Strangles starts with a sudden fever, then progresses to thick yellowish-green nasal discharge and visibly swollen lymph nodes under the jaw. These swellings eventually form abscesses that rupture and drain pus. The disease is caused by the bacterium Streptococcus equi and is one of the most recognizable infections in horses once the classic signs appear.
The First Signs: Fever and Behavior Changes
The earliest sign of strangles is a fever, often the only clue for the first day or two. A normal horse’s rectal temperature sits between 99 and 101.5°F. In strangles, that number climbs above 101.5°F, sometimes reaching 104°F or higher. At this stage the horse may look dull, go off its feed, and seem generally depressed, but there’s nothing visually distinctive yet. The incubation period after exposure ranges from 3 to 14 days, so a horse can be infected for nearly two weeks before showing any outward sign at all.
Within 24 to 48 hours of that first fever spike, the more recognizable symptoms appear. This narrow window is important: if you’re monitoring temperatures during an outbreak, catching the fever early and isolating the horse can slow the spread significantly. The horse won’t begin shedding bacteria from its nose until about two to three days after the fever starts, which means samples collected in the first 48 hours of fever can come back negative on lab tests even when the horse is truly infected.
Nasal Discharge: What It Looks Like
The nasal discharge in strangles follows a predictable progression. It begins as a thin, watery drip from one or both nostrils. Over a day or so it thickens into a mucus-and-pus mixture that is usually yellowish green, sometimes creamy white. This thick, opaque discharge is one of the hallmark visual signs of the disease. It tends to crust around the nostrils and can mat the hair on the horse’s muzzle and front legs if the horse rubs its face.
In horses with deep abscesses behind the throat (retropharyngeal lymph nodes), the discharge may be especially heavy because pus is draining internally into the guttural pouches and then out through the nose. These horses often hold their head and neck stretched out and may make noisy, labored breathing sounds because the swelling is pressing on the airway.
Swollen Lymph Nodes and Abscess Formation
The most dramatic visual feature of strangles is the swelling under and between the jawbones. The lymph nodes most commonly affected are the submandibular nodes, which sit in the soft tissue between the lower jaw, and the retropharyngeal nodes, which are deeper behind the throat. Occasionally the parotid nodes (near the base of the ear) and the upper cervical nodes are involved too.
At first the swelling feels warm and diffuse, like general puffiness in the throatlatch area. Over the following days it firms up as one or more abscesses form inside a thick fibrous capsule. You can often see the jaw area looking obviously asymmetrical or bulging. As the abscess matures, the overlying skin may become tight and shiny, and a clear or straw-colored serum sometimes oozes from the surface before the abscess is ready to burst.
Rupture typically happens between 7 days and 4 weeks after infection. When it does, thick, creamy, yellow-white pus drains from the opening. The volume can be surprising, sometimes several ounces or more. After drainage the area gradually flattens, the skin around the rupture site crusts over, and healing begins. Applying warm compresses to a maturing abscess can speed this process along, and in some cases a veterinarian will lance a mature abscess to facilitate drainage and speed recovery.
What Mild or Atypical Cases Look Like
Not every case of strangles looks dramatic. Horses with partial immunity, whether from previous exposure or vaccination, can develop a much milder version. In atypical cases the fever may last only 24 to 48 hours, followed by profuse nasal discharge and poor appetite but only moderate lymph node swelling. About half of horses in mild outbreaks develop noticeable jaw enlargement, and those glands may or may not progress to full abscess formation. Some horses recover quickly enough that owners mistake the illness for a routine upper respiratory infection. These mild cases still shed bacteria and can silently spread the disease to other horses on the property.
Metastatic Strangles: When It Spreads Internally
In a small percentage of cases, the infection doesn’t stay confined to the head and throat. This complication is called metastatic strangles (sometimes called “bastard strangles”), and it occurs when bacteria spread through the bloodstream and seed abscesses in lymph nodes elsewhere in the body, most often in the abdomen and less commonly in the chest. Because these abscesses are internal, there’s no visible swelling on the outside. Instead, the horse may show persistent or recurring fever, weight loss, intermittent colic, or general failure to thrive weeks after the initial infection seemed to resolve.
In rare cases, the bacteria can cause a brain abscess, making Streptococcus equi the most common cause of brain abscesses in horses. Signs of neurological involvement include incoordination, head tilt, or behavioral changes. These complications are uncommon but worth knowing about, particularly if a horse that had strangles weeks ago isn’t bouncing back as expected.
Guttural Pouch Complications
Some horses become long-term carriers of strangles because infected material persists in the guttural pouches, a pair of air-filled sacs connected to the back of the throat. When retropharyngeal abscesses rupture internally, pus can accumulate in these pouches. Over time the pus can dry and harden into solid, chalky masses called chondroids. A horse carrying chondroids may look perfectly healthy on the outside while continuing to harbor bacteria and intermittently shed them, posing a risk to other horses. Detecting this requires an endoscopic exam, where a camera is passed through the nostril to visualize the pouches directly.
What Recovery Looks Like
Once abscesses have drained, most horses begin to improve within a few days. The fever drops, appetite returns, and energy levels pick back up. The drainage site itself can look messy for a while: crusty, weeping, and surrounded by matted hair. Keeping the area clean and providing a warm, dry, dust-free environment helps the wound close. Full recovery from an uncomplicated case generally takes three to four weeks from the first sign of fever, though the drainage site may take a bit longer to fully heal over. During recovery, the horse should remain isolated from others because it can still shed bacteria for weeks after clinical signs resolve.