Low numbers of intestinal Shiga toxin-producing E. coli correlate with a poor prognosis in sheep infected with bovine leukemia virus

Abstract

Healthy ruminants carry intestinal Shiga toxin (Stx)-producing Escherichia coli (STEC). Stx has antiviral activities in vitro and STEC numbers correlate with reduced early viremia in sheep experimentally infected with bovine leukemia virus (BLV). This study assessed the impact of intestinal STEC on BLV-induced disease for one year post-BLV-challenge. High STEC scores (CFU/g feces x frequency of STEC-positive samples) correlated with good health, whereas poor weight gain, distress, and tumor development occurred only among animals with low STEC scores. STEC carriage was associated with increased percentages of B cells in peripheral blood.

Fig. 1

Low Shiga toxin-producing Escherichia coli (STEC) score correlated with poor health at the advanced stage of bovine leukemia virus (BLV) infection. STEC scores were calculated form 6 samples (average logarithm of CFU/g feces, multiplied by proportion of STEC- positive samples). The horizontal broken line separates low (STEC score ≤ 1.5) from high (STEC score ≥ 2.3) rank. Animals presenting with symptoms of poor health are indicated by letter "P", and letter "T" indicates an animal with tumors.

Fig. 2

Weight gain in sheep challenged with bovine leukemia virus (BLV) correlated with Shiga toxin-producing Escherichia coli (STEC) scores. Weight at 6 months post BLV challenge is plotted against STEC scores. (A) BLV-challenged sheep, (B) control sheep. Points in panel A were fitted with a second-power polynomial curve.

Fig. 3

Shiga toxin-producing Escherichia coli (STEC) treatment correlated with percentages of B cells in blood. Data are group averages + SEM of B cell percentages. A bracket indicates group 1 significantly different from control (ANOVA, p < 0.05).

Fig. 4

Peak B-cell percentages differentially correlated with Shiga toxin-producing Escherichia coli (STEC) scores. (A) % B-cells in bovine leukemia virus (BLV)-challenged sheep were negatively correlated with STEC scores. (B) % B-cells from BLV-free control sheep were positively correlated with STEC scores.