There are several different types of hantaviruses that cause different kinds of disease.
Andes virus, a hantavirus found in certain areas of South America, can cause a severe disease primarily affecting the respiratory system. Symptoms may include fever, cough, and in some cases nausea or diarrhea. Human infections with Andes virus have been very rare, but 20–50 percent of confirmed cases have been fatal. Andes virus does not occur naturally in Europe.
The most common hantavirus in Europe is Puumala virus, which occurs mainly in Finland and Sweden and causes nephropathia epidemica (bank vole fever). The disease is a self-limiting febrile illness, with more than one thousand cases diagnosed annually in Finland. Fatal cases are extremely rare.
Humans can become infected by inhaling particles originating from the urine, feces, or saliva of infected rodents.
Among hantaviruses, only Andes virus — confirmed as the cause of illness associated with a cruise ship outbreak in spring 2026 — can spread from person to person. In areas where Andes virus occurs, most human infections have resulted from rodent exposure, and person-to-person transmission has been very rare. Transmission has required close and prolonged contact with an infected person.
Symptoms caused by hantavirus infection usually begin about two weeks after exposure, but the incubation period can range from 1 to 6 weeks.
Each hantavirus is associated with a specific rodent species. The rodent species that serves as the host for Andes virus does not occur in Europe.
Outbreak clusters caused by Andes virus have been small. Although Andes virus can be dangerous for infected individuals, it does not pose the same large-scale epidemic risk as, for example, COVID-19, because Andes virus spreads between people only through close and prolonged contact.
Several people aboard a cruise ship travelling in the Atlantic Ocean became ill with Andes virus disease in late April and early May 2026. According to current information, all confirmed cases have been linked to the cruise ship.
Current assessments suggest that at least one passenger was exposed to Andes virus while staying in South America before boarding the ship. This person may then have transmitted the virus to other passengers onboard.
THL is monitoring the situation together with the European Centre for Disease Prevention and Control (ECDC) and the World Health Organization (WHO). Public health authorities in different countries are coordinating their actions closely.
Unlike COVID-19, Andes hantavirus does not spread easily from person to person. Human-to-human transmission is rare and requires prolonged close contact, often in enclosed spaces. In addition, the virus’s natural rodent host, the long-tailed pygmy rice rat (Oligoryzomys longicaudatus), occurs only in South America, making establishment of the virus in nature elsewhere in the world unlikely.
Genomic analyses of cruise ship passengers infected with Andes virus show that the outbreak-related virus is similar to Andes viruses previously circulating in South America and is not a new variant. At present, there is no evidence that the virus identified among cruise ship passengers spreads more easily or causes more severe disease than other Andes viruses.
The European Centre for Disease Prevention and Control has assessed the risk posed by Andes virus to the populations of Finland and other European countries as very low, because the virus requires prolonged close contact to spread between people. In addition, measures to control the outbreak are currently being implemented effectively.
At least 26 passengers are known to have disembarked on Saint Helena and travelled onward to their home countries or other destinations. None of them were Finnish citizens. The World Health Organization (WHO) has shared passenger information with the relevant countries, and passengers have been advised to contact local health authorities. Contact tracing is being carried out so that exposed individuals can be monitored.
Although transmission through passengers leaving the ship would be possible, Andes virus does not spread easily from person to person. Therefore, wider transmission is considered unlikely, especially while public health control measures are in place. In addition, the rodent species carrying Andes virus occurs naturally only in South America, making spread into nature elsewhere in the world unlikely.
Two Finnish travellers may have been exposed to Andes virus on an airplane in Johannesburg, South Africa, on 25 April 2026. THL received information about the exposed individuals through international public health channels on Friday, 8 May. After the individuals had been reached, the information was made public the same day.
The exposed individuals are asymptomatic and have been in close contact with the wellbeing services county authorities. As a precautionary measure, the physician responsible for communicable diseases in the wellbeing services county placed them in quarantine for six weeks from the date of exposure.
Healthcare services in Finland are well prepared to test and treat individuals suspected of having Andes virus infection. If a person exposed to Andes virus develops symptoms, they will be referred to healthcare services for evaluation and testing.
In accordance with WHO and ECDC guidance, contacts of infected individuals are traced and their exposure assessed for the two days preceding symptom onset. Finland has strong preparedness for contact tracing and prevention of further transmission through standard communicable disease control practices.
Testing for Andes virus is based on symptoms, because tests are reliable only during the symptomatic phase of illness. Asymptomatic individuals are not tested, since testing too early often produces a negative result and therefore cannot rule out infection.
Although known person-to-person transmissions have most likely occurred from clearly symptomatic individuals, the exact period of infectiousness is not fully known. It is possible that transmission may occur shortly before symptoms become clearly recognizable. For this reason, WHO and ECDC recommend tracing contacts of infected individuals also for the two days before symptom onset.
Treatment is supportive. No specific antiviral treatment or vaccine is currently available.
There is no reason for concern in Finland. The risk posed by the current situation to people living in Finland is considered extremely low.