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Strangles
• Disease transmission
• Prevention
• Control of infection
• Treatment
• Confirmation of freedom from disease
Cause
• Bacteria
• Streptococcus equi
• Severity of infection related to health & inherent resistance of the individual horse, rather than variations in the organism itself
Epidemiology
• Highly contagious – spread by direct and indirect contact
1. Carrier animals main source of infection – carried in guttural pouch for up to 5 years
2. Survives well in moist discharges – will survive for 7 – 9 weeks on wood, depending on temperature
Clinical Signs
• Incubation period 3 – 10 days
• High temperatures ( > 103 F )
• Depression / inappetance
• Nasal discharge
• Enlarged lymph nodes on head
• Difficulty swallowing
• Noisy breathing
Diagnosis
• Clinical signs
• Culture bacteria from the pus of abscessated lymph nodes, nasal discharge or throat swabs
• Swabs – extra long shaft and absorbent heads
Diagnosis of carrier state
• Sequential throat swabs
• Endoscopic examination & guttural pouch washes
Notification
• No legal notification procedures
• Advisable to inform the relevant breeders association if infection occurs
Complications
• Less common – up to 8% of cases
• Infection usually restricted to head and neck
• Can spread to lungs, muscles, heart, kidneys and intestines
• These complications can be fatal
Definitions
• Infectious
Capable of being communicated by an infection – eg, tetanus
• Contagious
Capable of being transmitted from animal to animal – eg, influenza
Disease Transmission
Direct Contact
• horse – horse• fairly close contact
between infected and susceptible animals
Indirect Contact
• Personnel• Equipment• Water troughs
Disease Transmission
• Bacteria shed from draining abscesses and the nose
• Survives in the environment
• for example : bacteria survive on wood for up to 9 weeks, depending on temperature
• Good hygiene is essential in controlling the disease
Disease Dynamics
infection
healthy incubation signs healthy
susceptible latent infectious immune, then susc
Disease Dynamics
infection
healthy incubation signs healthy
susceptible latent infectious immune, then susc
susceptible latent infectious “carriers”
Prevention
• ALL horses entering any premises should be monitored closely during the period immediately after arrival.
• Any horse that develops a nasal discharge should be separated and swabbed by a vet for presence of Strep equi.
Control of infection
• Can limit spread by early detection of shedders among newly affected horses and their in-contacts
• Segregate suspected cases immediately• All infected horses and their in-contacts
should remain in strict isolation.• Horses should not enter an affected
premises unless can be isolated
Control of infection
• Due to chronic nature and common occurrence of carrier animals, it is impossible to tell when it is safe to mix convalescing horses with others
Disease Dynamics
infection
healthy incubation signs healthy
susceptible latent infectious immune, then susc
susceptible latent infectious “carriers”
Control of infection
• No infected or in-contact animal should be released from isolation until three consecutive negative swabs have been taken over a 2 week period
• Carrier animals can retain potential to spread disease, even after 3 negative swabs
• Need endoscopic examination
Treatment
• Depends on stage of disease
• Controversial area
• Some ( ? a minority of ? ) vets consider antibiotics to be detrimental
My approach
1. Horses with early clinical signs :
( nasal discharge / difficulty swallowing )
• Intra-muscular penicillin
• May inhibit formation of natural immunity
My approach
2. Horses with lymph node abscesses :
• Drainage and flushing of abscesses
• Antibiotics may prolong time to taken for abscesses to resolve
My approach
3. Horses exposed to Strep equi :
• Treat with penicillin until isolated from infected horses
Treatment
• General nursing
• Clean nose / abscesses
• Change water frequently
• Feed soft, palatable feeds
• Recovery usually takes 4 weeks
Free from disease ???
• Shedding of the bacteria usually ends rapidly after recovery, although it may be intermittent.
• No convalescent horse, or in-contact, can be considered free from infection until had three negative swabs over a 2 week interval.
• But, carriers can still exist
Immunity
• 75% of horses that have the disease, won’t develop the disease again for at least 4 years
Vaccination
• Not available in UK
• Short duration of immunity
• Still see disease where vaccine used
• Serious side – effects
• Unknown effect on carrier animals
Conclusions
• Outwardly healthy carriers pose real problems
• Vaccine not straightforward
• Control measures are effective but expensive