Mon15 Apr04:45pm(15 mins)
Background: Previous research showed that experimental selection of paromomycin resistance (PMM-R) in Leishmania infantum triggered an increase in parasite fitness. Although no fitness gain was observed between wild type (WT) and PMM-R promastigotes, intracellular growth and in vivo infection capacity were clearly increased in PMM-R amastigotes. Given this enhanced fitness in the mammalian host, this laboratory study aimed to extend these findings by assessing the overall fitness of PMM-R parasites in the sandfly vector.
Materials and Methods: Female sandflies (Lutzomyia longipalpis and Phlebotomus perniciosus or P. argentipes) were artificially infected with WT and PMM-R promastigotes of L. infantum (MHOM/FR/96/LEM3323-cl4) or L. donovani (MHOM/NP/03/BPK275/0-cl18). Progression of the infection was closely monitored by microscopic evaluation of the parasite localization in dissected fly guts and quantification of the total parasite burdens at days 2, 5 and 9 post-infection.
Results: Although L. longipalpis is recognized as a susceptible fly for various Leishmania species, the infection burdens, metacyclogenesis rate and colonization of the stomodeal valve were considerably higher in the natural vectors P. perniciosus and P. argentipes. Despite these intrinsic differences in parasite susceptibility between both sand fly species, none of the models demonstrated significant dissimilarities between WT and PMM-R parasites.
Conclusion: The fitness gain linked to PMM-R is not observed in promastigotes. Despite their unaffected behavior in the vector, the enhanced virulence observed for PMM-R amastigotes in the mammalian hosts may nevertheless represent an advantage for transmission as this may lead to higher numbers of parasites acquired by bloodfeeding sandflies. To challenge this hypothesis, sandfly transmission studies on hamsters infected with either WT or PMM-R parasites are now being conducted.