| dc.description.abstract | Taenia saginata is among the zoonotic parasites that interfere with the hum~a.n
health and production of livestock, worldwide. The adult worm causes taeniasis in humans
while the larvae causes cysticercosis in cattle. The economic losses accruing from these
infections are substantial.
Meat inspection which is the most important public health control measure
practised, identifies only heavily infected animals when it is too late to avoid incurring
losses. For this reason, an ante-mortem diagnostic test would be very much desirable.
Currently, there is no established test for diagnoses of bovine cysticercosis in live cattle
but an antigen-ELISA (Ag-ELISA) which has been developed recently, has shown to be
feasible as a herd test. This study was carried out in order to determine the number of live
cysticerci that the Ag-ELlSA can reliably detect in infected cattle thereby validating the
test. The Ag-ELISA was compared with routine meat inspection method using total
dissection as a measure of the true status of infection in the animals.
Two groups of animals were used in these experiments, namely, 25 naturally
infected animals from pastoralists in Samburu District and 30 neonatal calves
experimentally infected with various doses of 1. saginata eggs. Both groups of animals
were bled immediately after arrival and before infection in the case of neonatal calves and
thereafter, every two weeks (neonatal calves) and monthly (naturally infected animals) till
slaughtered in the 15th week and 3rd month, respectively. All the sera frc .n either
experimentally or naturally infected animals were tested for circulating cysticerci antigens
by Ag-ELISA.
The results showed that in experimentally infected calves, the parasite antigens
were first detected 7-11 weeks post- infection. As in the naturally infected seropositive
animals, the antigen level fluctuated but remained above the cut-off point, until the animals
were slaughtered. Although the sensitivity of the test varied from one animal to another,
the minimum number of live cysticerci which was detected by the Ag-ELISA was 14 in
experimental calves and 2 in naturally infected animals. However, other animals with 12
and 17 live cysticerci in experimental calves and 1 to 2 live cysticerci in naturally infected
animals, escaped detection. Animals harbouring dead cysticerci gave negative reactions
as in non-infected experimental control calves, indicating that the assay only detected
products of viable cysticerci in cattle. There was a statistically significant positive linear
correlation between Ag-ELISA optical density values and burdens of live cysticerci as
obtained by total dissection in both experimentally (r = 0.798, n = 24; p > 0.05) and
naturally (r = 0.631, n = 25; p> 0.05) infected animals. In naturally infected animals, the
Ag-ELISA showed a good precision.
Comparison of Ag-ELISA with routine meat inspection method in naturally infected
animals showed that the Ag-ELISA was more than twice as sensitive as meat inspection
method, while the sensitivity of the two methods was the same in the experimental
infections. This was probably due to poor infection rates in the experimental calves.
However, there seemed to be very little overlap between animals diagnosed positive by the
two methods. In all the cases, however, Ag-ELISA diagnosed more animals as positive for
bovine cysticercosis than the routine meat inspection method whose regulations limits it
to examination of very few predilection sites.
The level of agreement between the two methods was, on average, lower in
naturally infected animals than in experimental calves. This was because in natural
infections, there were more light infections than in experimental infections and these
could not be detected by meat inspection method but could be detected by either Ag-
ELISA or total dissection.
From the results obtained by this investigation, it was concluded that the
monoclonal antibody-based antigen detection ELISA is of value for the diagnosis of bovine
cysticercosis infection in cattle as a screening test in a herd. This is because, the assay still
gives false-positive and negative reactions in : lightly infected cattle which,
epidemiologically, form the most important group in the transmission cycle of this
parasite. In a herd of heavily infected cattle, the assay can provide for individual diagnosis.
Although, as a screening test, it could be adopted as a control method for the parasite, more
work is still needed to increase its sensitivity in order to develop it as a field test | en |
