|KHV: Signs and Symptoms|
KHV is often characterized by large scale, rapid die off of fish populations. The main signs of fish infected with KHV include weakness, lethargy, loss of equilibrium, inappetence, erratic swimming, sunken eyes, "notch" in the snout of the fish, excessive mucous production, increased respiratory rate, discoloration, and hemorrhagic lesions on the skin and gills. The main organs affected by KHV include the gills, kidney and spleen.
Histolology reveals hyperplasia and fusion of gill laminae as well as the presence on intranuclear inclusion bodies in the brachial epithelium. The parenchymal cells of the liver, spleen and kidney may also be necrotic. The main gross pathological sign of KHV is extensive necrosis of gill tissue.
Despite this, the only way to accurately differentiate KHV from other viral diseases such as CyHV-1 or bacterial diseases such as Aeromonas spp. is via proper diagnostic tests such as PCR. Please see the section on Diagnostic Tests for more information.
One very important feature of the virus is that it is temperature sensitive causing disease only between 16 and 28oC. The virus does not seem to cause disease below 13oC or above 30oC however, fish may still carry the virus at these temperatures.
KHV is an extremely virulent disease with morbidity rates often as high as 100% and mortality rates between 70-100%. As well, secondary bacterial or parasitic infections are commonly associated with KHV. Also, like other herpes viruses, fish who survive KHV remain persistently infected and may intermittently shed the virus to other fish.