Paratransgenic control of vector borne diseases

Abstract

Conventional methodologies to control vector borne diseases with chemical pesticides are often associated with environmental toxicity, adverse effects on human health and the emergence of insect resistance. In the paratransgenic strategy, symbiotic or commensal microbes of host insects are transformed to express gene products that interfere with pathogen transmission. These genetically altered microbes are re-introduced back to the insect where expression of the engineered molecules decreases the host's ability to transmit the pathogen. We have successfully utilized this strategy to reduce carriage rates of Trypanosoma cruzi, the causative agent of Chagas disease, in the triatomine bug, Rhodnius prolixus, and are currently developing this methodology to control the transmission of Leishmania donovani by the sand fly Phlebotomus argentipes. Several effector molecules, including antimicrobial peptides and highly specific single chain antibodies, are currently being explored for their anti-parasite activities in these two systems. In preparation for eventual field use, we are actively engaged in risk assessment studies addressing the issue of horizontal gene transfer from the modified bacteria to environmental microbes.

Keywords: Chagas disease; Paratransgenesis; horizontal gene transfer; microbiology; risk assessment; sand flies; triatomine bugs; visceral leishmaniasis.

Figure 1

Antimicrobial peptide kill curves for dual-combination treatments of T. cruzi liquid cultures. Results averaged from triplicate samples in three separate experiments and displayed as the percent change in absorbance at 600 nm compared to untreated controls. Figure is adapted from Fieck et al, Trypanosoma cruzi: synergistic cytotoxicity of multiple amphipathic anti-microial peptides to T. cruzi and potential bacterial hosts, Exp Parasitol, 2010, 125:342-347

Figure 2

Confocal image of anti-sialy-Tn REDantibody targeting glycan structures on the surface of T. cruzi epimastigotes. Figure adapted from Markiv et al. Module based antibody engineering: a novel synthetic REDantibody. J Immunol Methods, 2011, 364:40-49

Figure 3

Paratransgenic strategy for control of leishmaniasis. In this scheme, we propose to transform sand fly commensal bacteria to express anti-leishmania molecules (1), these genetically altered microbes will be introduced to sand fly breeding sites (2) where they will be consumed by sand fly larvae (3). We have demonstrated that the genetically altered bacteria will be retained by the sand fly as it undergoes metamorphosis (4). Expression of the anti-leishmania molecule in the gut of the emergent paratransgenic sand fly (5) would kill invading leishmania species, therefore rendering the sand fly refractory to infection (6), and thus transmission of the parasite.

Figure 4

Whole mount of paratransgenic sand fly. A: shows the auto-fluorescence associated with the outer carapace and specific GFP fluorescence within the sand fly. B: shows GFP-specific fluorescence signal uncoupled from the background. These 4x-images were captures using a Nuance multispectral imaging system. GFP-specific fluorescence is contained to the midgut chamber of the adult sand fly with no evidence of transfer to other regions of the insect. Figure is adapted from Hurwitz et al, The paratransgenic sand fly: a platform for control of Leishmania transmission. Parasit Vectors, 2011, 4:e82