Strangles qPCR

About the Test

The qPCR test detects the genome (ADN) of Streptococcus equi variant equi, the pathogen (bacteria) responsible for Strangles.

Sample

• Nasopharyngeal swab - dry swab (see AAEP guidelines)
• Nasal swabs or draining lymph nodes
• Guttural pouch washes

Turnaround time

• 2 to 5 working days

What is Strangles?

• Strangles is a highly contagious upper respiratory infection of horses caused by the bacteria Streptococcus equi subspecies equi (S. equi). It is transmitted by inhalation or direct contact with contaminated surfaces (for example, horses sharing water buckets). The bacteria colonize the horse’s tonsils and pharynx within hours of infection, and then infect the lymph nodes under and behind the jaw, resulting in abscessation of these structures days later. Horses develop a fever initially, but are typically not contagious during the initial 48-72 hours.
• Rarely, infection spreads to other parts of the body resulting in abscesses in other organs such as the intestines, kidneys, lungs, spleen, or liver. This is often called “bastard strangles” or metastatic abscessation.
• A few horses may develop a hypersensitivity reaction to the bacteria with repeated exposure either in the form of infection or vaccination, otherwise known as purpura hemorrhagica. Horses that develop classic clinical signs and are not treated with antibiotics have the potential to develop immune protection for up to five years.

Clinical signs

• Classic clinical signs include a fever (often >103°F or 39.5°C) first, followed by one or more of the following symptoms: depression, thick nasal discharge, and lymph node enlargement under the jaw and/or in the throat latch region. The abscessed lymph nodes may drain externally or into the guttural pouches (blind-end sacs connected to the throat in horses) resulting in nasal discharge. Horses that have been vaccinated for strangles or horses that have previous partial immunity may develop milder signs of upper respiratory tract infection.
• Bastard strangles cases may develop colic signs, fever, and/or weight loss with or without a history of previous strangles disease or exposure. Horses with purpura hemorrhagica may develop edema of the head, trunk, and/or legs, and broken blood vessels or bruising of the mucous membranes of the mouth, eyes, and nose. Additional signs can include fever, severe depression, and muscle tightness. The severity of symptoms in purpura hemorrhagica cases ranges from mild to life-threatening.

Transmission

• Strangles is caused by oral exposure of a horse to S. equi bacteria. Once within the oral cavity, the bacteria invade the tonsils and subsequently colonize the lymph nodes.
• 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.).
• Flies may also act as vectors, spreading the bacteria from horse to horse.
• Under the right conditions, S. equi can survive in the environment for weeks or months.
• 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 three to six 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).
• Strangles may be transmitted by “silent shedders” who do not display signs of disease. These horses commonly carry the strangles organism in the guttural pouch, an air sac at the back of the horse’s throat. Detection of these animals requires guttural pouch endoscopy (passing an endoscope via the horse’s nose into the guttural pouch). Strangles is most commonly transmitted by acutely ill or recovering horses that are still shedding bacteria in their nasal secretions. Bacterial culture results have a turnaround time of 2 to 3 days. The DNA test known as Polymerase Chain Reaction (PCR) takes less than a day. However, it may take an additional 1 to 2 days to send samples to the laboratory.

Prevention

• Biosecurity on the farm is necessary to prevent the spread of disease.
• Isolate new horses for three weeks prior to introducing them to the rest of the population.
• Isolate any horse with a fever and signs of strangles.
• Do not share tack or equipment between sick horses and others.
• Perform twice daily monitoring of rectal temperatures of all horses in an outbreak to identify new cases.
• Stop all movement of horses to and from the farm when strangles is identified.
• Disinfect water buckets daily.
• Use strict hygiene between horses to reduce the spread of the disease.
• Ideally, three throat flush samples are obtained from recovering horses and any horses who were in contact with sick horses at approximately weekly intervals and tested for S. equi subsp equi by PCR and culture. Identification of strangles bacteria in clinically recovered horses may mean the guttural pouches have retained some infection. Endoscopy of the guttural pouches provides visualization of any pus or dried debris (chondroids) that harbor the bacteria. A small number of horses will recover from strangles and continue to shed bacteria from the guttural pouch, causing recurrent farm outbreaks. Detection and treatment of these “silent carriers” (S. equi bacteria in guttural pouches) via endoscopy and PCR is essential for preventing disease recurrence on a farm.
• Discuss vaccination types and recommendations with your veterinarian. Vaccination does not provide 100% immunity against S. equi infection. Vaccination is not recommended during or within two years of a strangles outbreak due to the increased risk of purpura hemorrhagica.

FAQs