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Tropical Tales Project Update: Raju & the Sand fly

December 9, 2010

Following on from our start a few months ago we have finished the first story with Bisakha Sarker and the production team (see previous posting).  This artwork is presented  as a sheet with numbers for each picture; the story is on a talking pen, recorded in four languages. The pen is placed on the relevant number and relevant part of the story is activated via the pen speaker.  Eimear Kavanagh created the beautiful artwork; some of it based on electron microscope images of the sand fly midgut!  There are sound effects created by Chris Davies and Dave Ward created the storyline.

This story is based on my work on the sand fly that transmits the parasite causing the disease leishmaniasis. The story is set in India where the sand fly Phlebotomus argentipes is the main vector of the deadly Leishmania donovani that causes visceral leishmaniasis (known in India as Kala Azar).

The basic story is that Raju and his sister are working together and Anu gets bitten by an infected sand fly and eventually gets leishmaniasis. They can’t afford the drug treatment and Raju wanders off into the forest where he falls asleep and dreams about being eaten by a sand fly. Inside the gut of the sand fly Raju fights with the leishmania parasites until the sand fly feeds on a plant and the plant sap kills the leishmania. Raju eventually wakes up, remembers his dream and goes and collects some plant herb that he dream’t about the sand fly eating and  then uses the herb to create a concoction that eventually cure Anu of her leishmaniasis.  Yes its a bit of a fairytale but there are elements of truth in this:-

  • Drug treatments are expensive and toxic..things called pentavalent antimonials that have been around since the 1930’s but there are now newer drugs such as liposomal amphotericin B (liposomes are used as a way to deliver the drug effectively into cells but i am wandering off the point here arent I?).
  • Sand flies don’t just feed on blood, in fact its only the female takes an occasional bloodmeal; perhaps twice in her short life. The rest of the time  she and he feed on plant sugars.  And research has shown that some sand flies will feed on plant sap that will actually kill the parasites in the sand fly gut (see footnote), this is a potential way  of controlling the spread of the parasite by encouraging plants that sand flies will feed on.  Also lots of research has been done on whether plant compounds can be developed as anti leishmania drugs.  A successful plant compound artemesinin is already being  developed as an antimalarial drug, but none so far for leishmaniasis.

Mortality of Leishmania major in Phlebotomus papatasi Caused by Plant Feeding of the Sand Flies

Y. Schlein, R. L. Jacobson Am. J. Trop. Med. Hyg., 50(1), 1994, pp. 20-27

The plant feeding of Phlebotomus papatasi and the effects of plant diets on the Leishmania major infections were investigated. Plant-fed flies had small free particles and membranous shreds in their gut that were stained by calcofluor as cellulosic plant tissues. They were found in 34.0% of the female and 14.3% of the male sand flies following feeding on the caper plant (Capparis spinosa). No plant residues were found in 54 females that had been fed on plant-derived honeydew secretions of Aphis craccivora offered on a branch of the host plant. Calcofluor-stained particles were also absent from the gut lumen of unfed flies. The proportion of sugar feeding, regardless of the intake of plant tissue, in the series that had been offered caper plant or honeydew was estimated by testing for the presence of fructose in the gut. The proportion of fructose-positive flies in each series, among both males and females, was 45%. Plant feeding in the field was demonstrated by finding tissue residues in the gut of 32.8% of female and 10.3% of male P. papatasi from the Jordan Valley. Feeding on specific plants was demonstrated using baits of branches suffused with food dye and finding the dye marker in wild-caught P. papatasi. The influence of plant diets on L. major infections in P. papatasi was as follows: Malva nicaeensis and the honeydew of Icerya purchasi produced thriving parasitemias; however, feeding on Ricinus communis, Capparis spinosa, and Solanum luteum caused > 50% mortality and deformation of parasites in 88%, 55%, and 46% of the infections, respectively. This type of injury was also observed in 21 of the 38 mature infections in field-caught flies. These observations imply that some plant diets of P. papatasi in the wild impair L. major infections in the flies, thereby decreasing their capacity to transmit leishmaniasis.

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