DJ, Clarke HE. Relative sensitivity of polymerase chain reaction assays used for detection of feline herpesvirus type 1 DNA in clinical samples and commercial vaccines. Am J Vet Res. 2005 Sep;66(9):1550-5.

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