What You Should Know About Equine Piroplasmosis

Equine piroplasmosis is a devastating disease deserving of vigilance by our regulatory agencies. If the vector responsible for transmission is in our environment, authorities will need to be aware of this so that steps can be taken to control the disease by eliminating this vector, as Florida and California did in the 1960s.  This disease can be devastating with a high mortality rate.  

Only certain ticks are known to be able to transmit this disease and these ticks have been considered eradicated from the USA.  Regular testing of ticks must be made to ensure that they cannot transmit this disease.  Positive horses whose source of infection was outside of the USA must be identified so that regulatory agencies will be able to establish that the disease is not re-emerging in our environment, and so that horses entering the USA will not bring the disease organism with them as a potential source of infection.

Horses coming from any country where piroplasmosis is endemic are tested upon entry into the USA at import facilities but a test is considered negative even when the result may show that the horse has a piroplasmosis titer, as long as that titer is below the threshold established by our federal guidelines.  Factors such as stress, exercise, and immune suppressant medications can temporarily and artificially reduce a horse's piroplasmosis titer. This is why it is important during the pre purchase process potential buyers test not only for piroplasmosis, but for immune suppressant medications such as Dexamethazone (Azium) as they normally would in general drug screening prior to purchase.

The reason the test is deemed "negative" by officials even in the presence of a weakly positive test is that horses can have some antibody production just from being in the environment where the disease is present, without ever having the infection.  It comes from general exposure and these horses cannot transmit the disease because they only have antibodies and not the disease organism itself.

In anticipation of the growing list of states and equestrian associations that will require proof of a negative test, horsemen may choose to have any horse tested prior to purchase, especially if they originated in a piroplasmosis endemic country, or from an area with a local outbreak in the USA, regardless of prior testing history.

It is reasonable to expect that a negative piroplasmosis test will be required in the coming years by many states and equine sports associations, in the same manner as we currently require proof of negative Coggins.  For example the Alltech/FEI World Equestrian Games, Kentucky 2010 required proof of negative piroplasmosis test for all horses entering the competition grounds including horses from the USA.

The USA is on a short list of countries where equine piroplasmosis has been deemed "eradicated", with no local source for new infections in horses. However, s of 2011 at least 409 horses, in multiple states have tested positive for equine piroplasmosis.  One source of infection was traced to horses that had illegally entered the USA from Mexico without screening at a federal animal disease inspection and testing import station.  Other horses' infection was traced to sharing of needles or other mechanical transmission directly from these illegally imported horses.  Another source in question involved a ranch in Texas where local ticks may have been the cause of that disease outbreak.

As a direct result of these recent equine piroplasmosis positive cases, several states, Canada, and several racing jurisdictions now require proof of a negative piroplasmosis test to enter the state, or race track.

General info on the disease


This is of local importance since it reports that FL racetracks are requiring a negative test based on recommendation of FL Dept of AG:

KY same thing-

The outbreak in TX with 409 horses-

Horsemen want more info on this topic-

Fact Sheet

This scientific paper was written by the head researcher/expert in the world on equine piroplasmosis. Essentially it explains that the C Elisa test is more reliable than a test that was used by our import stations prior to 2005 called the CF test.  Therefore, horses imported before 2005 could have easily had a false negative test. But both tests are vulnerable to error if immune suppressant drugs are present in the horse at the time of the test.

This paper mentions false negative tests resulting from either a horse exercising a lot or by medication. Essentially the physiology of stress supresses antibody levels and can cause false negatives.

This from an NIH paper
Diagnosis of equine piroplasmosis in Brazil by serodiagnostic methods with recombinant antigens.
Xuan X, Nagai A, Battsetseg B, Fukumoto S, Makala LH, Inoue N, Igarashi I, Mikami T, Fujisaki K.
National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan.

Serum samples from horses in the States of Sao Paulo and Mato Grosso do Sul, Brazil were examined for diagnosis of equine piroplasmosis by both the latex agglutination test (LAT) and enzyme-linked immunosorbent assay (ELISA) with recombinant antigens. Of the 47 samples analyzed, 38 (81%) and 42 (90%) samples were positive for B. equi infection and B. caballi infection, respectively. In addition, 35 (75%) samples were positive for both B. equi and B. caballi infections. These results indicate that equine piroplasmosis is widespread and therefore a cause for serious concern in the States of Sao Paulo and Mato Grosso do Sul, Brazil.