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Equine respiratory panel Q&A with Drs. Gillian A. Perkins & Linda D. Mittel

Dr. Gillian A. Perkins, director of biosecurity at Cornell University Hospital for Animals and Dr. Linda D. Mittel, senior extension associate at the AHDC, answer pressing questions about the diagnosis and management of acute respiratory disease in horses and how the AHDC’s new Equine Respiratory PCR Panel is helping to speed up diagnosis at a more affordable rate.

What pathogens does the Equine Respiratory PCR Panel detect?

The pathogens detected in the Equine Respiratory Panel include equine adenovirus 1 and 2, equine arteritis virus, equine rhinitis virus A and B, equine herpesvirus (EHV) types 1 and 4, equine influenza virus (all A subtypes), and Streptococcus equi.

Why is rapid diagnosis of these disease agents so crucial?

Many of these infections are extremely communicable and early diagnosis can prevent spread by informing the veterinarian of the results so that appropriate biosecurity precautions can be put in place. Additionally, knowing what “agent” you are working with allows for better treatments and care for the animal which will assist in the correct treatment plans, prognosis and return work for the horse.

How does the panel work?

The test being performed is a polymerase chain reaction (PCR) which looks for the DNA/RNA of each of these organisms. There are primers that recognize the particular DNA/RNA sequence or signature of each of these bacteria or viruses. Once the DNA/RNA is found, the primers make more of that DNA which can be detected by a PCR machine as a color change.

The advantage of this test is that it detects very small amounts of DNA/RNA and is therefore, what we call a very sensitive test. The disadvantage is that when small amounts of DNA/RNA are found there is often the question as to whether the organism is alive and replicating or whether there is residual DNA/RNA left over from the illness.

This can be a problem when an agent is dead and the animal is not infectious—from the testing one cannot tell the difference. This has been seen a number of times with strangles testing. Vaccines that have the actual genetic material of the agent, such as intranasal strangles vaccines, can cause a false positive if found in the nasal passages when sampling is done.

Why is it better than the previous system of individual tests?

The clinician is often concerned about each of the test pathogens when dealing with a horse with a fever of unknown origin or a horse with a fever and respiratory signs. This test has the capability of testing for a number of pathogens at once with a bundled fee. In addition, the test is rapid. This should reduce costs to the client while increasing the number of infectious diseases that we investigate.

When should I order the respiratory PCR panel?

Order the panel for any horse with a fever and serous nasal discharge for which a respiratory illness or infectious agent is suspected as well as instances in which strangles is suspected – a horse with a fever, snotty nose, and lymph node swelling.

Viruses or bacteria may present themselves in different ways in individual horses and the presenting signs may be atypical. It is good to rule out any agents you can, especially ones with high consequence. The AHDC has had cases that did not appear to be influenza and came back positive. It is also helpful to assist in determining if the animal is shedding virus particles. It will also give the entire barn, owner, and trainer in these cases peace of mind.

How should I submit samples?

Nasal swabs should be taken by placing a polyester-tipped swab into the horse’s nose and contacting the nasal mucosa for three to five seconds. The more nasal discharge on the swab, the more likely you are to have a positive test. The swab should then be placed in a sterile container (red top tube) and the ends of the swab broken off to facilitate closure of the tube.

This panel can use nasal swabs, transtracheal wash fluids, BAL, or nasal wash samples for testing. Once the sample is obtained, it is placed in a plain red top tube with a drop or two of sterile saline. This is not to assist with the PCR testing, but we will often try to grow a virus if it is found by PCR. We do this as a surveillance procedure to learn about new viruses.

People often ask about the length of the swab to use. In most cases a regular five-inch swab can be used, but some people use a long mare culture rod to get further back into the throat of the horse. Others may actually do a nasal wash (often used in testing for strangles) because you will cover more surface area and get a good sample. If you are testing for other respiratory agents that are not in the acute respiratory panel it may be helpful to check with the lab to know the very best sample to use.

How long does the test take?

The normal turnaround time (from the time it is received in the lab to the reporting of the results) is three to five days. The test can be run in a few hours, however. Expedited service (STAT) is available at the AHDC and results can be received in as little as three to five hours. There is an additional cost for this ($50.00). Prior arrangement must be made to get the results out STAT. In some cases STAT charges are much cheaper in the long run than treating animals and having them unable to do their work and waiting 3 to 5 days for results.

If a horse tests positive for any of these disease agents, what is the normal procedure for treatment and disease management?

Treatment depends on the cause of the illness. The most important part of disease management is to prevent the infection of other animals. Knowing what the agent is allows you to make the appropriate recommendations.

When should a horse be quarantined?

First, it is important to know the difference between quarantined vs. isolated. Quarantine is the process of keeping animals that are not ill yet, but have been exposed to infectious agent(s), separate from other horses. They can be given vaccines, undergo diagnostic testing and symptom monitoring, etc. Isolation occurs when an animal is ill and is being kept from others to prevent the spread of an infectious disease. In a barn, both quarantined and isolated horses may be handled the same when it comes to housing, but management will often be different. Any horse that has left the home stable and interacted with other horses should be quarantined when returning to the barn. This is not done at all stables due to limited space in some barns but should be done. Barns should find an area that can be used as a quarantine for resident horses as needed.