Have We Gotten a Little Too Smart on BRD Testing?

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Drs. Fulton and Confer, both veterinary professors at Oklahoma State, write here that the battery of Bovine Respiratory Disease diagnostic tests at a veterinarian’s disposal was “unthinkable” 25 years ago. The modern molecular tests available can quickly and accurately detect the presence of the numerous viruses and bacteria that can contribute to respiratory disease. Unfortunately, the high sensitivity of those molecular tests means they often find too much information, which can be as confounding to teasing out the real cause as too little. The rate at which academia and industry has developed molecular diagnostic tests has outrun our ability to validate, standardize and interpret them in diagnosing BRD.

Their bottom line? You should be working in conjunction with a quality diagnostic lab who can help your veterinarian put the results in perspective, answering the final question of any molecular test results: “Does the result make biologic sense?”

Bovine Respiratory Disease Test Options

Test

What it does

Pros

Cons

Serology

Finds antibodies the calf has produced in response to exposure

It can detect both past infection and response to vaccination

 

It doesn’t necessarily measure immunity to disease and can’t tell the difference between antibodies created by infection vs. those created by vaccination

Culture of the airways or fluid

Can find both bacteria and viruses

It can demonstrate active infection is taking place

Just because you culture a virus or bacteria doesn’t mean it’s causing disease in the lung; plus, it typically takes days to weeks for results

Culture of a lung lesion

Can find both bacteria and viruses

Finding the organisms usually indicates high concentrations are in tissue, plus, resistance to antibiotics can be measured

 

May miss true positives if several organisms are currently present or antibiotic therapy has reduced their concentrations. Results usually take days to week

Immunohistochemistry on lung lesions

Finds antigens in lung lesion

Gives strong evidence that the virus or bacteria found is actually related to the disease

Accuracy depends on tests being specifically tailored to the infectious agent

In-situ hybridization of  lung lesion

Detects the genetic material of virus in lesion

By localizing the infectious agent to the lesion, it gives strong evidence that it’s cause of the disease. Can identify small numbers of organism

Genetic sequence for the infectious agent has to be known

Single polymerase chain reaction (PCR) on respiratory tract swabs

Detects the organism’s DNA in a sample

Provides specific evidence the virus or bacterium is present (or has been recently)

Can’t tell the relative contribution of the organism to disease severity, plus not useful to gauge antibiotic resistance

 

Single PCR from lung lesion

Detects a piece of the organism’s genetic material

 

Evidence the specific organism is associated with disease

Even with association, it may not isolate the true cause within diseased tissue, also, can’t tell natural infection from modified-live vaccination

Multiplex PCR on respiratory tract swabs

Detects a piece of any of several infectious organisms’ genetic material

With a single test, potential evidence of one or more infectious agent associated with disease can be determined. Test provides more information than single PCR.

Even with association, it may not isolate the true cause within diseased tissue, also, can’t tell natural infection from modified-live vaccination

Multiplex PCR from lung lesion

Detects a piece of any of several infectious organisms’ genetic material

With a single test, potential evidence of one or more infectious agent associated with disease can be determined. Test provides more information than single PCR.

Even with association, it may not isolate the true cause within diseased tissue, also, can’t tell natural infection from modified-live vaccination


Source: Fulton RW, Confer AW.Laboratory test descriptions for bovine respiratory disease diagnosis and their strengths and weaknesses: gold standards for diagnosis, do they exist? Can Vet J. 2012 Jul;53(7):754-61.
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