A. Abraham’s scientific contributions

An indirect ELISA was used for the sero-diagnosis of caseous lymphadenitis (CLA) in dromedaries. The commercially available assay's goat/sheep conjugate was replaced by a horse radish labelled (HRP) protein A conjugate. 565 dromedary sera were tested with this altered ELISA. The sera originated from 3 farms, of which 2 were infected with CLA. The ELISA identified the CLA free farm and the 2 infected farms correctly.

The four commercial indirect MAP ELISAs were only able to detect paratuberculosis positive camel sera when the kit conjugate was replaced with either Protein A or the goat anti-camel IgG conjugates from Bio-X or CVRL. The Triple J conjugate did not perform well in contrast to the findings of Krámsky and co-workers who used this in a similar protocol to detect anti-MAP antibodies in llama and alpaca sera. With the former combinations, the Checkit and ID Screen MAP antigen coated plates showed considerable non-specific cross- reactivity with paratuberculosis negative camel sera, viz. %S/P values ≥ 25% in 4 and 2 out of 4 negative sera, respectively. The Paratub MAP antigen coated plate/ Protein A conjugate combination showed better non-specificity, although one camel sample E2A which had no history of paratuberculosis showed a % S/ P of 27% and also a reduced response in camel 6BI after the second vaccination dose. Parachek, and in-house MAP antigen coated plates worked well in combination with Protein A conjugate showing acceptable non-specific cross reactivity (%S/P ≤ 12%), and a good colorimetric signal that provided an excellent anti-MAP immune response in the two vaccinated camels, with a response range of greater than 2 and 1.2 absorbance units in camels 47B and 6BI, respectively, after the second vaccine dose compared to the pre-treatment level. Similar profiles were obtained for the in-house ELISA protocol that employed OPD substrate, a format that was in common to other ELISAs in our laboratory. It was therefore concluded, that the in-house MAP ELISA was the method of choice for future studies on M. paratuberculosis infection in camels.

Mineral and vitamin contents in the blood of racing dromedaries of the United Arab Emirates were tested over the last 5 years (2004-2008) at CVRL for the purpose of establishing reference values.