What Is RT-PCR in Veterinary Testing?

RT-PCR is a lab test that finds the genetic material of a germ in a sample such as a swab, blood, dung or fluid. It copies a tiny trace many times until it is easy to detect, so it can help find a virus that other tests may miss. A registered veterinarian reads the result with the animal's signs and history.

What does RT-PCR mean?

PCR stands for polymerase chain reaction. It is a way of copying a short piece of a germ's genetic material again and again until there is enough to detect. Think of a photocopier that doubles the page every time it runs: a faint page soon becomes easy to read.

Real-time means that the machine watches the copying as it happens. A glowing signal builds up as copies are made, and the machine records it. On this site, RT-PCR means real-time PCR. Some scientists also use RT for reverse transcription, which is the extra step explained next.

Why do some viruses need a reverse step?

Genetic material comes in two forms, DNA and RNA. The PCR machine copies DNA. Some viruses carry RNA instead. The viruses behind distemper, foot-and-mouth disease and equine influenza are examples. For these, the first step turns the RNA into a DNA copy. That step is called reverse transcription, and the copying starts after it.

Canine parvovirus carries DNA, so it does not need the reverse step, though it can still be tested in real time. The lab confirms the method when you book, and some molecular tests are done by an independent partner laboratory.

Which samples are used?

The sample depends on the germ and on where it lives in the body. Typical examples include:

• a nasal swab from a horse with fever and cough, for the Equine Influenza Virus RT-PCR
• whole blood or urine for the Canine Distemper RT-PCR, and blood or stool for the Canine Parvo RT-PCR, both for dogs
• fluid or skin from a blister, or a swab taken by a vet, for the FMD Virus RT-PCR in cows and buffaloes
• throat, eye or nose swabs for several breathing illnesses in dogs, cats, horses, cows and buffaloes

Foot-and-mouth disease is notifiable. Owners should tell their veterinarian or the animal husbandry department if they suspect it, and the vet takes the sample.

The lab confirms which sample is needed when you book. Swabs and tubes should be labelled and kept cool, and a vet usually takes them.

Some owners ask for several viruses at once. The Dog Viral RT-PCR Panel typically groups RT-PCR tests for several dog viruses in one booking. The exact list is confirmed when you book.

What can RT-PCR tell you?

RT-PCR is commonly used to find out whether the genetic material of a particular germ is present in the sample. A positive result may indicate infection with that germ. Because it can detect a very small amount of material, it can help when other tests are still silent. It needs a laboratory and special machines, so it is not a quick test done at the animal's side.

What can it not tell you?

• A negative result does not always rule out infection. The sample may have been taken too early or too late, from the wrong place, or stored poorly. The germ may also be present in very small numbers.
• It finds genetic material, not always a living germ, so it cannot always tell active disease from leftover traces.
• A recently vaccinated animal can sometimes give a positive result from the vaccine virus. Tell your vet about any recent vaccination.
• It does not say how ill the animal is.

For these reasons the vet reads the result with the signs, the examination and the history. The vet may repeat the test, add a rapid kit or an antibody test, or look for another cause. Please see a vet promptly for a sick animal, and do not wait for a report.

Read next

To learn why some molecular tests travel to another laboratory, read Why Some Tests Are Sent to Partner Laboratories. For a pet owner's view of the same method, see What Is a PCR Test for Pets? When Vets Use It and Its Limits.

Testing in Bhopal

To book an RT-PCR test, call or WhatsApp +91 88175 01118. Within Bhopal, sample collection is free, and a vet usually takes swabs and blood. Owners in other districts can send samples to C-200, C Sector, Shahpura by courier, bus parcel or through their vet. The lab confirms the method, sample needs and reporting time when you book.