Meningoencephalitis in Neonatal Calves Caused by Rare O161 Serotype Escherichia coli: A Case Report

Meningoencephalitis is a rare but fatal form of colibacillosis in neonatal calves. An outbreak of neurological disease characterized by high fever, lethargy, opisthotonus, and death occurred in approximately one-week-old calves on a dairy farm in Xinjiang, China; 13 calves died despite antibiotic therapy. Necropsy revealed severe meningeal hemorrhage and increased cerebrospinal fluid. Five Escherichia coli isolates were obtained from two dead calves (brain-derived CHN-XJ-B1–B4; liver-derived CHN-XJ-L). The isolates carried the K99 and STa virulence genes, and two representative strains were serotyped as the rare O161. All isolates were resistant to 12 of 16 tested antibiotics but susceptible to amikacin, cefazolin, and neomycin. The median lethal doses (LD50) in mice were 9.8 × 105 CFU (CHN-XJ-B1) and 2.3 × 106 CFU (CHN-XJ-L). Histopathology showed cerebral vascular congestion, neuronal degeneration and necrosis, and neutrophilic meningeal infiltration. All isolates harbored the invasion gene ibeB; this gene was nearly identical to that of the non-pathogenic E. coli K-12 strain MG1655 (98.5–100% nucleotide identity) and shared approximately 96% nucleotide identity with the human meningitis strain RS218. Deletion of ibeB significantly reduced bacterial burdens in the liver and spleen and in the brain at 48 h post-infection, increased the LD50 by approximately tenfold and significantly prolonged mouse survival, indicating that ibeB contributes to systemic dissemination and tissue colonization of the isolates in this model. This is the first report of calf meningoencephalitis caused by O161 E. coli in the international literature.