Biology Reference
In-Depth Information
preparations to replace or complement synthetic drugs, which are
currently in use. In addition to phytopharmaceutical research, the
possibility of using nematophageous fungi for the biological control of
A. suum
is currently being investigated. According to the study of
Ferreira et al.,
77
mycelia of
Pochonia chlamydosporia
, which were added
to the food of pigs, showed ovicidal activity against
A. suum
eggs after
passage through the gastrointestinal tract.
Recently, it has been shown that a number of infection parameters like
worm burden, total egg output, and raised antibody levels as well as
natural resistance to
A. suum
infections are heritable traits representing
the close genetic control of immunity against this parasite.
27,30
This,
understandably, opens the door to selective breeding of pigs with
increased resistance within the pig industry and could become relevant in
free-range systems.
78
Pigs build up natural resistance against recurring infections rather
quickly. Significant levels of protection were detected in pigs following
one or multiple inoculations with infective eggs or L3s of
A. suum
.
13,35
This provides some hope for future vaccination strategies. The
development of vaccines against parasites is highly desirable. The search
for a vaccine against
A. suum
has been ongoing for about half a century.
Still, their development so far has been very limited and the information
gathered on this topic remains scarce. An overview of the different
vaccination trials published in the literature is given in
Table 16.3
. During
the last decade, interest has shifted from native proteins towards
recombinantly produced proteins. Recombinants were generally
expressed in
E. coli
, though recently attempts have been made to produce
larval antigens in rice plants.
79,80
Immunizing mice by feeding them
transgenic rice elicited an antigen-specific antibody response, indicating
that the transgenic rice was able to prime the immune response of mice.
Orally immunized mice also showed a reduced amount of larvae
recovered from the lungs after challenge infection in comparison with
non-immunized controls.
79
In the future, this could provide an easy way
of producing and administering parasite antigens. However, this tech-
nique should be further optimized and evaluated.
A vaccination protocol, targeting the necessary components of the
host's immune system, could be efficient in providing protection to the
host against newly acquired larvae. However, it is possible that this
increased immunological response against migrating larvae invoked by
the vaccination would manifest itself as increased numbers of lesions in
the pig's liver. In a study by Vlaminck et al.,
36
significantly more white
spots were counted on the livers of vaccinated pigs on day 14 (
þ
86%) and
day 28 (
118%) after infection compared with non-vaccinated controls.
Furthermore, a vaccine against
Ascaris
will need to be highly protective.
Female worms are extremely fecund and can produce hundreds of
þ
