Prophylactic Efficacy of Equine Immunoglobulin F(ab')₂ Fragments Against Feline Parvovirus

Feline parvovirus (FPV), a type of parvovirus prevalent worldwide, can cause foetal death and acute enteritis in adult cats with severe leukopenia, and yet there are no effective drugs to prevent or treat FPV. Here, the immune effects of two FPV vaccines on horses were compared. IgG was extracted from FPV-immunized horse sera. Equine F(ab')₂ fragments were obtained from pepsin-digested IgG and then purified by protein-G column chromatography. The results showed that the inactivated FPV oil vaccine was more effective than the inactivated FPV propolis vaccine in helping healthy horses to produce hyper-immune serum. Four methods were tested, among which the optimized octanoic acid-ammonium sulphate precipitation method was proved to be the best process for extracting IgG. The optimal condition for preparing F(ab')₂ by pepsin digestion was 30 °C for 3.5 h, and the content, purity and recovery of F(ab')₂ were 8.64 mg/mL, 90.36% and 93.24%, respectively. Our equine immunoglobulin F(ab')₂ fragments effectively neutralized activity in vitro against FPV, alleviated the clinical symptoms of FPV-infected cats, reduced the viral loads in the intestine and had prophylactic effects in FPV-infected cats. These results indicate that the F(ab')₂ fragment prepared from inactivated FPV-immunized horses may be used as a prophylactic agent for diseases caused by FPV.