Abstract: An infectious nonpathogenic molecular clone (19-2-6A) of equine infectious anemia virus (EIAV) was modified by substitution of a 3.3-kbp fragment amplified by PCR techniques from a pathogenic variant (EIAV(PV)) of the cell culture-adapted strain of EIAV (EIAV(PR)). This substitution consisted of coding sequences for 77 amino acids at the carboxyl terminus of the integrase, the S1 (encoding the second exon of tat), S2, and S3 (encoding the second exon of rev) open reading frames, the complete env gene (including the first exon of rev), and the 3' long terminal repeat (LTR). Modified 19-2-6A molecular clones were designated EIAV(PV3.3), and infection of a single pony (678) with viruses derived from a mixture of five of these molecular clones induced clinical signs of acute equine infectious anemia (EIA) at 23 days postinfection (dpi). As a consequence of this initial study, a single molecular clone, EIAV(PV3.3#3) (redesignated EIAV(UK)), was selected for further study and inoculated into two ponies (613 and 614) and two horses (700 and 764). Pony 614 and the two horses developed febrile responses by 12 dpi, which was accompanied by a 48 to 64% reduction in platelet number, whereas pony 613 did not develop fever (40.6 degrees C) until 76 dpi. EIAV could be isolated from the plasma of these animals by 5 to 7 dpi, and all became seropositive for antibodies to this virus by 21 dpi. Analysis of the complete nucleotide sequence demonstrated that the 3.3-kbp 3' fragment of EIAV(UK) differed from the consensus sequence of EIAV(PV) by just a single amino acid residue in the second exon of the rev gene. Complete homology with the EIAV(PV) consensus sequence was observed in the hypervariable region of the LTR. However, EIAV(UK) was found to contain an unusual 68-bp nucleotide insertion/duplication in a normally conserved region of the LTR sequence. These results demonstrate that substitution of a 3.3-kbp fragment from the EIAV(PV) strain into the infectious nonpathogenic molecular clone 19-2-6A leads to the production of progeny virus particles with the ability to induce clinical signs of EIA. Therefore, EIAV(UK), which is the first pathogenic, cell culture-adapted molecular clone of EIAV to be described, should be of value in identifying viral determinants of pathogenicity.
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The research article discusses the creation and characterization of a harmful molecular clone of equine infectious anemia virus (EIAV). The clone was developed from a non-harmful one and induced definite clinical signs of the disease in tested animals, offering a potential tool for identifying factors contributing to the virus’s pathogenicity.
Research Objectives and Context
The primary aim of this study was to understand the pathogenesis of equine infectious anemia virus (EIAV). To achieve this, the researchers constructed a pathogenic, cell culture-adapted molecular clone of EIAV based on an infectious non-pathogenic clone.
This research is significant because it could lead to an improved understanding of viral determinants of pathogenicity, which could inform the design of innovative therapies and prevention strategies for diseases caused by EIAV.
Development of the Pathogenic Molecular Clone
Researchers began their study using a non-pathogenic molecular clone of EIAV, known as 19-2-6A.
The clone was modified by substituting a fragment, about 3.3 kilobases in length, derived from a pathogenic version of EIAV. This fragment integrated into the non-pathogenic clone, effectively transforming it into a pathogenic version. The modified clones were apportioned the name EIAV(PV3.3).
Experimentation and Results
Mixed viruses generated from five of the modified clones were tested on a single pony, which showed clinical symptoms of equine infectious anemia 23 days after infection.
Subsequently, a single clone drawn from the modified batch, then named EIAV(UK), was selected for further investigation. This clone was inoculated into two ponies and two horses. Within 12 days, a decline in platelet count and increased fever was observed in three of the four subjects.
The researchers were able to isolate EIAV from the plasma of these animals by 5 to 7 days post-infection. By 21 days, all had developed antibodies to the virus.
Molecular Characterization of the Pathogenic Clone
Nucleotide sequence analysis showed the EIAV(UK) clone differed from the pathogenic EIAV(PV) strain by just one amino acid in the rev gene’s second exon.
In addition, EIAV(UK) was observed to bear an unusual 68-base pair nucleotide insertion/duplication in a typically conserved region of the long terminal repeat (LTR) sequence, suggesting a possible mutation.
Implications and Conclusion
The study provided proof that introducing a 3.3-kbp fragment from a pathogenic EIAV strain into a non-pathogenic molecular clone leads to the replication of virulent virus particles. The resulting strain, EIAV(UK), translated into tangible clinical signs of equine infectious anemia in tested subjects.
EIAV(UK), therefore, is the first description of a pathogenic molecular clone of EIAV that is adaptable to cell culture. Its use could help identify determinants of the pathogenicity of the virus.
Cite This Article
APA
Cook RF, Leroux C, Cook SJ, Berger SL, Lichtenstein DL, Ghabrial NN, Montelaro RC, Issel CJ.
(1998).
Development and characterization of an in vivo pathogenic molecular clone of equine infectious anemia virus.
J Virol, 72(2), 1383-1393.
https://doi.org/10.1128/JVI.72.2.1383-1393.1998
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