The increasing burden of tick-borne orthonairovirus infections, such as Crimean-Congo hemorrhagic fever, is becoming a global concern for public health. In the present study, we identify a novel orthonairovirus, designated Yezo virus (YEZV), from two patients showing acute febrile illness with thrombocytopenia and leukopenia after tick bite in Hokkaido, Japan, in 2019 and 2020, respectively. YEZV is phylogenetically grouped with Sulina virus detected in Ixodes ricinus ticks in Romania. YEZV infection has been confirmed in seven patients from 2014–2020, four of whom were co-infected with Borrelia spp. Antibodies to YEZV are found in wild deer and raccoons, and YEZV RNAs have been detected in ticks from Hokkaido. In this work, we demonstrate that YEZV is highly likely to be the causative pathogen of febrile illness, representing the first report of an endemic infection associated with an orthonairovirus potentially transmitted by ticks in Japan.

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Parasitic helminths express various antigenic carbohydrates, which often account for serological cross-reactions. In serodiagnosis, it is essential to inspect cross-reactivity between the target parasite and other parasites in order to assess diagnostic performance. Our previous study showed that the Galbeta1-6Gal sequence was a common epitope between Echinococcus multilocularis (Em) and E. granulosus (Eg). Furthermore, compounds with this sequence from Fasciola hepatica (Fh) reportedly were recognized by sera with Eg infection. Our aim is to investigate whether this sequence is one of the widely common epitopes in many kinds of parasites. For various parasites, sera with Fh infection cross-reacted at the highest frequency (71.4%) against Em antigen. In patients with other parasitic infections, sera showed cross-reactions against Fh antigen bound to Em antigen with a high frequency (23.7%). Binding inhibition tests with commercial Galbeta1-6Gal disaccharide showed that Galbeta1-6Gal was the common epitope between not only Em, Eg and Fh, but also between various other parasites. Furthermore, the presence of the Galbeta1-6Gal epitope in Em antigen was confirmed by immunoblot testing with the specific antibody for this sequence. This study showed that the Galbeta1-6Gal sequence is one of the antigenic epitopes that accounts for serological cross-reactivity between Em and various other parasites.

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In serodiagnosis of cystic echinococcosis (CE) by Echinococcus granulosus infection, antigen B (AgB) has been utilized worldwide. However, it is known that about 40% of sera with alveolar echinococcosis (AE) by Echinococcus multilocularis infection recognize AgB. Furthermore, cross-reaction against AgB was also reported in sera from polycystic echinococcosis (PE) patients with Echinococcus vogeli infection. These findings indicate that AgB is widely common to the genus Echinococcus. On the other hand, AgB has several subunits, which are composed of the smallest 8-kDa subunit. In this study, reactivities of patient sera with three kinds of Echinococcus infections (CE, PE, and AE) were compared simultaneously under the same condition against three subunits of AgB (8, 16, and 24 kDa). Many articles have referred the fundamental 8- kDa subunit as a diagnostic antigen for CE. However, the reactivity for the 8-kDa subunit of the CE patient was not so high (47.7%) in this study. Furthermore, there are many cases in which serum of patients with PE or AE also recognizes this subunit (66.7% in PE; 45.9% in AE). AgB is effective for the detection of the genus Echinococcus infections, but it does not have high species specificity. Therefore, we need to pay attention to cross-reaction in serodiagnosis of CE in areas where plural species coexist.

In the serodiagnosis of alveolar echinococcosis, the detection of specific reactions against not only protein but also carbohydrate antigen is useful and both antigens supplement each other. Though recombinant protein antigens have recently advanced, the preparation of carbohydrate antigen still depends on extraction from crude antigens. In the latter case, it is not conventional to obtain carbohydrate antigen as a single component for examination and research. Therefore, chemically synthesized carbohydrate antigens were prepared for serodiagnosis by the enzyme-linked immunosorbent assay (ELISA). Four antigens with the structure of glycosphingolipids from Echinococcus multilocularis were examined and one antigen, Galbeta1-6(Fucalpha1-3)Galbeta1-6Galbeta1-ceramide, was found to show significant serodiagnostic potential in differentiating alveolar from cystic echinococcosis.