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Kansas State Veterinary Diagnostic Laboratory

Kansas State Veterinary Diagnostic Laboratory
Kansas State University
1800 Denison Avenue
Manhattan, KS 66506
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KSVDL Client Care
General Inquiries
785-532-5650 or
Fax: 785-532-4835

KSVDL Business Office
Billing Inquiries
785-532-3294 or
Fax: 785-532-3502

Regular business hours:
8 am - 5 pm Mon.-Fri.
8 am - noon Sat.

December 2018

Testing for Strangles to Identify Carrier Horses 

By Dr. Mike Moore

Strangles (or Strep equi) is a frustrating disease, and can be difficult to prevent. We now understand that Strangles is likely spread by carrier horses. One of the recommended methods for detecting carrier horses is nasopharyngeal lavage. 

This article explains the supplies and processes required to successfully perform this procedure.

Supplies needed:

  • #5 French tomcat catheter
  • Sterile saline                                                    
  • 50 cc conical tubes
  • 50 cc syringes                                                   
  • Clean exam gloves and personal protective equipment 
  • OB sleeves                                                        
  • Disinfectant

The horse should be sedated to allow for lowering of the head to utilize gravity to collect the sample. Measure from the nostril to the medial canthus of the eye to find the correct distance to pass the catheter. Pass the catheter along the left or right ventral meatus until you are in the horse’s pharynx. Position an OB sleeve below the nostrils to catch the wash fluid. Attach a 50 cc syringe filled with sterile saline to the catheter and flush slowly. Collect the wash fluid in the OB sleeve. Transfer the fluid to a labeled conical tube by cutting the tip of a sleeve finger and allowing the fluid to flow into the tube.

If sampling more than one horse, fresh gloves and PPE should be used for each animal. Equipment should not be reused between horses.

The outside of each tube should be disinfected to prevent the contamination of other samples or gloves. Consider all waste materials to be infectious including gloves and swabs, etc. Any restraining equipment such as twitches, nose chains, etc. must be disinfected between uses. Make sure to remove organic material before disinfecting.

To view a short video on this procedure: https://www.youtube.com/watch?v=gHm2lWEuQmo&list=PLNjV05pK4JEWOCoLSwRlS7HOuiBJ3rKZ0

Diagnostic test selection:
The nasopharyngeal wash should be submitted for both culture and PCR. PCR has become the diagnostic test of choice because of its diagnostic sensitivity and specificity. Positive PCR results can be obtained when bacterial culture is negative because of low bacterial sample concentration. To increase diagnostic sensitivity performing both tests is recommended. If a horse has a positive culture or PCR, it is considered to be infected.

Test/case interpretation:
To designate a horse as negative for Strep equi, three -negative culture and PCR tests, from samples collected over a three-week period, are required. 

Sample submission:
Samples should be shipped the day of collection on ice packs for overnight or two-day delivery. If samples cannot be submitted the day of harvest, samples should be stored under refrigeration until shipping. 

For more information please contact Client Care @ 866-512-5650 or clientcare@vet.k-state.edu


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