| dc.description.abstract | Eighteen Dorper sheep aged between six and twelve months were obtained from an area
known to be free of fasciolosis. The animals were divided into four groups (I-IV). Each of the
first three groups comprised of five sheep while the fourth group had three sheep. Each of the
five sheep ill group I was orally infected with a low dose (250) 01 metaccrcariac or Fasciola
giganiica whereas each of those in group LI got a high dose (400) or the metacercar iae. The five
sheepof the third group were infected with varying doses of between 210 and 490 metacercariae
per animal. The group III animals were slaughtered at weeks 7, 11,13,14 and IS post-infection
and flukes recovered. These nukes were processed and their antigens compared with somatic
antigens of Paramphistomum spp., Schistosoma mansoni, Stilesia hepatica, . hydatid cyst lluid and
F. gigantica (together with its excretory/secretory products) in a SDS-PAUE gel. An antigen,
AgF.g28, was found to be .both immunogenic and specific for F. gigantica by Western blotting. It
was eluted from the SDS-PAGE gels and used to immunise the three sheep in the fourth group.
Immunoglobulin G from the sera of the hyperimmuniscd sheep was isolated and conjugated with
horseradish perox idase enzyme.
Sera and faecal samples were collected weekly from the sheep in groups I and I [ from
three weeks. before infection to 21 weeks post-infection, after which they were slaughtered and
the adul: liver flukes in tile bile ducts, together with the Foscio eggs ill the: gilll bladders.
recovered and counted .. Tile faecal samples were subjected to LlH~rEST and tile number or
Fasciola eggs in 3 grams ascertained, while the sera were assayed tor antigen aile! antibody by
the antigen- and antibody-El.ISzv tests respectively.
The whole-worm SDS-PAGE protein profiles of the various ages of juvenile flukes and the
adult nukes recovered from sheer appeared identical. Ilowever, a protein band of' a MW of
about 42-kOa was present in the flukes recovered from sheep but was lacking ill tile adult fluke
recovered from bovine, whereas a protein band of about 70-kDa \\as nut as prom incur in the
fluke of bovine origin as it was ill those from sheer. The protein b.mdx ill the ES products were
fewer (hall those ill the whole-worm extracts. Apart from a halHI or ahout ()()k Da, all the
protein bands in the ES products were also present in the whole-worm extracts. Each of the
other parasites had its own unique protein profile. Nevertheless, COlli ilion protein bands ex isted
between F. gigantica and S. manson! (e.g bands of 40 and 94-kl)(\), l'. gigautic« and S. hepatica
(e.g bands of 25 and 80-kOa) and also between F. gigantica and the hydatid cyst fluid OX-kDa).
The 43-kOa band was present in all but thewhole-worrn protein profile of Paratnphistonunu spp.
A protein band of 28-kOa was identified and found to be specific Ior F. gigantic». This
antigen, code named AgF.g28, was present in all ages of the F. gigantica whule-worrn PI3S
extracts and also in the ES products. An antigen-ELISA developed for the I\gF.gn had a
sensitivity of 75 % and a specificity of 70% for the 21 weeks of infection. An nutibody-El.ISv',
for the same antigen hac! a sensitivity of 81 % and a specificity 01 20% for the same period.
Eight out of ten sheep in both the low and high dose infection groups tested posit ivc for
Iasciolosis at the first week post-infection by the antigen-ELISA, as compared to 2 out or 10 ill
the same period by the antibody-ELISA. The Faecal egg sedimentat ion technique first detected
fasciolosis at the l3u\ week post-infection.
Student's T-tests conducted showed that none of the three diagnostic tcsts was able to
distinguish between low and high levels of fasciolosis. Also, there was no significant difference
between the number of adult flukes recovered from the bile ducts, the number of eggs in the
faecesand in the gall bladder between the animals in the low and high dose infection groups.
A direct relationship was found to exist between the number of eggs in the faeces and those ill
the gall bladder, and also between the number of Fasciola eggs in the gall bladder and the
number of adult flukes recovered. However, no relationship existed between the number of
adult flukes recovered and the number or eggs in the faeces. 1\ rcurcssin» iliialysis at the 5 %
level revealed that the dose (i. e number of metacercariae ingcsted) did not ill Ilucncc the
dependent variables such as number of eggs ill the faeces and gall bladder, the percentage fluke
take (i. e the proportion 0 f mctacercar iae ingested that developed to aelulthood a11(1 were
recovered), and the optical density readings of the antigen- and antibody-El.ISzv. Tile statistical
results effectively imply that quantitative diagnosis or Iasciolosis cannot be ascertained by any
of the three diagnostic tests used in the present study.
The fact that the AgF.g28 was found in both the whole-worm extracts and the, ES
products means that it was most probably an ES antigen. This was also evident 1"1'0111 tile SDSPAGE
protein profiles where the antigen in the ES products was more prominent and distinct
than in the whole-worm extract. The antigen was not highly immunogenic, as shown by the
Western blot and this probably explains why the sensitivities of both the Antigco and Antibody-
ELiSAs were low.
Under the conditions or the present study, it was round that tile Antigen-EI.ISA was
superior to both the Antibody-ELISA and the FEST. Its sensitivity and specificity were together
higher than those of the other tests, and it was also able to detect fasciolosis ill infected sheep
relatively earlier. The success of a good diagnostic test is determined by its ability to detect
disease in infected animals as early as possible, and also to have a high sensitivity and
specificity. If the antigen, !\gF.g28, was produced in a purer form. aile! monoclonal antibodies
used instead of poly clonal, then the Antigen-ELISA developed to detect AgF.g28 in serum would
possibly be a good diagnostic test for fasciolosis, | en |
