The definition of a vector is any animal capable of producing discomfort or injury, including, but not limited to, mosquitoes, flies, other insects, ticks, mites, and rats but not including domestic animals according to the California State Health and Safety Code, Section 2002(K).
Vectors have the ability to transmit infectious organisms that cause human and animal disease. These diseases can be serious and possibly fatal. In Butte County several mosquito species are capable of transmitting West Nile virus (WNV), Saint Louis encephalitis (SLE), western equine encephalomyelitis (WEE), can transmit a variety of pathogens such as ehrlichiosis, babesiosis, Rocky Mountain spotted fever, and Lyme.
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• Eggs, Larva, Pupa, and Adult
There are over 3,000 mosquito species in the world, more than 50 reside in California, and 25 species are commonly found throughout Butte County. Regardless of adult mosquito populations, several species in Butte County are of public health concern including Culex tarsalis, Culex pipiens, Aedes melanimon, Aedes sierrensis, and Anopheles freeborni.
Common Name: Encephalitis Mosquito
Scientific Name: Culex tarsalis
Culex tarsalis is the primary vector of West Nile virus (WNV), Saint Louis encephalitis (SLE), and the western equine encephalomyelitis (WEE). Culex tarsalis breeds in a variety of aquatic habitats ranging from clean to polluted water sources including, but not limited to flooded agricultural lands, ditches, man made containers, ponds, and urban sources. In Butte County, this mosquito breeds year round and prefers to feed on birds, but does readily attack humans, horses, and cattle.
Common Name: Northern House Mosquito
Scientific Name: Culex pipiens
Culex pipiens is a major vector of West Nile virus (WNV) and can vector Saint Louis encephalitis (SLE), and the western equine encephalomyelitis (WEE). Larvae prefer polluted or foul water high in organic content. Usually found in artificial containers, storm drains, wastewater ponds, sumps, septic tanks, fountains, birdbaths, and un-maintained swimming pools. Birds are the principal blood meal, but will attack humans and invade their homes. Culex pipiens usually breed in the early spring to late fall in Butte County.
Common Name: None
Scientific Name: Aedes melanimon
Aedes melanimon is not only a major pest in localized areas near its larval breeding sources, but is a vector of West Nile virus (WNV) and it has been implicated as a secondary vector of western equine encephalomyelitis (WEE) virus in the Central and Sacramento Valleys. This species is most commonly found in intermittently flooded areas such as duck clubs and wildlife refuges. Aedes melanimon are very aggressive mosquitoes that readily feed on mammals and humans and can emerge as soon as five days after eggs hatch.
Common Name: Western Treehole Mosquito
Scientific Name: Aedes sierrensis
Aedes sierrensis is a major nuisance mosquito usually associated with the foothill regions in Butte County. This mosquito is the primary vector of Dog Heartworm. Larvae are generally found in treeholes and containers that have a lot of leafy material. Eggs hatch with the initial fall rains and over winter as larvae. This species of mosquito is a very small aggressive mosquito that usually surfaces in early spring and will be active into the summer months. Aedes sierrensis is a vicious biter of humans and other large mammals.
Common Name: Western Malaria Mosquito
Scientific Name: Anopheles freeborni
Anopheles freeborni is one of Butte County's most abundant pests and is the primary vector of Malaria. Larvae prefer clear, fresh water in sunlit or partially shaded pools. This mosquito is most commonly found in rice fields and roadside ditches with grass. An aggressive mosquito, most Anopheles freeborni commonly feed on mammals or humans and are most active at dawn and dusk.
How You Can Minimize Adult Mosquitoes
* Properly maintain swimming pools
* Empty and invert any container that holds water
* Change water frequently in bird baths and fountains
* Stock ornamental ponds with mosquito fish
(call BCMVCD to schedule a pick-up/delivery of mosquito fish)
* Check and clean rain gutters and downspouts
* Avoid over irrigation of lawns and fields
Personal Protection from Mosquitoes
* Reduce outdoor activity around dawn and dusk
* Wear long pants and shirts with long sleeves
* Use approved insect repellent
* Seal all openings on your window screens and doors to prevent mosquitoes from entering your home
Other Vectors and Insects Of Public Health Significance
• Africanized Honey Bees
Africanized Honeybees (AHB's) are problematic not because of their killer sting, but because of the way they respond to disturbances around their nests. AHB's respond sooner to disturbances, stay agitated and attack for a longer period of time, and follow an attack victim for longer distances than European Honeybees (EHB's). In more than 40 years of hybridization with resident European Honeybees, the AHB's behavior has not changed significantly. AHB's toxin is no more harmful or deadly than EHB's, but AHB's respond by sending most of the bees in the nest to attack. This can be thousands of bees. A victim's reaction to an AHB attack varies depending on the number of stings received, the location of the stings and any special sensitivity that may have been developed by prior exposure to bee venom. Most healthy individuals can tolerate many stings without serious effects. A victim that receives hundreds or thousands of stings may exhibit toxic effects similar to a rattlesnake bite and may even die. Stings on the mouth or throat can cause a life threatening respiratory obstruction.
AHB's and EHB's can only be distinguished by an extensive laboratory examination. So if you see or encounter a bee's nest or a swarm, stay away from it. It may be an Africanized colony. Immediately notify your county Agriculture Department. Noise and vibrations from lawn mowers, weed eaters, odor from insecticides, physical contact, or motion in close proximity to a nest may elicit a defensive response from the bees.
