Ticks and Tick-Borne Diseases in Napa County

Source: Tick-Borne Diseases, Napa County Mosquito Abatement District

Lyme disease is present in Napa County. There were three diagnosed cases in 2001.

Rocky Mountain Spotted Fever is present in Napa County. There was one case reported by the California Department of Health Services in 2000.

The tick vector for Tularemia is present in Napa County. No known diagnosed cases have been reported.

Source: Summary of Napa County Ticks, Napa County Mosquito Abatement District

Napa County has 10 confirmed species of ticks, including the following which are vectors of Lyme Disease, Q Fever, Rocky Mountain Spotted Fever, Tularemia, and Tick Paralysis to humans.

Ixodes pacificus
Western Black-legged Tick
Widespread Californian Tick. Life cycle can be completed in less than one year but usually lasts about two years. Females lay eggs in the spring on the undersides of brush and dried leaves. Eggs hatch during early summer. Nymphs and adults seek hosts (quest) from the tips of vegetation while larval ticks find hosts close to the ground. Most commonly encountered Ixodes tick in California. Adults occur year-round but are most commonly found November through May. Nymphs are most commonly found March through June but can be found year-round. Immature stages commonly found on Alligator Lizards, Fence Lizards, and ground inhabiting birds. Sometimes found on small rodents and rabbits. Large mammals are also important hosts for larvae and nymphs. Adults are common on deer and other large mammals (dogs, bears, cats, horses, humans, etc.).
Vector of Lyme Disease. Has caused tick paralysis in a dog.

Dermacentor occidentalis
Pacific Coast Tick
Common, widespread Californian tick. Adults are found year-round with peak activity in April and May. Nymphs are most common during spring and summer. Adult hosts tend to be cattle, horses, deer and humans. Rare on dogs and bears. Nymphs tend to feed on rodents and other small mammals.
Capable of transmitting many diseases. Vector of bovine anaplasmosis. Has been found naturally infected with Colorado Tick Fever virus, the Rickettsia of Q Fever and the bacterium that causes Tularemia. Known to cause tick paralysis in cattle, horses and deer. Spotted fever group Rickettsiae have been found in ticks collected from Mendocino County. Bite wounds are commonly mistaken for wounds caused by biting insects and spiders.

Dermacentor variabilis
American Dog Tick
Widespread Californian tick. Life cycle can be completed in less than one year or take longer than two years if suitable hosts are not available. Adults are present year-round while nymphs and larvae are most active late winter to summer. Adult females may take up to 13 days to complete feeding on a host and can produce as many as 6500 eggs during their lifetime. Immature ticks are capable of surviving extreme winter temperatures. Dogs are the preferred host although adults will feed on humans and many other species of large wild and domesticated mammals. Larvae and nymphs tend to feed on rodents and rabbits.
Important vector of Rocky Mountain Spotted Fever, especially in the Eastern United States. Vector of Tularemia to humans. Known to cause tick paralysis.