Contribution à l'étude de virus de mollusques marins apparentés ...

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PUBLICATION 2
Bull. Eur. Ass. Fish Pathol., 13(4), 130, 1993.
LYMPHOCYSTIS OUTBREAKS IN FARMED SEA BREAM,
SPARUS AURATA, FIRST REPORT ON FRENCH MEDITER­
RANEAN COAST
Bv R. M. L E DEUFF AND T. R ENAU LT
11/ 1 l'OdUCf i OIl
A mong the Iridov irus related infecti ons frequently
deseribed on many teleosts fi sh
spccies, Viral Eryth rocytic Necrosis (VEN)
(Pinto el al., 1989), Epi zootie Haematopoietic
Necrosis Virus (EHNV) (Langdon
el al .. 1988) as weil as Lymphocystis Discase
Virus (LDV) are not considered to directly
cause fatality. Indeed, Lymphocystis
outbreaks of farmed fi sh could be observed
in so rne cases. as a consequence of a bac terial
double infection or cannibalism (Ahne
el al .. 1991: Moate el al., 1992). Here, we
re port for the first time a strong LDV infecti
on, and an add ilional physical stress responsible
for mortalities of reared sea
brearn, Sparus aurata, From Toulon area, on
French Med iterranean coas t. Although,
sinee the first report oF Lymphocystis in sea
bream under aquaculture conditions in Israel
(Paperna et al .. 1982), LDVs were deseribed
in other farmed sea bream in ltaly
(Masoero el al. 1986), Portugal (Menezes el
al. 1987). Spain (Basurco el al .. 1990), Turke
y and Greece (Moate el al. 1992).
Resu/fS alld dis('uss;OIl
Consequent with a two days stonn, impor­
(an! mortalities were observed among the
very infected fish, whereas faintly or not infected
fi sh were not affected. Propagation of
the disease and losses were further considerably
attenuated by doubling the volume of
the cages. Young sea bream (8- 10 cm long)
showing a massive LDV infection at a late
stage eharacterised by numerous cysts
sprayed ail over the body and fins (Fig. 1)
were fixed for microscopie examination.
Histological sections stained with hemalun
eosin revealed irregular nucleus with peripherieal
packs of chromatin and basophilie
4 1
cytoplasmic inclusions (Fig. 2). Feulgen and
Rossenbeck stai ning showed these cytoplasmic
inclusions to contain DNA (Fig 3),
thu s, they can be considered as an accumu ­
lation of viral particles, or at (east of viral
DNA. Thesc histological Icsions could be
observed in derm cells and kidney. How·
ever, cytoplasmic inclusions present in ren al
interstitial cells could not be detected in re·
nal tubules. Thus, nucleus in jury of these
last cells could result in the proximity of
LDV infected cell s. Perhaps the presence of
numerous late lesions ail over the skin could
also provoke a general osmoregulative
breakdown resulting in disorder of kidney
cells, and thus abnormality of nucleus.
Thin sections of tumors and adjacent epi·
thelial ti ssue examined by transmission
electron microscopy revealed electron dense
virus-li ke particlcs (fig 4), which average
diameter was 2 11 nm (n = 43, range = 179
to 262 nm). Icosahedric shape and cyto·
plasmic location of virions in addition to the
presence of DNA associated with these partieles
may belong them to the Iridol'iridae
family . Moreover, due ta the presence of
tu mors corresponding to hypertrophied
dermal host cells together with the great
size of the viral partiel es contained in these
cysts and adjacent cells , they may be related
to the LympllOcystis virus genus
(Samalecos, 1986; Walker and Weissen·
berg, 1965). We intend ta improve
description of this isolate of LDV from sea
bream noticeably by determination of
protein electrophoretic pattern of purified
virus, and by antigenic characterization
using monoclonal and polyclonal antibodies
specifie for largemouth bass (Micropterus
salmoides) LDV (ATCC VR-342) produced
on BF2 fish cell line (ATCC CCL 91).
These results may be helpful for further
comparisons with other LDVs.