Hantavirus is a rare but deadly virus spread by infected rodents through their urine, droppings, and saliva. Infection can happen when people breathe in contaminated air, usually when cleaning rodent-infested areas. While hantavirus risks are low, exposure to fresh rodent droppings can lead to infection. But what about old, dried out droppings – can they still contain infectious hantavirus?
What is Hantavirus?
Hantaviruses are a family of viruses that are spread through rodent populations like mice, rats, and voles. Different hantavirus strains occur across the Americas, Europe, and Asia, carried by local rodent species.
In North America, Sin Nombre virus carried by deer mice is the main cause of hantavirus infections. Other strains include New York virus from white-footed mice and Black Creek Canal virus from cotton rats.
Hantaviruses do not appear to cause disease in their rodent hosts, allowing lifelong persistence in rodent populations. But some strains can cause severe disease when transmitted to humans, known as hantavirus pulmonary syndrome (HPS).
Early HPS symptoms are flu-like – fever, muscle aches, headaches. After around 5 days, fluid builds up in the lungs causing respiratory distress. HPS has a mortality rate of 38% in North America. There are no direct acting antiviral treatments, only supportive care.
Hantaviruses are enveloped RNA viruses. The lipid envelope means they are easily inactivated by disinfectants, sunlight and dryness. However, rodents can produce large amounts of virus in saliva, urine and droppings which helps maintain transmission.
Hantavirus Transmission
People usually catch hantavirus from breathing in contaminated dust when disturbing or cleaning rodent nests or droppings. Activities like opening up cabins or sheds, cleaning attics, barns or garages put people at risk if rodents have been present.
Less often, bites from infected rodents can transmit hantavirus. Eating food contaminated by rodent droppings or urine could also theoretically cause infection.
Person-to-person transmission is very rare, but has been reported. The virus is not spread through the air between people. Instead close contact is needed for example touching or kissing someone with an acute infection.
Recently, new hantavirus strains have emerged associated with pet rats and mice. Breeder rats carry Seoul virus which has also caused HPS in owners.
Risk Factors
Working or playing in dusty rodent-infested buildings greatly increases hantavirus risk. Other risk factors include:
- Living in rural cabins or farms with rodents
- Cleaning vacant homes, sheds and garages
- Military personnel on field exercises
- Camping or hiking where rodents live
- Owning pet rats or mice
In the US, most cases occur in spring and summer when people are more likely to be cleaning cabins or engaged in outdoor activities. HPS outbreaks have also been linked to climate factors like drought leading to more rodents in houses.
Can Old Droppings Contain Infectious Hantavirus?
Fresh urine, saliva and droppings from infected rodents can contain high amounts of virus. But hantaviruses do not survive long once excreted and exposed to the environment.
Key factors in hantavirus survival include:
Ultraviolet Light
Sunlight contains UV rays which damage viral genome and proteins. One study found 90% of hantavirus was inactivated after just 30 minutes of sunlight exposure.
Heat
Hantaviruses are sensitive to heat above 133°F. Temperatures during summer solar radiation can reach over 140°F inside structures like sheds and cabins, likely inactivating virus in droppings.
Drying Out
The lipid envelope around hantaviruses makes them vulnerable to desiccation once excreted. Studies show hantavirus loses infectivity within hours to days from dried saliva or respiratory secretions.
Older droppings in dust are very low risk since any hantavirus present has been destroyed by heat, sunlight and lack of moisture.
However, hantavirus RNA has been detected in decades old deer mice specimens preserved in museums. So some minimal genetic material may persist over longer timeframes without posing an infection risk.
Disinfectants
Many common detergents, bleach, peroxide and alcohols inactivate hantavirus by disrupting the lipid envelope. Rodent droppings and nesting materials should be soaked in disinfectant before cleaning up.
Persistence Indoors
Hantavirus survives longer indoors protected from sunlight and drying out. One study showed hantavirus stays infectious for 15-20 days in moist soil and bedding at room temperature.
Virus shed in dust and insulation within walls may remain viable for weeks to months before getting exposed to UV light. But amounts are very low posing minimal infection risk.
Safe Cleaning of Rodent Droppings
The main hantavirus risk comes from fresh moist droppings. But for safety, disinfectants should still be used when cleaning any rodent contamination.
Here are CDC guidelines for safely disinfecting and cleaning up after rodents:
- Air out enclosed areas for at least 30 minutes before working.
- Do not stir up dust by sweeping or vacuuming.
- Thoroughly wet contaminated areas with disinfectant or chlorine solution.
- Remove rodents, nesting material and droppings using damp towel and place in plastic bag.
- Clean the area with disinfectant.
- Wash hands and disinfect boots and tools after clean up.
Wearing gloves and an N95 respirator gives added protection when cleaning heavy rodent contamination. Work clothes should be removed and washed separately after cleaning.
Preventing Hantavirus Infection
Here are some tips for lowering risk of hantavirus infection:
- Inspect for rodents and seal up entry points in homes and outbuildings.
- Clear brush, grass and junk piles around structures that attract rodents.
- Use traps or rodenticides to reduce rodent infestations, especially around human dwellings.
- Air out sheds and cabins before entering after a prolonged shutdown.
- Spray rodent droppings and nesting areas with disinfectant solution before cleanup.
- Wear protective clothing including respirator when doing heavy rodent cleanup.
- Wash hands and disinfect shoes and tools after cleanup.
- Avoid coming into contact with wild rodents.
Following CDC precautions minimizes the change of hantavirus transmission, even when cleaning up after past rodent infestations.
Conclusion
Old dry rodent droppings present minimal risk of hantavirus infection. The main transmission risk comes from fresh moist contaminated material. Hantaviruses are rapidly inactivated by desiccation, sunlight and disinfectants. But decaying mouse nests and droppings may still contain viruses so protective precautions are warranted during clean up. With proper rodent control and precautions when exposed to contaminated areas, hantavirus infection is highly preventable.