Mesoniviridae is a family of enveloped, positive-strand RNA viruses in the order Nidovirales which infect mosquitoes.

The family is named after the size of the genomes relative to other nidoviruses, with meso- coming from the Greek word mesos, which means medium, and -ni being an abbreviation of nido.

A third member of this first species, named Dak Nong virus, was later found in Culex tritaeniorhynchus populations in Vietnam.

[6][4] The genomes are linear, positive-sense, polycistronic, single-stranded RNA, and are about 20,000 nucleotides in length, with a 3' poly(A) tail and seven major open reading frames (ORFs).

ORFs 1a and 1b contain six replicase domains, as well as the 3'-5' exoribonuclease (ExoN) that controls RNA replication fidelity and a 2'-O-methyltransferase, both of which are found in larger nidoviruses.