Equine Health Update Issue 2 Volume 19 - Page 16

EQUINE | Equine Disease Update the University of California (UC), Davis, School of Veteri- nary Medicine, reviewed data collected on 1,414 foals 14 days of age or younger at the university’s Veterinary Medical Teaching Hospital. One hundred thirty-three (9.4%) of those foals were diagnosed with thrombocy- topenia (platelet counts <100,000/ microliter of blood). Only 64.7% of foals with thrombocytopenia survived, whereas 86.1% of the control foals (those not diagnosed with thrombocytopenia) survived. “Despite the overall decreased survival rate within the thrombocytopenia population, the outcome was not as- sociated with the severity of thrombocytopenia,” Swain said. “This is important because foals with the lowest platelet counts were actually associated with a good prognosis relative to the other groups. This appears counterintuitive, but these foals that had dramatically low platelet counts were less affected by sepsis (the body’s inflammatory response to infection) compared to the other groups and more affected by a condition called alloimmune thrombocytopenia, which can be managed with treatment.” Foals with thrombocytope- nia suffered from a number of conditions, including sep- ticemia (bacteria in the blood that causes sepsis), gas- trointestinal disease, equine herpesvirus- 1, and Tyzzer’s disease. The researchers suspected alloimmune destruc- tion of the platelets in 9.8% of the 133 thrombocytope- nic foals. “These findings are important as a clinician, because a foal can appear markedly critical if it is unable to clot its blood normally, but if a diagnosis can be reached, even the most severely affected foals may be treated success- fully,” Swain said, adding that veterinarians can test for thrombocytopenia using routine bloodwork. The Go-To Drug Combo for Septic Foals In a world of increasing pathogen resistance to antibi- otics, many veterinarians and owners worry when faced with a sick horse, especially a delicate neonate. Will the 16 medications that once worked to save a sick foal still be effective? Researchers at UC Davis recently tested the efficacy of antibiotics frequently used to treat septic neonatal foals. Sepsis is a rapidly progressive disease that requires im- mediate antimicrobial therapy in foals, said David Wil- son, BVMS, MS, Hon Dipl. ACVIM, who presented the group’s study results on behalf of Mathijs Theelen, DVM, Dipl. ECEIM. In most cases, the exact bacteria aren’t known when treatment begins. The vet administers antibiotics empirically, selecting one or more based on the most likely cause of infection until culture results are back, which usually takes several days. Common antimicrobials used empirically either alone or in various combinations in septic foals include: ami- kacin, penicillin, ampicillin, gentamicin, ceftiofur and related drugs, chloramphenicol, and trimethoprim/sul- famethoxazole. To determine if these drugs were still good choices for this use, the team isolated bacteria from 213 septic foals brought to the hospital and tested their drug sensitivity. The team found that an amikacin and ampicillin combo was one of the most effective for empirical treatment of septic foals less than 30 days old. Bacteria in 91.5% of the foals were susceptible to it. Most of the other combinations were also effective, with susceptibilities between 80 and 90%. Trimethoprim/ sulfamethoxazole and gentamicin alone were the least effective, with susceptibilities of only 59.6% and 62%, respectively. “The combination of amikacin and ampicillin remains an excellent choice for empirical treatment of septic foals, assuming normal renal (kidney) function and while awaiting bacteriological culture and susceptibility re- sults,” said Wilson. • Equine Health Update •