The very first sign of strangles in horses is a fever, typically reaching 103°F to 106°F (39.4°C to 41.1°C). This spike in temperature appears 3 to 14 days after exposure to the bacteria and often shows up before any other visible symptoms, making it easy to miss if you’re not routinely checking your horse’s temperature.
Fever Comes Before Everything Else
Strangles is caused by the bacterium Streptococcus equi, and the infection follows a predictable sequence. Fever is the opening act. A normal horse’s resting temperature sits between roughly 99°F and 101.5°F, so anything at 103°F or above is a clear red flag. At this stage, the horse may look completely normal otherwise, which is why daily temperature checks during an outbreak are so valuable.
Alongside or shortly after the fever, you’ll likely notice your horse becoming lethargic and going off its feed. These are subtle changes. A horse that’s usually eager at feeding time but suddenly shows no interest, or one that seems dull and withdrawn, may be in the earliest phase of infection. These behavioral shifts can precede the more dramatic symptoms by a day or two.
Nasal Discharge and Its Progression
Nasal discharge typically appears soon after the fever sets in, but its appearance changes as the infection advances. Initially, the discharge may be clear and watery, easy to confuse with a mild respiratory irritation or allergies. Over the next few days it thickens, turning cloudy and then distinctly yellow or green as it becomes filled with pus. A horse with thick, purulent discharge from both nostrils is showing a hallmark sign of strangles, but by the time the discharge reaches that stage the infection is already well established.
Swollen Lymph Nodes and Abscess Formation
The feature that gives strangles its name is the swelling of lymph nodes around the throat and jaw. The nodes under the jaw (submandibular) and near the base of the ear behind the throat (retropharyngeal) are the ones most commonly affected. They become hot, firm, and painful to the touch, then gradually soften as abscesses form inside them.
When these abscesses grow large enough, they can compress the horse’s airway and make breathing audibly labored, a strangling sound that inspired the disease’s name. You may also notice your horse extending its neck or holding its head in an unusual position to relieve pressure. Difficulty swallowing is common at this point, since the swollen nodes press against the throat. Some horses drool or refuse water entirely.
Abscesses eventually rupture on their own, releasing thick pus. This material is highly contagious. Once the abscesses drain, most horses begin to improve relatively quickly.
When the Horse Becomes Contagious
One critical detail for horse owners managing a barn: a horse with strangles doesn’t start shedding the bacteria immediately. Nasal shedding usually begins 2 to 3 days after the onset of fever. That gap creates a narrow but important window. If you catch the fever early and isolate the horse before shedding starts, you can prevent the infection from spreading to other animals.
This also affects testing. Nasal swabs taken within the first 48 hours of fever frequently come back negative, even when the horse is genuinely infected. The bacteria simply haven’t reached detectable levels in the nasal passages yet. Waiting two to three days after fever onset gives a much more reliable result.
Once shedding begins, it typically continues for two to three weeks in most horses. Some animals become long-term carriers, harboring bacteria in pockets near the back of the throat for months without showing any symptoms themselves.
How It Spreads Between Horses
Strangles spreads through direct contact with infected nasal discharge or pus from ruptured abscesses. Shared water troughs, feed buckets, and handlers who move between horses without washing their hands or changing clothes are common routes of transmission.
The bacteria don’t survive long on outdoor surfaces. A study testing wood, painted wood, metal, and rubber surfaces found that S. equi died off within one to three days outdoors, with sunlight being the biggest factor in killing it. However, survival may be longer in shaded areas, inside barns, or in standing water, none of which were tested under the same conditions. Treating shared equipment as potentially contaminated for several days after contact with an infected horse is a reasonable precaution.
Signs That the Infection Is More Serious
Most horses recover from strangles within a few weeks, but a small percentage develop complications. The most concerning is a condition sometimes called “bastard strangles,” where abscesses form in unusual locations such as the abdomen, chest cavity, or even the brain. Signs that the infection has spread beyond the throat include prolonged or recurring fever after abscesses have drained, weight loss that doesn’t improve, persistent coughing, or neurological symptoms like unsteadiness or behavioral changes.
Another rare but serious complication is an immune-mediated reaction that can cause widespread swelling in the limbs and along the belly, sometimes appearing weeks after the initial infection seems to have resolved. Horses that seem to recover and then take a sudden turn for the worse need prompt veterinary evaluation.
What to Watch For Day by Day
If you suspect exposure, here’s the general progression to keep in mind:
- Days 3 to 8 after exposure: Fever appears first, often the only sign. The horse may seem slightly off, eating less or standing apart from the herd.
- Days 1 to 2 after fever onset: Clear nasal discharge begins. The horse becomes noticeably lethargic. Bacterial shedding has not yet started, so isolation at this point can still contain spread.
- Days 2 to 3 after fever onset: Nasal shedding begins. Discharge thickens. Lymph nodes under the jaw start to swell and feel warm.
- Days 4 to 10 after fever onset: Lymph node abscesses mature, soften, and eventually rupture. Breathing may become noisy. The horse may extend its neck or refuse to eat due to throat pain.
- Weeks 2 to 3: After abscesses drain, most horses improve steadily. Nasal shedding typically stops within two to three weeks.
The single most useful thing you can do if strangles is circulating in your area is take your horse’s temperature daily. Catching that initial fever before nasal discharge or swelling appears gives you the best chance of isolating the animal early and protecting the rest of your herd.