Using high throughput sequencing, researchers from MIT, Harvard and the Sierra Leone Ministry of Health and Sanitation have recently reported rapid changes in the Ebola’s genetic code. The Ebola virus genome, a single stranded RNA comprised of ~19,000 nucleotides encodes several structural proteins: RNA Polymerase, nucleoprotein, polymerase co-factors and transcription activators. The researchers used Illumina HiSeq 2500 platforms to achieve 2000x coverage of the Ebola genome. Using Genohub, we estimate the cost to sequence 100 such genomes at 2000x to be under $1,500: https://genohub.com/shop-by-next-gen-sequencing-project/#query=0929767cd66b8ec8a9fb209c99d75b27.
Sequencing 99 Ebola genomes from 78 patients, they found greater than 300 genetic changes that make the genomes sequenced from the current outbreak distinct from previous outbreaks. In fact, they found that the substitution rate was twice as high with this year’s outbreak compared to all other Ebola virus outbreaks. They also determined that mutations during this year’s outbreak were frequently nonsynonymous (mutation that alters the amino acid sequence of a protein). 50 mutational events and 29 new viral lineages were observed in this outbreak alone, suggesting potential for viral adaptation. To determine whether Ebola could be evolving away from defenses against it or whether it could become more contagious and spread faster, will require functional analysis. For their part, Gire et al., have published the full length Ebola genomes in the NCBI database. Tragically, the authors note that 5 co-authors died from the disease before the manuscript could be published. Last week The New Yorker, published The Ebola Wars, an excellent in depth story of the work involved to actually sequence the Ebola genome and track its mutations.
While basic PCR tests are sufficient for giving you a yes/no answer about infection, this new study highlights the important role of sequencing in characterizing patterns of viral transmission and mutations in an epidemic. We expect sequencing to play a greater role in development of diagnostics and treatments for this and other viral outbreaks.