Quantification of Leishmania infantum DNA in females, eggs and larvae of Rhipicephalus sanguineus

Abstract

Background: Leishmania infantum is a widespread parasite that affects dogs and humans worldwide. It is transmitted primarily by phlebotomine sand flies, but recently there has been much discussion on the role of the brown dog tick, Rhipicephalus sanguineus, as a potential vector for this protozoan. Recent laboratory and field investigations have contributed to this hypothesis, but a proof of the vector capacity of R. sanguineus has yet to be provided. Following a recent study suggesting that L. infantum passes transovarially from the female tick to her progeny the current study provides new evidence of the transovarial transmission of L. infantum in R. sanguineus.

Methods: Engorged females of R. sanguineus were collected from the environment in a dog shelter of southern Italy, where canine leishmaniosis is endemic. In the laboratory, 97 females that successfully laid eggs, their eggs and the originated larvae were subjected to DNA extraction and then tested by a TaqMan-based real time PCR targeting a fragment of the kinetoplast DNA (kDNA) of L. infantum.

Results and conclusions: L. infantum kDNA was detected in engorged females, their eggs and originating larvae, with a parasite load ranging from 1.8 × 10(-4) to 10.0 × 10(0). Certainly, the current study provides further evidence on the passage of L. infantum from R. sanguineus females to their offspring. The observation of promastigote forms in larvae is necessary to definitively confirm this hypothesis, which would raise interesting questions about the possible role of ticks in the maintenance of L. infantum infection among dogs in certain areas.

Figure 1

A standard curve of the log concentration of L. infantum DNA. Standard curve obtained from serial dilutions of L. infantum DNA, expressed herein as the number of parasites per reaction mixture (i.e., 2 μl of template DNA). Each point was tested in triplicate. Slope = -3.261; Efficacy = 102.6%; R² = 1.000.