Hantavirus is a serious disease that can be spread to humans through contact with urine, droppings, or saliva from infected rodents. The primary carrier of hantavirus in the United States is the deer mouse. Understanding the percentage of mice that carry hantavirus can help assess the risk of human exposure.
What is Hantavirus?
Hantavirus refers to a group of viruses that are found in rodents like mice, rats, and voles. Different strains of hantavirus exist, such as:
- Sin Nombre hantavirus – Found in North America and carried by deer mice. This causes hantavirus pulmonary syndrome (HPS) in humans.
- Seoul hantavirus – Found worldwide in rats. This can cause hemorrhagic fever with renal syndrome (HFRS).
- Puumala hantavirus – Found in Europe and Russia, carried by bank voles. Causes a mild form of HFRS called nephropathia epidemica.
In the Americas, Sin Nombre hantavirus is the most common strain. It causes a severe lung disease called hantavirus pulmonary syndrome (HPS) with symptoms like:
- Body aches
- Lung congestion and fluid buildup
HPS can progress rapidly and has a mortality rate of 38%. There are no vaccines or specific treatments available. Prevention relies on avoiding contact with rodents that shed the virus in their urine, droppings, and saliva.
Deer Mice – The Primary Carrier
While various rodents can carry hantaviruses, the primary reservoir in North America is the deer mouse (Peromyscus maniculatus). This small rodent is found through much of the United States, Canada, and Mexico in a variety of habitats including:
- Rural homes and farms
Deer mice are about 5-10 cm long and have distinguishing features like:
- White feet
- Gray to brown fur
- Large ears
- White belly
Hantavirus Prevalence in Deer Mice
Many studies have sampled wild deer mouse populations to detect Sin Nombre virus and estimate the percentage that are infected. Rates vary across different regions but overall infection prevalence ranges from 10-15%:
- A study across 24 US states found an average of 12.8% were antibody positive for Sin Nombre virus. Prevalence varied from 0% in some states up to 45% in New Mexico.
- In Montana, a study found 11% of deer mice were infected with Sin Nombre virus.
- In Canada, an analysis estimated hantavirus prevalence from 13% in Nova Scotia to 15% in British Columbia.
- On the West Coast, studies showed 11.2% of deer mice in California and 14.5% in Oregon were antibody positive.
- In the Four Corners region, up to 26% of deer mice carry hantaviruses.
Local environmental factors can influence infection rates like climate, vegetation, and deer mouse population density. Prevalence also varies seasonally, tending to peak in late spring and decline during winter periods.
Hantavirus Prevalence by Location
Here is a table summarizing the typical hantavirus antibody prevalence found in deer mouse populations by geographic region:
As illustrated, mice in the Western and Southwestern United States tend to have the highest rates of hantavirus infection, while lower rates are seen in Midwestern and Eastern states.
Factors Affecting Prevalence
The percentage of infected deer mice in a given area is influenced by multiple ecological factors:
Climate and Weather
Hot, dry weather provides optimal conditions for hantavirus transmission. A study across 29 US states found the prevalence of hantavirus antibodies in deer mice was highest in hot, dry areas. The virus is thought to survive longer in dry environments. Humid weather may inhibit spread of the virus.
Hantavirus prevalence increases when mice congregate due to limited food resources. Outbreaks have occurred following heavy rainfall or drought when fewer nuts, seeds, and vegetation are available to sustain the mice. With scarce food, closer contact between mice facilitates virus transmission.
Areas with dense deer mouse populations tend to have higher rates of hantavirus infection than low density populations. With greater numbers of mice, there are more opportunities for fighting and social interactions that spread the virus between mice. Overcrowding is linked to increased prevalence.
Deer mice populations and virus transmission fluctuate over the course of a year. Prevalence is highest in spring and early summer when mice are most active. It declines in winter as mice hibernate, reducing contact and spread. Young mice born during the spring and summer breeding season are most likely to get infected.
Preventing Human Infection
Humans most commonly get infected with hantavirus by breathing in dust contaminated with deer mouse urine or droppings. It’s not transmitted person-to-person. Prevention measures include:
- Avoiding contact with wild mice and keeping them out of homes and buildings
- Wearing gloves and a mask when cleaning areas with mouse droppings
- Using disinfectants to kill any virus
- Ventilating closed sheds and cabins before entering
- Keeping food in containers mice cannot access
If 10-15% of deer mice carry hantavirus, the risk of exposure exists anywhere they are found. But taking proper precautions can greatly reduce the chances of infection.
Hantaviruses are carried by a number of wild rodents, but deer mice are the primary reservoir in North America. Studies indicate that on average, 10-15% of deer mice are infected with Sin Nombre hantavirus. However, prevalence varies across geographic regions from 1% to 30% depending on environmental conditions. The highest rates are found in hot, dry areas of the Western and Southwestern United States. Knowing local hantavirus infection rates can help assess the risk and guide prevention efforts to lower human exposures by avoiding contact with deer mice.