Abridged validation of charm II screening tests for the detection of veterinary drug residues in fish farmed in Cameroon.

The intensification of aquaculture in Cameroon requires efficient screening methods to control veterinary drug residues in fish. This is why the charm II radio receptor technique for the detection of antimicrobial residues in aquaculture fish initiated in Belgium was transferred to Cameroon according to Commission Decision 2002/657/EC. The validation parameters included the following tests: repeatability, reproducibility and robustness in addition to the mandatory characteristics, detection capability and specificity. Selected veterinary drug-free fish samples of tilapia (Oreochromis niloticus), catfish (Clarias gariepinus), carp (Cyprinus Carpio) and kanga (Heterotis niloticus) were spiked at different target concentrations with different antimicrobials (ß-lactams, tetracycline, sulfonamides, macrolides and chloramphenicol). The detection capabilities (CCß) were at MRPL (0.3 µg/kg for chloramphenicol), or below the regulatory limits in a range of 0.25-0.5 MRL with 0% false-negative results. ß-lactams (penicillin G), tetracyclines (tetracycline, chloretetracycline and oxytetracycline) and macrolides (erythromycine A) were detected at half MRL (25, 50 and 100 µg/kg respectively), while sulfonamides (sulfamethazine) was detected at 25 µg/kg (0.25 MRL). The detection capabilities (CCß) obtained were satisfactory as the cut-off factors (Fm) were less than the mean values of blank fish readings (B) (Fm < B). Furthermore, the method was applicable since the cut-off factor was less than the positivity threshold (Fm < T). The variability of the data under repeatability and reproducibility conditions was acceptable, with a relative standard deviation less than 15%. Results were unaffected by delaying the reading time from 0 h to 24 h after the addition of scintillation fluid, with a precision below 16%. Likewise, non-target drugs were not detected even at high concentrations (100 MRL) in a cross-reactivity study. From the overall results, the performance characteristics (detection capabilities, precision, robustness and specificity) were suitable and comparable to the initial validation results, indicating that the transfer to Cameroon laboratory was valid, the method was reliable and could be used in aquaculture fish quality monitoring programs in Cameroon.

International experiences in assessing vitamin A status and applying the vitamin A-labeled isotope dilution method.

Inadequate vitamin A (VA) nutrition continues to be a major problem worldwide, and many interventions being implemented to improve VA status in various populations need to be evaluated. The interpretation of results after an intervention depends greatly on the method selected to assess VA status. To evaluate the effect of an intervention on VA status, researchers in Cameroon, India, Indonesia, Mexico, Senegal and Zambia have used serum retinol as an indicator, and have not always found improvement in response to supplementation. One problem is that homeostatic control of serum retinol may mask positive effects of treatment in that changes in concentration are observed only when status is either moderately to severely depleted or excessive. Because VA is stored mainly in the liver, measurements of hepatic VA stores are the “gold standard” for assessing VA status. Dose response tests such as the relative dose response (RDR) and the modified relative dose response (MRDR), allow a qualitative assessment of VA liver stores. On the other hand, the use of the vitamin A-labeled isotope dilution (VALID) technique, (using 13C or 2H-labeled retinyl acetate) serves as an indirect method to quantitatively estimate total body and liver VA stores. Countries including Cameroon, China, Ghana, Mexico, Thailand and Zambia are now applying the VALID method to sensitively assess changes in VA status during interventions, or to estimate a population’s dietary requirement for VA. Transition to the use of more sensitive biochemical indicators of VA status such as the VALID technique is needed to effectively assess interventions in populations where mild to moderate VA deficiency is more prevalent than severe deficiency.