![]() equi into non-endemic regions, the World Organization for Animal Health (OIE) and U.S. With over 9.2 million horses in the U.S., a widespread outbreak could have a large financial impact on the $39 billion horse industry. A large outbreak in Texas caused alarm when positive horses from 16 states were epidemiologically traced back to a single source ranch. These are most likely the outcome of importing asymptomatic horses that produced negative results during mandatory screening procedures. in California, Colorado, Florida, Georgia, Oklahoma and Texas. equi infection have been identified in the U.S. was thought to be free of EP since 1988 as the result of a twelve million dollar, 25 year-long eradication campaign that began in 1962. Although this parasite is less prevalent in countries such as the U.S., Australia, England and Canada, even with transport regulations there is a potential for spread from infected horses or ticks from endemic regions. equi the infection can cause a range of disease symptoms up to and including death. Thus, asymptomatic persistently infected carriers can serve as reservoirs of infection, which is one of the challenges for controlling the spread of this parasite. equi can still occur either iatrogenically, or when competent tick vectors feed on these horses. ![]() Although asymptomatic horses have low parasitemia, transmission of T. However, infections can be detected by serology and PCR. Due to the low parasitemia that is characteristic of a persistent infection the parasite is not detectable by microscopic examination of blood smears. If the horse overcomes the acute infection it will typically carry a life-long persistent infection that is usually asymptomatic. Once a horse becomes infected, the parasite undergoes asexual reproduction within erythrocytes high parasitemia is found during this acute phase of infection. In fact, iatrogenic transmission is thought to have been the primary mode of transmission in an outbreak in Florida, U.S., in 2008. equi has the potential to be transmitted iatrogenically. equi can be naturally transmitted by ticks of the family Ixodidae and, in addition to this biological route, T. equi is an obligate intracellular parasite that requires a tick host for sexual reproduction and an equine host for asexual reproduction during a haploid phase. The apicomplexan protozoan Theileria equi (also known as Babesia equi) causes equine piroplasmosis (EP) and is a growing threat to the horse industry. equi outbreaks and may help prevent the spread of this tick-borne parasite. When applied to a broader cross section of worldwide samples, these molecular tools should improve source tracking of T. ![]() equi into one monophyletic clade by 18S is suggestive of a limited source of introduction into the U.S. Single-clone infections were found in 27 of the 37 samples (73%), allowing us to identify 15 unique genotypes. ![]() Using Weir and Cockerham’s F ST estimator ( θ) we found strong population differentiation of the Texas and Georgia subpopulations ( θ = 0.414), which was supported by a neighbor-joining tree created with predominant single haplotypes. The field samples were mostly from a 2009 Texas outbreak ( n = 22) although samples from five other states were also included in this study. using microsatellite markers and found a moderate amount of genetic diversity (2–8 alleles per locus). This sample was collected at the Texas border, but may have originated in Mexico. The remaining sample fell into a second clade that was genetically divergent (48 SNPs) from the other U.S. equi, with just 0–2 single nucleotide polymorphisms (SNPs) among samples. The first clade ( n = 36) revealed a high degree of nucleotide similarity in U.S. ResultsĪ maximum parsimony analysis of 18S rRNA sequences grouped the samples into two major clades. We developed a DNA fingerprinting panel of 18 microsatellite markers using the first complete genome sequence of T. equi using the 18S rRNA gene and microsatellites. We used samples from 37 horses to determine genetic relationships among North American T. This parasite has a worldwide distribution but the United States was considered to be free of this disease until recently. Theileria equi is a tick-borne apicomplexan hemoparasite that causes equine piroplasmosis.
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