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Facts On Strangles

By Dr. Ryan Penno D.V.M.

Strangles is a highly contagious bacterial infection caused by Streptococcus Equi. It is not usually fatal, but can cause death either by excessive swelling that compresses the airway (hence the name) or by spread of the infection to other bodily organs besides the lymph nodes of the throat.

Incubation Period:

• Normally 2 to 6 days.
• Some horses may be inapparent carriers.
• Strangles can survive in the environment for 2 to 3 months in proper conditions.

            - studies show that the bacteria can survive on wood for 63 days at 2C

            - another study on glass or wood was found to survive for 48 days of 20C

Typical Symptoms:

Note: These symptoms can also be caused by other disorders. However, contact your vet immediately if you suspect strangles or any infection.

• Onset: mild fever, lethargy, nasal discharge (secous turning to mucopurulent).
• Sore throat and neck. (The horse may not want to eat, and may stand with head and neck extended.)
• Swollen lymph nodes in the throatlatch area, after initial fever and lethargy.
• Difficulty in breathing and signs of distress due to compression of trachea by enlarged lymph nodes in the neck - moderate to severe cases.
• Affected lymph nodes may rupture and discharge a foul smelling pus.
• Pneumonia is a possible complication.
• Possible systemic infection (7-10% of cases, ie. bastard strangles).
• Purpura hemorrhagica - a disorder where the blood vessels leak, characterized by edema (swelling) of the limbs – rare.
• Strangles is sometimes considered to be a disease of foals and young adult horses. Older horses are often immune to strangles due to prior exposure during their youth, or they may display only lethargy and nasal discharge without obvious lymph node swelling (however, these animals can still spread the disease or get Strangles not only through lymph nodes but organ tissue and muscles).  Foals over 3 months of age are also susceptible and horses between the ages of 1 to 5 years old are at higher risk.

Note: "Bastard Strangles" is a strangles infection involving lymph nodes elsewhere in the body besides the head and neck. Symptoms will vary depending on which area of the body is affected and prognosis varies on location. Bastard Strangles is serious and has a poor prognosis.

Testing and Diagnosis:

Note: Your vet may utilize other methods of testing than the ones listed below. This is not an inclusive list.

• Bacterial culture verifies the presence of the strangles bacteria, Streptococcus Equi.
• The horse shows typical strangles symptoms.
• Radiographs, endoscopy, ultrasound.

Treatment:

Note: Your vet may utilize some or none of the listed treatments. This is not an inclusive list of treatments.

• Antibiotics may be prescribed.
• Careful monitoring of vital signs to detect complications such as bastard strangles or pneumonia.
• Supportive care -- clean water, good food, protection from extreme heat or cold.
• Hot compresses may be applied to abscessed lymph nodes to encourage them to drain.
• Your veterinarian may lance affected lymph nodes.
• Affected horses should be quarantined, and all tack, equipment, stalls, etc. that were used by or around the affected horse(s) should be sterilized with approved compounds. Hand washing is also very important.

Strangles is highly contagious, with two modes of transmission:

• direct contact with nasal secretions or a ruptured abscess.
• environmental contamination

Prevention:

• Vaccines are available, but do not provide complete protection.
• Quarantine of all new horses for two weeks.
• Current vaccine of choice is intranasal due to local and systemic immunity.

What to do if your horse has been exposed:

(This is a touchy issue as there are many different opinions.  Any questions or concerns you may have should be discussed with your vet.)

• Those affected by the disease should be treated, but not vaccinated
• Horses with no known contact with the disease should be vaccinated immediately
• Horses known to have been in contact should be observed for seven to ten days and vaccinated only if they have a normal temperature and show no clinical signs of the disease

Factors effecting Strangles:

Exposure of a horse to S. equi does not necessarily mean that it will come down with strangles. Factors that influence the risk of disease include

• dose of bacteria (poor sanitation and direct contact with nasal secretions and pus increase the chance of disease);
• immune status of horse. Previously exposed horses are often immune to the disease, or do not get as sick as unexposed horses. During the first 0 to 3 months of life, foals are often protected by maternal antibodies. Vaccination can also increase resistance to the disease;
• stress (poor nutrition, overcrowding, lengthy transportation or pre-existing diseases increase the risk of strangles).

Bacteria can be transmitted through contact with pus or nasal discharges from an infected horse, or from contaminated bedding or barn equipment (water troughs, buckets, etc.).   If you think your horse may have strangles, contact your veterinarian for medical advice and to determine an appropriate course of treatment. This document is NOT intended to provide medical advice, but is merely for information only, and may contain inaccuracies. It is NOT intended as a guide to treatment or diagnosis.

Myths about Strangles:

The Strangles vaccine will prevent my horse from getting Strangles.  False

Several S. equi vaccines are commercially available. Vaccination of healthy animals on a farm during an outbreak is usually not effective, since at least 7 to 10 days for early 1gM response is required for the immune system to respond to the vaccine. Current vaccines produce only short-term (six months to one year) immunity, and require regular boosters to maintain adequate protection.

My horse has already had Strangles so I don't have to worry.  False

It is possible for a horse to get Strangles more than once in their lifetime.  After battling strangles, a horse will develop some immunity to the disease that should protect them for the remainder of the season; it just doesn't last forever. Strangle immunity could be compared to the flu – most of us might catch it once during flu season, but when we do, we're generally safe from catching it again that season. It doesn't make us immune to all future years, though.  One study reports 75% showed immunity to Strangles up to 4 years after infection.

Antibiotics can encourage bastard strangles to develop. False

Some people have proposed this happens because killing the organism could indirectly affect the development of immunity and thereby increase the risk of infection. But, there is no experimental or clinical studies that suggest that.  Most immune stimulation occurs before clinical signs and therefore, before treatment starts, which has little effect on bastard Strangles formation.

My horse can get strangles from the vaccine. True

Intranasal vaccine is a live attenuated bacteria meaning the bacteria has a much lower virulence then "wild" strains but CAN cause disease symptoms.

Once my horse is over Strangles, I have nothing to worry about.  False

Shedding the bacteria continues for up to one month after all clinical signs

are gone in 20 percent of horses.

How long should a horse be quarantined for then?

• 4 weeks for known affected barns.
• 2 weeks recommended as incubation period is 2-6 days and onset of clinical signs follow shortly thereafter.

NOTE: Horses can be asymptomatic (chronic) carriers and can harbour the organism in the guttural pouch for as long as 39 months.