Efficacy of a commercially available hyperimmune plasma product for the prevention of naturally acquired Rhodococcus equi pneumonia in foals

Steeve Giguere, DMV, PhD, DACVIM; Jack Gaskin, DVM, PhD, DACVM; Corey Miller, DVM, MS, DACT; James L. Bowman, DVM

From the Departments of Large Animal Clinical Sciences (Giguere) and Pathobiology (Gaskin), College of Veterinary Medicine, University of Florida, Gainesville, FL 32610; Ocala Equine Medical Center, 5640 SW 6th Place, Unit 800, Ocala, FL 34474 (Miller); and Lake Immunogenics Inc., 348 Berg Rd., Ontario, NY 14519 (Bowman).

Objective- To determine the efficacy of a commercially available hyperimmune plasma product for the prevention of naturally acquired Rhodococcus equi pneumonia in foals. The product is categorized as Rhodococcus Equi Antibody by the USDA and is commercially available under that product name (Lake Immunogenics Inc.).

Animals- 165 Thoroughbred foals on a farm with enzootic R. equi infections.

Procedure- Foals were randomly assigned to two treatment groups (hyperimmune plasma or non-treated controls) prior to birth. Foals diagnosed with failure of passive transfer of immunity were treated with hyperimmune plasma and considered in a separate group. Transfused foals were given two 950 ml doses of hyperimmune plasma by rapid intravenous infusion. The first dose was given between 1 and 10 days of age, and the second dose was given between 30 and 50 days of age. Foals were monitored daily for clinical signs of illness. Blood samples were also obtained periodically from each foal for white blood cell counts and measurement of fibrinogen concentrations. A tracheobronchial aspirate for bacterial culture was performed on every foal with clinical signs of lower respiratory tract disease or hematological evidence of infection.

Results- The incidence of R. equi pneumonia in foals without failure of passive transfer of immunity was significantly lower in foals transfused with hyperimmune plasma (19.1 %) than in non-treated controls (30 %) (P = 0.09). Despite receiving hyperimmune plasma, the incidence of R. equi pneumonia in foals with failure of passive transfer of immunity (35.7 %) was higher than that of transfused foals without failure of passive transfer of immunity. The incidence of undifferentiated pneumonia (all causes) was not significantly different between groups of foals.