Farms 1 and 3 had endured severe strangles outbreaks for several years. Farm 2 had only one previous outbreak. All horses
over the age of 5 months were screened on Farms 2 and 3. Only broodmares and longtime residents were tested on Farm 1.
"The economic losses and negative publicity sustained by farms with strangles outbreaks can be significant," says Smith. "This
protocol for detection and treatment of silent carriers was cost-effective on all three farms, given the morbidity rates experienced
in years past. The discovery and treatment of silent carriers allowed each of the farms to institute more thorough prevention
and control programs with a clean slate," Smith notes.
"It also provided an opportunity for the veterinarian to review and update vaccination programs, quarantine and isolation
procedures and other herd health practices on each farm."
Managing an outbreak
In order to limit the spread of strangles, it is important to recognize the disease early on and to properly manage and segregate
infected from uninfected populations.
"Since each farm setting is different, the veterinarian is the key person to assess and understand the principles of managing
an outbreak," says Sweeney.
A major concern to veterinarians is to have a plan in place to manage it. That begins with a thorough history of the premises.
"Immediately isolating the dirty horse or horses, quarantining those that are sick from those that are unaffected and have
not been exposed is of critical importance," Sweeney says.
Though some may contend that the whole farm has strangles, that is not accurate, Sweeney explains. Farms are often of such
large size and are set up so that exposed infected animals can be identified and kept separate.
"The object is not to have to shut operations down, but to let those with strangles get over the disease, be tested so they
are not carriers and be able to mix them back into the general population," Sweeney says.
She recommends the following steps to help control a strangles outbreak:
- Movement of horses on and off affected premises should be stopped. Segregate horses and implement hygiene practices immediately.
- Strangles cases and their contacts should be segregated into a "dirty" area of the farm.
- Rectal temperatures should be taken daily of all horses to determine any new febrile strangles-infected animals.
- Non-infected horses should be segregated in a clean area.
- All farm personnel should practice exceptional hygiene throughout the outbreak period.
- Lavage, swab and PCR screening of recovering strangles cases and their healthy contacts should be done regularly, with those
conducting the tests taking care to prevent contamination.
- Swabs and lavage fluid should be collected at weekly intervals for several weeks after recovery and tested for S. equi by conventional culture and PCR. Because PCR can detect living and dead bacteria, positive PCR is judged as provisional subject
to further investigation.
- Due to a concern for long-term carriage by asymptomatic carriers, endoscopy of the upper respiratory tract and guttural pouches
should be performed on outwardly healthy horses, in which S. equi is detected either by culture or PCR.
- Lavage samples from guttural pouches should be tested by culture and/or PCR, and sites such as nasal sinuses or tonsils should
be considered in horses shown to continue to harbor S. equi.
- Farm personnel should practice common-sense hygiene when handling tack, feed, water buckets, clothing, etc. Dedicated protective
clothing is a good option and personnel should limit their handling of infected animals.
- Equipment used with infected animals should be dedicated to them, and where possible discarded and/or thoroughly disinfected
with chlorine bleach. Water troughs and wood surfaces are of particular concern for indirect transmission of disease.
- Manure and waste from infected animals must be isolated from sites where uninfected animals are kept or handled.
Pastures where infected animals have grazed should be rested for at least four weeks.
On the premises, organic material is of most concern. "Use a phenolic compound to clean all water sources, stall areas, fencing,
brushes, halters, etc.," Holland recommends.