An experimental protocol based on a mathematical
epidemiology model was developed to study the
transmission, virulence, and recovery rates of White
Spot Syndrome Virus (WSSV). Two modes of transmission
were compared for WSSV in Litopenaeus
vannamei. We compared transmission by ingestion
of infected cadavers to transmission by cohabitation
with infected animals. In addition, we compared the
ingestion transmission of WSSV in L. vannamei and
in L. setiferus. Finally, we compared the virulence
and recovery rates of WSSV in L. vannamei and L.
setiferus. The transmission rate of WSSV to L. vannamei
by cohabitation was 0.01. The transmission
rate by ingestion of infected cadavers was over an
order of magnitude larger at 0.46, suggesting that
cohabitation is a much less important mode of transmission
for WSSV. A statistically significant difference
was detected between the estimates of ingestion
transmission of L. vannamei (0.46) and those of
L. setiferus (0.84), yet no differences in the virulence
or recovery rates were detected between hosts. The
overall estimated virulence rate was 0.34, and the
overall estimated recovery rate from a WSSV infection
was 0.007 for both species. According to epidemiological
theory the threshold density of hosts necessary
for an epidemic to occur is directly related to
the virulence and recovery rates and inversely related
to the transmission rate. Therefore, the epidemic
threshold density may be lower for ingestion
transmission than cohabitation transmission and
lower for L. setiferus than for L. vannamei. © 2001