The well-studied lab subject known as the fruit fly, a mere nuisance to
humans, now promises to help researchers better understand malaria, a
devastating human disease spread to people through the bite of a mosquito.
Scientists at the National Institute of Allergy and Infectious Diseases
(NIAID) and the Whitehead Institute in Cambridge, MA, have for the first
time grown malaria parasites in the fruit fly, creating an easily
manipulated model for studying how the parasite develops in insects. Their
research, reported in the current issue of "Science", has already identified
part of the insect immune system that naturally attacks malaria parasites.
The authors hope the new model will help identify factors critical to
malaria transmission, and accelerate efforts to develop
transmission-blocking vaccines and mosquitoes engineered to be
"Malaria is a major global health problem and a high-priority research area
within NIAID," states Anthony S. Fauci, M.D., director of the Institute.
"This research provides exciting new possibilities for understanding how the
malaria parasite interacts with its insect host."
The malaria parasite, "Plasmodium", must cycle between humans and
mosquitoes, specifically, female mosquitoes of the species "Anopheles", to
spread within a population. When the mosquito bites an infected person, the
insect can ingest the parasites present in the blood. Once inside the
digestive tract, the parasite reproduces and moves into the body cavity.
There it passes through several different life stages before traveling to
the insect's salivary glands, where it is released into the blood of another
person when the mosquito bites again.
"Plasmodium is not a simple organism like a bacterium or virus," says
Mohammed Shahabuddin, Ph.D., an investigator in NIAID's Laboratory of
Parasitic Diseases and co-author of the paper. "It has multiple
developmental forms, each of which is distinct from the other. One form
causes disease in humans, another is swallowed by mosquitoes, still another
form reproduces, others move through the insect's intestines, and yet
another enters the salivary gland of the mosquito and infects people."
Studying how the parasite interacts with its insect host is difficult, he
explains, because the mosquito's biochemical and genetic makeup are not
well-defined. Enter the fruit fly known as "Drosophilia". "Our ability to
grow "Plasmodium" in the fruit fly is especially fortunate because
recently determined the complete sequence of the "Drosophila" genome. So
now we can scan the entire genome and identify the specific genes involved
the fruit fly's response to "Plasmodium", and then look for the
genes in the mosquito."
Dr. Shahabuddin and Whitehead's David Schneider, Ph.D., produced their
mosquito surrogate by injecting "Plasmodium gallinaceum" -- which causes
malaria in chickens -- into the body cavities of fruit flies. The parasites
matured through their normal life stages, producing infectious forms
identical to those isolated from mosquitoes. Chickens infected with the
fly-grown "P. gallinaceum" developed malaria and transferred the parasites
susceptible mosquitoes when the insects fed. These studies proved that
"Drosophila" could serve as an effective model organism for growing
The researchers used the fruit fly model to discover the way most mosquitoes
resist malaria infection. In the fly, immune cells called macrophages
engulf and destroy the parasites at an early stage, before they can develop
further, suggesting the usefulness of the fruit fly in identifying
anti-parasite processes of malaria's natural carrier.
Dr. Shahabuddin notes that the new model allows them to study
"Plasmodium"-insect interactions with a new set of genetic and biochemical
tools long used with the fruit fly. "These studies will let us identify
factors in the insect that are critical to "Plasmodium survival", and may
ultimately lead to improved ways of breaking the parasite's life cycle and
blocking its transmission."
D Schneider and M Shahabuddin. Malaria parasite development in a Drosophila
model. Science 288:2376-79 (2000).