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Ticks and Human Diseases
Nature Bulletin No. 319-A November 2, 1968
Forest Preserve District of Cook County
Richard B. Ogilvie, President
Roland F. Eisenbeis, Supt. of Conservation
TICKS AND HUMAN DISEASES
Insects such as lice, fleas, mosquitoes and flies have been responsible
for the deaths of millions of people and have changed the course of
history. Now, within recent decades, we have learned that those eight-
legged parasites, the ticks, also transmit various diseases -- some of
them frequently fatal -- to wildlife, to domestic animals, and to man
himself.
Insects never have more than three pairs of jointed legs. Scorpions,
spiders, mites and ticks have four pairs, at least when adult. Scorpions
have jointed abdomens but the other three do not. Spiders, however,
have a "waist" between the thorax and the abdomen, whereas the
abdomen of mites and ticks is broadly joined to the rest of the body.
Mites, such as chiggers and chicken mites, are generally much smaller
than ticks. A tick must get blood from some animal in order to exist,
although some may live for a year without it. Before feeding it is round
or oval, and quite flat. After burying its beak and head beneath the skin,
and gorging itself, the bloated body may be five or six times as long. It
should be removed, as soon as possible, by a straight slow pull with the
fingers, without jerking. Otherwise the head may break off and a needle
or knife will be required.
A female tick lays several thousand eggs, on the ground, that hatch into
larvae or "seed-ticks" which have only six legs and seek to attach
themselves to some mammal or bird. Certain kinds molt and remain on
that animal until mature; others feed and then drop to the ground to
molt. There may be from 3 to 8 molts, depending upon the species,
before they become adult. Some kinds complete the life cycle in less
than a year, while others require up to four years. Some have simple
eyes. Others have no eyes but possess special sense organs that enable
them to detect animals many feet away. A camper, or a man standing in
the woods, may attract ticks from a large area and find scores of them
crawling up his legs.
In addition to tick paralysis, Colorado tick fever and relapsing fever,
none of which is fatal, ticks are known to be responsible for two
diseases which sometimes cause death to humans. Rocky Mountain
spotted fever has been known in the Bitterroot Valley of Montana since
1872 but now is found in most of the 48 states. Several cases are
reported each year in Illinois. It is spread among rabbits and other
rodents by the Rabbit Tick but it is spread from them to man by four
different species: principally the Rocky Mountain Wood Tick in the
west, and the American Dog Tick here and in eastern states.
Tularemia, or rabbit fever, is a disease which is spread among rodents,
especially rabbits, and several other animals, including pheasants and
quail, by rabbit ticks, lice and fleas. The American dog tick and the
Rocky Mountain wood tick also transmit the disease to animals,
including man. In western states, infections may also come from bites of
the deer fly and it was first named "deer fly fever". Hunters and others
handling infected animals, or eating their meat not thoroughly cooked,
may become infected themselves. About 25,000 cases have been
reported in the United States in the last 25 years, over 3000 of them in
Illinois alone, with death resulting in about 5 percent of the cases. The
places, or the years that produced an abundance of cottontails were the
ones that showed more tularemia in humans. Where warm mild weather
lasted well into the hunting season, there were more cases than in
autumns with several sharp freezing nights before the opening of the
season. Such cold weather forces the ticks to drop off and hibernate.
After another week, during which the diseased cottontails die, hunting
is far safer.
An alarm clock may have tick fever every morning.
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Update: June 2012
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