Tilapia Lake Virus (TiLV): A Guide to a Global Aquaculture Threat

Tilapia lake virus (Tilapinevirus tilapiae) causes high mortality in farmed tilapia. There is no treatment; control relies on biosecurity and surveillance.

Overview

Tilapia lake virus (TiLV) is an emerging viral disease of farmed and wild tilapia. The causative agent is Tilapinevirus tilapiae, a negative-sense, segmented single-stranded RNA virus and the sole member of the family Amnoonviridae. The enveloped virions measure roughly 55-100 nm in diameter. First identified in 2014 from fish in the Sea of Galilee, Israel, the virus has since been reported across Asia, Africa, and South America. It is a notifiable disease whose international management is guided by the World Organisation for Animal Health (WOAH/OIE).

Affected species

TiLV principally infects Nile tilapia (Oreochromis niloticus) and its hybrids, which are among the most economically important aquaculture species worldwide. Other cichlids, including giant gourami, ornamental African cichlids, and angelfish, have also been found susceptible. Because tilapia is a major and affordable source of fish protein, outbreaks carry significant economic and food-security consequences.

Clinical signs

• Lethargy, loss of appetite, and surface swimming away from the school
• Skin erosions, hemorrhage, and discoloration
• Exophthalmia (bulging eyes) and other ocular abnormalities, including lens opacity
• Abdominal swelling and ascites
• Scale protrusion and loss, gill pallor, and anemia
• Internal lesions consistent with hepatitis and encephalitis

Transmission

The virus spreads horizontally through cohabitation, contaminated water, and the movement of live infected fish between farms. Vertical transmission from broodstock to offspring is also considered possible. The combination of high contagiousness and the routine trade of live tilapia is a key driver of the virus's rapid global emergence.

Diagnosis

Confirmatory diagnosis relies on molecular methods, primarily reverse transcription PCR (RT-PCR), including nested RT-PCR assays, supported by histopathology that reveals characteristic hepatitis and encephalitis (brain) lesions. Because gross signs overlap with other systemic infections, laboratory confirmation is essential before management decisions are made.

Treatment, control and prevention

There is no specific treatment or widely available licensed vaccine for TiLV, although vaccine development has been reported. Management therefore depends entirely on biosecurity and surveillance.

• Restrict movement of live tilapia between farms and enforce health certification when trading
• Source and stock specific-pathogen-free (SPF) fingerlings where available
• Quarantine new stock and screen by RT-PCR before introduction
• Implement active surveillance to detect infection early and define its geographic extent
• Report large-scale mortalities to biosecurity authorities and follow WOAH aquatic animal health code protocols