Pharynx: nasopharyngeal swab in Horses (Equis) | Vetlexicon
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Pharynx: nasopharyngeal swab

ISSN 2398-2977

Synonym(s): Nasopharyngeal swab


  • Clinically healthy horses can carry Streptococcus equi equi in the guttural pouch or nasopharynx.
  • Asymptomatic carriage of the bacteria is considered important in the persistence of infection within herds and to the introduction of infection to naive groups of horses and subsequent outbreaks of strangles Strangles (Streptococcus equi infection).
  • It is recommended that all infected and new horses be quarantined and swabbed at weekly intervals.
  • Swabs should be submitted for PCR Polymerase chain reaction (PCR) and culture.
  • Horses should not be released to the herd until 3 consecutive negative results are obtained.
Print off the Owner factsheet on Samples - how they help your vet to give to your clients.


  • Identification of carriers of S. equi ssp equi.
  • Monitoring response to treatment and isolation of infected horses.


  • Simple technique.
  • Done in standing animal.
  • Repeated sampling (3 times) increases sensitivity to >90% if submitted for PCR Polymerase chain reaction (PCR) and culture.


  • Negative results are not significant (single samples have only 30-45% sensitivity if only culture performed).
  • False negative results are common for single swabs.

Technical problems

  • Some horses may resent passage of the swab.
  • In rare cases, epistaxis may occur due to trauma of the nasal passages.

Alternative techniques

  • Endoscopic lavage and sampling of the guttural pouch (88% sensitivity on a single sample).

Time required


  • Restraint: several minutes.


  • Passage of swab: 5 minutes.

Decision taking

Criteria for choosing test

  • History of strangles outbreak in a group of horses.
  • Screening program for identification of potential carriers.



Veterinarian expertise

  • Minimal equine veterinary experience required.

Materials required

Minimum consumables

  • Unguarded gauze swab Nasopharynx: nasopharyngeal swab 03 - unguardedapproximately 8-10 cm long mounted on wire for passage along the nose.
  • Transport medium (isotonic phosphate-buffered saline, pH 7.2 with 2% fetal calf serum and 0.0005% amphotericin B) in a transport container with screw top.



  • Standing physical restraint: head collar and stocks or stable.
  • Twitch may be necessary.
  • Extremely fractious horses may require sedation.



Step 1 - Measure the head

  • Assess the length of the swab that will need to be passed along the pharynx by holding the swab alongside the head Nasopharynx: nasopharyngeal swab 01 - assessing length.

Take care not to contaminate the swab.

Step 2 - Restrain the head

  • With the non-operative hand over the nose, use the thumb to elevate the alar fold and open the nostril.

Core procedure

Step 1 - Pass the swab 

  • Pass the swab along the ventral nasal meatus Nasopharynx: nasopharyngeal swab 02 - inserted.
  • At the level of the caudal soft palate, the swab should stimulate a swallow.


Step 1 - Withdraw the swab 

  • Remove the swab and place into the transport medium.


Immediate Aftercare

General Care

  • Transport the sample at 4°C/39.2°F for inoculation within 4 h.

Potential complications

  • In rare cases, epistaxis may occur due to trauma of the nasal passages.


Reasons for treatment failure

  • Intermittent shedding of the bacteria in horses where infection is localized in the guttural pouch means that despite repeated nasopharyngeal sampling, long-term carriers can remain undetected.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Pringle J et al (2019) Long term silent carriers of Streptococcus equi ssp. equi following strangles; carrier detection related to sampling site of collection and culture versus qPCR. Vet J 246, 66-70 PubMed
  • Boyle A G et al (2018) Streptococcus equi infections in horses: guidelines for treatment, control, and prevention of strangles-revised consensus statement. JVIM 32 (2), 633-647 PubMed.
  • Rendle D (2012) Making the most of samples from the equine respiratory tract - a clinician's perspective on clinical pathology. UK Vet 17 (4), 4-9 VetMedResource.
  • Newton J R et al (1997) Naturally occurring persistent and asymptomatic infection of the guttural pouches of horses with Streptococcus equi. Vet Rec 140 (4), 84-90 PubMed.