The study describes infection of Caspian White Fish with Spring
Viraemia of Carp Virus (SVCV) experimentally and describes the influence of
different challenge routes on virulence of the virus.
Spring Viraemia of Carp Virus (SVCV), a member of the
Rhabdoviridae Family, in capable of inducing an acute haermorrhagic and
contagious viraemia in several cyprinid species such as carps, zebrafish and
roach. SVCV account for up to 70% of carp’s mortality during the spring time
outbreaks (Ahne et al., 2002). Caspian White Fish, Rutilus frisii kutum, accounts for 60% of the bony fish population
in the Caspian Sea in the north of Iran. It is also a highly valued commercial
fish.
The aim of the current study was to evaluate susceptibility
of Caspian White Fish to SVCV and to test whether the outcome of the
experimental infection is influenced by the challenge routes.
The purpose of this investigation was to understand the
susceptibility of Caspian White Fish to SVCV and to prevent pandemic from
happening. This is because Caspian white fish is highly valuable as a food
source and is recently an important cultures species in Iran. Secondly, Caspian
White Fish is a wild fish living in large areas of the Caspian Sea and its
tributaries and infected fish may spread the virus to large aquatic areas. Thus,
a functional SVCV infection model for this fish is vital to minimize
SVCV-associated economic losses and to effort to control spread of the infection.
This study have shown that Caspian White Fish are
susceptible to infection by SVCV and virulence of the virus could be influenced
by the route of transmission. Infective route of transmission (from highest to
lowest) – immersion, intra-peritonea (i.p.) injection,
cohabitation and oral. They found that immersion was the best infectious route
of transmission with the highest mortality of 85% of test subjects, whereas
oral transmission showed the lowest mortality rate of at most 10%.
Transmission route through immersion is a natural route of
infection, the experimental model shown that this is the transmission route
that cause the highest mortality percentage, thus water could be regarded as
the major abiotic factor of virus transmission. The authors suggest that this
might be due to the entire body surface is potentially in contact with the
virus, allowing transmission through gills, skin and fin bases simultaneously. Other
reports have also suggested that gills are portal of entry and primary
multiplication site of SVCV. Cohabitation model, on the other hand, shown that
healthy fish could be infected by secondary infection via horizontal
transmission as the mortality kinetics progressed slower than immersion or i.p.
injection models.
Inoculation of homogenates from infected fish onto Epithelioma Papulosum Cyprini (EPC) cell monolayer from all
treatment groups except oral transmission showed a complete cytopathic effect (CPE) of the original viral strain. This
suggests that SVCV remained live during the experimental period in
Caspian White Fish and indicates possibility of the development of carrier
state in these fish in aquatic environments. Also supported by the RT-PCR
results that shown that SVCV is detected in both dead and survive fish. Which thus
indicate that survived fish may serve as a reservoir of the virus and transmit
infection to healthy population of susceptible fish. They also have shown that
SVCV did not lose infectivity potential during the experimental period. However,
possibility of change of infectivity and virulence of SVCV following several
passages in Caspian White Fish need more investigations.
This study has thus increased our understanding on the mode
of transmission in fish disease. It gives an indication that virus infection,
in particularly for SVCV, direct contact of virus with host caused highest
infection and mortality rate.
Ghasemi. M., Zamani. H., Hosseini. S. M.,
Haghighi Karsidani. S. and Bergmann. S. M. (2014). Caspian White Fish (Rutilus frisii kutum) as a host for Spring Viraemia of
Carp Virus. Veterinary Microbiology.
170(3-4), 408-413.
Ahne. W., Bjorklund. H. V., Essbauer. S., Fijan. N., Kurath.
G. and Winton. J. R. (2002). Spring viraemia od carp (SVC). Dis. Aquat. Org. 52,261-272.
Hi Li, when they were testing infection routes where about did they inject the fish? I find this a strange method to use as surely it has little real world relevance apart from being able to compare it to other infection routes. Possibly it would have been more beneficial to examine in the immersion infection route which, if any, out of skin, gills and fin bases had the highest rates of infection. This could be used to help narrow down on the main avenues of infection and understand how to combat this disease.
ReplyDeleteSince surviving fish can act as a reservoirs for SVCV, do the authors mention anything regarding how long the fish can act as carriers or how effective are they at infecting healthy fish? Also what would the transmission mechanisms be from one fish to the other, would it be just direct contact or excretion of fluids that would infect the water?
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