Use of ELISA to reveal rodent infections in plague surveillance and control programmes.

To assess its potential applications in plague surveillance and control programmes, an enzyme-linked immunosorbent assay (ELISA) that captures the specific Yersinia pestis F1 antigen was used to determine the amounts of this antigen present in samples of blood and spleens from laboratory rats with acute plague, in the buboes of rats with chronic plague, and in tissues from the carcasses of rats that had died from plague. In rats with acute plague, bacteria and F1 antigen were detected in samples of blood 2-4 days after the rats had been subcutaneously inoculated with virulent Y. pestis. Although F1 antigen was not detected in blood samples at the onset of bacteraemia, average antigen levels of 10,240 ng/ml for blood clots and 4829 ng/ml for sera were detected during severe bacteraemia. Immediately after the rats died from acute plague, antigen levels in their spleens of up to 410 micrograms/g of tissue were detected. For rats with chronic plague, ELISA antigen levels of 1600 ng/g to 51 micrograms/g were detected in buboes that contained viable plague bacilli. In samples of spleen, liver, kidney and heart from rat carcasses, F1 antigen was detected up to 20 days after death. In contrast, it was possible to isolate Y. pestis bacilli from these samples only up to 6 days after death.