Leishmania parasites (Kinetoplastida: Trypanosomatidae) are digenetic protozoa responsible for a group of parasitic diseases generally referred to as the leishmaniases. These diseases, most of which are zoonoses, are responsible for a huge burden on public health, causing considerable morbidity and mortality in about 88 countries over the world [1, 2]. Among the different clinical forms of the disease, the visceral one is of major importance for being life-threatening and for affecting mainly children and immunodepressed individuals [1, 2].
Leishmania infantum (synonym, Leishmania chagasi) is one of the causative agents of visceral leishmaniasis, an important zoonosis in Europe, Africa, Asia and America [1–4]. This protozoan is primarily maintained in nature by wild reservoir hosts, such as rodents, marsupials, edentates and canids . In the peridomestic transmission cycle, dogs play a role as reservoir hosts for L. infantum, mainly because they are quite susceptible to the infection and present a typically heavy skin parasitism , which ultimately facilitates the acquisition of the parasites by phlebotomine sand fly vectors (Diptera: Psychodidae), while they are taking a bloodmeal.
Although L. infantum is primarily transmitted by phlebotomine sand flies , secondary modes of transmission (e.g., transplacental transmission and via blood transfusion) have been claimed to exist [8–10]. Recently, it has been demonstrated that day-feeding midges (Diptera: Ceratopogonidae) of the genus Forcipomyia can support the development of an undescribed species of Leishmania that was originally detected in red kangaroos (Macropus rufus) in Australia around eight years ago . Moreover, there has long been speculation about the role of fleas and ticks as vectors of L. infantum and recent studies have reinforced this hypothesis [13, 14]. Nonetheless, a definitive proof that fleas or ticks can efficiently transmit L. infantum from dog to dog under natural conditions has yet to be provided .
In a recent study, L. infantum kinetoplast DNA (kDNA) was detected in eggs and larvae from infected females, even four months post-inoculation, suggesting the possibility of transovarial passage of the protozoa in R. sanguineus. However, the aforementioned study was performed using experimentally infected females, which were artificially inoculated with stationary-phase promastigotes . Undoubtedly, it would be valuable to reassess this hypothesis using naturally infected females. In this perspective, the present investigation was carried out in order to demonstrate the occurrence of transovarial passage of L. infantum kDNA in naturally infected R. sanguineus ticks. In particular, the research's specific objectives were to detect and quantify the amount of L. infantum kDNA present in engorged, wild-collected females, their laid eggs and the originating larvae, using a highly sensitive real time polymerase chain reaction (PCR) protocol.