Tilapia Lake virus, Serious thread to World Aquaculture and Food Production.

Tilapia farmers around the world are growing increasingly concerned about the growing number of incidences of Tilapia Lake Virus (TiLV), which has already been reported in Colombia, Ecuador, Egypt, Israel, and Thailand.

 

TiLV is a newly emerging and highly contagious virus associated with significant mortalities in tilapia, which is spreading amongst both farmed and wild stocks. In Thailand for example, outbreaks have led to the mortality of up to 90 percent of stocks. 

The virus belongs to the same family of viruses as infectious salmon anaemia (ISA), which has caused considerable losses to the salmon farming industry. 

TiLV is thought to represents a significant threat to the global tilapia industry, which recorded a production in 2015 of 6.4 million tons with a value in excess of USD 9.8 billion (EUR 8.7 billion). Worldwide trade was valued at USD 1.8 billion (EUR 1.6 billion). Tilapia is the second-most traded aquaculture species and one of the world’s most important fish for human consumption.

Countries importing tilapia have been asked by the Food and Agriculture Organisation (FAO) in a special alert through the Global Information and Early Warning System (GIEWS), to examine their biosecurity measures and to put appropriate risk management measures into place. These include intensifying diagnostics testing, enforcing health certificates, deploying quarantine measures, and developing contingency plans.

According to the FAO, the virus does not pose any risk to public health, but the loss of fish through mortalities poses a concern for global food security and nutrition. The low price of tilapia, its omnivorous diet, tolerance to high-density farming methods, and previously strong resistance to disease, help to make this fish an important protein source, especially in developing countries and for poorer consumers.

Affected countries, along with those importing tilapia, are encouraged to initiate public information campaigns to advise aquaculturists of the clinical signs of TiLV and the need to flag large-scale mortalities to biosecurity authorities. Many tilapia producers are small scale fish farmers or smallholders, who may not be aware of the growing threat. Infected fish may display a loss of appetite, have slow movements, dermal lesions, ulcers and cloudy eyes.

Active surveillance for TiLV is currently being conducted in China, India, Indonesia, and the Philippines, but there are many knowledge gaps about how it is spread. For example, it is not known if it can be transmitted through frozen tilapia products, and more research is required to determine whether TiLV is carried by other fresh water fish species or by piscivorous birds and mammals.

While there is currently no vaccine available against TiLV, an Israeli company is working to develop one. However, a diagnostic test is available, and authorities are being urged to use it to rule out the virus as the cause of unexplained mortalities. 

Around 80 countries currently farm tilapia. China, Indonesia and Egypt are the three leading aquaculture producers of tilapia and sub-Saharan Africa is seen as having the greatest potential for expansion. 

By Nicki Holmyard