Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2011
Publication Date: June 20, 2011
Citation: Neill, J.D., Newcomer, B.W., Marley, S.D., Ridpath, J.F., Givens, M.D. 2011. Genetic change in the open reading frame of bovine viral diarrhea virus is introduced more rapidly during the establishment of a single persistent infection than by multiple acute infections. Virus Research. 158(1-2):140-145. Interpretive Summary: Bovine viral diarrhea virus (BVDV) is a ubiquitous viral pathogen of cattle worldwide. It spreads readily between animals and between herds. Additionally, BVDV can infect pregnant cattle that can result in the birth of a calf that is persistently infected and spreads the virus for life. There is a great amount of sequence differences between strains of BVDV found in livestock herds and it is not known what really drives changes to occur. We sequenced the genomic RNA of 6 viruses causing severe acute (SA) disease that were earlier shown to be a single strain 9 viruses that were isolated from persistently infected calves to compare which introduced the greater number of changes. The 6 SA viruses showed low levels of changes over time ranging from 0.04 to 0.3% changes, while the viruses from the persistently infected animals showed changes ranging from 0.15 to 0.4% in a very short period of time. Also, using monoclonal antibodies against the major immunogenic protein of the virus, 2 persistent viruses showed antigenic changes. These results show the importance of persistent infections in driving antigenic change and the importance of screening herds for persistent infections and eliminating them.
Technical Abstract: Bovine viral diarrhea viruses (BVDV) are ubiquitous viral pathogens of cattle. There is a high degree of sequence diversity between strains circulating in livestock herds. The driving force behind change in sequence is not known but the inaccurate replication of the genomic RNA by a viral RNA polymerase without proof-reading capabilities as well as immune pressure on immunodominant proteins are thought to play major roles. Additionally, it is not clear when the majority of changes are introduced, whether in acute infections with exposure to innate and adaptive immune responses or in establishment of persistent infections (PI) in utero. To examine which generates more sequence diversity, a comparison was made between the number of nucleotide and amino acid sequence changes in six noncytopathic BVDV type 2 isolates from a series of severe acute (SA) BVD outbreaks that progressed over a large geographic region and over a year’s time with sequence changes found in six BVDV strains (one type 1a, two type 1b and three type 2 viruses) isolated from single in vivo ‘passages’ in PI animals. Here, changes were identified by comparison of the sequence of the progenitor PI virus to that of the progeny viruses from the single in vivo passage. The nucleotide sequence of the open reading frame (ORF) from the six SA viruses showed > 99% identity with only 30% of the nucleotide changes resulting in amino acid changes. The majority of the amino acid changes occurred in the nonstructural proteins (76%). Similarly, the viruses isolated from single passage PI animals had > 99% identity with the progenitor virus. However, the majority of the changes in the amino acid sequence were found in the structural proteins (56%), with 66% of these occurring in the immunodominant E2 protein. Antigenic mapping studies using a 27 antibody monoclonal antibody panel specific for the BVDV E2 protein showed that there were no antigenic differences amongst the six SA viruses. Also, there were no antigenic differences found between the progenitor and progeny type 1a and type 2 persistent viruses. However, there were slight antigenic differences observed in type 1b viruses where two antibodies of the panel showed altered staining patterns. These results suggest that the establishment of a persistent infection results in more rapid generation of genetic diversity in BVDV strains than a series of acute infections and may contribute to antigenic diversity in the absence of an immune response.