INFECTIOUS DISEASES
tion with valacyclovir,” she said. “Seventeen horses with clinical disease received heparin metaphyactically, 2 at the onset of neurologic disease and 15 at the onset of fever. Of these 15 horses, 4 went on to develop EHM.” Only 4 horses with clinical signs of EHM did not receive heparin and were euthanized for the development of 5/5 ataxia. “When evaluating the population of horses that developed clinical signs, targeted treatment was significantly associated with a decreased incidence of EHM. The 4 horses that did not receive our targeted treatment did receive other treatments like anti-inflammatories and antioxidants. However, they did not receive valacyclovir and heparin, and they failed to survive,” Dr. Marchitello said. “So overall, the take-home message is that all horses that received valacyclovir and heparin survived and all horses that did not receive this targeted treatment were euthanized,” she said. Understanding how EHV-1 infection occurs can help explain how this combination could be effective for infected horses, according to Dr. Marchitello. The virus enters the respiratory tract, infects the lymph nodes and then moves to the bloodstream. In the case of EHM, the virus can then disseminate to the lining of the blood vessels of the central nervous system, causing damage to the spinal cord or brain.
Heparin blocks thrombin production, which can decrease the viral load; valacyclovir decreases viremia and nasal shedding, she explained. The study had several limitations, Dr. Marchitello admitted. “Because of the retrospective nature of this study, our referral hospital was introduced to these outbreaks at different times of infection. And it was also difficult to enforce a standard treatment protocol due to varying client compliance,” she said. In addition, financial constraints limited the number of horses that were tested, so they did not know the true prevalence of infection. “Lastly, our reliance on qualitative rather than quantitative PCR may have decreased our sensitivity in detecting EHV, especially in the horses that experienced fevers and may have been low shedders,” she said. She said a case-control study is needed to evaluate this treatment plan, as well as other therapeutics that could block viral fusion or endocytosis. These studies would be worthwhile, because EHV-1 is one of the most prevalent infections among U.S. horses. Equine herpesvirus is ubiquitous in horse populations with prevalence ranging from 60% to 80%. “So, for practical purposes, the veterinarian should presume that most horses are latently infected,” Dr. Marchitello said. MeV
New Treatment May Prevent Overprescribing of Antibiotics Researchers at Texas A&M University and the University of Georgia found that gallium maltolate (GaM), a semimetal compound with antimicrobial and anti-inflammatory properties, could be a viable alternative to overprescribed antibiotics for Rhodococcus equi pneumonia. Current methods to screen for R. equi are imprecise and many foals are given prophylactic antibiotics, such as the combination of a macrolide with rifampin (MaR), even though they would not have developed pneumonia. For the study, the team screened 57 foals from 4 farms in central Kentucky for subclinical pneumonia, then divided the foals into 3 equal groups. Two groups contained foals with subclinical pneumonia, meaning ultrasounds found lesions on their lungs but the foals had no clinical signs. The foals also all lived on farms with positive cases of R. equi pneumonia that year. Those groups were given either MaR or GaM for 2 weeks. The third group served as a control group and was made up of similar aged, healthy foals, which were monitored and not given any treatment. After 2 weeks, researchers analyzed fecal samples from each foal. DNA tests revealed that the MaR treated group had an increase in both the number and diver12
Issue 7/2020 | ModernEquineVet.com
sity of antibiotic-resistant genes in the bacteria. Most alarming was the discovery that the bacteria were resistant to multiple drugs and antibiotics. The GaM-treated and control groups showed no change in the number or diversity of resistance genes, a positive finding. The team also experimentally infected soil plots with resistant and nonresistant strains of R. equi to see how foals might contaminate their environment with their excrement that can contain unabsorbed and metabolized antibiotics. MaR tended to reduce the number of bacteria in a plot's soil but increase the proportion that were resistant. MeV The research was funded by Morris Animal Foundation.
For more information: Alvarex-Narvaez S, Berghause LI, Morris ERA, et al. A common practice of widespread antimicrobial use in horse production promotes multi-drug resistance. Scientific Reports. 2020 Jan 22 [epublished]. https://www.nature.com/articles/s41598-020-57479-9
