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నైరూప్య

Evaluation by ELISA of Ricin Concentration in Fluids and Tissues after Exposure to Aerosolised Ricin, and Evaluation of an Immunochromatographic Test for Field Diagnosis

Gareth D Griffiths, Simon J Knight, Jane L Holley and Philippe Thullier

Introduction: We have formerly developed a point-of-care Immunochromatographic Test (ICT) for the diagnosis of ricin pulmonary intoxication, which was intended to be utilised after nasal swabbing. The requested limit of sensitivity for such a diagnosis was calculated but not tested experimentally, and no other sample source was considered. Here, this approach was evaluated on various samples taken from mice intoxicated by a low dose of aerosolised ricin, to push the system to its limits. The best source of sampling for the diagnosis of ricin intoxication was assessed, as was the validity of the ICT.

Methods: Mice were intoxicated by 3LCt50 of aerosolised ricin and bodily fluids (nasal and lung lavages, blood and urine) were sampled until the 24th hour after intoxication to evaluate their ricin content, using a sensitive ELISA. The ricin concentrations in solid tissues (lungs, liver, heart and kidneys) were also evaluated in ELISA at a late stage, in order to provide a source of samples for forensic diagnosis if needed. In addition, using a standard solution of ricin, the ICT signals were compared to the ELISA. When the ricin concentration in body fluids was above the ICT limit of sensitivity, the rapid test was utilised to assess the best source of sampling and evaluate the validity of this approach.

Results: The ELISA limit of sensitivity was 150ng/L and the ICT provided a semi-quantitative signal when utilised on ricin diluted in Phosphate Buffered Saline (PBS), with a limit of sensitivity close to 1 μg/L. In the animal model, it was observed that the ricin concentration in nasal fluid decreased after intoxication, becoming lower than the ICT sensitivity limit 4 hours after exposure. In contrast, ricin concentration in lung lavage quickly increased until 4 hours and then remained stable until the 16th hour, so that lung lavage was the best sample source during that timeframe. Liver was the best source of solid tissue to sample for diagnosis at the 24th hour. There was also evidence to suggest that urine could be utilised for diagnostic purposes but the ICT was not able to report on this type of sample.

Conclusion: Following inhalation of ricin, nasal wash was a good sample source as formerly calculated, but for a limited timeframe; here, ricin was probably quickly cleared by physiological mechanisms. Lung lavage may be utilised as an alternative body fluid sample source that can be successfully tested by ICT. Liver is the best solid tissue sample source at later stages of poisoning, for forensic diagnosis. More generally, when the pulmonary route of intoxication is suspected, analysis of pulmonary lavage should be considered, even if nasal fluid turns out to be negative. Lung lavage should be made available in field hospitals to provide the trigger to treat ricin pulmonary intoxication, and perhaps also other bio weapons or contaminants by this route.