We compared the biological properties of Oshima 5-10 (tick-borne encephalitis [TBE] virus isolated in Hokkaido, Japan) and Sofjin-HO (Far-Eastern subtype TBE virus) including plaque formation, virus replication and virus protein synthesis in BHK-21 cell cultures to reveal strain differences. We also determined the complete nucleotide sequences of both strains and compared the deduced amino acid sequences. Plaques of Oshima 5-10 were smaller than those of Sofjin-HO. Virus titers in culture fluid of Oshima 5-10 were 1/100 of those of Sofjin-HO at 9 and 12 hr after infection. Less viral protein and RNA syntheses of strain Oshima 5-10 was observed than with Sofjin-HO. Genetic analysis revealed 1.4% of amino acids to differ with Sofjin-HO. No difference between the two strains was detected in the motif sequence of the viral enzyme, cleavage sites of viral protein or glycosylation sites of NS1.

Mx1 (Myxovirus resistance protein) and Oas1b (Oligoadenylate synthetase-1), induced by type 1 interferon (IFN), play a role in early antiviral innate immunity by inhibiting the replication of viruses. In mice, Mx1 and Oas1b confer resistance to the infection of orthomyxoviruses including influenza viruses and flaviviruses including West Nile viruses, respectively. Laboratory mice have been used to study the mechanisms of the pathogenesis of these virus infections; however, it is possible that they are not a suitable model system to study these viruses, since most of the inbred laboratory mouse strains lack both genes. It has been reported that feral mouse-derived inbred strains show resistance to the infection of these viruses due to the presence of intact both genes. In this study, we generated congenic strains in which the Mx or Oas locus of the MSM/Mx (MSM) mouse was introduced to the most widely used mouse strain, C57BL/6J (B6). B6.MSM-Ms mice showed resistance to the infection of influenza virus but not of West Nile virus. On the other hand, B6.MSM-Oas mice showed resistance to the infection of West Nile virus but not of influenza virus. Our results indicate that Mx1 and Oas1b show highly antiviral specificity in mice possessing the same genetic background. Therefore, these congenic mice are useful for not only infection study but also investigation of host defense mechanism to these viruses.

West Nile virus (WNV) is a neurovirulent mosquito-borne Flavivirus that is maintained in nature by a zoonotic transmission cycle between avian hosts and ornithophilic mosquito vectors, mostly from the Culex genus. Until the 1990s, WNV was considered to be an old-world arbovirus, but in 1999, WNV emerged in the United States (US) and spread rapidly, becoming a major threat to public health. WNV adapted to the transmission cycle involving American mosquitoes and birds and reached Central and South America in subsequent years. In 2003, the National West Nile Fever Surveillance System was created in Brazil based on serological screening of animals and sentinel vectors, as recommended by the Pan American Health Organization (PAHO) and the World Health Organization (WHO). Since 2008, serological evidence of WNV infection in Brazilian horses has been reported, and the circulation of WNV has been monitored through the regular serological screening of sentinel horses and reporting of encephalomyelitis cases. Horses are highly susceptible to WNV infection, and outbreaks of neurological disease among horses often precede human cases. In this regard, equine surveillance has been essential in providing early warning to public and animal health authorities in several countries, including Brazil. This demonstrates the need for animal and public health intervention programs to allocate resources to make veterinarians aware of the role they can play in the human surveillance processes by monitoring horses. This review discusses the importance of equine surveillance and the gap that veterinarians can fill on the front line in human surveillance, in Brazil and worldwide, in the context of “One Health”