Going Beyond Insecticide

Don't Let the Bugs Bite

Ben Harder

Aug. 14, 2004

Science News, Vol. 166, No. 7

This article discusses the possibility of genetic engineering to defeat different diseases spread by insects. In the mid 20th century there were many efforts to eliminate diseases by spraying insecticides. They were able to eliminate malaria in the US and Europe with the use of insecticides (together with other methods) but many insects, especially in the tropical regions of the world have proved to be too strong to be easily eradicated simply by spraying chemicals. Researchers have since realized that they are not going to be able to get rid of mosquitoes and other insects so they have moved on to genetic engineering, which will either leave the insects incapable of spreading illness or at least curtail some vector populations. One example of this kind of disease control is the release of sterilized insects into the population. These insects then compete with fertile populations for mates, thereby reducing the number of offspring.

In the case of Chagas disease, researchers are using the bacterium Rhodococcus rhodnii, which typically lives in the soil and the guts of certain species of “kissing bugs”, several species of insects which carry the Chagas parasite. The insects cannot live without the nutrients made by the bacteria and young insects acquire it by eating the feces of older insects so it contains enormous potential. In July of 2003, CDC experiments showed that an inserted test gene was passed down through at least 100 generations in 8 out of 9 strains of the engineered bacteria.

In previous experiments, researchers had genetically modified the bacteria by inserting a gene that encodes a peptide which is harmless to the insect but toxic to the Chagas parasite. They found that the gene eliminated most to all of the insects parasites. In another experiment researchers built a mock hut inside of a lab and deposited genetically engineered bacteria in fake feces throughout the enclosure. They found that the majority of the insects picked up the engineered bacteria. They are now working on a way to translate this approach to insects living in the wild. Furthermore, they must determine if all species of insects which carry Chagas can pick up the bacterium.

Although these experiments show a lot of potential there are several large obstacles to their use. One of them is the general fear of genetic engineering, which may mean that the general population and many governments will be resistant to allowing these genetically modified insects or bacteria be released. Furthermore, researchers will need to continuously monitor the modified insects after releasing them in order to make sure they are properly controlling the disease and not further mutating. However, because of the money currently available for studying infectious disease, such as from the Gates Foundation, this science has a chance to progress quite rapidly.