Hantavirus Outbreak: How Weather and El Niño Raise the Risk

The hantavirus outbreak that originated on a cruise ship is dominating the headlines around the world this week. How does the weather play a part in the outbreak of this deadly virus? Meteorologists are weighing in on what you need to know.

How Weather Influences the Odds of a Hantavirus Outbreak

Weather patterns can influence the chances of a hantavirus problem. But how? Experts point to research that indicates that higher amounts of rain have been linked to a more active rodent population. The weather can also influence the prosperity of a rodent's habitat, as well as its food supply. Because the virus is spread from rodents to humans, it makes sense that a greater amount of rodent activity and a more robust population will also increase the potential risk to humans.

Hantaviruses are carried by rats and mice. The virus can spread to humans through contact with infected bits of rodent saliva, droppings, and urine. According to the U.S. Centers for Disease Control and Prevention (CDC), humans can also become infected if they breathe in the contaminated particles that may float through the air after being stirred up from nesting materials. While it is possible to become infected through rodent bites or scratches, this type of transmission is rare.

Most of the hantaviruses confirmed in the U.S. are connected to people cleaning spaces where rodents have been active. These types of enclosed spaces include sheds, garages, cabins, and other types of structures that are often closed for long periods of time.

A recent CDC Emerging Infectious Diseases study noted that various environmental factors have indirectly boosted the exposure to Sin Nombre virus (SNV) in humans by driving rodent habitat and population numbers across the western U.S., particularly in the Four Corners region.

SNV is the most common cause of hantavirus pulmonary syndrome (HPS) across North America. This virus is transmitted primarily by the western deer mouse (Peromyscus sonoriensis). People can become infected with SNV by inhaling aerosols that contain rodent saliva, urine, or feces. There are also documented cases of the virus being spread through rodent bites and scratches.  

What is worrisome now is that the CDC study found an increase in SNV during the 1992 - 1993 El Niño phase. Forecasters have predicted that El Niño will begin to emerge as the dominant climate phase as the summer progresses. The latest forecast models are now predicting the likelihood of what is known as a "Super El Niño" to develop by the end of the fall season.

The El Niño pattern has been shown to drive rainfall and hurricane activity along the Pacific Coast of the U.S. and Mexico. This moisture train translates to increased precipitation in a zone from the southern Plains to the East Coast during the summer and fall months. As a result, climatologists and health experts will both be watching how the chance of higher-than-usual amounts of moisture in the months ahead may lead to a more robust rodent population throughout much of the country.