Yellow Head Disease (YHV) is a significant concern in shrimp farming due to its devastating impact. It gets its name from the distinctive yellowing that occurs in the front part and head of infected shrimp. YHV is an extremely virulent pathogen capable of causing a 100% mortality rate in a pond within a matter of days from the first signs of infection. Infected shrimp exhibit an initial period of indiscriminate feeding for approximately two days, followed by a sudden cessation of feeding and erratic swimming along the sides of the pond. Just before succumbing to the disease, their hepatopancreas undergoes a notable yellow discoloration.
Yellow Head shrimp Disease is attributed to a viral infection in shrimp and was first identified in Thailand in 1990. Subsequently, it has been reported in various regions across Asia and the Americas.
YHV is categorized as a positive-sense single-stranded RNA (ssRNA) virus. Initially, it was thought to be related to rhabdoviruses, but subsequent research has linked it to coronaviruses and arteriviruses. It is now officially classified within the new genus Okavirus and the new family Roniviridae, falling under the viral order Nidovirales.
The onset of Yellow Head Disease is characterized by a rapid increase in mortality, usually within two to four days following a period of unusually high feeding activity. This sudden spike in mortality coincides with a sudden cessation of feeding behavior.
Diagnosing Yellow Head Disease involves several key indicators, including high and rapid mortality among shrimp in their early to late adolescence.
Additional signs include the yellowing of the cephalothorax, body whitening, and shrimp congregating at the edges of the pond. Histologically, dying shrimp display widespread cell necrosis originating from ectodermal and mesodermal cells. This is accompanied by the formation of intensely basophilic cytoplasmic inclusions, which can be observed through hematoxylin and eosin staining.
These inclusions arise from the phagocytosis of nuclei and viral adhesions. However, it’s important to note that these visible signs and histopathological examinations are not always definitive indicators of YHD. To confirm the disease, molecular methods such as RT-PCR, western blot analysis, nucleic acid in situ hybridization, and TEM are required.
Currently, no effective vaccination method has been developed to combat this dangerous shrimp disease
We hope this article has provided you with a clearer grasp of this topic.
To learn more about other shrimp diseases, please refer to the articles below :
Cefas and OIE