Biology Reference
In-Depth Information
TABLE 5.1 Parameter(s) investigated in experimentally infected model organisms
excluding mice (see
Table 5.2
) and pigs (see Chapter 14).
Model organism
Parameter(s) investigated
Reference number
Guinea-pig
Larval migration
Immunological response
52
,
75
,
79
,
80
,
82
83
,
91
95
e
e
Rabbit
Immunological response
Larval migration
Hepatic pathology
Pulmonary pathology
52
,
75
,
81
,
96
98
e
Gerbil
Larval migration
99
Rat
Larval migration
93
,
100
Cow
Larval migration
Immunological response
Pathology
101
104
e
Lamb
Larval migration
92
Goat
Larval migration
92
swallowed, thereby returning to their former location within the small
intestine where they mature into adults.
4
The explanation for the perpetuation of this perilous journey is far from
understood. Smyth
5
speculated that such an extra-intestinal migration
might represent “evolutionary baggage” left over from a previous life-
cycle, perhaps originally based on skin penetration. However, other
authors have argued that migration may confer significant fitness benefits
given the associated risks of immune-mediated damage and mortality
within the tissues
6,7
and therefore by adopting this complex route, rather
than just developing in the lumen of the small intestine where eggs
originally hatch, the parasite gains a significant advantage. There is some
evidence to suggest that migration confers enhanced parasitic growth
6
and Jungersen et al.
8
demonstrated that A. suum larvae infected intrave-
nously in pigs, do not undergo larval migration, and develop more
slowly.
THE IMPACT OF LARVAL MIGRATION
IN NATURAL HOSTS
The public health significance of larval migration by Ascaris in humans
remains poorly understood. The difficulty in designing appropriate and
ethical studies of larval migration in humans has hindered research into
