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Zambezi hit by killer fish disease

Risks spreading to other parts of Africa

Photo: ©FAO/R. Subasinghe
Fishing on the Zambezi River in Zambia

21 July 2009, Rome – A killer disease is decimating fish stocks in the Zambezi River Valley, threatening the food security and livelihoods of rural populations in an area shared by seven countries, FAO warned today.

An alert issued by FAO’s Global Information and Early Warning System (GIEWS) said the disease, known as Epizootic Ulcerative Syndrome, or EUS, is caused by the fungus Aphanomyces invadans, which forms ugly lesions on fish and has a high rate of mortality. It is one of the most serious aquatic diseases affecting finfish.

“If not properly contained there is the risk of the disease spreading to other countries surrounding the Zambezi River as well as river systems in the region,” said Rohana Subasinghe, Senior Fishery Resources Officer. The 1,390,000 km² Zambezi River Basin is home to some 32 million people, of whom 80 percent are dependent on agriculture or fishing and fish farming.  

Up and downstream

Indications are that EUS, which was first confirmed in Africa in 2007, is spreading both upstream and downstream of the Zambezi and risks taking hold in other parts of Africa.  The GIEWS alert serves notice on the international donor community that a food security crisis is developing and that assistance and funding will likely be required.

The most affected country is Zambia, where two thirds of the Zambezi River Basin lies. Over 2000 villages and some 700,000 people are at risk of food insecurity because fish is not only a source of revenue in many rural districts but is also the cheapest available source of protein.

Fish infected with EUS do not normally pose health hazards to humans, although the deep ulcerations and tissue decay characteristic of the disease could harbour secondary, more threatening pathogens. It is therefore recommended not to eat EUS-contaminated fish unless it is thoroughly cooked.

Irreversible damage

EUS-affected fish is un-marketable, causing severe economic loss to fishers and fish farmers. Some 50 species of finfish are susceptible to the disease, with outbreaks often affecting younger fish in particular so that irreversible damage to fish populations and severe loss of biodiversity often occurs.

EUS first appeared in Japan in the early 1970s then spread to Australia and much of Asia, while the United States was hit in 1984. It is now present in at least 24 countries in the world.

FAO has since 2007 been helping build capacities for coping with the disease in the seven Zambezi River Basin countries – Angola, Botswana, Malawi, Mozambique, Namibia, Zambia and Zimbabwe. This includes basic EUS diagnosis, targeted EUS surveillance and basic aquatic animal health management.

Urgent requests

In response to urgent requests from a number of countries FAO, in close cooperation with the Paris-based World Organisation for Animal Health (OIE), is helping develop and implement an aquatic biosecurity framework for Southern Africa and build capacity for the management of Zambezi River resources.

The programme will strengthen institutional and human capacity for managing aquatic animal health in the wild in the affected countries through appropriate policies and regulations.

Control of EUS in natural waters such as rivers is impossible but is relatively simpler in fish farming operations where a number of simple biosecurity measures can minimize or prevent its spread. They include preventing possible carriers or vectors getting into water bodies or fish ponds, removing dead fish and improving water quality.