Abstract
The widely used pseudorabies virus (PRV) Bartha-K61 vaccine has played a key role in the eradication of PRV. Since late 2011, however, a disease characterized by neurologic symptoms and a high number of deaths among newborn piglets has occurred among Bartha-K61–vaccinated pigs on many farms in China. Clinical samples from pigs on 15 farms in 6 provinces were examined. The PRV gE gene was detectable by PCR in all samples, and sequence analysis of the gE gene showed that all isolates belonged to a relatively independent cluster and contained 2 amino acid insertions. A PRV (named HeN1) was isolated and caused transitional fever in pigs. In protection assays, Bartha-K61 vaccine provided 100% protection against lethal challenge with SC (a classical PRV) but only 50% protection against 4 challenges with strain HeN1. The findings suggest that Bartha-K61 vaccine does not provide effective protection against PRV HeN1 infection.
Highlights
Pseudorabies virus (PRV; family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus) contains a double-stranded DNA genome with strong genetic stability
PCR Survey of Clinical Samples pseudorabies virus (PRV) was detected by PCR in 88 (57.1%) of the 154 clinical samples tested
Nonpregnant adult pigs do not show obvious clinical signs and symptoms of infection, except for weight loss; among pregnant sows, the disease causes stillbirths and the birth of weak piglets with neurologic symptoms that lead to death
Summary
Pseudorabies virus (PRV; family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus) contains a double-stranded DNA genome with strong genetic stability. Bartha-K61 is widely used and has played a key role in the eradication of pseudorabies This vaccine is an attenuated strain of PRV produced by extensive in vitro passage and contains a well-characterized deletion of several viral proteins (i.e., complete gE and US9, partial gI and US2) that attenuates virulence [8,9,10]. Since the initial outbreak in late 2011, the disease has occurred in 6 provinces in China with extensive pigraising industries and caused many piglet deaths and great economic loss [13]. The PRV Bartha-K61 vaccine is widely used to protect pigs against pseudorabies; there has been no reported. In 2012, to determine the cause of recent PRV outbreaks among Bartha-K61–vaccinated pigs, we obtained clinical samples from piglets with suspected pseudorabies. A breakthrough PRV was isolated from the samples, and we identified the pathogenicity and immunologic protection of the novel isolate
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