Waterborne and cannibalism-mediated transmission of the Yellow head virus in Penaeus monodon

Abstract 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 naive 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.