1a.Objectives (from AD-416):
The pestivirus genus, within the flavivirus family, includes economically important animal pathogens, such as the bovine viral diarrhea viruses (BVDV) and classical swine fever virus. The HoBi-like viruses are an emerging pestivirus species that have been isolated from cattle or cattle-derived products originating in South America and Southeast Asia. Like the bovine viral diarrhea viruses, HoBi-like viruses can establish persistent infection in cattle and have been isolated from commercial fetal calf serum. Based on phylogenetic and antigenic differences it is probable that diagnostics and vaccines designed to detect and prevent infection with the bovine viral diarrhea species, BVDV1 and BVDV2, will not be effective against HoBi-like viruses. Consequently, introduction of HoBi-like viruses into new geographic regions would have serious consequences for BVDV control programs. The overarching objective of this collaboration is to determine the prevalence of HoBi-like viruses in U.S. and Brazilian domestic cattle herds. To do this it will be necessary to develop surveillance tools that differentiate between exposure to bovine viral diarrhea viruses and exposure to HoBi-like viruses. The goals of this SCA are to design, develop and test such surveillance tools and to use these tools to establish the prevalence of HoBi-like viruses in Brazilian and U.S. cattle.
1b.Approach (from AD-416):
In a previous study we generated polyclonal antibodies against several pestivirus species including BVDV1, BVDV2, and classical swine fever virus. Based on cross neutralization studies it was possible to differentiate the serum antibody response raised against different pestivirus species. In the initial phase of this collaboration we will generate polyclonal antibodies against a HoBi-like virus strain and compare the ability of this serum to bind viruses from other pestivirus species. If we can differentiate antibodies raised against HoBi-like viruses from antibodies raised against BVDV1 and BVDV2, the next step will be to develop assays based on this observation that can be used in the field. The generation of polyclonal antisera and development of the differential serum antibody test will be conducted at the NADC. A graduate student from the Federal University of Santa Maria will spend a six-month sabbatical at the NADC to assist in this research. The next step will be to use the test to survey Brazilian and U.S. cattle sera. Surveillance testing will be done both at the NADC and at the Federal University of Santa Maria. If the serum survey indicates that animals in Brazil or the U.S. have significant exposure to HoBi-like strains we will develop a test that can be used to screen for animals persistently infected with HoBi. Development of this test will be a joint effort between the NADC and the Federal University of Santa Maria. Any HoBi-like virus isolated from field cases in the course of these studies will be characterized and sequenced.
Two tests have been developed for the detection of current infections with HoBi-like viruses and detection of exposure of an animal to HoBi-like viruses in the past. The test for detection of current infections is based on the detection of viral genes in infected cells and is referred as a polymerase chain reaction based test or a PCR test. The test for exposure to HoBi-like viruses in the past is based on detection of antibodies in blood serum and is referred to as a viral neutralization (VN) test. HoBi-like viruses can cause two different kinds of infection, acute (which lasts for about 2 weeks) and persistent (which is a life long infection). Most of the work this year was validating the VN test using sera from acutely infected animals and validating the PCR based test using samples from persistently infected animals. Both tests performed well in the laboratory. The plan for next year is to use these tests to conduct surveys in Brazil.