Deadly Horse Diseases: What You Can do to Save Your Horse's Life

September 18, 2018

Infectious horse diseases can cause a major negative impact on both the horse and rider. In most cases, these diseases are those that horses can get from each other, or via a transmitter such as a mosquito or tick, which may transmit the disease from horse to horse. Knowledge of these diseases and their warning signs are the key to prevention. This blog will cover some of the most common infectious horse diseases.

Potomac Horse Fever (PHF)


Most commonly seen in spring, summer, and early fall, this disease is associated with pastures bordering water sources including creeks or rivers. PHF is an acute enterocolitis syndrome producing mild colic, fever and diarrhea in horses of all ages. Furthermore it also causes abortions in pregnant mares.

The bacterium responsible for the disease, Neorickettsia risticii, has been identified in flatworms that develop in aquatic snails. When the water warms up, infected immature flatworms are released from the snail into the environment. These flatworms can be ingested through drinking infected water, but more commonly by aquatic insects. Infected insects (such as mayflies) will hatch in mass and might carry the organism to horses to ingest as they graze (


Signs of PHF:


  • loss of appetite

  • fever

  • depression

  • decreased intestinal sounds

  • diarrhea

  • mild colic


Affected horses might also display signs of laminitis. PHF can range from mild to life-threatening. So, if you think your horse is showing signs of PHF you should contact your veterinarian immediately. If caught early, it can be treated successfully with oxytetracycline.




Several vaccines for PHF are available. These might not completely prevent illness, but may reduce its severity. Consulting with your veterinarian to decide the best course of action highly encouraged.

Equine Herpesvirus (EHV)/Rhinopneumonitis


With recent outbreaks of EHV, most horse owners are somewhat aware of the dangers of this highly contagious virus. Type 1 (EHV1) and Type 4 (EHV4) are the most clinically important.  EHV is characterized by respiratory infection, paralysis, abortion, inflammation of the spinal cord, and occasional deaths in young horses. EHV is extremely contagious. Owner should know that it can be spread through nasal secretions, contact with infected horses and contaminated feed and water utensils.


Signs of EHV:



• Nasal discharge

• Incoordination

• Hind limb weakness

• Loss of tail tone

• Lethargy

• Urine dribbling

• Head tilt

• Leaning against a fence or wall to maintain balance

• Inability to rise


If you think your horse may have been exposed to the virus start isolation procedures immediately, which prevents it from spreading through your entire herd. Check temps of all horse on your farm several times a day. If fever is detected, check for EVH-1 and consult with your equine veterinarian for further guidance.




There are two things you can do to help prevent an EVH outbreak on your farm, which includes vaccination and implementation of biosecurity practices. While there are several vaccines available, unfortunately there is no licensed vaccine that has a claim for protection against the neurological strain of the virus. In terms of biosecurity practices, this includes quarantining any new animals on the farm, or those that have traveled recently before introducing them to your herd, and disinfecting instruments such as grooming supplies between use on each animal.

Equine Influenza (Flu)


Equine influenza, is one of the most common infectious diseases of the respiratory tract seen in horses. This is a highly contagious virus that can be contracted through direct contact with an infected horse or by a contaminated environment. Infected horses incubate the disease for one to three days before displaying symptoms, which is why outbreaks can spread so rapidly. Unfortunately, influenza is endemic in the US, meaning it circulates continuously in the equine population.


Signs of Equine Influenza:


  • Fever

  • A harsh, dry cough of sudden onset that persists for two to three weeks or more

  • Clear nasal discharge progressing to thick, green-yellow discharge

  • Lethargy/depression

  • Loss of appetite




Implement good biosecurity practices, including quarantining newly arrived or traveling horses for at least 14 days. There are also vaccinations available that can be used before exposure.

Streptococcus equi (Strangles)


Strangles is characterized by abscessation of the lymphoid tissue of the upper respiratory tract. Streptococcus equi causes the disease, and is transmitted by direct contact with infected horses or subclinical shedders. It is also indirectly transmitted through water troughs, water hoses, feed bunks, pastures, stalls, trailers, tack, grooming equipment, nose wipe cloths or sponges, attendants’ hands and clothing, or insects contaminated with nasal discharge or pus draining from lymph nodes of infected horses.


Signs of Strangles:


  • Nasal discharge

  • Depression

  • Difficulty swallowing

  • Respiratory noise

  • Extended head and neck

  • Swollen lymph nodes


In a small percentage of cases, these abscesses spread to other parts of the body (a condition known as ‘bastard’ strangles) which is nearly always fatal. Due to it being so contagious, affected horses should be isolated and cared for by separate caretakers wearing protective clothing.




Vaccination is often the best preventive measure for Strangles.

Tetanus (Lockjaw)


Tetanus is caused by the bacterium Clostridium tetanii, which can be found in soil and manure. This bacteria is found in just about every environment and can survive for long periods of time. Wound contamination is generally what leads to infection; a clean wound is not as likely to result in tetanus. Tetanus proves deadly in 50-75% of cases.


Signs of Tetanus:


  • Muscular stiffness and spasms

  • Difficulty moving and eating

  • Tail often held straight out

  • Development of an anxious expression due to facial spasms

  • Sweating

  • In advanced cases, the horse will collapse with spasms, convulsions and death from respiratory failure.




Tetanus is a preventable disease, in which vaccination is key. Good first aid practices are also important, which include keeping wounds clean and ensuring your turn out areas are safe, clean, and clear of dangerous items that could cause injury.

Overall, prevention is key to keeping all of your equine friends safe, healthy and alive. You should always pay attention to your horse's behavior and other warning signs that may be displayed. As always, if any abnormalities occur, consult your veterinarian immediately for further guidance.


To learn more about these diseases and others alike visit:







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