Actinobacillosis is caused by bacteria in the genus Actinobacillus. Several different forms of disease occur, depending on the particular species of Actinobacillus involved and the type of animal infected. Soft tissue infections are common, and lymph node involvement is frequently a step in the spread of the disease throughout the animal's entire body. Bony tissue close to muscles or other infected tissue may also be infected.

Actinobacillus equuli infects both foals and adult horses. Foals may become infected through a contaminated umbilical cord or by inhaling or ingesting the bacteria. Signs of infection include diarrhea, followed by inflammation of the brain and spinal cord, pneumonia, inflammation of the kidneys, or bacterial arthritis. The chance of infection in foals can be reduced with careful attention to sanitation in the birthing environment and to ensuring that the foal receives milk containing antibodies from the nursing mother shortly after birth. An infection in an adult can result in abortion, blood poisoning, and inflammation of the kidneys or heart. Infection may be treated with antibacterial drugs.

Actinobacillus lignieresii causes tumorous abscesses of the tongue, a condition often called wooden tongue. This infection occurs most frequently in cattle, but is also seen in horses. Treatment may include surgical removal of the contaminated tissue, potassium iodide given by mouth, or antibacterial drugs.

Last full review/revision July 2011 by Otto M. Radostits, CM, DVM, MSc, DACVIM (Deceased); Delores E. Hill, PhD; Barton W. Rohrbach, VMD, MPH, DACVPM; Charles J. Issel, DVM, PhD; Max J. Appel, DMV, PhD; David A. Ashford, DVM, MPH, DS; Daniela Bedenice, DrVetMed, DACVIM, DACVECC; Farouk M. Hamdy, DVM, MSc, PhD, MPA (Deceased); Kenneth R. Harkin, DVM, DACVIM; Johnny D. Hoskins, DVM, PhD; Eugene D. Janzen, DVM, MVS; Jodie Low Choy, BVMS; John E. Madigan, DVM, MS; Dale A. Moore, MS, DVM, MPVM, PhD; J. Glenn Songer, PhD; Joseph Taboada, DVM, DACVIM; Charles O. Thoen, DVM, PhD; John F. Timoney, MVB, PhD, Dsc, MRCVS; Ian Tizard, BVMS, PhD, DACVM; Brian J. McCluskey, DVM, MS, PhD, DACVPM; Bert E. Stromberg, PhD; Peter J. Timoney, MVB, MS, PhD, FRCVS