Newborn calves are particularly at risk for developing septicemia and meningitis since they are dependent upon colostral antibodies for immunity. Though E. coli is the main bacterial pathogen associated with septicemia in calves, Salmonella, Campylobacter, Klebsiella and different Staphylococcus species have also been isolated from the blood of septic calves, notes Geof Smith, DVM, PhD, Dipl. ACVIM (LAIM), North Carolina State University. Invading bacteria can establish focal infections in areas such as the joints, meninges, heart valves, or growth plates.
Speaking at the 2011 Annual Western Veterinary Conference, Smith says exactly how bacteria get into the meninges is poorly understood. Specific mechanisms may include the development of a sustained and high grade bacteremia in the highly perfused dural venous system and choroid plexuses, adherence of fimbriae from some strains of E. coli, or the phagocytosis of the pathogens by circulating monocytes and endocytosis through the microvascular endothelial cells.
Calves with septicemia and/or meningitis are often presented because they have lost their suckle reflex and appear lethargic. "Previous treatment for diarrhea is common," Smith says. "Fever is often present unless NSAIDs have been given or if the animal is in an extremely cold environment."
Smith says the calves may have an extended head and neck and attempts to flex or reposition the neck can result in a tonic extension and thrashing of the limbs. Calves with meningitis almost always have abnormal mentation. As the disease progresses, profound depression develops and eventually the animal becomes comatose and non responsive, or may develop seizures.
Presumptive diagnosis of meningitis is based on demonstration of failure of passive transferand the presence of abnormal neurologic signs. "However, the definitive diagnosis is based on an abnormal cerebral spinal fluid (CSF) analysis. Collection of CSF from the lumbosacral space is easy and safe in ruminants," Smith says.
The number of nucleated cells and the protein concentration is markedly increased. The proportion of neutrophils may reach as high as 80 percent. The ratio of CSF to plasma glucose concentration is <1 in animals with bacterial meningitis because of bacterial metabolism of glucose in the CSF. Xanthochromia (yellow color) is inconsistent. Free or intracellular bacteria may be observed in some cases.
Smith says meningitis is particularly difficult to treat successfully. "Prevention of failure of passive transfer through good colostrum management is essential."