Leishmania : Now Found in Midges Down Under

                Leishmania was originally considered to have a limited geographic range that is determined by the traditionally accepted vector (sand flies). Phlebotomus is the commonly known vector of Leishmaniasis, and it is commonly accepted that no other vectors had been proven to exist. Recent investigation done by Dougall et al. (2011) has proven that Leishmania is present in Australia, and has also produced significant evidence that there is an additional vector of Leishmania in that region.

                Dougall et al. (2011) began research into the Leishmania outbreak in Australia in 2004 when cutaneous Leishmania was identified in wallabies, wallaroos and kangaroos within a wildlife facility. Several methods were used to gather potential vectors in two field sites in Northern Territory, Australia including sticky traps, emergence traps, light traps, or directly aspirating potential vectors when they were feeding on animals. All of the traps were left out overnight and checked the following morning (Dougall, et al., 2011). The phlebotomine flies and day feeding midges that were collected were then identified to the species level, if possible.

                It was discovered that the Phlebotomus sand flies were not present where the transmission of Leishmaniasis was occurring, which indicated that the vector was a different species. Dougall et al. (2011) tested 1818 female Sergentomyia sand flies (which were found within the field sites) for Leishmania using real-time PCR and came up negative. When day feeding midges were examined using the same testing methods, the prevalence of infection in all individually screened midges (F. pereginator and Forcipomyia sp.1 ) was 5.8% . While that percentage seems low, it compares very favorably to the typical sand fly infection rate (Dougall, et al., 2011). They also found that some midges that were dissected had promastigotes in their guts. All of the midges that were aspirated directly from the animals had promastigotes in their guts that were revealed upon dissection.

                In order to officially conclude that the day midges are a vector of Leishmaniasis , they had to meet five criteria, and the collected data supported four out of five of those criteria. Firstly, the day feeding midges were in the same environment as the infected animals. Secondly, the day feeding midges were observed biting reservoir hosts. Third, the dissections demonstrated development of Leishmania beyond a blood meal. That is, not only does the day midge take a blood meal, but the parasite is developing beyond the initial stage consumed. Dougall et al. (2011) proved that there were some day midges that hadn’t taken a blood meal, but still had evidence of promastigotes revealed in dissection.

The fourth criterion that was investigated by Dougall et al. (2011) is that the parasites from the wild caught vectors are identical to those in the reservoir host. RNA polymerase subunit II gene was used to compare Leishmania retrieved from a day midge to cultured parasite from the skin lesions found on infected red kangaroos. The only criterion that was not met was the demonstration of transmission of Leishmania from one infected host to an uninfected host via the midge bite. Dougall et al. (2011) mentioned the need for additional experiments to prove the last criteria. However, many of the accepted vectors of Leishmania were incriminated without that evidence, indicating that the last criteria is not very significant and does not affect the significance of the rest of the study.

This article doesn’t have anything to do with Balaenophilus or turtle parasites (my previous and future article topics) but is closely related to the in-depth class discussion on Leishmania. It was presented in the book and in lecture that there is only one vector of Leishmania and that the parasite is only present in very specific geographic locations. Dougall et al. (2011) presented very strong and convincing evidence that opens up the possibility of Leishmanias in many other geographic locations, including Australia (and possibly others that are unknown). If a day midge is a vector, then that introduces the possibility of additional life cycles and habitats that need to be taken into consideration to help prevent further transmission of the parasite. Phylogenetic analysis of a gene indicated that the Australian cutaneous leishmaniasis is very closely related to Leishmania enriettii, which is found in Brazil (Dougall et al., 2011). This investigation and article is a great example of the continuously expanding knowledge about parasites, specifically who their vector hosts are and their geographic locations.

Work Cited:

Dougall, A. M., B. Alexander, D.C. Holt, T. Harris, A.H. Sultan, P.A. Bates, K. Rose, S. F. Walton. 2011. Evidence incriminating midges (Diptera: Ceratopogonidae) as potential vectors of Leishmania in Australia. International Journal for Parasitology 41: 571 – 579.