Hantavirus outbreak sees 2 Indians quarantined in Netherlands: Why the virus’s long incubation matters

Hantavirus is a rodent-borne infection that can be transmitted to humans through contact with the urine, faeces, or saliva of infected rodents or by touching contaminated surfaces. It is also possible to get the infection by breathing air that contains viral particles stirred up from these droppings.

According to the current information available from the WHO, shared by health ministry officials in the meeting, there are eight probable cases of the infection on the vessel. Of these, five have been confirmed with laboratory tests. And, three deaths have been reported so far. The WHO was notified about the incident in the first week of this month.

Is the long incubation period of the virus a matter of concern?

The hantavirus outbreak has raised concern, particularly because of the virus’s relatively long incubation period and its potential severity in some patients. However, infectious disease experts stress that the overall public health threat remains low. “Hantavirus is not a newly emerging pathogen but an old, well-studied family of viruses that has circulated in rodent populations for decades. It is primarily a zoonotic infection, meaning it spreads from infected rodents to humans, usually through inhalation of viral particles from rodent urine, droppings or saliva, especially in enclosed, poorly ventilated spaces such as cabins, storage compartments or other closed environments,” says Dr Neha Mishra, HOD and consultant, Infectious Diseases, Manipal Hospital, Bengaluru.

The symptoms may not appear immediately after exposure. The incubation period can range from one to eight weeks, with most people who develop illness showing symptoms within two to six weeks of exposure. This delayed manifestation means people, who may have been exposed, need to monitor themselves for symptoms over several weeks rather than expecting immediate illness. “This is why quarantine and active health surveillance are often recommended after confirmed exposure, even if the people feel well initially,” says Dr Mishra.

If a patient manifests symptoms after six to eight weeks, will the infection be mild or severe?

The incubation period mainly reflects how long the virus takes to replicate enough to trigger noticeable illness. “A slower onset doesn’t reliably predict a milder or more severe course. The more important issue is what happens after symptoms begin. Once symptomatic hantavirus disease starts, particularly Hantavirus Pulmonary Syndrome, it can worsen rapidly over 24–48 hours, progressing from what looks like a flu-like illness (fever, muscle aches, fatigue) to cough, breathlessness, low blood pressure, and respiratory failure. It can also lead to Haemorrhagic Fever with Renal Syndrome (HFRS) that causes sudden fever with intense headaches and nausea initially followed by low blood pressure, renal failure and internal bleeding.

So if someone develops symptoms even at week six or eight, they need prompt evaluation, especially if there was known rodent exposure or they were part of an exposure event like the MV Hondius,” explains Dr Mishra.

What triggers the severity of infection?

According to Dr Mishra, this depends on the kind of hantavirus strain involved, with some being more aggressive than others. “Other than that, we must know the viral exposure level (how much virus the person was exposed to), the person’s overall health and underlying conditions, especially lung, kidney, or cardiovascular function and how quickly medical care begins once symptoms appear,” she adds.

What about person-to-person transmission?

Despite concerns, person-to-person transmission is extremely rare. Most hantavirus strains do not spread between humans. “The only well-documented exception is the Andes strain reported in parts of South America, where transmission has occurred after prolonged close contact with a symptomatic patient. There is no evidence that asymptomatic individuals transmit the virus. This means that routine contact with someone under observation does not usually pose a significant risk,” says Dr Mishra.

Even the flight attendant, who was flagged for observation and testing because of possible exposure to a woman from the affected ship with an advanced stage of the disease, was found to be negative. Mortality varies depending on the strain, but severe forms affecting the lungs or kidneys can have fatality rates ranging from 30 to 50 per cent, particularly in people with underlying organ disease.

What about testing?

Testing is usually done through serology-based antibody tests, which detect the body’s immune response to the virus. “Screening asymptomatic individuals immediately after exposure is often not helpful because antibodies may not yet be detectable. Instead, current international travel medicine protocols recommend symptom monitoring and prompt testing only if symptoms develop,” says Dr Mishra.

What about treatment?

There is currently no specific antiviral treatment approved for routine hantavirus infection. “Management is largely supportive and depends on early recognition. Patients may require oxygen support, intensive care monitoring, dialysis if kidney involvement develops, and aggressive management of complications,” says Dr Mishra. This is why experts emphasise immediate medical evaluation for anyone who develops fever, body aches, severe fatigue, headache, abdominal symptoms or breathlessness within six weeks of potential exposure.

For the general public in India and Asia, health officials say the threat remains limited. Hantavirus is considered more of a traveller-associated or environmental exposure risk than a widespread community threat in the region.