Australian red claw crayfish (Cherax quadricarinatus) is susceptible to yellow head virus (YHV) infection and can transmit it to the black tiger shrimp (Penaeus monodon)

The Australian red claw crayfish (RCC), Cherax quadricarinatus was introduced in Thailand more than two decades ago for culture in freshwater areas where marine penaeid shrimp are also frequently farmed. Despite many reports of various diseases that occur in RCC in Australia (both from natural habitats and from farms), there have been no reports of its diseases when farmed in Thailand. Our recent study on RCC cultured in Thailand revealed that it is susceptible to WSSV infection and that it can transmit the virus to native shrimp species such as the black tiger shrimp (Penaeus monodon). Thus, we decided to continue by testing whether RCC were also susceptible to endemic yellow head virus (YHV) and also capable of transmitting it to black tiger shrimp (BTS). Using three different exposure methods (injection, feeding and cohabitation) with test RCC, we obtained no YHV pathology or positive immunoreactions using monoclonal antibodies against all 3 structural proteins of YHV. By contrast, a standard RT-PCR assay targeting the RdRp gene of YHV with RNA extracted from the experimentally exposed red claw did give positive results. In addition, BTS that tested negative for YHV and were then cohabitated (separated by a plastic net) with RT-PCR positive RCC became infected with YHV and died, exhibiting the severe histopathology typical of yellow head disease. This was confirmed by strong positive immunohistochemical reactions for YHV and positive RT-PCR results. These results suggested that the experimentally exposed RCC were susceptible to YHV infection at sufficient level to allow transmission to BTS but not sufficient to allow detection by the standard histological methods currently used. Statement of relevance The loss due to the yellow head virus is second only to that of white spot syndrome virus (WSSV) in South East Asia. Despite the continual search for its reservoir, since its discovery in the early 1990s, the reservoir for YHV-1 (the most virulent strain of YHV found in Thailand) has still not been identified. Outbreaks of the virus in cultivated, exotic whiteleg shrimp P. vannamei that originate from SPF stocks known to be free of the virus, suggesting that the outbreaks occur via horizontal transmission from an environmental source. Based on our results, exotic red claw crayfish (Cherax quadricarinatus) that are cultured in fresh water areas where marine penaeid shrimp are also frequently farmed should be added to the list of potential reservoirs. Red claw crayfish, fromour results, is susceptible but highly tolerant to the virus. Infected red clawcrayfish could transmit the viruswithout showing any signs of yellow head disease. These facts make them perfect carrier for the virus. YHV infection in red claw crayfish could be detected by RT-PCR only not by routine histology or immunohistochemistry. (C) 2015 Elsevier B.V. All rights reserved.