"We've been having problems for more than two years and it's getting worse with the mosaic destroying our crops," said Rose Ambeto, who has several cassava fields.
The virus, known as cassava mosaic disease (CMD) attacks the leaves of the plant and limits the growth of its roots. It is spread by insects or by diseased cassava being transplanted to new areas.
"Our harvests are getting worse and worse. That's why bags of fufu and roots are so expensive in the markets," she said.
Fufu is eaten across Africa and is made by boiling starchy roots like cassava, also known as manioc, in water and then pounding them until they reach a porridge-like consistency.
Veronique Okaka, who grows cassava in Ouesso in Congo's Sangha department, also complained of hard times due to the cassava mosaic.
"Before, we had enough to feed our children and to make some money for other things. But lately, because of this disease, we sometimes get fufu from Cameroon," she said.
The price of a bag of fufu has soared from 15,000 CFA (US$28.50) to 35,000 CFA ($67) in recent months in Congolese markets, partly because of the problems faced by growers and traders of cassava.
Specialists in Congo's agricultural ministry say the disease might lead to a drop of between 60 and 90 percent in harvests and could throw entire communities into a critical food situation.
CMD has been spreading throughout central Africa and arrived in the Republic of Congo in the mid-1990s.
The International Committee of the Red Cross (ICRC) has been at the forefront in the battle against the disease. The only known way to fight it is to develop varieties that are resistant to the virus and distribute them to farmers.
In Pool, one of Congo's worst-hit departments, the ICRC has been growing these resistant varieties. Over a two-month period last year, it took cuttings from these plants and distributed them to groups of cassava growers in the area.
The ICRC has handed out 330,000 cuttings to about 100 different groups, benefiting about 1,500 families. These groups received training in how to stop the spread of CMD, and were also given ploughing equipment.
In October, the ICRC joined the Congolese Red Cross and the agriculture ministry to provide training in Kinkala in the Pool Department on ways of fighting the disease.
The departments of Pool and Plateaux, also badly hit by the epidemic, recently received more than 330,000 cuttings of six different varieties of cassava developed in 2004 by the International Institute of Agricultural Technologies (IITA) in Kinshasa, in neighbouring Democratic Republic of Congo.
Another 175,000 cuttings, taken from four new resistant strains, are being distributed in four other departments.