Arbovirus of Marine Mammals: a New Alphavirus Isolated from the Elephant Seal Louse, Lepidophthirus macrorhini

Abstract

A novel alphavirus was isolated from the louse Lepidophthirus macrorhini, collected from southern elephant seals, Mirounga leonina, on Macquarie Island, Australia. The virus displayed classic alphavirus ultrastructure and appeared to be serologically different from known Australasian alphaviruses. Nearly all Macquarie Island elephant seals tested had neutralizing antibodies against the virus, but no virus-associated pathology has been identified. Antarctic Division personnel who have worked extensively with elephant seals showed no serological evidence of exposure to the virus. Sequence analysis illustrated that the southern elephant seal (SES) virus segregates with the Semliki Forest group of Australasian alphaviruses. Phylogenetic analysis of known alphaviruses suggests that alphaviruses might be grouped according to their enzootic vertebrate host class. The SES virus represents the first arbovirus of marine mammals and illustrates that alphaviruses can inhabit Antarctica and that alphaviruses can be transmitted by lice.The genus Alphavirus in the family Togoviridae represents a group of enveloped, plus-strand viruses comprising over 40 known members. Alphaviruses are classified as arboviruses since they are maintained in nature by a biological transmission cycle between susceptible vertebrate hosts and hematophagous arthropods, usually ticks or mosquitoes. Alphaviruses have been grouped by geographic distribution into Old and New World viruses (28). The New World alphaviruses, which include Venezuelan equine encephalitis (VEE), eastern equine encephalitis (EEE), and western equine encephalitis (WEE) viruses are pathogenic for humans, horses, and certain bird species (26,28). The Old World alphaviruses are associated with rheumatic disease in humans and include the Australian Ross River (RR) and Barmah Forest viruses, the Asian/African chikungunya virus, the African o'nyong-nyong virus, and the European Ockelbo virus, which is a subtype of Sindbis virus (28). Weaver et al. (39) hypothesized that alphaviruses may have originated a few thousand years ago in the New World, possibly through recombination with plant viruses (9), and spread to the Old World via bird migration. Recently, two fish alphaviruses have been described, salmon pancreas disease virus (40) and rainbow trout sleeping disease virus (37), suggesting either aquatic origins for alphaviruses or an invasion of the marine environment by terrestrial alphaviruses.Macquarie Island is located some 2,000 km south (54°30'S, 159°E) off the Australian mainland. The island has been a rich source of tick-borne arboviruses. A flavivirus of penguins (22) has been identified on Macquarie Island, as have flaviviruses, bunyaviruses, and orbiviruses, whose enzootic hosts are also likely to be birds (3, 23, 33). The island is also home to about 12% of the world's population of southern elephant seals (Mirounga leonina), roughly 78,000 animals (16), which are known to be infested with the blood-sucking louse Lepidophthirus macrorhini (25). The Macquarie Island elepha...

Sub-clinical infection of farmed Atlantic salmon Salmo salar with salmonid alphavirus— a prospective longitudinal study

“…Additional work is required to confirm this preliminary finding, particularly in light of the poor specific antibody response typically observed in gadoids to infectious agents (Samuelsen et al 2006) Although insect vectors have not been identified for SAV, they form an important part of the epidemiology of other alphavirus infections (Walton et al 1973, Bowers et al 1995. Recently, the elephant seal louse Lepidophthirus macrorhini has been proposed as the vector for the newly identified alphavirus named southern elephant seal virus (SESV) (La Linn et al 2001). It can be speculated that the high levels of Caligus sp.…”

Eilat virus, a unique alphavirus with host range restricted to insects by RNA replication

“…Last, the aquatic alphaviruses comprise two groups, Southern elephant seal virus and salmon pancreas disease virus (SPDV) (6,7). SPDV and its subtype sleeping disease virus are distantly related to all other alphaviruses (7).…”

“…Alphaviruses infect a wide range of vertebrate and insect hosts, including mosquito species encompassing at least six genera as well as ticks and lice (6,(8)(9)(10). Vertebrate hosts include fish, equids, birds, amphibians, reptiles, rodents, pigs, humans, and nonhuman primates (9).…”

Evolutionary Relationships and Systematics of the Alphaviruses

“…Parasitic lice have been implicated in the transmission of the newly discovered southern elephant seal alphavirus (SESV) from the coast of Australia. SESV has been grouped genetically with the Semliki Forest virus complex (32).…”