Antisense antiviral compound and method for treating ssRNA viral infection

A method of treating an infection by a Flaviviridae positive strand RNA virus selected from yellow fever virus, Dengue virus, tick born encephalitis virus, and West Nile virus, comprising:

• administering to a subject a therapeutically effective amount of an antisense morpholino oligonucleotide, wherein the morpholino oligonucleotide has
• (i) a targeting sequence that comprises the sequence set forth in SEQ ID NO:
• 47, 49, 51, or 55,
• (ii) a subunit length of up to 25 subunits, wherein morpholino subunits of the oligomer are joined by intersubunit linkages in accordance with the structure:
• wherein Y1=O, Z=O, Pj is a purine or pyrimidine base-pairing moiety effective to bind, by base-specific hydrogen bonding, to a base in a polynucleotide;
• and X is —NR2, where each R is independently hydrogen or methyl;
• and
• wherein the antisense morpholino oligomer forms a heteroduplex with the target region to disrupt the stem loop structure and inhibit Flaviviridae virus production.