Abscesses and Caseous Lymphadenitis

Joan S. Bowen, DVM

External lumps and bumps in dairy goats have many causes, but most owners assume that all lumps are abscesses and that all abscesses are caused by Corynebacterium. Although Corynebacterium is a significant cause of external masses in goats, one should not assume that all lumps are abscesses or that all external masses occurring in a herd result from the same cause. Determining the correct origin of an external mass requires a detailed history, a thorough physical examination and aspiration or biopsy. Once a diagnosis has been made, an appropriate therapy can be chosen and a prognosis for recovery can be determined.

Abscesses caused by a wide variety of bacteria are the most common cause of external masses in dairy goats. Numerous bacteria live on the surface of healthy skin and mucous membranes and can be introduced into body tissues through small ulcers and puncture wounds. Coarse hay, grass awns, wood splinters, unsanitary injection needles and accidental trauma can introduce bacteria into soft tissue. Once introduced into tissue and deprived of oxygen, these bacteria replicate rapidly, destroy healthy tissue, and attract white blood cells to fight the infection. The body lays down fibrous connective tissue around the infection to wall off the organisms and an encapsulated abscess forms. A similar inflammatory response, sometimes referred to as a "sterile abscess", may occur following the injection of noxious chemicals such as tetracycline, calcium solutions or vaccine adjuvants. In most cases, the immune system functions properly to destroy the bacteria and infected or inflamed tissue, and the abscess is either resorbed or breaks through the skin to the outside. Occasionally, due to location, an abscess will interfere with body function and may need to be surgically drained or removed.

In order to select an appropriate treatment or offer a prognosis, the cause of the abscess should be determined by bacteriologic culture. The skin over the abscess should be clipped and aseptically prepared prior to aspiration, and the aspirated sample should be refrigerated and transported to a diagnostic laboratory for culture. Abscesses caused by common bacteria such as Staphylococcus, Streptococcus, or Pasteurella usually do not require treatment unless the goat shows symptoms of systemic involvement such as swelling, anorexia or fever. Lancing superficial abscesses caused by common skin bacteria may shorten the course of the disease and yield a more cosmetically pleasing scar. Abscesses caused by these bacteria occur commonly in the mouth, lips, cheeks, and injection sites, and do not spread among animals.

Contagious abscesses, caseous lymphadenitis or "boils" are caused by the bacteria Corynebacterium pseudotuberculosis or C. ovis. This organism is found in the thick greenish discharge from ruptured abscesses and can survive for many years in contaminated soil, barns, and on equipment and instruments. While wounds increase the infection rate with this organism, C. pseudotuberculosis can penetrate intact skin and cause disease. This bacteria produces a toxin, phospholipase D, which allows it to spread from lymph node to lymph node throughout the body, even though the immune system tries to encapsulate it with connective tissue. The vast majority of lesions begin in the head and neck and then travel to the internal lymph nodes around the lungs, heart, liver, kidneys and small intestine. Corynebacterium abscesses frequently increase in size with age and interfere with body function. Due to the affects of these abscesses on the respiratory and digestive systems, Corynebacterium is the most common cause of wasting in goats. Goats infected with Corynebacterium are permanently infected and will shed the organism in body fluids, abscess contents, and coughed aerosol droplets. One study indicated that goats can develop clinical disease within three months of exposure and that the organism can be spread from open abscesses for as long as three weeks. Accurate serologic tests are not readily available that would allow a herd owner to screen their animals to identify infected goats. Herds infected with caseous lymphadenitis should work to eliminate the disease through culling affected individuals, careful screening and isolation of purchased animals, and raising young stock away from adults on a pasteurization program.

Colorado Serum Company produces two sheep vaccines, Case-Bac and Caseous DT, that might be helpful in infected herds. They recommend use of their vaccine only in herds that currently suffer from caseous lymphadenitis or those that are at extreme risk for infection. Because this vaccine is not labeled for use in goats, goat producers who use these vaccines in goats do so at their own risk, as there have been reactions reported when the sheep vaccine was used in goats. The manufacturer recommends two doses of two milliliters administered subcutaneously in the axillary space two weeks apart, followed by a single annual booster. This vaccine contains both a cellular component to stimulate antibodies against the bacteria itself and a toxoid to stimulate antibodies against phospholipase D, the toxin that allows the organism to spread throughout the body. "Caseous DT" and Case-Bac are the only licensed Corynebacterium vaccines available for use in the United States. "Glanvac" is a toxoid produced in Australia and occasionally available illegally from Canada. Current FDA regulations prohibit the use of "Glanvac" in goat herds producing milk or meat for human consumption.

Careful physical examination, aspiration and biopsy can be used to determine the cause of external masses on dairy goats. Accurate diagnosis can lead to correctly chosen treatment and prevention programs. Although not all causes of external masses can be prevented, their incidence can be markedly reduced through good management practices.