Researchers investigating vector-borne pathogens have identified the biting midge Culicoides sonorensis as a permissive vector capable of supporting the development of Leishmania enriettii complex parasites. Laboratory experiments demonstrated that these midges can develop late-stage infections of the parasite, offering new insight into the epidemiology of a disease complex that remains poorly understood.
Experimental Vector Competence in Biting Midges
The transmission dynamics and biological vectors of the Leishmania enriettii complex have historically lacked clear documentation. While biting midges of the genus Forcipomyia have previously been implicated in parasite transmission in Australia, widespread testing of the more common Culicoides genus had not been conducted. To test vector potential, investigators experimentally infected female midges from colonies of Culicoides nubeculosus and Culicoides sonorensis, alongside the sand fly Lutzomyia longipalpis, with parasite strains originating from Australia and Brazil.
The results showed distinct variations in susceptibility among the tested dipteran species. Culicoides nubeculosus showed no susceptibility to infection by the parasites. In contrast, Culicoides sonorensis supported the development of late-stage infections, with parasites successfully colonizing both the thoracic midgut and the stomodeal valve. The sand fly Lutzomyia longipalpis also supported development, though infection rates were relatively poor compared to other Leishmania species.
Host Pathology and Xenodiagnosis Results
To further test infectivity, researchers utilized xenodiagnosis on infected animal models, including golden hamsters and guinea pigs. The clinical manifestation of L. enriettii infection varied significantly between the two rodent species. Hamsters developed only mild symptoms following experimental inoculation. Conversely, guinea pigs experienced aggressive parasite growth, resulting in large, ulcerated, tumor-like lesions.
When vectors fed on the affected areas of these guinea pigs, a high proportion of Culicoides sonorensis—reaching up to 80 percent—became infected, particularly when feeding on the ears and nose. These findings confirm that C. sonorensis can acquire the parasite through blood-feeding on symptomatic hosts, establishing a potential pathway for transmission studies going forward.
Implications for Vector-Borne Disease Research
The identification of Culicoides sonorensis as a competent laboratory vector for Leishmania enriettii expands the known host range for these parasites beyond traditional phlebotomine sand flies.
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