7 December 2015 – It is now well understood that mosquitoes require access to resting sites, plant sugars and, in the case of females, also a blood meal, in order to survive and transmit malaria. Preliminary studies have shown that mosquitoes also feed on plant sugars produced by many invasive plant species.
This emerged at a workshop held in Naivasha, Kenya, from 2-4 December 2015 that brought together scientists and subject experts from different parts of the world to explore linkages between invasive plants and malaria.
Almost all invasive plants flower and stay green for longer periods, compared to native plants, thereby providing mosquitoes with an extended source of nectar and possibly also shelter. Because invasive plants are abundant and widespread they can provide malaria vectors with a food and energy source that was never available in significantly large amounts and for longer periods than in the past, said Dr Arne Witt from CABI.
The increased abundance and distribution of some invasive plants may not only result in an increase in Anopheles mosquito abundance, but may also result in an increased incidence of malaria.
We have seen malaria infections rise after the water hyacinth was introduced into Lake Naivasha. The plant has quickly spread and is now covering a large part of the lake. It provides a breeding ground for the mosquitoes, said Eric Chege, a resident in Naivasha.
A lot of fragmented information and research exists on the subject, but there is a growing need to organise and bring together this knowledge. This will help scientists understand the relationship between invasive plants and malaria incidence better. This is vitally important in the fight against malaria.
Malaria remains a major threat to human health in many parts of the world, especially Africa. Although the incidence of malaria has decreased as a result of indoor insecticide spraying, and the use of bed nets, a considerable number of people are still being infected. As such, it is imperative that additional actions be undertaken to reduce malaria infection rates even further. This can be achieved through an integrated management approach by reducing the prevalence of plant nectars and shelter, two key factors which contribute to improved survivorship and malaria transmission rates by Anopheles mosquitoes.
New research should focus on providing additional evidence to demonstrate that some invasive plant species not only increase the abundance of Anopheles mosquitoes but also increase the incidence of malaria. Research planned for 2016 will attempt to provide evidence for these links, for some selected invasive plants. If there is, indeed, a link between some invasive plants and malaria it will provide renewed impetus to manage invasive plants more effectively as an important tool to reduce the incidence of malaria and possibly also other diseases in Africa. Invasive plants can be managed effectively through the use of host specific biological control agents and other means.
The workshop was organized and hosted by CABI with funding from the Bill and Melinda Gates Foundation.
See more about the malaria workshop.
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