Repeated Sand Fly Bites of Infected BALB/c Mice Enhance the Development of Leishmania Lesions

Abstract

Sand fly saliva has considerable immunomodulatory effects on Leishmania infections in mammalian hosts. Studies on several Leishmania – sand fly - host combinations have demonstrated that co-inoculation with Leishmania parasites enhances pathogenicity, while pre-exposure of hosts to sand fly bites provides significant protection against infection. However, the third scenario, the effect of sand fly saliva on parasite development in hosts infected before exposure to sand flies, remains an understudied aspect of Leishmania–host–vector interaction. Here we studied the effect of exposure of L. major-infected BALB/c mice to repeated sand fly bites. Mice infected intradermally with sand fly-derived Leishmania were repeatedly bitten by Phlebotomus duboscqi females every two weeks. The lesion development was recorded weekly for ten weeks post-infection and parasite load and distribution in various organs were tested post mortem using qPCR. Repeated sand fly bites significantly enhanced the development of cutaneous lesions; they developed faster and reached larger size than in unexposed mice. Multiple sand fly bites also increased parasites load in inoculated ears. On the other hand, the distribution of parasites in mice body and their infectiousness to vectors did not differ significantly between groups. Our study provides the first evidence that multiple and repeated exposures of infected BALB/c mice to sand fly bites significantly enhance the progress of local skin infection caused by Leishmania major and increase tissue parasite load, but do not affect the visceralization of parasites. This finding appeals to adequate protection of infected humans from sand fly bites, not only to prevent transmission but also to prevent enlarged lesions.

Steppe lemmings and Chinese hamsters as new potential animal models for the study of the leishmania subgenusMundinia(Kinetoplastida: Trypanosomatidae)

“…Interestingly, only lemmings used for xenodiagnoses developed pathological signs on the ears. This is consistent with results previously published by Vojtková et al (2021) (52) in BALB/c mice infected with L. major, showing that sand fly bites post infection enhance formation of skin lesions.…”

“…It would be interesting to perform long term experiments and observe dynamics of the infection in several time intervals. Interestingly, only animals exposed to sand flies remained infected, whereas no parasites were observed in other animals, which also supports the influence of sand fly bites on the course of infection (Vojtková et al 2020) (52).…”

Steppe lemmings and Chinese hamsters as new potential animal models for the study of the Leishmania subgenus Mundinia (Kinetoplastida: Trypanosomatidae)

“…Interestingly, only lemmings used for xenodiagnoses developed pathological signs on the ears. This is consistent with previously stated hypothesis of enhancing effect of sand fly bites to the course of infection by Vojtkova et al (2021), who observed significantly faster and to a larger size lesion development in L. major infected BALB/c mice exposed to repeated bites of P. dubosqci compared to the unexposed group of mice, and the tissue parasite load was higher in rodents exposed to repeated bites [55]. Also in hamster model, increased transmissibility of L. donovani was observed following multiple exposures of hamsters to Lutzomyia longipalpis bites [56].…”

“…major infected BALB/c mice exposed to repeated bites of P . dubosqci compared to the unexposed group of mice, and the tissue parasite load was higher in rodents exposed to repeated bites [ 55 ]. Also in hamster model, increased transmissibility of L .…”

Characterization of bacteria expectorated during forced salivation of the Phlebotomus papatasi: A neglected component of sand fly infectious inoculums

“…It is also possible that the forced feeding process egestes more bacteria than normal which should wait for more details in future studies. Moreover, studies on multiple Leishmania -sand fly-host combinations have uncovered that pre-exposure of hosts to sand fly bites confers significant protection against Leishmania infection [ 80 ]. In the distant years, this pre-immunity was attributed to at least 20 diverse salivary proteins with anti-hemostatic and anti-inflammatory properties [ 24 ], but studies in recent years have emphasized the role of bacteria transmitted along with saliva [ 18 , 20 ].…”