Leishmaniasis transmission
Visceral Leishmaniasis (LV) is a neglected tropical zoonosis that, in our region, is caused by the parasite Leishmania infantum and transmitted by the sandfly (Lutzomyia longipalpis) to dogs and humans[1]. Dogs are the main reservoir of the disease, that's because they have high multiplication of the parasite on their skin, increasing the chances of the sandfly to acquire leishmania when they bite them.
Figure 1: Leishmania Cycle
After a blood meal, the sandfly increases trypsin production. That's because digestive proteases such as trypsins and chymotrypsins are responsible for the bulk of the blood digestion in sand flies, as well as in other hematophagous Diptera[2].
Microorganisms inhabit the midgut of sandflies, forming the microbiome. Every time a sandfly takes an infectious blood meal, the ingested Leishmania parasites will encounter these microbes[3]. In this encounter, the parasites will be in their most vulnerable form, the promastigote one. Therefore, strategies that want to prevent the development of leishmania, like paratransgenesis, should preferably act at this stage.
Paratransgenesis
This technique consists in modifying bacteria present in the microbiome of a disease's vector to produce effector molecules that can prevent the transmission of the parasite responsible for the disease.
The first example of use of this technique was in 1997[3]. In the research, the endosymbiont Rhodococcus rhodnii of the vector Rhodnius prolixus was transformed to express cecropin A, a peptide lethal to the parasite, Trypanosoma cruzi, the etiological agent of the disease. A 99% reduction in the intensity of Trypanosoma cruzi infection in the hindgut of R. prolixus was observed without interfering with insect fitness.
The use of the paratransgenesis technique to control Leishmania transmission was first published in 2011[5]. The scientists demonstrated that Bacillus subtilis could be used to produce heterologous molecules (GFP) inside Phlebotomus argentipes midgut. In addition, the same laboratory has proven in other studies that the antimicrobial peptide (AMP) melittin exerts potent activity against promastigote forms of L. donovani at micromolar concentrations. They concluded that the targeted delivery of leishmanicidal molecules by a commensal bacterium within this region of the adult sand fly would disrupt the developmental transition, thereby generating paratransgenic sand flies that are refractory to L. donovani infection.
In BioPank, we combine patransgenesis with a synthetic biology approach, bringing engineering and modularity to the technique. Our conceptual framework uses B. subtilis to produce DRS-N1 (an AMP) within L. longipalpis, the disease vector. This AMP is a proven leishmanicidal and will halt the development of L. infantum, the parasite that causes visceral leishmaniasis, thereby breaking the cycle of the disease.
References
[1]. Thomaz-Soccol V, Pasquali AKS, Pozzolo EM, Leandro AS, Chiyo L. Baggio R, Michaliszyn MS, et al. More than the eyes can see: the worrying scenario of canine leishmaniasis in the Brazilian side of the triple border. PloS One. 2017;12(12)
[2]. Telleria EL, Pitaluga AN, Ortigão-Farias JR, de Araújo AP, Ramalho-Ortigão JM, Traub-Cseko YM. Constitutive and blood meal-induced trypsin genes in Lutzomyia longipalpis. Arch Insect Biochem Physiol. 2007 Oct;66(2):53-63. doi: 10.1002/arch.20198. PMID: 17879236
[3]. Prevention of insect-borne disease: An approach using transgenic symbiotic bacteria. Ravi V. Durvasula, Andrew Gumbs, Anil Panackal, Oleg Kruglov, Serap Aksoy, R. Bruce Merrifield, Frank F. Richards, Charles B. Beard. DOI: 10.1073/pnas.94.7.3274