Rodent-Borne Diseases in Contra Costa County

Rats and their fleas are capable of transmitting a variety of human diseases including plague. While there have not been any recent reports of plague in Contra Costa County, the potential for an outbreak may increase as rat populations expand into rural areas where ground squirrels and other wild rodents may serve as a reservoir of the disease. Leptospirosis is a bacterial infection that may be contracted through contact with water or ingestion of food contaminated with urine of infected rats. Salmonellosis is a bacterial "food poisoning" that may be transmitted when rodents contaminate foods. Arenaviruses carried by wood rats may be associated with human illness in California.


Hantavirus pulmonary syndrome (HPS) is a serious, often deadly, respiratory disease that has been found mostly in the rural areas of the western United States including California. Although infected deer mice have been found throughout the State, the majority of human cases have occurred at high
elevations in the mountains. The reason for this is not known. There have been two cases in Contra Costa County; one was contracted elsewhere but the source of the other case has not been determined. HPS is caused by a hantavirus that is carried by deer mice (pictured) and passed on to humans through infected rodent urine, saliva, or droppings. Early symptoms are flu-like and include fever, headache, abdominal, joint and lower back pain and occasionally nausea. These may progress rapidly to difficulty in breathing due to fluid buildup in the lungs, which can lead to respiratory collapse and death. There is no cure, but supportive care including supplemental oxygen can reduce mortality.

Hantavirus Prevention

Most cases of hantavirus have involved persons breathing contaminated dust while cleaning enclosed spaces like cabins or sheds that are heavily infested with deer mice. You can reduce your risk by following some simple precautions while cleaning rodent-contaminated areas:

1. Air out enclosed spaces before cleaning.

2. Always wear rubber gloves when cleaning up droppings or disposing of dead rodents.

3. Wearing a dust mask can also help prevent accidental hand to mouth contamination.

4. Use snap traps to control mice indoors. Spray mouse and trap with disinfectant and then dispose of both by placing in a sealable plastic bag and placing in the trash.

5. Do not vacuum or sweep areas contaminated with rodent droppings. Spray the area with a household disinfectant or 10% bleach solution and wipe or mop.

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