PREVALENCE AND CHARACTERIZATION OF NEW WORLD HOBI-LIKE VIRUSES
2011 Annual Report
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.
This project will generate information regarding the impact of pestivirus variants on bovine viral diarrhea virus (BVDV) surveillance programs as it relates to objective 1 of the inhouse project. ARS researchers in Ames, IA, in collaboration with researchers from the Federal University of Santa Maria compared the proteins produced by BVDV to those produced by HoBi-like viruses. The proteins are similar enough that some diagnostic tests designed to detect BVDV may also detect HoBi-like viruses. However, they are different enough that tests designed to detect exposure to BVDV or vaccines designed to prevent infection with BVDV will not reliably detect exposure or prevent infection with HoBi-like strains. These findings are important because they indicate that HoBi-like viruses in tissues may be misdiagnosed as BVDV and that current surveillance and protection tools in use for BVDV control will not work for HoBi-like viruses. This means that new diagnostic tests, surveillance tools, and vaccines must be designed for the control of HoBi-like viruses. A manuscript detailing these studies will be submitted to a peer-reviewed journal and an abstract will be submitted to the upcoming BVDV symposium. Progress was monitored by two conference calls and emails.