by Portia DeLoache DVM
“Strangles” is the laymen’s term for an upper respiratory infection in horses caused by the bacteria Streptococcus equi equi. Strangles is most common in young horses (<5 years old) but can affect horses of all ages. This disease is highly contagious and if a horse is suspected of having or carrying the bacteria, quarantine protocols are recommended to prevent further spread of the disease.
The disease is spread through direct contact with infected horse, carrier horses, or contaminated equipment. Although humans cannot be infected with the bacteria they can carry the bacteria to other horses if proper disease control and hygiene protocols are not followed.
Incubation period between exposure and the start of clinical signs is usually 3-14 days. Once a horse is infected clinical signs include fever, nasal discharge, and swelling of the lymph nodes near the head.
Testing to confirm infection includes a nasal wash sample to be submitted by your veterinarian. An upper airway scope may also be recommended.
Two vaccines are available an injectable killed vaccine and a modified live intranasal spray. Our clinic recommends using the intranasal vaccine if possible due to faster local immunity in the upper airway. An initial 2 dose series (first dose and then second 2-3 weeks later) is recommended for non-vaccinated at risk horses followed by annual to semi-annual boosters. Recent vaccination (<6wks) can result in false positives on some tests, if you request testing by your veterinarian make sure to have an up to date vaccine history.
We do NOT recommend vaccinating horses showing signs of fever or upper respiratory disease (nasal discharge, cough, etc).
Some general guidelines have been listed below as an example in a case of confirmed positive on a farm.
Disease Control Guidelines
Do not move horses on or off facility until all horses on the facility are confirmed clear/negative
Separate confirmed, exposed, and “clean” horses to prevent additional exposure
Strangles confirmed: keep in well-marked quarantine area
Do not allow contact with other horses
Feed and handle LAST then change clothing prior to handling other horses (this includes shoes)
Do not share equipment and clean and disinfect equipment after each use
If personal protective gear is available it is highly recommended
Dressing order – gloves, gown, boots
Undressing order – boots, gown, gloves
Exposed horses should be kept segregated and prevent contact with other non-exposed or confirmed horses for a minimum of 2 weeks
Monitor rectal temperature DAILY (normal 98.5-100.9F)
Unexposed (“clean”) horses should be fed/handled FIRST
Monitor rectal temperature DAILY (normal 98.5-100.9F) for 2 weeks
If a fever or nasal discharge is noted, separate that horse and notify a veterinarian immediately
Do not share equipment between groups
Do not wear possibly contaminated clothing (this includes shoes – rubber boots are inexpensive and can be disinfected easily)
Clean water troughs regularly and do not share water between groups
Possibly contaminated pastures should be rested for 4 weeks before being considered “clear”
Manure, bedding, and waste feed should be composted in an isolated area and NOT spread on pastures
Your veterinarian may recommend screening tests for possibly exposed individuals in addition to segregation during the incubation period