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, leading to 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】

The earliest recorded clinical manifestations resembling hantavirus disease date back approximately a 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 the 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 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】

Hantaviruses belong to the family Hantaviridae within the order Bunyavirales; 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 for host cell attachment and enzymes for 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 using New World mice (Sigmodontinae and Neotominae) as hosts. This phylogenetic distinction determines the nature of the clinical syndrome: viruses associated with Sigmodontinae and Neotominae primarily cause HCPS, while those linked to Murinae cause HFRS.

Major hantavirus species causing human disease show distinct geographic distributions and clinical severity. Hantaan virus (HTNV), associated with the striped field mouse (Apodemus agrarius) in East Asia, causes severe HFRS. Dobrava virus (DOBV), using 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 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), associated with 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】

Each hantavirus species has evolved to adapt to a specific rodent host. Infection in the host is asymptomatic and lifelong; for example, the bank vole sheds PUUV throughout its life via feces, urine, and saliva. Although in recent years hantaviruses have been detected in non-rodent animal species, their ability to transmit infection 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 identified as hosts.^【8】

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

In EU/EEA countries, 1,500 to 5,000 cases are reported annually; the most frequently 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 trigger outbreaks. Dobrava virus causes severe HFRS cases in the Balkans and surrounding regions.

The first laboratory-confirmed case of hantavirus infection in Türkiye occurred in January 2009. In this initial outbreak covering the provinces of Zonguldak and Bartın, 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 predominantly occurs in the Black Sea region and during spring to autumn months; farmers, foresters, military personnel, and laboratory staff constitute the primary risk groups.

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 only been documented 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.

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 patient, and three individuals with mild symptoms 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 the situation was still evolving. WHO’s overall risk assessment for the general public remains low.

Both clinical syndromes share two central mechanisms: loss of vascular permeability and a reduction 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.

The initial symptoms of hantavirus infection are typically nonspecific and can be mistaken for many other illnesses such as 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).

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 infection. 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 decreases and 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】

HCPS is a syndrome unique to the Americas caused by viruses that primarily affect the lungs and heart. After initial influenza-like symptoms, cough and dyspnea develop within 4–10 days; the condition can rapidly progress to pulmonary edema and cardiogenic shock.^【17】 The mortality rate ranges from 30% to 50%, depending on treatment conditions.^【18】

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

Laboratory diagnosis relies on two primary methods. Serology detects antibodies against the virus in the blood; at the time of hospital presentation, most patients test positive for acute-phase-specific antibodies. RT-PCR directly detects 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.

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

In HFRS, the main approaches include correcting 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; studies have shown it significantly reduces mortality in severe cases. Corticosteroid use is discouraged in HCPS. Research continues on antiviral drugs, immunotherapies, and vaccine candidates.

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

The cornerstone of prevention is reducing exposure to rodents. Key recommended measures include: installing 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 wetting them with disinfectant before wiping with a damp cloth and avoiding dry sweeping; using appropriate masks, gloves, and eye protection in high-risk areas; and ventilating enclosed and long-unused spaces before cleaning.

The World Health Organization (WHO) issued a statement regarding the risk of hantavirus spread following cases identified aboard the Dutch-flagged vessel "MV Hondius."

WHO spokesperson Christian Lindmeier, during a weekly press briefing at the United Nations Office in Geneva, noted that while hantavirus poses a serious threat to infected individuals, the risk level for the general population remains low.

Lindmeier stated that the situation surrounding cases identified aboard the Dutch-flagged "MV Hondius," which traveled from Argentina to Cape Verde in West Africa, is being closely monitored. He noted that a crew member of KLM Royal Dutch Airlines, who was hospitalized in Amsterdam due to contact with a confirmed case, tested negative, which he described as a positive development.

The WHO spokesperson emphasized that hantavirus does not exhibit a transmission pattern similar to COVID-19 and that contact tracing measures have been effectively implemented. Lindmeier highlighted that monitoring close contacts is crucial for controlling transmission risk and reiterated that the virus primarily poses a threat to infected individuals.

The statement also noted that the MV Hondius was temporarily held in Cape Verde and that two doctors dispatched from the Netherlands boarded the vessel to conduct health assessments. Decisions regarding the ship’s arrival in the Canary Islands are being evaluated within the framework of coordination between the operating company and relevant national authorities.

The Republic of Türkiye Ministry of Health announced that no confirmed positive cases of hantavirus have been identified in Türkiye in response to international reports. In its written statement, the Ministry indicated that developments regarding hantavirus are being closely monitored in accordance with scientific principles and that no positive findings have been detected in nationwide investigations to date.

The statement emphasized the importance of the public relying solely on official announcements and urged caution against unverified information circulating in the media. The Ministry affirmed that screening, prevention, control, and surveillance efforts for communicable diseases threatening public health are being continuously carried out by all relevant units.

Authorities stated that there is currently no extraordinary situation related to hantavirus in Türkiye and that global developments are being continuously monitored in coordination with international health organizations.

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