Serum haptoglobin: an objective indicator of experimentally-induced Salmonella infection in calves

Experimental models of Salmonella-induced gastroenteritis have previously r elied on crude subjective clinical markers of infection to assess disease s everity. The aim of this study was to investigate the possibility that chan ges in serum levels of the acute phase protein, haptoglobin, may be used as an objective, quantitative measurement of infection. Eight 3- to 4-week-ol d animals were challenged with a mixture of three Salmonella serotypes cont aining 6 x 10(10) bacteria and compared with five animals given a placebo p reparation. Animals were monitored and characteristic clinical symptoms of infection; diarrhoeal scores, morbidity scores and rectal temperature, were recorded. Serum samples, from both animal groups, taken prior to challenge and again on days 1, 3, and 5 post-challenge, were analysed for haptoglobi n levels using a direct serum binding assay. Prior to challenge, all 13 ani mals had normal levels of haptoglobin in their serum. By day 3 post-challen ge six of eight animals challenged with Salmonella had abnormal serum hapto globin levels (median level = 212 mug ml(-1)), while haptoglobin levels rem ained normal in placebo-challenged animals (median level = 0 mug ml(-1)). T he change in haptoglobin levels during the 5-day observation period was sta tistically significant in the Salmonella-challenged animals (P = 0.0003, H = 16.477). Serum haptoglobin levels showed a statistical correlation with c linical measures of disease severity; diarrhoeal scores (P = 0.0015, H = 8. 988), morbidity scores (P = 0.0004, H = 15.711) and rectal temperature (P = 0.0001, Z = 4.304). Thus, serum haptoglobin levels closely reflect the cli nical symptoms of infection and are therefore a useful marker of infection severity in salmonellosis in calves. (C) 2000 Harcourt Publishers Ltd.