Marine Viruses Family Nodaviridae There are two genera in the family Nodaviridae Viruses in this taxa are generally spherical in shape, (from 25 to 33 nm in diameter) and lack an envelope and discernible surface structure The genome of nodavirids consists of two molecules of RNA (approximately 4500 nt in total length) that have 50 caps and lack poly(A) tails Nodavirids are capable of infecting a variety of insect species including two species of Aedes mosquitos, in which they cause paralysis and death Viruses in the genus Betanodavirus infect and cause disease in marine fish Examples include flounder, grouper, and pufferfish, among others In addition, several nodavirid-like viruses not yet approved by the ICTV infect prawns Family Togaviridae This family comprises two genera, the alphaviruses and rubiviruses While the Alphavirus genus has approximately 40 recognized members, the Rubella virus is the only member of the Rubivirus genus The particles of these viruses are enveloped, spherical in shape and have an approximate diameter of 70 nm The genome of a togavirid is a single strand of RNA that is from 7700 to 11,800 nt in length and has a 50 cap and a poly(A) tail While most togavirids are transmitted via an arthropod intermediary, transmission of the alphaviruses that infect marine mammals and fishes not appear to require a vector Alphaviruses have been isolated that infect elephant seals, Atlantic salmon, and rainbow trout Group V: Negative-Sense ssRNA Viruses Order Mononegavirales The Mononegavirales is a large order of negative-sense singlestranded viruses that includes four families, two subfamilies, and 16 genera Although the morphology of these viruses can vary widely (ranging from 80 to 805 nm in size), all virions are enveloped and most possess spike-like structures that are involved in attachment to and fusion with the host cell The genomes of mononegavirads are linear and nonsegmented, range from 8900 to 19,100 kb in size, lack a 50 cap and a poly(A) tail, have a characteristic gene order (wherein from the 30 end, core protein genes are followed by envelope genes and then the polymerase), and encode an RNA-dependent RNA polymerase whose sequence is highly conserved During replication, each cistron is transcribed utilizing a stop-start mechanism starting at a single promotor region located on the 30 end The Mononegavirales is a taxon of particular relevance to human health, because it includes virulent human pathogens such as the Ebola virus, rabies virus, and measles and mumps viruses, but also includes many representatives infecting marine organisms Family Paramyxoviridae The paramyxovirids are viruses of vertebrates that are responsible for notorious diseases in humans and animals such as measles, mumps, pneumonia, rinderpest, and Newcastle disease The family is organized into two subfamilies comprised of seven genera The virions of paramyxovirids are spherical in shape and approximately 150 nm in diameter The genome of these viruses is a single molecule of negative- 139 sense RNA that can be from 13,300 to 18,200 kb in length All genomes of paramyxovirids encode a protein, creatively named ‘‘F,’’ which causes the fusion of the virus and cell membranes at neutral pH An interesting characteristic of the replication of paramyxovirids is the ‘‘rule of six.’’ This rule alludes to the fact that the efficiency of RNA replication in these viruses is severely diminished if the number of nucleotides in the RNA template being replicated is not exactly a multiple of six It is believed that the precise packaging requirements of the virus drive this surprising requirement (Lamb and Parks, 2007) The Cetacean morbillivirus and the Phocine distemper virus are species in the genus Morbillivirus that infect marine mammals, while the Newcastle disease virus has been isolated from the common murre (Lang et al., 2009) Family Rhabdoviridae More than 200 different strains of rhabdovirids have been isolated from plants, invertebrates and vertebrates The most distinctive feature of this family of viruses is that they all possess a bullet or rod-like morphology (Rhabdo from Latin, rhabdos, ‘‘rod’’) that can be from 100 to 430 nm in size (Figure 3(j)) The genome of a rhabdovirid is a single molecule of negative-sense RNA that can be from 11,000 to 14,900 kb in length Viruses in the genus Novirhabdovirus infect diverse fishes, including salmon, flounder, and eels Two novirhabdoviruses of note, infectious hematopoietic necrosis virus and viral hemorrhagic septicemia virus, are responsible for the mortality of significant numbers of wild and farm-raised salmon each year (Lang et al., 2009) The rhabdovirid Dolphin rhabdovirus-like virus was isolated from a white-beaked whale in the North Sea (Bressem et al., 1999) Families Not Assigned to an Order Family Orthomyxoviridae The virions of orthomyxovirids are enveloped, spherical in shape, and range in diameter from 80 to 120 nm (e.g., Figure 3(h)) They contain a negative-sense RNA genome composed of six to eight segments of different length that are in total from 10,000 to 14,700 kb in size Because of their ubiquity and virulence, orthomyxovirids have been intensely studied since the early twentieth century This research has resulted in an unprecedented understanding of the mechanisms of zoonosis and evolutionary history of these viruses Analyses of genomic data suggest that wild aquatic birds may be the primary reservoir of the orthomyxovirids that now infect a wide range of vertebrates, including the human-infecting H1N1 strain responsible for the worldwide human pandemic of 1918 (Palese and Shaw, 2007) Of the five genera in the family, the genera Isavirus and Influenzavirus A have viruses that infect fishes and marine mammals Family Bunyaviridae The family Bunyaviridae comprises five genera whose viruses infect vertebrates and plants primarily via an arthropod vector Among other distinguishing features, bunyavirids have a genome comprised of three unique molecules of negative or ambisense ssRNA, that range in total size from 11,400 to 19,200 kb, that encodes four structural proteins The particles of these viruses are pleomorphic and range in size from 80 to