Shelbi Green
Bio 1615
Tuesday 10:00-1:00PM
Equine Piroplasmoses at the Reintroduction Site of the Przewalski’s Horse in Mongolia
During the 1960’s the Przewalski horse become extinct to the wild. Soon after becoming extinct
to the wild they were reintroduced to the wild by the Przewalski horses that were keep in captivity.
Reports and samples were being kept on these horses to see if they could readapt to their native land in
Mongolia. Early on these studies showed the Morality rate were increasing, this increasing morality rate
were believed to be caused by a disease called Equine Piroplasmosis. There are two types of
Piroplasms; one being Babesia caballi and the seconds being Theileria equi.
Two studies were preformed on both the wild Przewalski horse and the domestic horse. Studies
were done on both domestic and the wild horses to see if Equine Piroplasmosis was common in both of
the two populations. The two studies preformed were Cross-sectional study and a longitudinal study.
The Cross-sectional study had blood and blood smear samples from 141 domestic horses and
only 23 wild Przewalski horses. These samples were gathered over a two year period. They then used
chi-square tests to determine which horses had antibodies and Piroplasms depending on their gender
and date groups. The horses were sampled in seven equal time intervals over the course of 18 days. To
make this study more accurate they split up the population of horses into five groups according to age.
The Przewalski horse also had the same test performed on its herd.
The Longitudinal study gathered samples from yearlings from a herd of 250 domestic animals.
They gathered samples over a nineteen day period. To see if the yearlings had antibodies and
Piroplasms present they compared with the chi-sample test during the six and four sampling days.
To compare both the domestic horse herd with the wild Przewalski’s herd they used the exposure of
time standard prevalence ratio (SPR)
Shelbi Green
Bio 1615
Tuesday 10:00-1:00PM
For the results of the Cross sectional study only 134 samples out of the 141 samples from the
horses were able to be used because some of the samples did not have a blood smear. In nine out of
the 134 blood smear slides only nine turned out positive for Piroplasms. Seven out of the 134 had the
Theileria equi parasite and three out of the 134 horses had the Babesia caballi parasite. Only one of the
horses had both of the parasites. The age and gender between the horses never seemed to be a factor
in who had the disease or parasites. Although age and gender did not play a role in which horses had
the disease or not, age did have a big impact of the antibodies. Younger horses had up to 40.6%-62.5%
of antibodies being present unlike the older horses which had higher percentages to antibodies; 85.3%96.3%.
The results for the longitudinal study were not as clear as the cross sectional study because they
did not sample the same horses every day. In seven of the yearlings that they did sample had
Piroplasms. Ten of the yearlings had the Theileria equi parasite, and eight yearlings tested positive for
the Babesia caballi parasite.
A study preformed in Takhin Tal. Showed that 90% of adult horses had antibodies against the
Piroplasms and both of the parasites, the foals at birth had 100% antibodies against this disease which is
not the case for the studies they have just completed in Mongolia. For the most recent study performed
by the scientists in Mongolia showed that 9 out of 13 foals had the Theileria equi parasite and only one
of those foals created antibodies against it. Even thought lots of foals were affected they still had a
lower rate on getting the disease then the adult horses. Overall the Przewalski wild horses have a much
lower rate on creating antibodies against the Piroplasms and both of the parasites. To understand why
these wild horses immune response is slower than the domestic horse more tests would need to be
done, which was not able to happen in this study. Scientists also are starting to change their hypothesis
due to the fact that the results were not what they were hoping for. The results that they found due to
Shelbi Green
Bio 1615
Tuesday 10:00-1:00PM
their studies does not give a clear answer to if these parasites are a factor to the high mortality rate on
these newly introduced wild Przewalski horse. This is why the study is still considered not to be one
hundred percent complete, but with future studies they might be able to find more information on why
these wild horses are dying and hopefully able to keep the breed alive