Hantavirus Outbreak

Hantavirus is a zoonotic virus group characterized by an enveloped, single-stranded, negative-sense RNA genome belonging to the family Hantaviridae and the order Bunyavirales. In current taxonomy, the species that cause disease in humans are classified under the genus Orthohantavirus. This virus group uses rodents as its natural reservoir and transmits the pathogen from animals to humans, resulting in two distinct clinical syndromes: hemorrhagic fever with renal syndrome (HFRS) in Europe and Asia, and hantavirus cardiopulmonary syndrome (HCPS) in the Americas. Annual case numbers are estimated between 10,000 and 100,000, with the highest disease burden observed in Asia and Europe.^【1】

History

The earliest recorded clinical manifestations resembling hantavirus disease date back approximately one thousand years to China. In modern medical literature, the disease came to prominence during the Korean War (1951–1953) with an outbreak of about 3,200 cases among United Nations troops.^【2】 This condition, then known as "Korean hemorrhagic fever," is considered an early description of HFRS. The causative virus was only identified in 1976 when it was isolated from the striped field mouse (Apodemus agrarius) near the Hantaan River; the virus was subsequently named after this river.^【3】

A milder clinical form known in Northern Europe as "nephropathia epidemica" (NE) has been recognized since the 1930s, but its etiological agent, the Puumala virus (PUUV), was not isolated until 1980 from the bank vole (Myodes glareolus) in Finland.^【4】 Historical records indicate that hantavirus infections played a decisive role in military outbreaks; outbreaks among soldiers during World War II and the Balkan Wars are believed to have been associated with PUUV and Dobrava virus.^【5】

In the Americas, a different clinical syndrome, HCPS, was discovered in 1993 during an outbreak in the Four Corners region of the southwestern United States; the causative agent, Sin Nombre virus, was isolated from the deer mouse (Peromyscus maniculatus).^【6】

Classification and Virology

Hantaviruses belong to the family Hantaviridae within the order Bunyavirales; the species causing human disease are grouped under the genus Orthohantavirus. These enveloped, single-stranded, negative-sense RNA viruses have a genome composed of three distinct segments encoding surface proteins responsible for host cell attachment and enzymes regulating replication.

Virus species are classified into three main clades based on their rodent hosts: Old World mice and rats (Muridae); the subfamily Arvicolinae, comprising voles and lemmings; and species that use New World mice (Sigmodontinae and Neotominae) as hosts. This phylogenetic distinction also determines the nature of the clinical syndrome: viruses associated with Sigmodontinae and Neotominae primarily cause HCPS, while those linked to Murinae cause HFRS.

The major hantavirus species causing human disease exhibit marked differences in geographic distribution and clinical severity. Hantaan virus (HTNV), associated with the striped field mouse (Apodemus agrarius) in East Asia, causes severe HFRS. Dobrava virus (DOBV), which uses the yellow-necked field mouse (Apodemus flavicollis) as its host in the Balkans, is responsible for HFRS cases with high mortality. Seoul virus (SEOV), transmitted via the brown rat (Rattus norvegicus), is the only hantavirus species with a global distribution. Puumala virus (PUUV), associated with the bank vole (Myodes glareolus) in Europe, typically causes a mild form of HFRS.

In the Americas, Sin Nombre virus (SNV), linked to the deer mouse (Peromyscus maniculatus), is responsible for the majority of HCPS cases in the United States; Andes virus (ANDV), endemic to South America, is distinct among hantaviruses due to its limited capacity for human-to-human transmission.^【7】

Host Ecology and Reservoirs

Each hantavirus species has evolved to adapt to a specific rodent host. Infection in these hosts is asymptomatic and lifelong; for example, bank voles shed PUUV throughout their lives via feces, urine, and saliva. In recent years, hantaviruses have been detected in non-rodent animal species, but their ability to transmit the virus to humans has not yet been proven.

A comprehensive field study conducted in the United States between 2014 and 2019 detected hantavirus antibodies in 15 different rodent species, six of which were newly reported as hosts previously not identified.^【8】

Epidemiology

Global Distribution

A meta-analysis incorporating 110 studies across four continents estimated the global seroprevalence at 2.93%.^【9】 The case fatality rate varies between 1% and 15% in Asia and Europe, but can reach up to 50% in the Americas.^【10】

In East Asia, particularly in China and Korea, HFRS causes tens of thousands of cases annually; however, incidence has declined over the past decade. This decline is attributed to improved economic conditions and more effective rodent control measures.

Europe

In EU/EEA countries, between 1,500 and 5,000 cases are reported annually; the most commonly identified agent is Puumala virus.^【11】 Cyclical fluctuations in rodent populations in Northern Europe and rodent population explosions in Central Europe linked to seed abundance in forested areas can trigger outbreaks. Dobrava virus causes severe HFRS cases in the Balkans and surrounding regions.

Türkiye

The first laboratory-confirmed case of hantavirus infection in Türkiye occurred in January 2009. In this initial outbreak covering Zonguldak and Bartın provinces, 12 cases were confirmed, with PUUV identified as the dominant agent.^【12】 In 2010, severe cases associated with Dobrava virus were reported in Istanbul. Between 2012 and 2018, at least 20 additional cases were recorded from various provinces, primarily Düzce.^【13】 In Türkiye, the disease occurs predominantly in the Black Sea region and during spring to autumn months; farmers, foresters, soldiers, and laboratory personnel constitute the main risk groups.

