| Respiratory Infections the Mini Horse
Strangles is a bacterial infection which can spread if other horses
come in contact with an infected horse's nasal discharge or material
draining from abscesses.
viral respiratory infection.
thick, yellow pus to drain from the
nose as seen in horse on the right.
Bacterial infections can be
secondary to a viral infection or it
can be the primary cause of the
Miniature horses are hardy but they can experience contagious respiratory diseases.
We will show you how to identify the signs and symptoms of infection, when to call for
the veterinarian, and what you can do to prevent infection in your mini horse.
The most commonly encountered equine respiratory viruses include: equine influenza viruses,
equine herpesviruses and equine arteritis virus.
It is often impossible to differentiate viral respiratory diseases and whether a miniature horse
has a disease caused by equine influenza, equine herpesvirus, and Streptococcus equi var. equi
based on the symptoms alone. Blood testing can be important to differentiate the disease involved.
A common feature of all viruses is their ability to cause outbreaks of disease as a result of their
Despite this contagious element, clinical cases may appear in either individual animals or as
outbreaks in large populations of animals, depending on the specific virus, the individual mini horse’
s immunity or the level of immunity within the entire herd. Importantly, how the animals are
managed may determine if exposure to a virus will actually infect a miniature horse. The individual’
s state of health, vaccination level and environmental conditions, such as a comfortable, healthy
barn and proper nutrition is believed to determine if a mini actually contracts the infection he has
been exposed to.
Rhinopneumonitis is the name for the Equine Herpesvirus which casues an upper respiratory illness
in young miniature horses and those under stress, such as moving to a new home or the stress of
the show ring. A mini horse will have a fever and nasal discharge which occurs 3 to 7 days following
exposure to the virus. This virus can also cause abortion in a pregnant mini or death in a young foal.
It is usually diagnosed based on the symptoms seen in the miniature horse, but blood tests can
confirm the virus involved in the illness.
Secondary bacterial infections can develop secondary to a respiratory infection caused by a virus,
which causes nasal discharge with pus, prolonged fever, and breathing problems leading to
pneumonia. Antibiotics can cure the bacterial secondary infection, while supportive care will assist
the mini horse as he recovers from the viral infection.
EQUINE INFLUENZA VIRUS
The most common respiratory viral infection in horses is the equine influenza virus (EIV), while
the most important viral respiratory infection is Equine herpesvirus type 1 (EHV-1), a member of
the Varicellovirus genus and it is an important pathogen of horses worldwide. Infection with EHV-1
may result in rhinopneumonitis, abortion in pregnant mares, and fatal myeloencephalopathy,
Equine influenza virus is the most common virus in a horses respiratory tract, but it is not as
serious as the equine herpesviruses. Equine influenza originally emerged in Miami, Florida in 1963,
and subsequently spread to all horses including miniature horse populations around the world.
EQUINE BACTERIAL RESPIRATORY DISEASES
Streptococci are the most important respiratory bacterial pathogens of the horse and are the
major etiological agents, either as single infections or mixed infections with other pathogens, of
all four of the major equine bacterial respiratory syndromes:
● strangles is the most common
● bronchopneumonia in foals up to 6–8 months old
● inflammatory airway disease
● pneumonia/pleuropneumonia in mature horses.
There are four principal equine streptococci:
● Streptococcus equi subsp. equi
● Streptococcus equi subsp. zooepidemicus
● Streptococcus dysgalactiae subsp. equisimilis
● Streptococcus pneumoniae.
Symptoms you will see in equine streptococci infection:
Abscesses initially develop in the lymph nodes draining the head. This horse has a draining
submandibular lymph node abscess. Abscesses can also develop in the parotid and retropharyngeal
Streptococcus equi infection can result in large, non-ruptured retropharyngeal lymph nodes may
compress the nasopharynx and trachea causing dyspnea. This radiograph shows ventral deviation of
the trachea by a large retropharyngeal lymph node abscess.
Characteristics of Streptococcus equi
Opportunist pathogens of the respiratory tract
Cause both mucosal respiratory infections and invasive systemic disease
S. equi subsp. equi can infect only equine
S. equi subsp. zooepidemicus; S. pneumonia can also infect a variety of animal species and humans
Variably transient immunity following natural infection
Treatment of Streptococcus equi infection is attained with antibiotics and supportive care
Strangles is a bacterial infection which can spread if other horses come in contact with an
infected horse's nasal discharge or material draining from abscesses. A secondary infection caused
by a bacteria can occur in following a viral respiratory infection.
A bacterial infection will cause thick, yellow pus to drain from the nose as seen in horse on the
right. Bacterial infections can be secondary to a viral infection or it can be the primary cause of
Frankeny, R. L. Miniature Horses: A Veterinary Guide for Owners and Breeders. 2003.
Rush, B. Equine Respiratory Diseases. 2004.
Ramey, D. Concise Guide to Respiratory Disease in the Horse. 2004.