Table 2.

Aims and associated measures used to aid in control and transmission of S. equi.

	Aim	Measure
1.	To prevent the spread of S. equi infection to horses[Link]	• Quarantine new arrivals for 3 weeks. Additional screening for subclinical carriers by guttural pouch endoscopy, culture, and PCR testing should be part of any screening program. If animal is known to be unvaccinated and is located in a country that has access to the combined SeM and SEQ_2190 serology, then seropositives should be identified and investigated further via endoscopy (See “Serology” section). • Stop all movement of horses on and off the affected premises immediately. Quarantine should last for a minimum of 3 weeks past the resolution of the last clinical case and all cases declared S. equi negative. Animals may be infectious for 6 weeks after discharges clear. Persistent guttural pouch infection may result in intermittent shedding for years.
2.	To prevent indirect cross infection by S. equi from horses in the “dirty” area to those in the “clean” area of the premises	• If S. equi infection is suspected, the horse should be isolated immediately to minimize the risk of transmission to in contact animals.
3.	Cohorting	• Create 3 color‐coded groups, even if limited space dictates that horses must remain in the same paddock only separated by 2 layers of electric fence to avoid nose to nose contact. The red group should include horses that have shown 1 or more clinical signs consistent with strangles. Horses in the amber group are those that have had direct or indirect contact with an infected horse in the red group and may be incubating the infection. The remaining horses, in the green group, are those which have had no known direct or indirect contact with affected animals. • The rectal temperature of all horses in the green and amber groups should be measured twice daily and any febrile horse should be moved to the red group. • Clearly color‐coded buckets and other equipment should be used to ensure that indirect mixing between groups does not occur. Eliminate all sharing of water and disinfect water and feed buckets daily. • Wherever possible, dedicated staff should be used for each color‐coded group. If separate staff are not an option, staff should always move from the lowest risk to highest risk groups, that is, from green to amber to red groups in that order and not back again.
4.	To establish whether convalescing horses are infectious after clinical recovery.	• Testing for potential carrier status should begin no sooner than 3 weeks after resolution of clinical signs or potential exposure with no clinical signs. • Testing horses that have been treated with antibiotics should not commence before 3 weeks after the cessation of antibiotic treatment. • If nasal discharge persists longer than 2 weeks, guttural pouch examination is indicated to identify horses that may have empyema and require additional treatment. • 1 endoscopically guided guttural pouch lavage qPCR on cases and their contacts to screen for carriers provides increased efficiency and sensitivity over 3 nasopharyngeal washes over 3 weeks. All equipment must be disinfected between horses when sampling multiples on a farm. • Continual positive tests despite endoscopically normal guttural pouches should be considered infections and thought given to treatment with systemic antibiotics and sinus radiography. Sites such as the sinuses should be considered in horses that continue to harbor S. equi in the absence of pathology. Purulent discharge at the nasomaxillary opening should be sampled if noted on endoscopy. Sinoscopy and qPCR testing of sinus lavage is possible, but obviously invasive. • If the outbreak is located in a country that has access to the combined SeM and SEQ_2190 serology, then seropositives identified in the in‐contact population can be further investigated via endoscopy (See “Serology” section). • Animals are considered safe to move out of isolation on the basis of absence of obvious guttural pouch pathology in conjunction with negative guttural pouch lavage qPCR results.

There is no current consensus on the use of vaccines to prevent S. equi. This is limited by geographical restrictions, varied experience, current lack of accepted proven efficacy, and DIVA (Differentiating Infected from Vaccinated Animals) capabilities with the latest diagnostic assays (See Vaccination).