Hantavirus Infections — Treatment & Prevention

Hantaviruses are negative-sense, single-stranded, tri-segmented RNA viruses of the family Hantaviridae (order Bunyavirales). They are transmitted to humans via inhalation of aerosols from infected rodent excreta (urine, faeces, saliva) — there is no human-to-human transmission (except for Andes virus, uniquely).

Two distinct clinical syndromes dominate:

• Haemorrhagic Fever with Renal Syndrome (HFRS) — caused by Old World hantaviruses (Hantaan, Seoul, Puumala, Dobrava-Belgrade); fatality rate 1–15%; endemic in Asia and Europe. Features: fever, haemorrhage, acute kidney injury in 5 phases (febrile, hypotensive, oliguric, diuretic, convalescent)
• Hantavirus Pulmonary Syndrome (HPS) / Hantavirus Cardiopulmonary Syndrome (HCPS) — caused by New World hantaviruses (Sin Nombre virus/SNV, Andes virus); fatality rate 36–40%; endemic in the Americas. Features: prodromal flu-like illness → rapid non-cardiogenic pulmonary oedema → cardiogenic shock

Treatment remains largely supportive. Key supportive measures include: careful fluid management, renal replacement therapy for HFRS, and ECMO for HPS with severe cardiogenic shock.

Mechanism of Action

• Purine nucleoside analog; phosphorylated intracellularly to ribavirin triphosphate (RTP)
• Multiple proposed mechanisms: (1) inhibition of inosine monophosphate dehydrogenase (IMPDH) → depletes GTP pools; (2) direct RdRp inhibition; (3) lethal mutagenesis — increased error rate in viral RNA replication; (4) immunomodulatory effects on T-helper cell polarisation

HFRS — Effective: 83% Mortality Reduction

• IV ribavirin reduces HFRS mortality by 83% in a randomized controlled trial (Huggins et al., NEJM 1991) — the landmark study establishing ribavirin's role
• Must be given early (within first 4 days of febrile phase) for maximum benefit; efficacy declines markedly if started in oliguric phase
• Loading dose: 33 mg/kg IV, then 16 mg/kg q6h × 4 days, then 8 mg/kg q8h × 3 days
• Also used for Puumala and Seoul virus HFRS; oral ribavirin used in some settings with reduced but significant benefit
• Mechanism of superior activity in HFRS: Hantaan virus RdRp is highly susceptible to ribavirin mutagenesis; renal concentration of drug may enhance local effect

HPS / Sin Nombre Virus — Ineffective

• Ribavirin does NOT reduce mortality in HPS/SNV — the CONCORD study (Mertz et al., 2004) showed no benefit in IV ribavirin for HPS
• In vitro activity of ribavirin against SNV exists, but does not translate to clinical benefit — likely due to: rapid progression of cardiopulmonary failure before drug effect; immunopathological (rather than viral-replication-driven) disease mechanism in HPS; different host cell tropism
• HPS deaths occur primarily from immune-mediated capillary leak and myocardial depression — not viral replication per se
• Oral ribavirin studied prophylactically after rodent exposure — no controlled data supporting this use

• RNA-dependent RNA polymerase inhibitor; acts as a purine nucleotide mimic after intracellular activation to favipiravir-RTP
• Mechanism: incorporated into viral RNA → causes lethal mutagenesis (increased error rate beyond viability threshold)
• In vitro: active against Hantaan virus, Puumala virus, and Andes virus in cell culture models; effective at concentrations achievable in humans
• Animal models: Syrian hamster model of Andes virus infection — favipiravir significantly reduced viral RNA levels and lung pathology; hamsters treated prophylactically showed near-complete protection
• Advantage over ribavirin for HPS: favipiravir may offer activity against New World hantaviruses where ribavirin fails — animal data more promising
• No controlled clinical trials for hantavirus at time of publication (2020); case reports of compassionate use in severe HPS with anecdotal benefit
• Approved in Japan for novel influenza (Avigan); studied in COVID-19, Lassa fever, and multiple RNA viruses
• Dose: high loading doses required (6,000 mg day 1 → 2,400 mg/day); teratogenic — contraindicated in pregnancy

Vandetanib — VEGFR-2 Inhibitor

• Multikinase inhibitor targeting VEGFR-2 (vascular endothelial growth factor receptor 2), RET, and EGFR; FDA-approved for medullary thyroid cancer
• Rationale for hantavirus: The pathophysiology of HPS/HCPS involves hantavirus-induced VEGF upregulation → VEGFR-2 activation → increased vascular permeability → non-cardiogenic pulmonary oedema. Blocking VEGFR-2 would reduce capillary leakage
• In vitro and animal data: vandetanib reduced vascular permeability in Andes virus-infected endothelial cells; hamster model showed reduced lung oedema and improved survival
• Proposed mechanism: EBOV (Andes virus) activates VEGFR-2-mediated VE-cadherin phosphorylation → disrupts endothelial junctions → vandetanib preserves VE-cadherin integrity
• No controlled clinical trials for hantavirus; FDA compassionate use possible; repurposing from oncology is scientifically compelling

Lactoferrin

• Multifunctional iron-binding glycoprotein found in breast milk, saliva, tears, and secondary granules of neutrophils
• Antiviral activity against hantaviruses documented in cell-based assays — inhibits viral attachment to heparan sulfate proteoglycans on cell surface
• Immunomodulatory: promotes M1 macrophage polarization; enhances NK cell activity; modulates cytokine storm
• Bovine lactoferrin (bLf) showed activity against Hantaan virus in vitro at non-toxic concentrations
• Status: experimental; no clinical trial data for hantavirus; potential adjunctive role in early disease

Endothelin A Receptor Antagonist (ETAR)

