Biomedical Engineering Reference
In-Depth Information
CHAPTER 8
Blood-Feeding Human
Hookworm Proteases
A. LOUKAS,*
a
N. RANJIT,
a,b
D. A. PICKERING
a
AND
M. S. PEARSON
a
a
Queensland Tropical Health Alliance, James Cook University, Cairns,
QLD 4878, Australia;
b
School of Veterinary Medicine, University of
Pennsylvania, Philadelphia, PA 19104, USA
8.1 Introduction
Parasitic hookworms are large, multicellular organisms belonging to the phy-
lum Nematoda. They infect their mammalian host as an immature larva either
orally or by penetrating the skin. They then typically migrate to the vasculature
where they are passively swept through the heart to the lungs. Once in the
lungs, the larvae break through the alveoli, creep up the trachea, and are
swallowed, eventually reaching the small intestine as immature adult worms. In
the duodenum, the adult worms bury their anterior ends beneath the mucosa
and secrete a suite of proteins (rich in proteases) which digest the tissue and
allow the parasite to feed on extravasated blood. Adult worms are dioecious
(separate sexes); males and females mate, and each female releases thousands of
eggs per day with the faeces of the host. The eggs contaminate the environment,
and if conditions are favorable (warm and wet), larvae hatch from the eggs,
feed on environmental bacteria, and moult twice to become third-stage larvae
(L3), which are infective to the mammalian host. The major species of hook-
worm that infects humans is Necator americanus.
1
It infects more than 500
