Rocky Mountain Spotted Fever (RMSF)
Information About Ticks
The organism that causes RMSF is transmitted by the bite of an infected tick. In Arizona, the brown dog tick (Rhipicephalus sanguineus) is the main arthropod (vector). In northern Arizona, the Rocky Mountain wood tick (Dermacentor andersoni) also transmits RMSF. In other parts of the country, the American dog tick (Dermacentor variabilis) and Rocky Mountain wood tick (Dermacentor andersoni) are the most common vectors.
Life Cycle of Hard Ticks that Spread Disease
Four life stages of the brown dog tick
Most ticks go through four life stages: egg, six-legged larva, eight-legged nymph, and adult. After hatching from the eggs, ticks must eat blood at every stage to survive. Ticks that require this many hosts can take up to 3 years to complete their full life cycle, and most will die because they don't find a host for their next feeding.
Ticks can feed on mammals, birds, reptiles, and amphibians. Most ticks prefer to have a different host animal at each stage of their life, but some, like the brown dog tick, prefer only one host during their entire life cycle.
How Ticks Find Their Hosts
Ticks find their hosts by detecting the breath and body odors of animals, or by sensing body heat, moisture, and vibrations. Some species can even recognize a shadow. In addition, ticks pick a place to wait by identifying well-used paths. Then they wait for a host, resting on the tips of grasses and shrubs. Ticks can't fly or jump, but many tick species wait in a position known as "questing."
While questing, ticks hold onto leaves and grass by their third and fourth pair of legs. They hold the first pair of legs outstretched, waiting to climb on to the host. When a host brushes the spot where a tick is waiting, it quickly climbs aboard. Some ticks will attach quickly and others will wander, looking for places like the ear, or other areas where the skin is thinner.
How Ticks Spread Disease
Ticks transmit pathogens that cause disease through the process of feeding.
- Depending on the tick species and its stage of life, preparing to feed can take from 10 minutes to 2 hours. When the tick finds a feeding spot, it grasps the skin and cuts into the surface.
- The tick then inserts its feeding tube. Many species also secrete a cement-like substance that keeps them firmly attached during the meal. The feeding tube can have barbs which help keep the tick in place.
- Ticks also can secrete small amounts of saliva with anesthetic properties so that the animal or person can't feel that the tick has attached itself. If the tick is in a sheltered spot, it can go unnoticed.
- A tick will suck the blood slowly for several days. If the host animal has a blood-borne infection, the tick will ingest the pathogens with the blood.
- Small amounts of saliva from the tick may also enter the skin of the host animal during the feeding process. If the tick contains a pathogen, the organism may be transmitted to the host animal in this way.
- After feeding, most ticks will drop off and prepare for the next life stage. At its next feeding, it can then transmit an acquired disease to the new host.
How Can Ticks Be Controlled?
The most effective strategy to control ticks is an integrated approach which includes:
- Using appropriate spot-on treatments, tick collars, sprays, or dips to control ticks on pets. Follow the label and your veterinarian's instructions.
- Apply appropriate pesticides to control ticks in your yard. You can use a pest control service or do it yourself. Be sure to use a pesticide product specifically labeled to kill ticks, and follow label instructions for the pesticide product. Repeated applications may be needed.
- Remove tick habitats on your property, including leaf litter, brush, and yard clutter (boards, mattresses, old furniture, etc.).
- Community-based integrated tick management strategies can be an effective public health response to reduce the tick-borne illness. However, limiting exposure to ticks is presently the most effective method of prevention of tick-transmitted diseases.
For more information on tick control, see the Tick Management Handbook.
(Courtesy of The Connecticut Agriculture Experiment Station)