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Hantaviruses are found practically all over the world and cause hemorrhagic fevers in man. Each year about 150,000 people are hospitalized in these zoonotic infections which can be of two types: hemorrhagic fever with renal syndrome (HFRS) or hantavirus cardiopulmonary syndrome (HCPS), depending on the infecting virus. Hantavirus infections are emerging infectious diseases. That is, the number of reported cases of hantaviral disease is increasing, new hantaviruses are discovered continually, and already known hantaviruses are expected to spread to new areas. Therefore, knowledge and monitoring of these viruses are imperative from a public health perspective.

In this thesis, the characterization of a local human Puumala (PUUV) virus isolate is described. Genetic and serological relationships to other hantaviruses are investigated and the viral protein interactions, critical for genome packaging and assembly, are studied. We found that the nucleotide and amino acid sequences of the local PUUV strains are significantly different from the PUUV prototype strain Sotkamo, a difference that indicates that there might be a risk of misdiagnosing PUUV infected patients when using reagents derived from the prototype strain. These data contributed to the introduction of locally derived diagnostic tools to the Laboratory of Clinical Virology at the Umeå University hospital, which is the reference centre for hantaviral diseases in Sweden. Furthermore, when studying the underlying mechanisms of genome packaging, we identified several regions and amino acids absolutely required for nucleocapsid protein interactions. Also, a region that appeared to regulate this interaction was discovered. Finally, the serological immune responses in DNA-vaccinated mice and PUUV infected patients were investigated. We found that the cross-reactive antibody response in vaccinated mice and in infected individuals was unique and independent of homologous titres. Furthermore, four immunodominant epitopes with specific cross-reactive characteristics were identified.

Our findings have highlighted the complexity of the serological immune responses to hantavirus infections, and they emphasize the importance of customizing the diagnostic tools and performing clinical analyses on locally derived strains. In conclusion, we believe that these results are valuable in the development of new serological, genetic, and epidemiological tools.

Puumala viruses, a member of the Hantavirus genus in the Bunyaviridae family, are enveloped by a lipid bilayer and possesses a tripartite single stranded RNA genome with negative polarity. The hantaviruses encode four proteins: a nucleocapsid protein (N), two membrane spanning glycoproteins (GN and GC) and a RNA dependent RNA polymerase (RdRp). Hantaviruses cause two forms of diseases, hemorrhagic fever with renal syndrome (HFRS) in Europe and Asia, and hantavirus pulmonary syndrome (HPS) in the Americas. The hantaviruses are mainly rodent borne, and humans are mostly infected by inhalation of aerosolized rodent secrete. Human Puumala virus infection results in nephropathia epidemica (NE), a mild haemorrhagic disease.

It is of importance to have a good understanding of the epidemiology and genetics of these viruses for the development of new diagnostic methods and for future vaccine development.

In this thesis we determined the complete viral genome sequence and characterized the structural proteins based on studies of expression and glycosylation patterns, for a unique human virus isolate; performed a genomic analysis of local Puumala viruses and their individual rodent host, Clethrionomys glareolus, from six different locations was performed. It was seen that the virus genetic variation between different locations could be stable over relatively large distances while there could be large variation over a short distance. For the bank voles no such variation could be seen; developed and evaluated Genetic vaccines, based on PCR-generated linear DNA. We showed that it was important to protect these fragments against nuclease degradation at that attachment of a nuclear localization signal peptide further improved the immune response. We also designed, fabricated and evaluated a 2000 probe cDNA-microarray for identification and differentiation of hantaviruses. The chips was based on 12 different strains of six hantaviruses and could differentiate between both different hantaviruses and strains within one hantavirus serotype.