Bacterial symbiosis and paratransgenic control of vector-borne Chagas disease

The triatomine vectors of Chagas disease are obligate haematophagous insect s, feeding on vertebrate blood throughout their entire developmental cycle. As a result of obtaining their nutrition from a single food source, their diet is devoid of certain vitamins and nutrients. Consequently, these insec ts harbour populations of bacterial symbionts within their intestinal tract , which provide the required nutrients that are lacking from their diet. We have isolated and characterised symbiont cultures from various triatomine species and developed a method for genetically transforming them. We can th en reintroduce them into their original host species, thereby producing sta ble paratransgenic insects in which we are able to express heterologous gen e products. Using this methodology, we have generated paratransgenic Rhodni us prolixus that are refractory for infection with Trypanosoma cruzi. Two e xamples of potentially refractory genes are currently being expressed in pa ratransgenic insects. These include the insect immune peptide cecropin A an d active single chain antibody fragments. We have also developed an approac h that would allow introduction of genetically modified bacterial symbionts into natural populations of Chagas disease vectors. This approach utilises the coprophagic behaviour of these insects, which is the way in which the symbionts are transmitted among bug populations in nature. The production a nd ultimate release of transgenic or paratransgenic insects for public heal th applications is potentially very promising but also worthy of much caref ul consideration with respect to environmental, political, and human safety concerns. (C) 2001 Australian Society for Parasitology Inc. Published by E lsevier Science Ltd. All rights reserved.