Hantavirus

What are hantaviruses?

The reservoir, or natural source, of hantaviruses that can affect humans are rodents. For the most part, each type of hantavirus has a specific rodent host. It appears these viruses and their rodent hosts co-evolved, and that the viruses cause lifelong infections in the rodents without causing clinically apparent illnesses.

Media sources typically speak of hantaviruses as if they were one entity, but this is far from the truth. There are different hantaviruses and some are more dangerous than others in humans. Let’s use dogs as an analogy: Rottweilers and chihuahuas are both dogs, but understandably, they potentially pose different levels of danger to humans.

In the same way, the illness caused by hantaviruses vary. Two generalizations are made: Old World hantaviruses (present in Africa, Asia and Europe) are said to cause hemorrhagic fever with renal syndrome, or HFRS, while those in the New World (North and South America) cause hantavirus pulmonary syndrome, or HPS. The latter is sometimes referred to as hantavirus cardiopulmonary syndrome, or HCPS, as the heart can be targeted by New World hantaviruses. Thus, Old World hantaviruses are said to cause renal failure, whereas New World hantaviruses cause cardiopulmonary failure.

How are hantaviruses spread?

Hantaviruses that affect humans belong to the genus Orthohantavirus. Humans most commonly acquire infections from hantaviruses through inhalation of virus-contaminated rodent excretions (feces, saliva, urine) that get airborne when they are disturbed through cleaning of soiled surfaces and other activities. It is also possible to acquire infections through bites from infected animals, since the virus may be in saliva.

A unique concern: Andes virus

Humans are “dead-end” hosts for most hantaviruses, meaning infected persons don’t transmit the virus to non-infected people. But one hantavirus that can affect humans, Andes virus (species Orthohantavirusandense), has been documented to spread from person to person. The U.S. Centers for Disease Control and Prevention identifies Andes virus as the most common and deadly variant in South America. Four variants of Andes virus have been found, mostly in Chile and in Argentina, home to the largest number of Andes virus cases and fatalities.

Unfortunately, the virus causing the cruise ship outbreak has been identified as Andes virus. It is not clear what the infectious dose is for Andes virus, but it is thought to be low. The time interval from when the virus is acquired to the time symptoms of infection occur, known as the incubation period, of Andes virus-induced HPS has been estimated to range from three to 14 days. Unlike HFRS, wherein the mortality rate ranges from 1 to 15%, the fatality rate for HPS ranges from 40 to 50%. Both susceptibility and outcome of infection by Andes virus are not well understood; for example, age may be an important factor, as well as presence of underlying health conditions. Of note, the first passengers who died from HPS were older people.

Symptoms and disease progression

Early clinical signs and symptoms of HPS include fatigue, fever, muscle aches (especially in large muscle groups such as the back and thighs), abdominal pain, chills, dizziness, headaches, nausea and vomiting. Diagnosing hantavirus infection at an early stage of infection is difficult since the symptoms are common to those encountered with other respiratory viruses.

Patients with HPS can rapidly progress to coughing and shortness of breath, leading to pulmonary or heart failure within a matter of days after initial symptoms appear. At the early, or “acute,” phase of infection, diagnosis is most often confirmed using an RT-PCR test that detects hantavirus RNA in an appropriate human specimen. Evidence of recent or previous hantavirus infection is performed using antibody tests. There is no specific treatment for HPS or HFRS. Patients should receive supportive care, including hydration, rest and treatment of symptoms. Patients with HPS may need breathing support, such as intubation, wherein a tube is placed in the lungs from the mouth to help the patient get oxygen. Extracorporeal membrane oxygenation, or ECMO, can be used for HPS patients with severe pneumonia and cardiogenic shock.

What happens next?

Based on this information, especially the fatality rate associated with Andes virus, it is easy to see why there is concern about the outbreak on the MV Hondius. How and where did the patients get infected by the virus? Chances are, they were infected before they embarked on the cruise, either from exposure to a sick individual in Argentina, or exposure to rodent excretions during a visit to a wildlife preserve. The potentially long incubation period of the virus makes tracking the source complicated. Early reports indicate that there was no evidence of rodents or their excretions on board the ship, temporarily ruling that out as a source of the virus. But how sure are we about that? How will the ship be thoroughly decontaminated?

And once again, similar to what happened during the start of the COVID outbreak, the U.S. does not have a rapid mechanism for funding entities to perform widespread tests for hantaviruses. Should Andes virus spread into the population at large, this would be another disaster of our own making.