Transmission Routes

The primary route of human infection is inhalation of aerosolized particles from the feces, urine, or saliva of infected rodents. Rodent bites, though rare, are also considered a possible transmission route. Activities such as agriculture, forestry, camping, and cleaning long-unoccupied enclosed spaces increase exposure risk. Smoking has been shown to increase transmission risk.

Human-to-human transmission has been documented only for the Andes virus (ANDV), which is endemic to South America. This transmission occurs under conditions of close and prolonged contact within the same household.

Recent Development: MV Hondius Outbreak (2026)

Between April and May 2026, a cluster of hantavirus cases involving multiple nationalities was identified aboard the MV Hondius cruise ship. According to a World Health Organization (WHO) statement dated 4 May 2026, seven cases were reported, including two laboratory-confirmed and five suspected; three deaths, one critical case, and three mild symptomatic cases were recorded.^【14】 The agent was confirmed as Andes virus; WHO noted the possibility of limited human-to-human transmission. The European Centre for Disease Prevention and Control (ECDC) assessment on 6 May 2026 confirmed that the outbreak was ongoing. WHO’s general public risk assessment remains low.

Pathogenesis

Two common mechanisms underlie both clinical syndromes: loss of vascular integrity and a decrease in platelet count. These processes are influenced by the immune response, coagulation system dysfunction, and damage to the vascular endothelium. Genetic susceptibility has also been shown to affect disease severity. In HFRS, the primary target organs are the renal microvasculature; in HCPS, the lungs are primarily affected.

Symptoms

The initial symptoms of hantavirus infection are typically nonspecific and may resemble those of many other illnesses, including influenza. Symptoms appearing one to eight weeks after exposure include high fever, severe headache, muscle pain, fatigue, nausea, vomiting, and abdominal pain. Facial flushing and periorbital edema may also occur in some patients. Depending on the causative virus, the disease progresses either toward signs of renal failure (HFRS) or respiratory distress (HCPS).

Clinical Syndromes

Hemorrhagic Fever with Renal Syndrome (HFRS)

HFRS is traditionally divided into five phases, although these phases often overlap. The incubation period averages three weeks. Febrile phase (3–7 days): begins with fever, headache, and myalgia; visual symptoms are common in PUUV infections. Hypotensive phase (several hours to 2 days): vascular leakage begins; severe cases may present with shock and hemorrhage. Oliguric phase (1–16 days): urine output declines, acute kidney injury develops; dialysis may be required in severe cases. Polyuric phase: indicates the beginning of renal recovery. Convalescent phase may last up to six months.^【15】

Disease severity varies significantly depending on the causative virus. Case fatality rates for Hantaan and Dobrava virus infections range from 5% to 15%, while those associated with Puumala virus are below 1%.^【16】

Hantavirus Cardiopulmonary Syndrome (HCPS)

HCPS is a syndrome caused by viruses endemic to the Americas, primarily affecting the lungs and heart. After initial influenza-like symptoms, cough and dyspnea develop within 4 to 10 days; the condition can rapidly progress to pulmonary edema and cardiogenic shock.^【17】 Mortality rates range from 30% to 50%, depending on treatment conditions.^【18】

Diagnosis

Early clinical diagnosis of hantavirus infection is difficult; symptoms overlap with those of influenza, COVID-19, leptospirosis, and sepsis. A detailed history including rodent exposure, occupation, and travel is critical.

Laboratory diagnosis relies on two primary methods. Serology detects antibodies against the virus in the blood; patients presenting to healthcare facilities typically test positive for acute-phase-specific antibodies. RT-PCR allows direct detection of viral genetic material and is more sensitive during the first week of illness. Virus isolation is performed only for research purposes under specialized biosafety conditions.

Treatment

There is currently no approved specific antiviral drug for hantavirus infection. Treatment is based on close clinical monitoring and supportive care.

In HFRS, the main approaches include balancing blood pressure with electrolyte infusions, administering dialysis when necessary, and providing respiratory support. Ribavirin has been used intravenously in severe HFRS cases; however, it has been reported to show insufficient efficacy in mild cases and to cause adverse effects.

In HCPS, the most effective intervention is extracorporeal membrane oxygenation (ECMO), which temporarily assumes the functions of the heart and lungs; it has been shown to significantly reduce mortality in severe cases. The use of corticosteroids in HCPS is discouraged. Research into antiviral drugs, immunotherapies, and vaccine candidates is ongoing.

Prevention and Control

There is currently no approved hantavirus vaccine in widespread use in the United States or EU/EEA countries. Inactivated HTNV and SEOV vaccines are used in South Korea and China; however, their efficacy is reported to be low.

The cornerstone of prevention is reducing contact with rodents. Key recommended measures include: implementing physical barriers to prevent rodent entry into homes, storage facilities, and workplaces; storing food in sealed containers inaccessible to rodents; cleaning surfaces contaminated with rodent excreta by first wetting them with disinfectant and then wiping with a damp cloth, avoiding dry sweeping; using appropriate masks, gloves, and eye protection in high-risk areas; and ventilating enclosed and long-unused spaces before cleaning.

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