Chapter 30 - Viral Nervous Necrosis Disease

Abstract

Viral nervous necrosis (VNN) as a worldwide and disastrous disease could be classified as one of the most important diseases in marine fish, which occurred often in fry and juvenile fishes with high economic losses. Sometimes, it was occurred in adult fish, such as golden grey mullet in Caspian Sea. In last decade, VNN was reported in all continents except Africa; but recently, some official outbreaks were reported in wild groupers in North beaches of some African countries such as, Tunisia, Algeria, Libya, and Senegal. This infectious viral disease can be spread in marine waters or freshwater of tropical, moderate, and cold areas in fishes that can live in warm or cold waters, and also in ornamental and marine fish. So far, morbidity and sensitivity of more than 50 fish species of wild marine or reared fishes have been reported to VNN virus since 1986. Furthermore, according to official reports of OIE, VNN was recognized as most important fish health challenge in Mediterranean region and inhibitor factor in development of East-South Asian aquaculture. Regarding to epidemiological studies, first outbreak of VNN was occurred in wild red spots groupers (Epinephelus akaara) in Japan, and mortality rate reached 80% in 1991. Same mortality was reported in marine sea bass (Dicentrarchus labrax) in Greece, and mortality rate was recorded between 11% and 60% in 1997, but mortality rate in cage-reared halibut fry (Hippoglossus hippoglossus) was recorded in Norway about 100% in summer of 1997. Also, the sensitivity of Salmonidae family was confirmed to barfin flounder nervous necrosis virus serotype in Norway. It would be concluded that VNN could be considered main reason of morbidity and mortality of some important marine fish in the world. So, all aspects on VNN as most important catastrophic emerging viral disease in marine aquaculture would be discussed.