Animals P by: Geoffrey LaPage Published by ... - PSSurvival.com

Animals Parasitic in Man
Ancylostoma, the males being 5 to 9 mm. (i to $ inch) and the
females 9 to 11 mm. (Q to nearly Q inch) long. It has been
suggested that it was taken to America in the bodies of
Africans who were imported to that country as slaves and
also perhaps in the bodies of other people who immigrated to
America.
It is difficult to estimate the number of people in the world
who are infected with Necator amerikanm and species of the
genus Ancytostoma, because the geographical distribution of
the species of these two genera varies; but St011 ( 1947) estimate&that
457 million people in the world were, at the time
when he made his investigations, infected by one species or
another of these genera of hookworms.
Th Life History of Hookworms
The life histories of all the species of human hookworms are
similar. They have already been outlined in chapter 9, but
they may be given in rather more detail here. The adult male
and female worms live in the small intestine of man, where
they suck blood. They produce fertilized eggs, which are
passed out in the excreta of the host. Inside the eggs a young
worm, called thefirst Zarva, develops and this hatches out of
the egg and feeds on bacteria in the human excreta, until it
has grown too big for its skin. It then moults its skin and becomes
the second Zarva, which also feeds on bacteria and moults
its skin to become the third larva. The third larva is formed in
about a week, or less, after the first larva left the egg. It also
moults its skin, but this moulted skin is kept on this larva as a
loose sheath which protects the third larva inside it to some
extent from the injurious effects of its environment. Because
this third larva is thus enclosed inside the cast skin of the
second larva, it cannot feed and must rely on reserves of food
stored up in its intestinal cells.
The three larval phases just described, which live in human
excreta or in soil on to which these excreta have been deposited,
are all non-parasitic and the formation of the third larva
marks the end of this non-parasitic phase of the life history.
The function of the third larva is to infect a new host, either
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