In summary, data reported here confirm that juvenile
Macrobrachium rosenbergii have lower susceptibility
to infection and more effective mechanisms
for clearing infection and thus protecting themselves
against disease than penaeid shrimp. These abilities
were particularly evident here with a WSSV strain of
lower apparent virulence. However, when challenged
with a strain of higher virulence or with high
doses of the low virulent strain, similar numbers of
infected cells are established as in the more susceptible
Penaeus vannamei challenged using identical
conditions. This finding clearly indicates that once
some acute infection load threshold has been passed,
whatever defense mechanisms are mounted by M.
rosenbergii become swamped, and the clinical outcome
of disease through to mortality progresses similarly
to that in shrimp with acute infection. The dose
and strain variables assessed in this study are likely
to explain in part why differences in the susceptibility
of juvenile M. rosenbergii have been reported,
and highlight the importance of using well-characterized
WSSV strains and standardized challenge
conditions. M. rosenbergii and other palaemonid
prawns can serve as useful model crustaceans for
understanding anti-WSSV protection mechanisms
and how these might be primed to protect these and
cultured penaeid shrimp against disease caused by
WSSV and other problematic viruses.