Mosquito Saliva Modulates Japanese Encephalitis Virus Infection in Domestic Pigs

Abstract

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that is the leading cause of pediatric viral encephalitis in Asia. Japanese encephalitis virus is transmitted by Culex species mosquitoes that also vector several zoonotic flaviviruses. Despite the knowledge that mosquito saliva contains molecules that may alter flavivirus pathogenesis, whether or not the deposition of viruses by infected mosquitoes has an impact on the kinetics and severity of JEV infection has not been thoroughly examined, especially in mammalian species involved in the enzootic transmission. Most JEV pathogenesis models were established using needle inoculation. Mouse models for West Nile (WNV) and dengue (DENV) viruses have shown that mosquito saliva can potentiate flavivirus infections and exacerbate disease symptoms. In this study, we determined the impact of mosquito salivary components on the pathogenesis of JEV in pigs, a species directly involved in its transmission cycle as an amplifying host. Interestingly, co-injection of JEV and salivary gland extract (SGE) collected from Culex quinquefasciatus produced milder febrile illness and shortened duration of nasal shedding but had no demonstrable impact on viremia and neuroinvasion. Our findings highlight that mosquito salivary components can differentially modulate the outcomes of flavivirus infections in amplifying hosts and in mouse models.

Re-Examining the Importance of Pigs in the Transmission of Japanese Encephalitis Virus

“…However, natural infection and disease in young piglets are not commonly reported from the endemic areas, possibly due to the presence of maternal antibodies, which can last up to six months of age [ 46 , 47 ]. While non-specific clinical signs such as fever, anorexia, and depression are observed early with JEV infection, neurologic signs such as hind limb tremors or ataxia can sometimes develop after five days post-infection [ 48 , 49 , 50 , 51 , 52 ]. Some infected pigs can progress into developing a wasting-like syndrome [ 52 , 53 ].…”

“…To date, laboratory studies have demonstrated that domestic pigs from various geographic regions are all susceptible to JEV and can be infected with the representative strains of endemic GI-b and GIII using different routes of infection, including intravenous, subcutaneous, intradermal, and intranasal challenge [ 19 , 51 , 52 , 53 , 66 ]. Similar pathologic outcomes and immune responses were observed in these infected pigs regardless of the challenge modality [ 19 , 66 ].…”

“…Viremia can be detected as early as 1-day post-infection (dpi) and persists for 4 to 5 days, and it is somewhat surprising that there are no demonstrable differences in the level and kinetics of viremia between different routes of challenge [ 19 , 66 ]. The highest viremic titers generally exceed 10 5 50% tissue culture infectious dose (TCID 50 )/mL or 10 6 plaque forming unit (PFU)/mL between 1 and 5 dpi [ 19 , 50 , 51 , 66 , 68 ]. These viremic titers have been proven to be sufficient for the infection of Cx.…”

“…The YL2009-4 strain (approximately 5 log 10 focus forming unit (FFU)/mL) was reported to multiply to higher titers than the CH1392 strain (approximately 3 log 10 FFU/mL) at least at 2 dpi. Other experiments have also proven that another GI-b strain, JE-91, can also multiply to approximately 5 log 10 PFU/mL between 2 and 3 dpi [ 51 ]. These observations imply that JEV strains belonging to GI-b may have the fitness advantage over JEV GIII strains, and one cannot exclude that the higher viremic titers in pigs may facilitate the enzootic and epizootic transmission of GI-b JEV in specific ecological conditions.…”

“…The development of viremia leads to the rapid and systemic spread of JEV in pigs. Viral dissemination and neuroinvasion coincide with the peak of viremia, leading to the detection of infectious viruses and viral genome in multiple types of tissues [ 50 , 51 , 68 , 75 ]. In contrast to other mammalian species, the neuroinvasive phenotype of JEV does not cause lethal diseases in pigs.…”