7.8.2013: Forschung international

Biodiversität senkt Risiko von Malariaausbrüchen

La biodiversité diminue le risque d’épidémie de malaria


Gabriel Laporta

Forschungsresultate aus dem brasilianischen Regenwald zeigen, dass eine intakte Biodiversität vor Krankheiten schützen kann. Der Mensch profitiert dabei von einem Verdünnungseffekt: Malariaerreger treffen mit höherer Wahrscheinlichkeit auf resistente oder weniger empfindliche Arten, wodurch die Übertragungsrate gebremst wird. Eine Abnahme von 80% der nicht übertragenden Mückenarten und 70% der nicht übertragenden Wirbeltiere würde einen Malariaausbruch ermöglichen. Dies zeigt, dass die Erhaltung des Waldes und die Kontrolle der Malaria Hand in Hand gehen.

Les résultats de recherches scientifiques dans la forêt tropicale brésilienne montrent qu’une biodiversité intacte peut protéger des maladies. L’homme profite d’un effet de dilution: l’agent pathogène a davantage de chances de rencontrer une espèce résistante ou moins sensible, moyennant quoi le taux de transmission est freiné. Une diminution de 80% des mouches non vecteurs et de 70% des vertébrés non vecteurs déclencherait une épidémie de malaria. Ceci met en évidence que la conservation de la forêt et une régulation de la malaria sont compatibles.


According to the World Health Organization, there is an urgent need for better understanding of the ecology and biology of vectors that spread disease, such as mosquitoes and ticks. Five species of parasites can cause malaria, and the species Plasmodium vivax, spread by mosquitoes through their bites, is associated with 80 to 300 million cases of malaria worldwide. Better knowledge of its biology and interaction with ecosystems could improve strategies for mosquito control and reduce the number of infective bites.
A well-known way to measure the transmission of malaria and evaluate the impacts of control programmes is to calculate the ‘basic reproduction number’. This is the number of cases of malaria expected to arise from a single case in a susceptible population. Using this measure, the study investigated the effects of two possible changes in biodiversity on malarial outbreaks in south-eastern Brazil. It focused on a region known as the Serra do Mar, in the Atlantic Forest, which is home to P. vivax and a rich community of animals that play a role in the spread of malaria. Although malarial epidemics are uncommon in the Atlantic Forest, there can be occasional and local clusters of malarial cases and the Serro do Mar area has many tourists who could introduce the malarial parasite.
Using real data on factors that influence the spread of disease, such as the biting rate of mosquitoes and the transmission rate of malarial parasite from mosquito to human, the study modelled the effects of varying the number of species of mosquito that cannot carry the malarial parasite (‘non-vector’ species), and varying the number of vertebrate species that cannot host malarial parasites.
The results indicated that a decrease of approximately 80% in non-vector mosquito species and a 70% decrease in non-host vertebrates would cause the basic reproduction number to rise. This would allow malarial invasion to occur in the village populated by the indigenous Guarani Mbya tribe. In the Maruja village a reduction of just 50% in non-vector mosquito species would allow malarial invasion.
The researchers suggest that these results can be explained by the ‘dilution effect’, whereby a diverse community of species dilutes the effects of disease transmission. In this case, fewer species of non-vector mosquitoes would reduce competition for food and space, which would allow malarial mosquitoes to thrive. The decrease in non-host vertebrates would mean that humans are more likely to end up hosting the parasite. The results suggest that biodiversity can contribute to disease control and that ecosystems in tropical forests could be managed to enhance the competitive and dead-end effects. Past policies of removing native vegetation to eliminate the habitat of malarial vectors have weaknesses because they may also reduce the non-vector community that protects against malarial transmission. As such, forest conservation and malaria control need not be incompatible.

Quelle: Science for Environment Policy, European Commission


Keywords:
Malaria, Verdünnungseffekt, Gesundheit, Parasiten, tropischer Wald

Art der Publikation:
Fachpublikation

Literatur:
Laporta G.Z. et al. (2013). Biodiversity Can Help Prevent Malaria Outbreaks in Tropical Forests. PLOS Neglected Tropical Diseases 7(3): 1-12.

Artikel
gabrielzorelo@usp.br


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