Experimental Infection of Dogs with Toscana Virus and Sandfly Fever Sicilian Virus to Determine Their Potential as Possible Vertebrate Hosts

Abstract

The sandfly-borne Toscana phlebovirus (TOSV), a close relative of the sandfly fever Sicilian phlebovirus (SFSV), is one of the most common causes of acute meningitis or meningoencephalitis in humans in the Mediterranean Basin. However, most of human phlebovirus infections in endemic areas either are asymptomatic or cause mild influenza-like illness. To date, a vertebrate reservoir for sandfly-borne phleboviruses has not been identified. Dogs are a prime target for blood-feeding phlebotomines and are the primary reservoir of human sandfly-borne Leishmania infantum. However, there are no definitive studies to assess whether dogs play a significant role as a reservoir host for human phlebovirus survival in the environment. Here, we have evaluated the susceptibility of domestic dogs to infection by TOSV and SFSV following the direct inoculation of the infectious virus. After experimental infection, the presence of viral RNA was investigated in plasma, urine, saliva, conjunctiva, faeces, semen, and bone marrow samples from 0 to 91 days postinoculation (dpi), as well as in plasma, saliva, and tears samples at 760 dpi. None of the challenged dogs developed clinical signs of infection with either TOSV or SFSV. SFSV RNA was never detected. TOSV RNA was not in any of the specimen types, except for plasma samples that showed low viral loads, although irregularly. None of the dogs developed detectable neutralizing antibodies after a single challenge dose of either TOSV or SFSV. However, a second challenge dose of virus given 56 days later elicited neutralizing antibodies, implying that the first inoculation of virus primed the animals for an anamnestic response following the second challenge. These results demonstrated that healthy domestic dogs are not highly susceptible to infection by TOSV or SFSV and do not develop significant viremia or excrete virus following infection. Consequently, dogs are unlikely natural reservoir hosts of infection and do not appear to play a significant role in phlebovirus transmission cycles.

Transmission Dynamics of Punique Virus in Tunisia

“…The question of the vertebrate reservoir remains unanswered. It was suggested that vertebrates play a minor potential role in the transmission and the ecology of the virus but rather provide the blood necessary for the development of eggs [ 44 ]. However, the question of a putative animal reservoir may be relevant as, for example, TOSV was isolated from the brain of a bat ( Pipistrellus kuhlii ) captured in an endemic area in Italy [ 45 ].…”

Exposure to Phlebotomus perniciosus sandfly vectors is positively associated with Toscana virus and Leishmania infantum infection in human blood donors in Murcia Region, southeast Spain

“…The epidemiology of these infections is distinctly different. Dogs are the primary reservoir of L. infantum but not for TOSV, and the epidemiological cycle and reservoir hosts of TOSV have not been determined (Muñoz et al., 2020 ). Finally, it is important to consider that the observed prevalence of L. infantum in blood donors may be an underestimation of the true prevalence in Murcia.…”

Serological Evidence of Phleboviruses in Domestic Animals on the Pre-Apennine Hills (Northern Italy)

“…According to a recent study, healthy domestic dogs are not highly susceptible to infection by TOSV or SFSV and do not develop significant viremia or excrete the virus following infection. Consequently, dogs are unlikely natural reservoir hosts of infection and do not appear to play a substantial role in phleboviral transmission cycles [5]. However, dogs can be considered to be potential sentinels for exposure to TOSV transmission by sand flies in the Mediterranean region.…”

“…Many phleboviruses have been detected in domestic animals, although their pathogenic role remains unclear [5] or has only been recognized years after their effective discovery; indeed, the first evidence that TOSV caused disease in humans was reported 12 years after its initial isolation [6]. The epidemiology of phleboviruses is enigmatic; for instance, the existence of vertebrate reservoirs is still debated.…”