The term equine piroplasmosis is used to refer to infection with 1 or both of the blood parasites Theileria equi (T. equi) and Babesia caballi (B. caballi). Equine piroplasmosis is a tick-transmitted disease affecting all equine species, such as horses, mules, donkeys and zebras.
Equine piroplasmosis and the risk to human health
Infected equines pose no risk to humans.
While the infective agents of equine piroplasmosis are not known to cause disease in humans, the ticks that transmit these parasites could have the ability to transmit other diseases as well. Human piroplasmosis is uncommon and is associated with different strains of Babesia.
Clinical signs of equine piroplasmosis
The clinical signs of equine piroplasmosis vary and are often non‑specific; the disease can easily be confused with other conditions. Equine piroplasmosis can occur in several different forms:
- peracute: animals may be found dead with no previous sign of being sick
- acute: the acute form is characterized by fever, loss of appetite, sudden onset of immobility and reluctance to move, as well as severe lethargy
- the fever may subside after 1 day and become intermittent
- other signs include anemia, jaundice, peripheral edema and an enlarged spleen and liver
- severe cases can result in death
- sub-acute: clinical signs in sub-acute cases are similar to acute cases and may be milder and accompanied by intermittent fever and weight loss
- chronic: chronic cases usually present non-specific clinical signs such as mild loss of appetite, poor performance and loss of body weight, though symptoms may be more severe in younger animals
- concurrent illness or other forms of physical stress can result in return of clinical signs
- persistent infections of mares may cause abortions
- foals can become infected before birth, resulting in either weak, anemic foals or inapparent carrier foals
- inapparent carrier: a large proportion of infected equines are inapparent carriers of the disease
- these equines show no apparent signs of infection but act as a reservoir for disease, allowing it to be spread to other equines
- inapparent carriers may become clinically sick when they are stressed or after the administration of immunosuppressive medications
Where equine piroplasmosis is found
Equine piroplasmosis has never been found in a Canadian horse; however, potential tick vectors do exist in Canada. Equine piroplasmosis is found in parts of Europe, Africa, South and Central America, the Middle East and Asia. The U.S. has reported sporadic outbreaks in the past few years.
How equine piroplasmosis is transmitted and spread
Equine piroplasmosis is not directly contagious. The feeding activity of ticks transfers the blood parasites from an infected equine to other susceptible equines. Ticks are the main vector of transmission as they are a natural host for the parasites. Use of contaminated blood products, needles and syringes can also transmit the disease. Foals can become infected while in the uterus, particularly with T. equi.
Some equines can carry the parasite in their blood for a long time and can act as sources of infection for ticks. Introduction of these inapparent carrier animals into disease-free areas can lead to new cases of piroplasmosis if ticks are present.
As infection risk is related to the presence of ticks, infections can be seasonal and are more likely to occur after peaks in the tick population.
The main risk factor for introducing equine piroplasmosis into Canada is through importing infected animals.
How equine piroplasmosis is diagnosed
A veterinarian may suspect piroplasmosis in equines with a history of travel that have anemia, yellowing of the gums or eyes, or fever. Laboratory tests are necessary for a definitive diagnosis.
How equine piroplasmosis is treated
Piroplasmosis can be difficult to treat. At this time, Canada does not have an approved treatment program for piroplasmosis, nor is there a vaccine to prevent an equine from becoming infected. Positive equines remain a reservoir of infection for other equines. The Canadian Food Inspection Agency (CFIA) controls piroplasmosis by the requirement to report suspect cases to the CFIA, identification and destruction of infected animals, compliance with established import testing requirements and efforts to prevent the spread of the parasites by controlling tick vectors.
A CFIA-approved treatment program for piroplasmosis is under consideration. Treatment programs used in other countries tend to take a long time, are costly and the medications used may cause the equine to become ill. Side effects include colic, diarrhea and, rarely, death.
Regulations to prevent transmission of equine piroplasmosis
The CFIA places strict regulations on the import of animals and animal products from countries where equine piroplasmosis is known to occur. These regulations are enforced through port-of-entry inspections done by both the CFIA and the Canada Border Services Agency (CBSA).
Equine piroplasmosis is a reportable disease under the Health of Animals Act. Owners, veterinarians and anyone having care and control of animals must report all suspected cases to the CFIA for immediate investigation by inspectors.
Equine owners can take the following precautions to reduce the risk of infection:
- use strict hygiene practices when vaccinating or collecting blood samples from equines
- use disposable needles and syringes, and do not use the same needle on more than 1 equine
- implement tick-control measures
- test equines if they are showing clinical signs of disease
- consult your veterinarian if you suspect your equine may be infected with piroplasmosis
Canada's emergency response strategy to an outbreak
Disease control methods for equine piroplasmosis
Canada's emergency response strategy to an outbreak of equine piroplasmosis would be as follows:
- eliminate the disease
- take action to ensure that Canada is once again absent of piroplasmosis as quickly as possible
In an effort to eliminate equine piroplasmosis, the CFIA may use some or all of the following disease control methods:
- humane euthanasia of infected animals (currently no CFIA‑approved treatment protocol)
- surveillance and tracing of potentially infected or exposed animals
- strict quarantine and animal movement controls to prevent spread
- zoning to define infected and disease-free areas
An owner whose animal is ordered euthanized may be eligible for compensation.