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[WINDHOEK] A deadly but as yet unidentified infection among fish in backwaters of the Zambezi River has been detected, sparking fears that the disease could be transmitted to humans.

The infection could affect up to four out of every five fish caught in some parts of Africa's fourth largest river, which supports an estimated 40 million people.

Fishermen in Katima Mulilo, Namibia, began reporting serious sores on fish in early October, according to Nyambe Nyambe, a Zambian environment and development consultant to the government.  

The infection causes blisters and sores, and eats away at the fins and tails of multiple fish species — notably breams, minnows and catfish — eventually killing them, although the fatality rate is unknown. There are fears that some villagers are eating infected fish.

"Some fish parasites can be transmitted to humans," said Christopher Magadza, a fresh water specialist in Zimbabwe and former director of the University of Zimbabwe's Lake Kariba Research Station. He added that they can cause muscular cysts and intestinal worms.

"Fish must be cooked thoroughly, otherwise people might ingest fish parasites, smoke drying does not kill the fish parasites," he told SciDev.Net.

"There are reports that some people who ate some affected fish fell sick and our officials are on the ground talking to medical staff who may have treated these people," said Charles Maguswi, Zambia's director of fisheries.

He told SciDev.Net that the infestation was very serious, and called for experts in all affected countries to share information about the issue.

Expert opinion is divided as to the nature, cause and extent of the infestation, which could be caused by a parasite or bacteria. Samples of the infected fish are being examined to comprehend the cause, extent and likely consequences of the outbreak.

"It could be [caused by] a sudden arrival of migrant birds," Magadza suggested.

'Craters' on a fish where worms
have been removed

"Extremely high temperatures can also cause the rapid development of fish parasites, and this seems to be a very serious infestation, but the lack of data on water temperature and fish deformities makes it difficult to read the trends," he said.

Fishmongers reported that they have removed worm-like parasites from some of the caught fish.

"I think this is a regional problem and we are thinking of a collaborative effort in dealing with it," said Shaft Nengu, Botswana's deputy director of fisheries.

The Zambezi River has its source in Zambia and is the largest river flowing into the Indian Ocean. It runs for 2,700 kilometres and its basin also drains Angola, Botswana, Malawi, Mozambique, Namibia, Tanzania and Zimbabwe.

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