Using fish to fight the Dengue Fever

Together we designed and piloted studies that targeted more than 6000 households across Lao and Cambodia with community-based education on dengue and how to use guppiesMobilising our health, stakeholder engagement and programme management expertise, we’ve shown that guppies are an effective biological weapon in the fight against a major disease.

This is the first time that the advantages of biological control have been clearly shown. In combination with simple behavioural changes, it’s a practical and sustainable solution to a major health problem. Henrietta Wells, Mott MacDonald project manager.

We have led a two year pilot programme in Cambodia, Lao and the Philippines using guppy fish to eat the larvae of mosquitoes that spread the life-threatening tropical disease, dengue fever. Following impressive results, the Government of Lao is introducing guppies into its national disease control strategy. Worldwide, three billion people are vulnerable to dengue fever. Half live in south east Asia, where urbanisation and increased population density are contributing to the rapid spread of dengue-carrying mosquitoes.

In Cambodia, Lao and the Philippines 80% of mosquito breeding occurs in large ceramic jars that most households use to store water, with 20% taking place in water accumulated within discarded waste. “Dengue is a major public health issue, with seasonal outbreaks putting health systems under serious strain in many countries,” says Henrietta Wells, project manager with Mott MacDonald’s specialist health consultancy HLSP. “There is no specific medication and development of a vaccine is complicated by the existence of four different viral types. Prevention is key.”

Winning support

The guppy, a 25-60mm long freshwater fish, has been employed for mosquito control on an ad hoc basis. But use of guppies as the core component of a public health strategy had never been explored. In 2010, the Asian Development Bank contracted HLSP to lead and manage a programme exploring the possibility, working with the governments of Cambodia, Lao and the Philippines, plus the World Health Organisation.

Together we designed and piloted studies that targeted more than 6000 households across Lao and Cambodia with community-based education on dengue and how to use guppies. The project also incorporated other simple strategies for preventing mosquitoes breeding, such as turning over unused water jars and clearing away rubbish.

Using motorised tricycle taxis known as tuk-tuks, health workers travelled from village to village teaching a catchy dengue song, giving talks and distributing leaflets. School drama competitions were staged and judged by provincial governors. In Lao, primary school children played a key role in breeding and distributing fish.

“An important part of the study was to find out if water jars are a good habitat for guppies – and how people felt about having fish in them,” says Henrietta. The team also analysed the costs of introducing the approach nationally.

100% kill rate

Twelve months into the study, following the first full dengue cycle, none of the water jars containing guppies had any evidence of larvae. “Even a single fish could keep the jar mosquito free,” Henrietta reports. For comparison purposes, we set up ‘control’ jars without any fish. Larvae were found in a quarter of these.

Sustainable solution

The guppies suppressed normal seasonal fluctuations in mosquito breeding. Just how effective the fish are was demonstrated during a local dengue fever outbreak in Cambodia. Unplanned by the project team, local authorities used a chemical pesticide to kill off larvae, yet the numbers went straight back up only a few weeks later. In contrast, by using guppies to tackle the outbreak we were able to keep water jars larvae-free, demonstrating that the fish are effective in control as well as prevention of the disease.