Diseases Spread By Tick Bites

Ticks transmit diseases to humans and animals through their feeding activities. They feed on blood and lymph depending on the stage of their life cycle, with larvae favoring lymph and nymphs and adults preferring blood. Tick mouthparts are specially designed to enable them to pierce the skin of the host and feed efficiently.

They prefer to feed on hairless areas such as the insides of ears and between the toes. This can make them quite difficult to find, and means that they can remain on the pet for a several days before being noticed. The longer they are attached to your pet, the greater the likelihood of their transmitting diseases.

Ticks cut through the skin and secrete salivary enzymes to help break down tissues. They then insert a 'hypostome' into the bite wound, which features barbs shaped like an arrowhead so that it can be easily inserted but more difficult to pull back out. This is one reason why it can be difficult to remove ticks.

A tube runs down the center of the hypostome transports a number of substances which assist feeding. The host's blood is also withdrawn through this tube.

The saliva of hard ticks contains a cementing substance which sticks its mouth parts to the host's skin, enabling the tick to hold on to the host. When the tick is full of blood, or engorged, it secretes enzymes to disolve this cement, allowing it to drop off.

The saliva also contains lytic enzymes, which break down tissues. These assist by causing blood leakage from vessels in the area around the bite site so it can be sucked up by the tick. An anticoagulant is also secreted to prevent the blood from clotting and make sure that it remains in a liquid state, so it can be sucked through the small tube.

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Some ticks also secrete local anesthetics or anti-inflammatory substances. These desensitize the host's skin or reduce its immune reaction and thus maximizes the parasite's chances of fully engorging without being removed by an irritated animal.

Salivary glands are also the primary site for the transmission of disease. Bacteria or other agents which cause diseases are injected along with the saliva. However, this does not occur as soon as the tick attaches to the pet. It takes from a few hours to several days to transmit a sufficient dose to cause disease. If ticks are removed from a pet within 24 hours of attachment, they are much less likely to have transmitted any diseases. This is why it is so important to check pets for ticks every day and remove them as soon as they are found.

Ticks should not be crushed during or after removal, though, as this may release any diseases they are carrying.

References
Farley D. Fighting Fleas and Ticks. In: FDA Consumer. US Food and Drug Administration. 30:6, 1996. http://www.fda.gov
Payne, P.A., Dryden, M.W., Carter, G.R. External Parasitic Diseases of Dogs and Cats. In: A Concise Guide to Infectious and Parasitic Diseases of Dogs and Cats International Veterinary Information Service, Ithaca NY. www.ivis.org
Tilley L.P., Smith, F.W.K. The Five Minute Veterinary Consult Canine and Feline. Second Edition. Lippincott Williams & Wilkins, Baltimore, 2000.
Vredevoe L. Background Information on the Biology of Ticks. Department of Entomology, University of California, Davis. http://entomology.ucdavis.edu
What you should know about External Parasites. American Veterinary Medical Association. Schaumberg, IL. www.avma.org