A rhabdo-like virus of blue crab, C. sapidus, originally reported by Jahromi (1977) and redescribed by Yudin and Clark (1978, 1979) as ecdysal gland virus 2 (EGV-2), was further redescribed by Johnson (1983) as rhabdovirus A (RhVA), since the particles occur primarily in the mandibular organ, rather than in the ecdysal gland. Rhabdovirus A infects crabs from Maryland, Virginia and Texas (Yudin and Clark, 1978; Johnson, 1988b; Messick and Kennedy, 1990) and may have a broad distribution over the geographical range of blue crab. Infected crabs do not generally show signs of disease until stressed by transportation, artificial holding conditions, eye-stalk ablation or concurrent infection by other viruses, e.g. RLV, EHV, CBV, BFV and baculo-B (Johnson, 1983, 1984). Experimental infections with various combinations of these viruses demonstrated a synergistic pathogenic effect with RhVA and RLV infections (Johnson, 1983).
In addition to the mandibular organ, RhVA infects a wide range of tissues: Schwann cells, endothelial cells, haemocytes in the gastric mill muscles, connective and reserve tissues, nerve tissue, bladder epithelium and haemopoietic and epicardial tissues. Glial cells appear to be more heavily infected than other cells. The virions are predominantly bacilliform, 20-30 nm x 110-170 nm, although longer, filamentous, forms (< 600 nm in length) also occur (Johnson, 1983). These aggregate in nuclear membrane cisternae and endoplasmic reticulum, and may also form extracellular parallel arrays perpendicular to the plasmalemma.
Blue crab, C. sapidus, from the Gulf of Mexico have a second rhabdo-like virus, which was originally described as ecdysal gland virus 1 (EGV-1) by Yudin and Clark (1978, 1979) but renamed rhabdo-like virus B (RhVB) by Johnson (1983) for the same reason as RhVA. No clinical signs have been attributed to
RhVB infections, which primarily occur within the mandibular gland. The virus is differentiated from RhVA by morphology: RhVB measures 50-70 nm x 100-170 nm and is more ovoid than the bacilliform/filamentous forms of RhVA. Mature RhVB virions aggregate beneath the basal lamina of the mandibular organ and have surface spikes (Yudin and Clark, 1978). There have been no further reports of RhVB since the original description.
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