Rats and Mice


 

Our Program
Contra Costa Mosquito and Vector Control District provides rat prevention and control for sewers, creeks and marinas and assists cities, parks etc. with rat control in public areas. We do not trap or bait rats/mice in or around private homes; however, homeowners with rat/mice problems can obtain advice and request a site visit from one of our expert technicians to assist them in rat/mice prevention and control.

What types or rats/mice are found in our county?

The Roof rat or black rat (Rattus rattus) is the major problem species in Contra Costa County. This rat is slender and agile, and the tail is longer than the head and body. Roof rats will enter buildings if given the opportunity, and often use utility lines and fences as runways. Roof rats prefer to feed on fruits, nuts, ivy, and pet food commonly found in residential areas.

The Norway rat (Rattus norvegicus) is less common in Contra Costa County than the roof rat. It is generally found in agricultural areas, creeks, sewers, and occasionally in developed neighborhoods. The Norway rat is larger and more aggressive than the roof rat. The eyes and ears are smaller than the roof rat and the tail is shorter than the combined head and body length. This species usually lives in underground burrows, and feeds on garbage, meat scraps, cereal grains and vegetables.

     The wood rat (Neotoma fuscipes) rarely enters homes. Wood rats are pale buff, gray, or reddish brown, with white undersides and feet. They have relatively large ears and, usually, hairy or bushy tails. Basically nocturnal and vegetarian, wood rats live in nests built of plant material, such as twigs or branches. The nest is placed in a tree or on the ground. Wood rats are commonly called pack, or trade, rats because they collect various bits of material to deposit in their dens. They sometimes pick up shiny objects in camps and may at the same time leave something they were carrying, thus giving the impression that they are "trading" one item for the other.

The house mouse (Mus musculus) is a common domestic pest throughout the County. House mice are dusky gray in color, have large ears, average 2.5 to 3.5 inches in body length and resemble miniature roof rats. They may nest in any portion of a building near food and are active mostly at night. House mice will feed on almost any type of human food.

   California voles (Microtus californicus) do not commonly invade homes.   They have a compact, heavy body, short legs, short, furred tail, small eyes, and partially hidden ears. Vole populations regularly go through cycles from low to high numbers with occasional eruptions that can send numbers soaring (up to several thousand per acre).  While this may seem alarming, it is a natural process not associated with any public health risks.

What diseases do rodents carry?
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.

The deer mouse (Peromyscus maniculatus) is the vector of hantavirus. Note the large eyes and ears and light underside that distinguish it from the house mouse.

What is hantavirus?
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 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.




How can I prevent hantavirus? (also applies to arenavirus)
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:

• Air out enclosed spaces before cleaning

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

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

• 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

• 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.