Streptococcus equi (commonly referred to as Strangles) is an infectious upper respiratory disease that is highly transmittable in equine populations. Without proper biosecurity protocols, a single case can become a clinical shutdown. Fortunately, the disease itself is treatable and measures can be taken to prevent outbreaks. On August 30th, Dr. Nicola Pusterla (PhD, Diplomate ACVIM and AVDC-Equine) and Dr. Rob Keene (DVM) provided an overview on Strep. equi in the webinar “Streptococcus equi – What Your Clinic Needs to Know.” Topics of discussion included clinical presentation of the disease, proper sampling techniques, diagnostic procedures, and outbreak management, with real world examples to illustrate.
About Strep. equi
Clinical symptoms typically appear within the incubation period of 2-14 days. More generic symptoms include fever, lethargy, anorexia, and general symptoms of respiratory distress; however, the tell-tale signs of Strep. are bilateral nasal discharge and lymph node abscesses along the bottom of the jawline. With vaccination, these symptoms can be milder. According to Dr. Nicola Pusterla, somewhere between 10 and 20% of Strep. cases will develop life-threatening complications, but most symptoms of the disease are treatable and will not have long-term effects.
Sampling methods vary and have different pros and cons. According to Dr. Robert Keene, the appropriate method is dependent on the outcome desired. Because Strep. equi does not colonize in the upper respiratory tract, there is a period of non-shedding towards the beginning of the infection. This can give veterinarians time to isolate and prepare for a positive test, but false negatives are very likely during this period. In an outbreak, communal water sources can carry the disease and provide a large sampling area.
Dr. Keene recommends sampling the highest surface area available. If the patient has abscesses, an aspirate would be an appropriate sample, as high levels of bacteria would be present. A flocked nasal swab or nasopharyngeal swab/wash can allow for a very sensitive diagnostic test if cross-contamination is mitigated. If possible, a guttural pouch lavage wash is the most invasive measure but can provide the most accurate samples. Each veterinarian must weigh the practicality of the test versus the level of test sensitivity required. While testing abscesses may be the preferred method, not all horses will present with this symptom, and a wash may be too time-consuming for the answer required.
While cultured samples from draining abscesses have been considered the gold standard, they are slow due to the required incubation period and are not the most sensitive. qPCR tests allow for quick turnaround times with high sensitivity and specificity during all stages of the infection, but do not differentiate live bacteria from dead. With the simplicity of the nasal swab, many veterinarians are turning to qPCR for their results.
By quickly identifying active infections and separating these horses from the others, outbreaks can be contained or even prevented. When managing outbreaks of Strep. equi, it is important to keep in mind the goals of outbreak mitigation:
1) Preventing the spread of the infection directly between infected and non-infected patients.
2) Preventing cross infection from infected patients to non-infected areas of the premises.
Through proper containment, clinical shutdowns can be averted. Your patients deserve the best care, and practicing strong biosecurity measures can protect them.
Watch the full webinar here: Streptococcus equi - What Your Clinic Needs to Know
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