If you are attacked, leave the area quickly. Cover your face to protect your eyes and mouth. Get into a shelter where bees cannot enter, such as a car or house. Do not dive or go underwater. AHB's have demonstrated tremendous patience in that they will wait for a victim to surface for air and then deliver stings to the mouth area. Individual bees can only sting once. After stinging, a bee leaves the stinger and poison sac imbedded in the victim. The poison emits an alarm pheromone (odor) that stimulates other bees to direct their sting in the same area of the victim's body. It is important to remove these poison sacs as they continue to pump poison into your body after it has detached from the bee. Don't pull the sac out with your fingers; that will squeeze more venom into you. The sac should be scraped out with a dull edge by dragging the edge along your skin. A credit card works well for this. Victims of multiple sting attacks need immediate medical attention.
The paper wasp is made up of mostly the Polistes genus. They are easy to distinguish from other bees, hornets and yellowjackets as they are less aggressive and they build a hexagonal, open paper nest. Markings and colors vary but include yellows, browns and blacks. The nest is constructed in protected areas above the ground. Common areas their nests can be found include on walls or under eaves of homes and other buildings. Nest construction begins in the spring and construction and maintenance continues as long as the colony continues to grow. Wasps gather fibers from old decaying wood or dead, dry plants, chew them up and mix the debris with water to make their gray paper nest. Populations in these nests rarely ever exceed 200.
Ticks are found wherever their hosts are found. Some ticks feed on only one type of host, while others suck blood from many different animals. When not attached and feeding on their hosts, most hard ticks live on the ground in vegetation, such as grassy meadows, woods, brush, weeds, leaf litter, etc. Most ticks will crawl to the tips of grasses, brush, leaves, or branches and wait. With their front legs outstretched, they will wait for a host to brush up against them. This behavior is called questing (see photo left). When the tick does come into contact with an animal, it will grab on and crawl to an appropriate area on the animal to feed.
Rats and Mice
• The House Mouse
Mice have litters of 3-14 young. The unborn mice develop in 19-21 days. One female can have 5-10 litters per year. The newborn are blind and furless. Females reach sexual maturity at about 6 weeks and males at about 8 weeks, but both can breed as early as 35 days. House mice usually live under a year in the wild.
• The Roof Rat
• The Norway Rat
As with all rodents, their teeth grow continuously, and thus they gnaw on many surfaces to wear down their teeth. They can chew through almost any material including masonry, steel, plastic, electric cables, water pipes, etc. posing a threat of flooding or fire.
• Rodent Removal
Cutting off sources of food and water for rodents is the first step towards elimination. Store food, birdseed, pet food, garbage, compost, and recyclables in secure metal, glass, ceramic, or heavy-duty plastic containers with tight-fitting lids. Feed pets at scheduled times. Put unfinished food in the refrigerator. Promptly clean up spills and crumbs. Keep bird-feeding areas clean of spilled seed. Move firewood, garbage cans and debris piles away from the house.
Next, entry points need to be identified and sealed off. Poke steel wool or wire mesh into entry holes with a screwdriver or attach flashing. Prune branches away from the roof. Seal openings underneath and behind appliances with latex caulk. Seal gaps around water, gas, and heating pipes, heat registers, air ducts, electrical chases, and false ceilings.
Rats tend to be very shy and cautious animals. When confronted with a new object in their environment, such as a trap, they will often avoid it for days until they are used to its presence in the area. They have poor eyesight so they leave behind a strong pheromone odor telling them where to run. Set traps at night, when mice and rats are most active, and check or remove them in the morning. A dab of crunchy peanut butter on the trigger is an enticing lure. Live trapping with box traps or glue boards may be used for monitoring and for removal. It's better to trap intensively for a few days than to set only a few traps for a long time. Snap traps can be attached to rafters with nails and to pipes with wire. The trigger should snap towards the wall.
Rodenticides are sold in many different forms, including pellets, powder, blocks, and meal. If you choose this option, follow the manufacturer's label carefully or work with a professional. They are very effective in eliminating domestic rodent pests. Pesticides can be hazardous to children, pets, and wildlife. In addition, animals that eat poisoned mice could be poisoned themselves. Poisoned rodents may die inside walls and sub floors where they cannot easily be removed. Their slow decomposition creates foul odors and attracts other pests, such as flies and beetles.
• Clean Up Procedures
Hantavirus pulmonary syndrome (HPS) is a deadly disease transmitted by infected rodents through urine, droppings, or saliva. Humans can contract the disease when they inhale aerosolized virus.
Murine typhus occurs worldwide and is transmitted to humans by the bite of rat fleas.
Rat-bite fever (RBF) is a systemic bacterial illness caused by Streptobacillus moniliformis that can be acquired through the bite or scratch of a rodent or the ingestion of food or water contaminated with rat feces.
Salmonella causes a typhoid-like disease in mice. In humans S. Typhimurium causes severe disease. The disease is characterized by diarrhea, abdominal cramps, vomiting and nausea, and generally lasts up to 7 days.
Leptospirosis is a bacterial disease that affects humans and animals. Humans become infected through contact with water, food, or soil containing urine from these infected animals.
Eosinophilic meningitis is an infection of the brain. In a complex life cycle between rats, slugs and snails, humans become infected by accident when they eat an infected snail or food that has been contaminated by slugs or snails, particularly salads.