Biology Reference
In-Depth Information
proposed as precursors of the lymphonodular type WS (LN-WS);
25,26
as
the appearance of the latter on 10 days post-infection coincides with the
healing of GT-WS.
28
Coupled with the characteristic WS, necrotic and
hemorrhagic migratory trajectories are observed in porcine livers.
Certainly the potential for liver damage in human subjects is likely to be
underestimated.
29
Larval migration through the host lung tissues is known to produce
a range of symptoms including asthma, dyspnoea, cough, and substernal
pain that contribute to respiratory distress in both humans
30
e
33
and
pigs.
34
While studying tuberculosis, Loeffler
35
described a transient or
seasonal syndrome of pulmonary infiltrates, mild to marked respiratory
symptoms, and peripheral eosinophilia that he subsequently attributed to
larval Ascaris in the lungs, later termed “Loeffler's syndrome.”
36
Gelpi
and Mustafa
37
described a temporally constrained pneumonitis and
eosinophilia that co-occurs with the seasonally-transmitted pattern of
ascariasis in Saudi Arabia.
In humans, dyspnoea and bronchospasm may be severe
38
and have
also been documented in pigs.
22,39,40
Moreover, bronchovascular damage
caused by the parasite may result in secondary infections by opportunistic
bacteria that may proliferate in the inflamed tissue and invade the
vasculature, adding further complications associated with the migratory
stages of this parasite.
41
e
43
ANIM
AL MODELS OF LARVAL ASCAR
IASIS
Modeling the Ascaris life-cycle and its epidemiology remains chal-
lenging and plays a part in its status as a neglected disease. As defined by
Boes and Helwigh,
44
an appropriate animal model of helminth infection
should mimic the human host, the parasite, and the human host
parasite
system or the way in which the host and parasite interact. A. suum
infection in the pig represents the naturally occurring host
e
parasite
system whereby the parasite completes its entire life-cycle. Furthermore,
A. suum is closely related to the human parasite A. lumbricoides (see
Chapter 10) and therefore, not surprisingly, A. suum infections in pigs
have played a major role as a model for both human and porcine Ascaris
infection and ascariasis (see Chapters 14 and 16).
However, despite
e
the undoubted advantages of
this natural
host
parasite system, the pig model has some disadvantages including
its large size, cost, husbandry challenges, a lack of inbred strains, and an
associated broad range of immunological reagents that could be used to
dissect the immune response.
Trichuris trichiura, another important human geohelminth infection has
the advantage of a rodent counterpart, Trichuris muris, the closely related
e
