| dc.description.abstract | The studies described in this thesis were conducted to evaluate field
application of the antigen-detection tube Enzyme Linked Immunosorbent Assay
(ELISA) kit developed by Nantulya (1989) for diagnosis of Trypanosoma evansi
infections in camels. The study was carried out on a herd of 100 camels in a T.
evansi endemic area of Marsabit District, Northern Kenya. Blood samples were
collected from each camel on four occasions; twice in the dry season and twice in
the wet season. A total of 394 samples were collected. The results obtained using
the tube-ELISA kit were compared with those of antigen trapping microplate
ELISA, packed cell volume (PCY), the buffy coat technique (BCT) , and antibody
ELISA.
From each camel 3 ml of blood was collected by jugular venipuncture into a
vacutainer tube containing ethylene diamine tetra acetate (EDTA) as anticoagulant,
mixed and stored in a cool place. The EDT A blood was used for the following tests
in the field: Packed cell volume (PCY) determination, buffy coat smear and antigen
trapping tube ELISA. Simultaneously, lOml blood was collected from each camel
into a silicon coated vacutainer tube for serum separation. The serum was separated
12 hours after collection, transported to the laboratory and stored at -200C until
required for tube and microplate antigen trapping ELISA, and antibody ELISA.
For tube ELISA, 500,LLI of whole blood or serum were used per tube and
each sample was tested in duplicate. Fifty microlitres of serum were used per well
in the antigen trapping microplate-ELISA, while 10 - 20,LLI were used in antibody
ELISA. An optical density greater than twice that of the negative control serum
was regarded as positive in the case of microplate ELISA. The criterion for
positivity in tube ELISA was development of a visible green colour in the tube.
Anaemia was the only presenting clinical sign: PCV values below 25 % were
recorded in 7% of the blood samples examined. However, anaemia did not
correlate well with other findings and was thought to have been due to factors other
than trypanosomiasis.
Trypanosomes were observed in the buffy coat in 1% of the samples
examined, while antigens were detected in 10% of the samples by tube ELISA both
in the field and in the laboratory, and in 5% by microplate ELISA. Antibodies
were detected in 45 % of the samples by antibody ELISA. The differences in the
ability to detect infection of antigen trapping tube-ELISA, the microplate ELISA,
the BCT and antibody ELISA were all statistically significant.
These findings indicated that of all the tests carried out, antibody ELISA
obtained the highest prevalence rates of infection. However, the presence of
antibodies in the blood does not necessarily indicate that the animal has an active
infection. Thus, the high prevalence rates of infection detected by antibody ELISA
could be due to persistence of antibodies in cured animals.
Of all the tests that detect active infections, the antigen trapping tube-
ELISA, whether performed in the field using whole blood or in the laboratory using
serum, obtained higher prevalence rates of infection than the microplate antigen
trapping ELISA and the BeT. The tube ELISA was easy to perform in the field
and the results were obtained within three hours after sampling all the animals.
Thus, it would be possible, using this test, to treat the positive animals before they
are released from the "boma".
Regarding sensitivity and specificity of the three field applicable tests,
namely; tube-ELISA using both whole blood and serum, and the BCT, tube-ELISA
using whole blood was the most sensitive and ranked second after the BeT in
specificity. The BeT was, however, the least sensitive. These findings support the
use of tube-ELISA and BCT as complementary tests in the field diagnosis of camel
trypanosomiasis. | en |
