Disease outbreaks caused by yellow head virus (YHV) can result in significant economic losses for shrimp aquaculture;
however, little is known about how YHV is transmitted. Here we evaluate the role of direct and indirect
contact with YHV among Penaeus monodon. One in 3 specimens released into 5 experimental tanks was inoculated
with the virus, and 100 μm-filtered water from each tank was allowed to circulate through another tank containing
an additional set of 3 naive P. monodon. All of the injected shrimps died within 4 d; 9 of the 10 shrimps
cohabitating with them died within 10 d. Only 5 of the 15 shrimps in the water-exposed tanks died within
14 d. As determined by RT-nested PCR, YHV infection was also lower among shrimp exposed to water. To assess
the potential of moribund shrimp to transmit disease, gill samples from individuals inoculated with YHV at either
12 h or 24 h after the onset of the first obvious signs of morbidity were injected into naïve P. monodon housed in
individual tanks. Over a 30-d period following inoculation, the mortality rate was higher among shrimps injected
with 12 h gill extracts than in those injected with 24 h gill extracts. Taken together, these data suggest that cannibalism
of moribund shrimps presents a far greater potential to transmit the yellow head disease than does
water exposure alone. Removing moribund shrimps as soon as morbidity becomes evident could represent an
efficient measure to reduce YHV transmission and disease outbreaks.