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New weapons against dengue

A bacterium is the raw material of bioinsecticides that kill mosquito larva

Eduardo CesarThe summer and early autumn months in Brazil are those that record the largest number of cases of dengue. The rains, which fall in great quantity at that time of the year, bring about the hatching of the eggs of the female Aedes aegypti mosquito, the main transmitter of the disease, which last year alone reached the mark of 769,076 notifications in the country, against 421,574 in the previous year. The insecticide applied in the epidemic regions by the use of sprayers, known as ‘fumacê’ in Poirtuguese (smokey), eliminates only the adult form, but is not at all effective to finish off the larvae. To control these mosquito breeding grounds, two new bacterial weapons are being prepared.

The first should be on the market soon, in April, in the form of a liquid insecticide that has as its main component Bacillus thuringiensis israelensis, developed by the team from Bthek Biotecnologia coordinated by agronomist Marcelo Soares, one of the owners of the company. A natural enemy of Aedes, this bacterium produces a toxin that, when ingested by the larva, causes damage to the insect’s intestines and brings about its death. The other weapon, with the same bacillus in pill form, was created in Rio de Janeiro, at the Instituto Far-Manguinhos, by biologist Elizabeth Gomes Sanches. The difference between the two products is that the liquid Bti, as the new product is called, is chiefly intended for lakes and pools, that is, large open spaces, while the pills were produced for domestic use, as in water tanks, swimming pools and cisterns.

Product perfected
Soares tells how the idea of producing the bioinsecticide against the dengue larva arose in 1999, when he was doing postdoctoral studies in microbial control at Embrapa Genetic Resources and Biotechnology. One year later, he founded Bthek Biotecnologia, in Brasilia, and kicked off the project. The first measure taken was to turn to Embrapa to buy some pure strains of the Bacillus thuringiensis bacterium, which are important for a proper formulation of the product. “After learning how to produce the bioinsecticide, I got on touch with the Technological Research Institute (IPT), which undertook to develop and to perfect the means of production”, Soares recalls.

The institute also provided advisory services for setting up the industrial plant, reports Luiz Carlos Urenha, a chemical engineer at the Industrial Fermentations Laboratory, of the IPT’s Biotechnology Group, which also took part in the project. The product will start to be sold, to begin with on a small scale, to the northern and northeastern regions of Brazil, for health agencies and specialized companies. Its use in households and large centers still calls for some modifications, such as forms of presentation in pastilles, sachets, powder or gel. Its production on an industrial scale is forecast for September, when the factory will be with its full capacity installed. Soares says that Bti will have the price of similar imported products, which today compete in the market at US$ 25 a liter. For an area of 1 hectare, 1 or 2 liters of the product are needed, depending on how infested by mosquitoes it is.

As for the pills developed by Far-Manguinhos, they are ready, but will only start being made when negotiations are concluded with a Brazilian company in the fermentation industry. “We are looking for a partner company with the capacity to make the product on an industrial scale, so as to meet the demand of the National Health Foundation (Funasa), which is very big”, says Elizabeth Gomes. The researcher says that the product has been tested and approved, within international safety standards, by an independent company contracted by Far-Manguinhos. “Our product can be used in a water tank, because it is not toxic”, says Elizabeth. “The formula was dimensioned for domestic use.” But it can be applied by health agents or specialized companies, seeing that the National Agency for Sanitary Surveillance (Anvisa), of the Ministry of Health, does not allow this kind of product to be sold to the lay population.

Temephos, a chemical larvicide widely employed to combat dengue, started to be replaced in some Brazilian states at the beginning of 2000 by imported bioinsecticides based on Bacillus thuringiensis after populations of mosquitoes were found that are resistant to the product. “The chemical insecticides, which are currently used in Brazil for the prevention of dengue, have a series of disadvantages, particularly in environmental aspects”, says Maria Filomena de Andrade Rodrigues. She is responsible for the Industrial Microbiology Laboratory, also belonging to the IPT’s Biotechnology Group, which worked on the development of the process for producing and formulating the liquid bioinsecticide.

“Their systematic application contaminates the soil and the water, jeopardizing the flora and fauna and killing other harmless insects, not to mention that the person applying it can become intoxicated with the product.” The bioinsecticide, though, in the researcher’s assessment, as it has a specific activity, allows the pest to be controlled without causing environmental disturbances and damages to human beings.

Maritime voyages
Maria Filomena says that educating the population and making it aware is still the best way for controlling Aedes, which arrived in Brazil in the 18th century, on board the ships that brought the slaves. From its origins in Africa, the mosquito spread to Asia and America, chiefly by maritime voyages. The mosquito’s eggs are resistant and can survive even without being in contact with water throughout one year. Accordingly, all it needs is rain for them to originate the larvae, in less than 30 minutes. And in one week the new insects will be ready to bite their victims.

A big campaign carried out by the Pan American Health Organization (Paho) went so far as to eradicate Aedes aegypti from Brazil and several other countries of the Americas in 1955. There were, however, some failures that prevented the objective from being fully achieved, and the mosquito remained present in several Caribbean islands, Guyana, Surinam, Venezuela and south of the United States, from where it once again spread out. By the end of the 1970’s, Brazil had the vector back with its presence in its main metropolitan areas.

Dengue is currently regarded as one of the main public health problems inn the world, according to the Ministry of Health. Estimates by the World Health Organization (WHO) indicate that some 80 million persons contract the disease every year. Of this total, around 550 need to be hospitalized, and 20,000 die as a consequence of the infection. These figures show that the arsenal available for fighting this insect of tiny dimensions and a high capability for adaptation needs to be expanded. Bacterial control is a strong candidate for playing an effective role in the crusade against this urban epidemic.