Puumala orthohantavirus: prevalence, biology, disease, animal models and recent advances in therapeutics development and structural biology

Abstract

Puumala orthohantavirus (PUUV) is an emerging zoonotic virus that was first discovered in the Puumala region of Finland in the early 1980s and is the primary etiological agent of nephropathia epidemica (NE), a milder form of a life-threatening disease known as hemorrhagic fever with renal syndrome (HFRS). PUUV and other members of the Old World hantaviruses (OWHVs) predominantly circulate in rodents or insectivores across Eurasia, accounting for several thousand of reported HFRS cases every year (with many more unreported/misdiagnosed cases suspected). The rodent reservoir of PUUV is the common bank vole (Myodes (M.) glareolus), and transmission of the virus to humans occurs via inhalation of contagious aerosols and through contact with contaminated droppings or urine. Although PUUV is the subject of extensive research, due to its potential to cause severe disease outcomes in humans and its considerable economic and social impact, neither licensed vaccines nor specific antiviral treatments are available against PUUV. However, many important advancements have been made in terms of PUUV research over the last years. This included the elucidation of its glycoproteins, the discovery of broadly neutralizing hantavirus antibodies as therapeutic candidates and expanded research on the mRNA vaccine technology which will likely enable the development of strong PUUV vaccine candidates in the near future. Currently, there is still a lack of suitable animal models for the preclinical evaluation of experimental vaccines and antivirals, which hampers vaccine and antiviral development. Current attempts to decrease hantavirus-associated human infections rely primarily on prevention and countermeasures for rodent control, including reduced contact to droppings, saliva and urine, and disinfection of areas that are contaminated with rodent excreta. Here, we review these recent advances and other aspects including PUUV prevalence, virus biology, diagnosis and clinical features, and current animal models for vaccine and treatment development.

Keywords: Puumala orthohantavirus; animal models; antiviral treatment; glycoprotein; nephropathia epidemica; vaccine research.

Figure 1

The virus particle and genome structure of Puumala orthohantavirus (PUUV). (A) The genome structure of orthohantaviruses, based on PUUV strain Sotkamo, accession numbers MN832782.1, MN832783.1, and MN832784.1 for the L, M, and S segment, respectively. (B) The S segment encodes for the nucleoprotein (433 aa) and the non-structural protein (90 aa), the M segment encodes for a glycoprotein precursor (1,148 aa), and L segment encodes for an RNA-dependent RNA polymerase (2,156 aa). Created with BioRender.com.

Figure 2

The organization of hantavirus spikes and the glycoprotein shell. The left panel shows a surface representation of the hantavirus spike in a side view. In the front protomer, Gn^H, Gn^B, and Gc are colored red, cyan, and yellow, respectively, as indicated. The TMIS is colored orange, and the N-glycans are shown in green. For clarity, the other protomers are colored differently: Gn in gray, and Gc in brown. The approximate positions of the viral membrane and the symmetry axis are indicated with lines. The right panel is a reconstruction of the hantavirus glycoprotein shell, with Gn and Gc colored red and yellow, respectively.

Figure 3

Hantavirus life cycle. The hantavirus life cycle consists of ten major steps, that are necessary to release new viral particles. [1] Hantaviruses bind to their respective receptor on the surface of the host cell with the envelope glycoproteins Gn/Gc. [2] Entry of the viral particles occur either via clathrin-dependent (OWHVs, e.g., PUUV) or clathrin-independent endocytosis (NWHVs). [3] The viral glycoproteins dissociate from the cellular receptors and traffic through the endocytic pathway. [4] Low pH of the endosomes and other cellular factors trigger a membrane-fusion process between viral and cellular membranes. [5] Viruses are uncoated and viral genome and proteins are released into the cytoplasm. [6] Viral RNA (vRNA) is transcribed by the RNA-dependent RNA polymerase (RdRp) and [7] mRNA is subsequently translated into different viral proteins, which are necessary to hijack the host cell machinery. [8] vRNA is synthesized and [9] new viral particles are assembled at the [9a] Golgi-complex (OWHVs, e.g., PUUV) or at the [9b] cell membrane (NWHVs). [10] Viral particles are released by fusion of the Golgi-complex (OWHVs, e.g., PUUV) or viral vesicle (NWHVs) with host cell membrane. E.E., early endosome; L.E., late endosome. Created with BioRender.com.

Figure 4

Antiviral type I interferon (IFN) response pathway and known evasion mechanisms of orthohantaviruses. Based on data from Hantaan orthohantavirus (HTNV) (127), Puumala orthohantavirus (PUUV) (–131), Tula orthohantavirus (TULV) (128, 129, 131, 132) and Andes orthohantavirus (ANDV) (–136). In infected cells, viral components or by-products, called pathogen-associated molecular patterns (PAMPs) are recognized by pathogen recognition receptors (PRRs), such as melanoma differentiation-associated gene 5 helicase (MDA-5), retinoic acid-inducible gene I helicase (RIG-I) or Toll-like receptors (TLRs). Receptor-ligand binding activates the type I IFN pathway resulting in the activation of TANK-binding kinase 1 (TBK1) and IkappaB kinase (IKK), which causes the phosphorylation and activation of IFN regulatory factors (IRF) 3/IRF7 and/or NfκB, leading to the expression of different type I IFNs. IFNs are released and bind to type I IFN receptors, thereby activating Janus kinase 1 (Jak1) and tyrosine kinase 2 (Tyk2). Once activated, the two proteins activate signal transducers and activators of transcription 1 and 2 (STAT1 and STAT2), which become phosphorylated and form a complex with IRF9, subsequently inducing the expression of different IFN-stimulated genes (ISGs). Hantaviruses evolved different immune evasion mechanisms to avoid detection by PRRs or interfere with downstream factors of the type I IFN pathway. These antagonisms are associated with hantavirus N (, , –137), Gc/Gn (127, 132, 136) or NSs (128, 129, 131). MAVS, mitochondrial antiviral-signaling protein; STING, stimulator of interferon genes; TRIF, TIR-domain-containing adaptor inducing IFN-β; TRAM, TRIF-related adaptor molecule; TRAF, tumor necrosis factor receptor associated factor; TRIM, tripartite motif-containing; IFNAR, interferon α/β receptor. Created with BioRender.com.

Figure 5

Schematic representation of the Puumala virus (PUUV) infection kinetics in humans. Typically, the severe clinical course of nephropathia epidemica (NE) that is caused by PUUV can be divided into five stages, which are not easily distinguishable: febrile, hypotensive, oliguric, diuretic and convalescent. The incubation period of PUUV infections ranges between 2-6 weeks, and is associated with an increase in viral load. The onset of the first symptoms is accompanied with an increase in antibody titers. Adapted from Avšič-Županc T et al. (138) and Mustonen et al. (145). Created with BioRender.com.

Figure 6

Clinical representation of hemorrhagic fever with renal syndrome (HFRS) and nephropathia epidemica (NE) caused by Puumala orthohantavirus. The main clinical symptoms are myalgia, backache, abdominal pain, vomiting, diarrhea, cough, headache, fever, systemic inflammation and blurred vision. Created with BioRender.com.