Other Infectious Diseases

By William C. Rebhun.

Lymphosarcoma (Bovine Leukemia, Bovine Leukosis) is an infectious disease that results in leukemia and lymphoid tumor formation in some cattle infected with the bovine leukemia virus. The bovine leukemia virus is widespread, especially in dairy cattle, and current statistics estimate that 20 to 25 percent of dairy cattle in the United States may be infected with it.

Most cattle that are infected with the virus merely form antibodies against the virus and do not develop disease. However, of the total number of cows affected, a low percentage (probably less than 5 percent) develop clinical tumors that result in death. These clinical cases usually form antibodies to the virus but the antibodies do not protect them from tumor formation.

Signs observed in cattle with lymphosarcoma tumors are tremendously variable, based on location of the tumors and the number of major organs involved. Typical cases have multiple enlarged lymph nodes externally or internally and tumors in the heart, abomasum, spinal canal, uterus, and behind the eye.

However, each case is slightly different, and a major tumor in any location can lead to signs referrable to the involved organ. In some cases only a single tumor is found, but this is rare.

Because of the typical organ location of tumors, clinical cases may have heart failure, bleeding from the abomasum with a black color imparted to the feces, reproductive failures, bulging eyes, or paralysis. In addition, rare cases of multiple skin tumors(skin form), enlargement of the thymus gland (thymic form), and multiple lymph node enlargement (juvenile form) occur in calves and young cattle.

The virus lives in white blood cells of infected cattle. Therefore, secretions and blood contain the virus. The infection is spread by biting insects, needles and syringes contaminated with blood from infected cows, and in some secretions from infected cows. In affected herds, the virus can spread to involve up to 80 percent or more of the cattle.

Infection with the virus usually is innocuous, and only a low percentage of infected cattle develop tumors.

Calves generally are not infected before birth or via milk from infected cows. Although the virus may be able to infect sheep, it appears that other species and people are not at risk.

Economic Aspects

There is no treatment or vaccine for this disease. Bovine leukemia has tremendous economic implications because it results in mortality and carcass condemnation, as well as the fact that many foreign countries will not accept cattle or products of cattle such as semen which are, infected.

Diagnosis of infection is best accomplished by blood tests via radioimmunoassay or agar-gel immunodiffusion that detect antibodies to the virus. In addition, some cattle infected with the virus have persistent elevations in the number of lymphocytes in their peripheral blood.

Control of the disease is very difficult and requires housing non-infected animals away from infected ones. Since many infected cattle are valuable production and breeding cattle, slaughter of all infected cattle is impractical and unwarranted since usually they do not develop clinical disease.

Genetics are very important in this disease because certain lines of cattle are less resistant to the virus and more prone to clinical tumor formation.

Because of the complex nature of this virus, the clinical disease, and the means of spread of the virus, the herd owner should discuss control with a veterinarian.

Pinkeye

Pinkeye, or Infectious Bovine Keratoconjunctivitis, is a highly infectious ocular disease of calves and cattle caused by the bacteria Moraxella bovis.

This bacteria lives in the conjunctiva of recovered adult cattle and calves. It is present in a non-virulent form in these animals until activated by sunlight into a virulent form. Face flies then carry this organism from recovered or infected cattle to non-infected calves and adults.

Signs of the disease consist of ocular discharge which at first is watery and later contains pus. Within a few days following watery discharge and inflammation in the conjunctiva (red eye), a painful ulcer develops on the cornea of the eye and the bacteria invades the cornea to cause an obvious deep ulcer.

The affected eye appears gray, red, yellow, or a combination of all these colors. One or both eyes may be affected.

The infection spreads quickly during the fly season to involve most calves and some adult cattle that have not been exposed previously to this organism.

Other species are not affected. The disease occurs all across the United States and probably is more of a problem in beef cattle since they are usually pastured and thus exposed to sunlight and a greater population of face flies.

This disease causes serious economic loss due to poor growth and gain in affected calves, blindness, as well as drug and labor costs for treatment.