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Case Description: A 7-year-old Quarter Horse gelding used for unsanctioned racing was examined because of fever and anorexia., Clinical Findings: Physical examination revealed fever, tachycardia, and tachypnea. Results of a CBC indicated anemia and mild thrombocytopenia. Results of microscopic examination of a blood smear indicated piroplasms in erythrocytes, consistent with Babesia spp. Regulatory authorities were contacted, and results of serologic testing at the National Veterinary Services Laboratories confirmed acute Babesia equi infection., Treatment and Outcome: Equids on the home premises of the index horse were placed under quarantine. Those equids were tested for piroplasmosis, and 6 of 63 horses had positive results for B equi. Another horse that had previously been housed on the index premises also had positive results for B equi. Competent tick vectors for piroplasmosis organisms were not identified. All 8 horses with piroplasmosis were Quarter Horses that participated in unsanctioned racing and were trained by the same person. Two of the horses were illegally removed from the index premises; these 2 horses and the other horse with piroplasmosis that was previously housed on the index premises could not be found. The other 5 horses with piroplasmosis were euthanized. Investigators concluded that transmission of B equi among horses was most likely iatrogenic., Clinical Relevance: The United States has been considered piroplasmosis free. However, veterinarians should consider piroplasmosis in horses with signalments and clinical signs similar to those of the index horse of this report. Regulatory authorities should be contacted regarding horses in which piroplasmosis is suspected.

Arthropod-borne apicomplexan pathogens that cause asymptomatic persistent infections present a significant challenge due to their life-long transmission potential. Although anti-microbials have been used to ameliorate acute disease in animals and humans, chemotherapeutic efficacy for apicomplexan pathogen elimination from a persistently infected host and removal of transmission risk is largely unconfirmed. The recent re-emergence of the apicomplexan Theileria equi in U.S. horses prompted testing whether imidocarb dipropionate was able to eliminate T. equi from naturally infected horses and remove transmission risk. Following imidocarb treatment, levels of T. equi declined from a mean of 10(4.9) organisms/ml of blood to undetectable by nested PCR in 24 of 25 naturally infected horses. Further, blood transfer from treated horses that became nested PCR negative failed to transmit to naïve splenectomized horses. Although these results were consistent with elimination of infection in 24 of 25 horses, T. equi-specific antibodies persisted in the majority of imidocarb treated horses. Imidocarb treatment was unsuccessful in one horse which remained infected as measured by nested PCR and retained the ability to infect a naïve recipient via intravenous blood transfer. However, a second round of treatment eliminated T. equi infection. These results support the utility of imidocarb chemotherapy for assistance in the control and eradication of this tick-borne pathogen. Successful imidocarb dipropionate treatment of persistently infected horses provides a tool to aid the global equine industry by removing transmission risk associated with infection and facilitating international movement of equids between endemic and non-endemic regions.

We report an outbreak of equine piroplasmosis in southern Texas, USA, in 2009. Infection prevalence reached 100% in some areas (292 infected horses). Amblyomma cajennense was the predominant tick and experimentally transmitted Theileria equi to an uninfected horse. We suggest that transmission by this tick species played a role in this outbreak.

Contagious equine metritis (CEM) is a highly contagious venereal disease of horses caused by Taylorella equigenitalis. During testing for semen export purposes, a stallion in Kentucky was found to be T. equigenitalis culture positive in December of 2008. This finding triggered an extensive regulatory investigation to search for additional positive horses, determine the extent of the outbreak, identify the potential source of the outbreak, and ultimately return the United States to CEM-free status. The investigation included over 1000 horses located in 48 states. Diagnostic testing found a total of 22 stallions, 1 gelding and 5 mares culture positive for T. equigenitalis. Epidemiologic analysis indicated that all of the positive horses were linked to a single common source, most likely a Fjord stallion imported into the United States in 2000. The T. equigenitalis strain subsequently spread to other stallions via undetermined indirect mechanisms at shared breeding facilities, and to mares via artificial insemination and live breeding. This CEM outbreak and investigation represent the largest ever in the United States based on the number of exposed horses tested and their geographic distribution., (Published by Elsevier B.V.)