 The Open Door Web Site |
||||||||||||||
|
Parasitic relationships: Human parasites Fleas The flea is a successful parasite. The body of the flea is long and thin. It is able to jump from one host to another. When the flea jumps it reaches a height of 200 times its body length at an acceleration of 200 times the normal gravity.
Fleas are not found on monkeys, apes or horses. They are, however, common on rats, mice and squirrels. Between 1349 and 1352, a disease called the bubonic plague killed one third of the population of Europe. It quickly became known as the Black Death. This disease, which is caused by a bacterium, was started by infected rat fleas biting humans. Lice
Lice (sing. louse) are common human parasites, particularly in dirty and overcrowded places. The louse is an insect. Its body grows to 11mm in length and is flattened. It has hooks on its legs which help it to hold onto its host. Lice spread to a new host by body contact with an infected person. This is particularly easy for head lice if an infected person's hair is in contact with someone else's hair. Lice feed by biting the skin and sucking up the released blood. They lay their eggs, called nits, on hairs. These eggs are difficult to remove because the lice produce a glue-like substance to keep the eggs attached. The eggs hatch into miniature adults which quickly grow as they feed from their host.
Human head lice are quite common but they can be removed by washing hair with a special shampoo. The nits are more resistant and may need to be combed out with an especially fine comb. Before the introduction of insecticides, lice were much more widespread than they are today. They were responsible for transmitting diseases such as typhoid fever.
Lice are found on birds and all mammals except the duck-billed platypus, anteaters, armadillos, bats and whales. Lice are especially numerous on sick or injured animals. One sick fox was infested with 14000 lice and a sea bird with a damaged beak was home to 7000 lice! Healthy animals manage to keep the numbers down by grooming, seen in mammals, and preening, seen in birds. Most birds have at least 4 species of lice on different parts of their bodies.
|
© Paul Billiet and Shirley Burchill 2009 |
||||||||||||
