During November–December 2021, three persons in Germany experienced typical initial signs of hantavirus disease (fever, malaise, myalgia, chills, low-back pain, nausea) (Table 1). The patients lived ≈25 km apart. All 3 patients had acute kidney injury with reduction of glomerular filtration rate, proteinuria, and microhematuria. Moreover, biochemical analysis revealed typical thrombocytopenia and signs of inflammation, including elevation of C-reactive protein and transaminases. Serum creatinine levels remained within reference ranges or were only transiently higher. The patients recovered and were discharged after 3–6 days (Table 1).

All 3 patients developed IgM and IgG against diagnostic antigens from the group of murine-associated hantaviruses, including Hantaan virus, Dobrava-Belgrade virus, and SEOV. After onset of disease, we performed panhantavirus PCR, reverse transcription PCR based on amplification of a 412-nt region of the genomic large segment (8), to detect hantavirus genetic material from serum samples of patients 1 and 3 (Table 2).

Patients 1 and 2 were married to each other and lived in the federal state of North Rhine-Westphalia. Their children (persons 12a and 12b) (Table 2) remained healthy and did not seroconvert. The family was known to keep pet rats at home. Patient 3, who lived in Lower Saxony, reported that his girlfriend also kept pet rats. Investigation of his girlfriend (person 4) showed that she remained healthy; however, her hantavirus IgM negative/IgG positive serostatus suggested a previous subclinical infection (Table 2).

Figure

Figure. Phylogenetic tree of partial large segment Seoul virus sequences from humans and rats, Germany. Segments were 412-nt long, positions nt 2919–3330 based on reference sequence (KM948594_Cherwell_GBR_BR). The partial large segment...

The family of patients 1 and 2 permitted us to test their pet rats. We amplified the corresponding region from the genomic large segment. Phylogenetic analysis of the amplified virus sequences from patients 1 and 3 and the pet rats revealed almost identical sequences (Figure). We compared them to the amplified virus sequences from a previous unrelated patient and her pet rat from Lower Saxony (4).

Phylogenetic analysis disclosed the detected virus sequences as SEOV and, moreover, demonstrated the high relatedness of virus sequences from patient and pet rats from North-West Germany. The high similarity of SEOV sequences from Germany to sequences derived from breeder rats in the Netherlands, France, and the United States, but not to sequences from wild rats of those countries, suggests an intensive exchange of pet rats between neighboring countries in Europe and between Europe and the United States (7).

Human SEOV infections might be underestimated because the nucleocapsid proteins used in serologic assays share high amino acid sequence similarity and cross-reactivity with different hantavirus species. To explore this hypothesis in an external quality assessment, we sent a serum sample from patient 3, obtained 2 months after complete recovery, to 8 expert laboratories in Europe. All laboratories analyzed the sample in their routine hantavirus diagnostics, including commercial and lab-derived enzyme immunoassays, immunofluorescence assays, rapid assays, and immunoblots for confirmation (Appendix Tables 1, 2). Results revealed strong cross-reactivities to related hantavirus nucleocapsid proteins in IgG and IgM screening and in confirmation assays, making correct serotyping impossible. Thus, in cases of unexpected pattern in serodiagnostics or cases of known contact to rats, we strongly recommend verifying positive results with molecular methods or by typing of neutralizing antibodies. Only the laboratory using a focus reduction neutralization assay identified the SEOV infection (Appendix Table 1).

A total of 6 molecularly proven SEOV-infected patients in Germany have been described: 1 imported case (9), 1 autochthonous case (4), and the 3 symptomatic case-patients and 1 asymptomatic case-patient we described in this report. Five of these persons had been admitted to hospital for several days. In all autochthonous cases, pet rats were confirmed as source of infection, strongly suggesting a need for close cooperation between public health and animal health institutions in the One Health frame. Pet rats, in addition to wild and breeder or feeder rats, should be considered threats for SEOV infection in humans.