Prevention of Rhodococcus equi pneumonia of foals using two different inactivated vaccines
Veterinary Microbiology vol, 56 (1997) pages 205-212
reprinted with permission of Elsevier Science
J. Varga, L. Fodor, M. Rusvai, I. Soos, L. Makrai
Abstract
Two different, inactivated, aluminum salt absorbed vaccines, one containing a R. equi strain (serotype 1, 109 CFU / ml and equine herpesvirus 2 (EHV-2) (1.5 x 107 /ml) and another containing R. equi only were used on three studfarms to determine whether the disease can be prevented by vaccination of both pregnant mares and their foals. Pregnant mares received two 3 ml doses of vaccine intramuscularly 6 and 2 weeks of age. The efficacy of the vaccines was evaluated on the basis of the clinical signs, serlogical response ( indirect haemagglutination and virus neutralisation tests ) and culture of R. equi from sick or dead foals. On studs A and B where the bivalent vaccine was used, 24 and 14 foals were born respectively to the vaccinated mares but no clinical case or death occurred due to R. equi pneumonia, while out of the 10 nonvaccinated control foals (stud B) two succombed to R. equi pneumonia and four other foals had to be treated with antibiotics because of fever, coughing, and dyspnea. In stud C, where the vaccine containing R. equi strain alone was use, all 15 vaccinated foals remained healthy but one of the 11 control foals died of suppurative R. equi pneumonia and one foals had to be treated due to R. equi pneumonia. R. equi strains (serotype 1) were isolated from the lungs of all dead foals. The serological response was very weak to both R. equi and the EHV -2 strain. Antibody titres in the colostrum of the vaccinated mares against R. equi (in studs A and B, geometric mean 3.79 + 1.63 and 4.14 + 1.46, respectfully) were practically not higher than titres in the controls (in stud B geometric mean 2.12 + 1.96). More antibody was present in the colostrum samples against EHV-2 (geometric mean 6.1 + 1.4 compared to 2.5 + 1.2). In all foals antibody levels were hardly detectable against both R. equi and EHV-2 until five weeks of age. From the fifth week, antibody levels gradually increase and by the ninth seek their reached a titter of 5.5 + 1.8 (2.7 + in the control foals) against R.equi and 5.2 + 1.4 against EHV-2. The favorable clinical results and the low antibody titters in the sera of the vaccinated foals during the first week of life suggest that protection probable was due to repeated vaccination of young foals rather than to vaccination of mares. @ Elsevier Sciencs B.V.
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