How hantavirus lurks in the lungs before patients suddenly struggle to breathe

What starts as a simple viral fever can quickly turn into a life-threatening lung emergency in a matter of days. It often begins quietly. A bit of fever. Body pain Flu-like tiredness, seasonal. But in some patients infected with hantavirus, the disease can take a dangerous turn. Within days, breathing becomes difficult, oxygen levels drop, and the lungs start to fill with fluid from the inside.

"The most dangerous aspect of hantavirus infection is that the early symptoms can seem so deceptively mild," said Dr. Arjun Khanna, HOD, Pulmonology Medicine, Amrita Hospital, Faridabad.

“Many patients first complain of fever, headache, muscle pain, nausea or weakness. But once the lungs get involved, it can go downhill very quickly. Some patients become very breathless within hours,” he said.

Hantavirus is spread through contact with the urine, saliva or droppings of infected rodents. People usually get infected by breathing in small particles containing the virus in dusty or poorly ventilated places, such as closed storerooms, old warehouses, barns, cruise cabins or rodent-infested areas.

What makes the disease medically concerning is that the virus does not attack the lungs like ordinary pneumonia.

Instead pulmonologists say hantavirus attacks the inner lining of tiny blood vessels in the lungs, called endothelial cells. “When the virus activates an overactive immune response, these blood vessels become overly leaky,” Dr. Khanna says. “Fluid starts to leak into the tiny air sacs of the lungs where oxygen exchange normally takes place.”

This condition is known as pulmonary edema. In simple terms, when air in the alveoli is replaced by fluid, the lungs begin to drown from the inside out. Oxygen transfer drops dramatically and patients may experience chest tightness, rapid heart rate, severe shortness of breath, blue lips, and dangerously low oxygen saturation.

Researchers refer to this phenomenon as “microvascular leakage” and it is now considered the hallmark of severe Hantavirus Pulmonary Syndrome (HPS). The Centers for Disease Control and Prevention estimates that nearly 38 percent of patients with severe respiratory hantavirus disease may not survive, especially if diagnosis and ICU support are delayed.

The disease can also affect the heart in advanced stages, sometimes causing shock and sudden circulatory collapse, doctors say. Hantavirus has been back in the headlines worldwide after the World Health Organization reported severe respiratory illness following an investigation into a cruise ship cluster. Currently there is no specific antiviral treatment for hantavirus. Treatment is largely based on early detection, oxygen support, ICU management and mechanical ventilation in severe cases.

One warning sign that should never be dismissed, pulmonologists say, is flu-like symptoms followed by sudden difficulty breathing after possible rodent exposure.

“People tend to underestimate rodent-contaminated environments,” Dr. Khanna explains. “Using masks and gloves when cleaning dusty, enclosed spaces can help significantly in reducing the risk of inhaling infected particles.

Medical experts consulted This article includes expert inputs shared with TOI Health by:

Dr. Arjun Khanna, HOD, Pulmonology Medicine, Amrita Hospital, Faridabad

Inputs were used to explain how hantavirus can affect lungs and breathing ability.