Ticks are eight-legged, blood-feeding ectoparasites that are closely related to spiders, scorpions, and mites and live on mammals and birds.  There are about 800 different species of ticks.

Lyme disease (lyme borreliosis) is caused by the bacteria Borrelia burgdorferi and is spread by the deer tick.  It is one of the most common tick-transmitted veterinary diseases in the world.  Lyme disease can affect both cats and dogs.  Its most common clinical symptoms are arthritis, lameness, anorexia, and depression.  It can also cause cardiac, neurological, and kidney disease.

Canine ehrlichiosis (tick-borne fever) is caused by Ehrlichia canis and is spread by the brown dog tick Rhipicephalus sanguineus.  It occurs throughout the United States, but is most common in the Southeast.  Ehrlichiosis damages and decreases the production of blood cells and leads to anemia, lowered disease resistance, and abnormal bleeding.  Diagnosis is usually based on a blood test.  Treatment involves antibiotics and supportive care.  Though the prognosis is usually good, ehrlichiosis can be fatal.

Rocky mountain spotted fever is caused by the bacteria Rickettsia rickettsii and is spread by the American dog tick (Dermacentor varabilis) and the wood tick (D. anderson).  Symptoms include fever, lethargy, depression, anorexia, swelling, a stiff gait, abnormal bleeding, breathing problems, and eye pain.  Rocky mountain spotted fever is difficult to differentiate from canine ehrlichiosis.  The prognosis is good if the dog receives prompt treatment, including antibiotics and supportive care.

Treatment
If pet owners find a tick on their dog or cat, they should remove it by grasping the tick with fine-pointed tweezers and gently pulling it free.  The more quickly the tick is removed, the lower the risk of disease transmission to the pet.  You should wash your hands thoroughly with soap after handling a tick. 

Disposing of ticks
To dispose of the tick, drop it into alcohol to kill it, then dispose of it.  Flushing them down the toilet WILL NOT KILL THEM.  Squishing them with a thumbnail is not recommended, and is not easy anyway.  You might save the tick in a jar of alcohol for identification, to help decide whether possible infection has occurred.

Combating and Preventing Ticks
If you have heavy infestations of ticks in your area, spraying your backyard against ticks may be a good idea, especially if your pet is indoor/outdoors.

If you have a dog, a new product called Preventic appears to be highly effective.  It is a tick collar that kills ticks shortly after they attach to your dog.  The active agent is Amitraz, which prevents attachment and kills but does not affect fleas.  Amitraz is not an insecticide (flea killer) but an "arachnicide" (8-legged bug killer - ticks and spiders are in the same class.) 

The collar works best if it is kept dry.  Rain is OK, but swimming is out as exposure to water reduces its effectiveness.  Removing the collar is apparently non-trivial.  You don't need a prescription, although the only place you might find it is at the vet's or in a mail-order catalogue.  Twenty-four hours after putting it on, your dog is protected from ticks. 

Many people have written about how effective it was for their dog.  It is NOT recommended for cats, however, and some dogs appear to have individual sensitivity to it.  If your dog becomes lethargic or irritable, remove the collar.

NOTE THAT THE COLLAR IS TOXIC -- if your pet eats any part of the Preventic collar, take him in to the vet immediately.  Symptoms include vomiting, white gums and unsteadiness.  There is an antidote for it, called Yobine.

Ticks don't typically infest houses, unless you have a pet that had an overlooked tick that dropped off and hatched its eggs.  In the Northeast US and other temperate climates the tick Rhipicephalus sanguineus is almost exclusively limited to domestic habitats, particularly kennels.

Because the entire life cycle occurs inside, control strategies become similar to that of controlling fleas.  You will have to spray your house in this case as ticks hatch an unbelievable number of eggs.

Your local hardware store can give you tips on what is best to spray with.  You are not too likely to find "natural" or low-toxic sprays for ticks. On the other hand, one spraying is likely all you need to clear them out of your house. They are not tenacious the way fleas are.

Common recommendations for reducing ticks in your backyard are to keep the weeds or grass well-mowed.  There are commercial sprays effective against ticks.  If you live in tick-infested areas, always examine your dog (and yourself!) after being outside.  Control vermin around your house and discourage deer and other wild or feral animals from your property, as they are often vectors for ticks.