Tiny crustaceans help defeat dengue fever

By Rachel Nowak in Melbourne Putting tiny crustaceans in Vietnamese water tanks and wells to eat the mosquitoes that carry dengue fever is helping to control the disease, a new study reports. “It’s blown us away. We’ve had almost total success in 37 communes, and it’s been done by the local people,” says Brian Kay of the Queensland Institute of Medical Research in Brisbane, Australia. The mosquito-control programme Kay set up with entomologist Vu Sinh Nam of the Ministry of Health in Hanoi, Vietnam, may have protected over 380,000 people from the disease. The dengue virus causes high fever and muscle cramps so painful that the disease is sometimes called break-bone fever. And the severe form of the disease – dengue haemorrhagic fever – can be lethal. Since 1970, dengue haemorrhagic fever has spread from nine countries to 60, with cases occurring in Asia, the Americas, and the Pacific. The cause of the upsurge is not fully understood, but the mixing of the four different viral strains by international travellers is thought to play a key role. The rise of densely populated “shanty towns” around cities also contributes. These towns lack services, and discarded containers, or containers used to store water, become breeding grounds for the virus-carrying Aedes aegypti mosquito. A key aspect of the low-tech strategy used in Vietnam was enlisting local people to catch crustaceans – called Mesocyclops – from water tanks and wells, and transfer them to uninfested water. The “mesos” feed on mosquito larvae that develop into adults in still water. Local people were also encouraged to get rid of small water containers. “We’ve never visited a village that didn’t have some Mesocyclops. They are only one millimetre long, but they swim with a characteristic jerky movement. The kids can pick them out very quickly,” says Kay. Kay and Nam developed their programme in nine communes, or small clusters of villages, in Northern Vietnam. In 2001, local health and community leaders introduced the programme into 37 additional communes in the north, totally eliminating the mosquito in 32 of them. There have been no reported cases of the disease in any of the communes since 2001. The impact should be even greater when the programme is rolled out in the central districts of Vietnam, which have a far worse problem with dengue, with rates as high as 113 cases per 100,000. Simon Hales, an epidemiologist at Wellington School of Medicine and Health Sciences in New Zealand, is impressed by the Vietnamese programme. But different approaches may be needed in countries with more urban communities, where large numbers of small water-collecting containers are a bigger problem. “In 25 years, the problem of dengue fever will be greatly magnified, as the number of people living in urban areas of poor countries doubles to about four billion,” says Hales. “Adequate infrastructure and sanitation is vital.” Another factor which might limit the crustacean approach is that, in some countries, Mesocyclops acts as an intermediate host for a parasitic worm called Guinea worm, which infects humans. However, this problem occurs mainly in Africa, which is not a dengue region. Journal reference: The Lancet (vol 365, page 613) More on these topics:
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