• Hantavirus infection upregulates endothelin-1 → activates ETA receptors on endothelial cells → vasoconstriction and increased permeability
• ETAR blockade proposed as adjunctive strategy to reduce vascular leak in HPS; animal data limited; no human trial data

Corticosteroids

• Rationale: the immunopathological nature of HPS (T-cell and NK-cell-driven cytokine storm) suggests potential benefit from immunosuppression
• Clinical evidence: mixed; retrospective data suggests high-dose methylprednisolone may reduce duration of shock phase in HCPS; no randomised trial
• Risk: immunosuppression during active viral replication may worsen outcomes; use remains controversial and centre-dependent
• Not standard of care; considered in extreme cases with ongoing immunopathological deterioration

Passive transfer of immunity via convalescent plasma (CP) — plasma from recovered hantavirus patients containing neutralising antibodies — has been explored as a treatment option, particularly for HPS where ribavirin fails.

• Andes virus HPS: Two Chilean studies showed significantly lower mortality in CP-treated patients (case series; Vial et al. 2015 showed trend toward benefit); Andes virus is uniquely amenable because neutralizing antibody titres are high in convalescent individuals
• Sin Nombre virus HPS: Controlled clinical trial (PAHO/CDC) did not show mortality benefit — neutralizing antibody responses in SNV convalescents are lower, and immune-mediated pathology may be more dominant
• Timing: CP must be given early (prodromal or early cardiopulmonary phase) to show benefit; once cardiogenic shock established, passive immunisation is insufficient
• Standardization challenge: donor plasma must have sufficient neutralizing antibody titre (≥1:160 PRNT80); variable between donors; limited supply during outbreaks
• Monoclonal antibodies against hantavirus Gn/Gc glycoproteins under development — could replace convalescent plasma if titers and efficacy confirmed

Since no approved hantavirus vaccine exists outside of South Korea and China, primary prevention through rodent control remains the cornerstone of hantavirus prevention in most of the world.

Non-Pharmacological Prevention

• Avoid contact with rodents and their excreta (urine, droppings, nesting material)
• Rodent-proofing of homes and workplaces; snap traps and rodenticides for indoor rodent control
• Aerosol risk reduction: ventilate enclosed spaces before entering; wet-mop (don't dry-sweep) potentially contaminated areas; wear N95 mask if risk exposure unavoidable
• Camping hygiene: avoid sleeping on bare ground; store food in sealed containers; avoid rodent-infested cabins
• No human-to-human transmission for all hantaviruses except Andes virus — standard PPE sufficient for healthcare settings (except Andes virus cases in South America, where droplet precautions needed)

First-Generation Vaccines — Formalin-Inactivated

• Hantavax: formalin-inactivated Hantaan virus grown in suckling mouse brains; licensed in South Korea (1990); 3-dose schedule IM
• Efficacy: variable; seroconversion rates 70–97% after 2 doses; waning immunity — boosters required; limited protection against heterologous hantavirus strains
• Disadvantages: risk of residual mouse brain proteins (neurological adverse effects rare but reported); limited batch reproducibility; no cross-protection for New World hantaviruses
• Inactivated Hantaan and Seoul vaccines licensed in China; used in high-risk agricultural populations

Second-Generation Vaccines — Recombinant & VLP

• Recombinant subunit vaccines: Gn and Gc surface glycoproteins expressed in yeast, baculovirus, or mammalian cells as vaccine antigens; generate neutralizing antibodies targeting receptor-binding domain
• Virus-like particles (VLPs): Self-assembling hantavirus M-segment proteins (Gn/Gc) without genomic RNA; safe (non-infectious); elicit strong humoral and cellular responses; studied for Hantaan and Andes virus
• Adjuvant studies: AS01B, MF59, and Alhydrogel compared — AS01B-adjuvanted formulations show superior antibody titres and T-cell responses in preclinical models
• Status: multiple candidates in Phase I/II trials; none yet licensed outside Asia

Third-Generation Vaccines — Vector & DNA Vaccines

• GLS-5700: synthetic DNA vaccine encoding Andes virus Gn/Gc; Phase I clinical trial completed — safe and immunogenic; 100% seroconversion; strong T-cell responses; administered with CELLECTRA electroporation device for enhanced uptake
• MVA-vectored (Modified Vaccinia Ankara): recombinant MVA expressing hantavirus Gn/Gc — strong cellular immunity; used as prime or boost in heterologous prime-boost regimens
• Adenovirus-vectored: Ad5/Ad26 vectors expressing hantavirus glycoproteins; single-dose potential; thermostable formulations under development for field use
• mRNA vaccines: hantavirus Gn/Gc mRNA-LNP candidates in preclinical development post-COVID-19 mRNA platform validation — rapid development timeline possible

Vaccine Summary Table

• Ribavirin's differential efficacy is the key clinical fact: 83% mortality reduction in HFRS (IV, early); zero benefit in HPS/SNV — the syndrome determines the drug choice
• Favipiravir is the most promising candidate for HPS: active in vitro and in Andes virus hamster models where ribavirin fails; awaits clinical trial validation
• Vandetanib addresses the mechanism of HPS: VEGFR-2-driven vascular leak is the proximate cause of death in HPS — blocking this pathway is scientifically compelling; animal data encouraging
• Convalescent plasma works for Andes but not SNV: reflecting the different immunopathological mechanisms between Old World and New World hantavirus diseases
• ECMO is life-saving in refractory HPS shock: the single intervention with strongest evidence for preventing death once cardiogenic shock is established
• Rodent control is the most effective prevention: no universally approved vaccine outside East Asia; primary prevention remains behavioural
• GLS-5700 Phase I is a landmark: first DNA vaccine for hantavirus to demonstrate safety and immunogenicity in humans — paves the way for 3rd-generation vaccine development