Hard ticks feed on two or three hosts during their development because the larval, nymphal and adult stages each require nourishment in the form of a blood meal. Mated females lay thousands of eggs on the ground. The eggs hatch into larvae or “seed ticks” which only have 6 legs. These larvae remain close to the emergence site and climb up on grass and low vegetation so they may attach themselves to small animals which pass by. After feeding for 2 to 9 days on their hosts, the larvae drop to the ground, digest the blood and then moult to the 8-legged nymphal stage. The nymphs attach themselves to second hosts. After feeding on these hosts, the nymphs moult to the 8-legged adult stage. Other species are nest-associates and remain within a nest or burrow. Ticks can overwinter as eggs, larvae, nymphs or as adults depending on the species. Ticks are adapted for prolonged periods of starvation. The entire life cycle may require 3 years to complete. After an adult female attaches itself to a host, it often takes up to a week to complete its feeding. Once the female has become engorged, it drops to the ground, mates and lays its eggs. Mating can also take place on the host before or during feeding. Adult males die after completing fertilization. Female adults die after egg-laying is complete.
EFFECTS OF TICK BITES
Tick bites usually cause irritation of the skin and swelling only. However, if some of the tick’s mouthparts remain in the skin, the wound usually becomes infected. Occasionally, an infection may become severe enough that it may lead to blood poisoning. Tick bites on humans usually occur one at a time. Livestock and wild animals, however, may be infested with many ticks at once. Feeding by large numbers of ticks can lead to anaemia, unthriftiness or emaciation. Some animals become weakened and die.
TICK-BORNE DISEASES OF HUMANS
A small percentage of the members of tick populations carry diseases. The diseases are transferred from host to host by the blood-feeding activity of the ticks. The following tick-borne diseases have been reported to occur in Canada: Rocky Mountain spotted fever The American dog tick can transmit Rocky Mountain spotted fever, a rickettsial disease (Rickettsia rickettsii), to humans in central and eastern North America. The initial symptoms of this disease, which can occur anytime from 2-14 days after the tick bite, are headaches, intense aching in the lumbar region and marked malaise. A rash appears on the wrists and ankles and then spreads to other parts of the body. A fever of 40 °C may occur in cases that are more pathogenic. If symptoms occur, one should see a physician.
Tularemia, or rabbit fever, is a bacterial disease of rodents which sometimes affects man and other large mammals. It is caused by the bacterium, Francisella tularensis. Deer flies and ticks are important vectors of this disease. In eastern Canada, the American dog tick is usually responsible for transmitting this disease. Pain and fever occur soon after the tick bite. The lymph glands become swollen and inflamed. The fever may last up to 6 weeks, with the patient recovering slowly.
Tick paralysis is a disease which may be transmitted by the American dog tick and some Ixodes species. The feeding activity of one female tick, usually at the back of the head, can cause symptoms in less than 6 days. A neurotoxin, secreted by the salivary glands during feeding, is responsible for the symptoms. The first symptom to occur is a numbness of the feet and legs. The patient also experiences difficulties in walking. This is followed by a numbness of the hands and arms. The throat muscles and tongue may become partially paralyzed. Death from respiratory failure may occur if the tick is not removed in time. Recovery is rapid if the tick is removed soon after attachment.
Lyme disease is caused by a coiled bacterium called a spirochaete. This spirochaete, Borrelia burgdorferi, is usually maintained in populations of mice. The tick most often responsible for transmitting the disease to other animals, including humans, is the blacklegged tick. A growing bull’s eye rash centred at the site of the bite is an important first symptom of Lyme disease. Other early symptoms of the disease include fatigue, headaches, stiffness in the muscles, joints, or the neck, jaw discomfort, fever or swollen glands. Later symptoms include skin rashes, arthritis, neurological disorders and cardiac disease.
HOW TO AVOID TICKS
Control of ticks in an infested area is extremely difficult due to their tremendous reproductive potential, their habits, and their habitat. However, preventative measures against tick attack can be taken.
Avoid tick infested areas if possible. Wear protective clothing (eg. secure trouser cuffs inside boots and leggings to prevent ticks from gaining access to legs).
Check your body thoroughly for ticks. Also, before your pets enter the house, check them thoroughly for ticks as well.
If ticks are found embedded in the skin, remove carefully, using small tweezers. Grasp the tick with the tweezers at the point where the mouth parts enter the skin, and use a gentle, firm, tugging motion until the tick releases hold of one’s skin. Do not kill the tick before it has been removed. Treat the bite wound with antiseptic to avoid infection, and save the tick in a jar labelled with the date and location, in case complications arise.
An insect repellent containing DEET sprayed on the clothes is also effective at repelling ticks.