Hantavirus and Deer Mice — What a Philadelphia area Pest Expert Wants You to Know

If you've been scrolling YouTube lately or catching headlines, you've probably seen hantavirus popping up. There was a recent outbreak on a ship that got a lot of people concerned. I've been taking courses on pest-borne diseases since the 1990s, so let me break this down.

Understanding the etiology

Hantavirus, as the name suggests, is a virus. But unlike most viruses people are familiar with, its epidemiology is unique — it doesn't spread through a bite, a sneeze, or casual contact.

The epidemiology — how it actually spreads

The epidemiology of hantavirus is tied to deer mouse droppings. When an infected deer mouse's droppings dry out, disturbing them — by sweeping, vacuuming, or just moving things around, particles from those droppings become airbornn — and breathing them in is the transmission pathway.

What likely happened on that ship

Deer mice had probably been living in that ship's ventilation system for a long time with nobody addressing it. The heating system dried out the droppings, and the ventilation circulated those particles through air that everyone on board was breathing. I wasn't on that ship — but the moment I heard the story, this was my first thought.

Hantavirus Concerns in the Philadelphia Region — What You Should Know Right Now

In the 1990s there was a hantavirus outbreak that shaped a lot of my education in this field, and it happened in the Southwestern states. At that time there was enough alarm in the industry that most of our rodent coursework was heavily focused on hantavirus — I heard the same information repeatedly, which is probably why it stuck. The arid climate is what allows the deer mouse droppings to dry out.

It's also worth noting that hantavirus is not known to be present in the deer mouse population in the Philadelphia region. For it to show up here, there would need to be a vector — an infected deer mouse traveling from an area where the virus is already active. That cruise ship would have to dock in Philadelphia, a deer mouse would have to get off the ship and come in contact with another deer mouse, and even then we are unsure if the disease would spread. That's not impossible, but it is unlikely, and has not been the case in the past. To my knowledge, known cases of hantavirus during the 1990's outbreak were linked to people who had spent time in the southwestern states. The disease doesn't just appear.

That does not mean it can't happen here. Droppings will still dry out in Delaware County under the right conditions. If mice get into a heating system and leave droppings, those particles can absolutely be blown through your home.

What generally protects us is our overall humidity level. However — and this is relevant right now — we've had an unusually dry spring this year. Combined with the fact that some people still have their heat running through this cold stretch, conditions are closer to the risk profile than they normally would be in May. It's not cause for panic, but it is worth knowing.

Know your mouse

Not all mice carry the same risk. The carrier is the deer mouse, and it looks different from the common house mouse.

The house mouse is gray, small-eyed, and jumps about six to eight inches.

The deer mouse is brown with a white belly, big eyes, and a longer tail. It can jump nearly three feet in the air. Deer mice are more common in suburban and rural areas — Delaware County included — and less common in dense urban Philadelphia.

Photo: "DiGangi-Deermouse" by 6th Happiness, CC BY-SA 3.0, via Wikimedia Commons

Photo: Peromyscus maniculatus by Superior National Forest, CC BY 2.0, via Wikimedia Commons

How to handle droppings safely

Do not sweep them. Do not vacuum them. Both actions can send particles into the air.

Spray the droppings with Windex or any liquid first. Wetting the material can help prevent particles from becoming airborne. Then clean carefully and call me.

What I tell my customers

Knowledge diffuses ignorance, and ignorance causes fear. The outbreak on that ship happened under specific conditions — an enclosed space, likely a long-term unaddressed infestation, and a ventilation that distributed those particles throughout the vessel. The natural humidity in Delaware County works in our favor. I'm hoping this knowledge will keep you and your family safe.

If you're finding evidence of deer mice — droppings, shredded paper or cardboard — don't disturb those droppings. Spray them with any liquid and call Pest Platoon at 610-497-2300 for a free inspection.