Evaluation of cross-protection between O1 Manisa and O1 Campos in cattle vaccinated with foot-and-mouth disease virus vaccine incorporating different payloads of inactivated O1 Manisa antigen

Serology is used to predict vaccine induced protection against challenge with a heterologous strain of the same serotype of foot-and-mouth disease virus (FMDV). To evaluate the accuracy of such predictions, we compared the protection afforded to cattle vaccinated with the O-1 Manisa strain of FMDV against challenge with either a homologous (O-1 Manisa) or a heterologous strain (O-1 Campos). Serology by virus neutralization test (VNT) using O-1 Manisa antiserum predicted an acceptable protection against such a challenge. Two experiments were carried out to compare the results for consistency. A total of 78 nave cattle were vaccinated with different antigen payloads (60-0.94 mu g) of O-1 Manisa. They were challenged by intradermolingual inoculation with live FMDV, either O-1 Manisa or O-1 Campos. Unvaccinated nave control cattle (n=20) were also challenged with either the O-1 Manisa or O-1 Campos viruses and all developed generalized FMD. The protection results for the vaccinated cattle revealed that higher payloads of O-1 Manisa vaccine were needed to protect against heterologous challenge compared to that for homologous challenge. The 50% protective dose (PD50) values for the vaccine in experiments 1 and 2 were found to be 28.78 and 9.44 for the homologous challenge and 3.98 and 5.01 for heterologous challenge. Furthermore, protection against O-1 Campos required a higher level of vaccine-induced antibody against this virus compared to the level of O-1 Manisa neutralizing antibody associated with protection against homologous challenge. The 50% protective level of in vitro neutralizing antibody was found to be log(10) 1.827 for O-1 Campos and log(10) 0.954 for O-1 Manisa based on O-1 Manisa based virus neutralization test. (C) 2011 Elsevier Ltd. All rights reserved.