Hantavirus in Missouri: What You Need to Know

Hantavirus pulmonary syndrome (HPS) is a rare but serious respiratory disease caused by hantaviruses carried by certain rodent species. Missouri has documented hantavirus cases, and the primary carrier — the deer mouse — is widely distributed throughout the state, including Franklin and Gasconade counties. Understanding the risk, how transmission occurs, and how to safely handle rodent contamination can prevent exposure.

The Carrier: Deer Mouse vs. House Mouse

This is the most important distinction for Missouri homeowners: the common house mouse (Mus musculus) — the small gray-brown mouse found in most residential infestations — does not carry Sin Nombre hantavirus, the strain responsible for HPS cases in the United States.

The primary carrier is the deer mouse (Peromyscus maniculatus), a native Missouri species. Deer mice are distinguished from house mice by:

• Sharply bicolored tail — dark on top, white on the underside (house mouse tail is uniformly gray-brown)
• White feet and white underside (house mouse underside is lighter gray, not white)
• Larger eyes and ears relative to head size
• More common in rural, wooded, and semi-rural settings — less common in urban kitchens

Deer mice are more likely to be encountered in outbuildings (sheds, barns, detached garages), woodpiles, cabins, and rural structures than in the main living areas of urban homes. Their habitat preference for rural and wooded areas matches much of central Missouri's landscape.

How Hantavirus Is Transmitted

Hantavirus is shed by infected deer mice in their droppings, urine, and saliva throughout their lives — infected mice do not appear ill. Human infection occurs primarily through:

• Inhalation of contaminated dust: The most common transmission route. Sweeping, vacuuming, or disturbing dry rodent droppings or nesting material aerosolizes particles that can be inhaled. This is why the no-sweeping rule for rodent cleanup is specifically important in areas that may harbor deer mice.
• Direct contact: Touching contaminated surfaces and then touching the mouth, nose, or eyes
• Bite: Rare — rodent bites occasionally transmit the virus directly

Person-to-person transmission of Sin Nombre hantavirus has not been documented.

Hantavirus Symptoms

HPS progresses in two distinct phases:

• Early phase (1–5 days after exposure): Flu-like symptoms — fever, fatigue, muscle aches (especially in the thighs, hips, and back), headaches. Some patients experience nausea, vomiting, diarrhea, and abdominal pain. There is no runny nose or sore throat, which helps distinguish early HPS from a typical respiratory cold.
• Late phase (4–10 days after first symptoms): Sudden onset of difficulty breathing as the lungs fill with fluid. This is a medical emergency — HPS progresses rapidly once respiratory symptoms begin.

The case fatality rate for HPS in the United States is approximately 36%. There is no specific antiviral treatment — management is supportive, and intensive care including mechanical ventilation may be required. Early hospitalization is critical. Any flu-like illness following known or suspected rodent exposure — particularly in a deer mouse habitat — warrants immediate medical evaluation with disclosure of the potential exposure.

Safe Cleanup in High-Risk Situations

When cleaning up rodent contamination in areas potentially used by deer mice — outbuildings, rural structures, woodpiles, cabins that have been closed for an extended period:

• Air out the space for at least 30 minutes before entering — open all doors and windows
• Wear rubber gloves and, for significant contamination, an N100 respirator (not an N95, which does not filter hantavirus-sized particles adequately)
• Do not sweep or vacuum dry droppings — spray with disinfectant and allow to soak
• Wipe up with paper towels and double-bag all contaminated material
• Disinfect all surfaces after cleanup
• For heavily infested spaces with extensive nesting material, professional cleanup with full PPE is the safest approach

For the typical house mouse infestation in a residential kitchen or basement, hantavirus risk is very low since house mice do not carry the virus. The precautions become most relevant when dealing with deer mice in rural outbuildings and natural settings.