Anaplasmosis

Diagnosis, Treatment and Vaccination

Abstract

An introduction to the subject assigned for discus-sion should include abrief review of the transmission and pathogenesis of anaplasmosis.

Anaplasmosis may be defined as an infectious and transmissible disease of cattle characterized by progressive anemia associated with the presence of intraerythrocytic inclusion bodies termed anaplasma. The disease appears in acute and chronic or "carrier" forms. The causative agent is generally classified as a rickettsia and is transmitted by biological or mechanical means. Several species of ticks are biological vectors of the organism. Ticks may be responsible for anaplasmosis being introduced into previously disease-free areas if transported on infected animals.

Mechanical vectors include those insects which feed on blood and have penetrating mouth parts which will inject infective organisms into susceptible cattle. The horsefly is by far the most efficient insect vector of the disease. Transfer of oganisms by these flies must take place within a few minutes (less than five) after feeding on an infected host. Horseflies and perhaps other flies are known to travel very short distances when feeding. The transfer of infection therefore is not likely to occur over a distance greater than one mile. Mosquitos, horn flies, stable flies and face flies should be considered as spreaders of anaplasmosis.

The most efficient transmitter of the disease is man. As veterinarians we must exercise special precautions to avoid passage of the organism by means of intravenous and vaccinating needles or dehorning and castration instruments. Investigation of one outbreak of the disease reportedly followed the pregnancy examination of several dairy cows.

When an infective dose of blood is injected into a susceptible animal, a prepatent (incubation) period of 15 to 45 days follows. This period of incubation has been known to vary upward to three months. The termination of the incubation period is marked by the presence of serum antibody or the appearance of marginal bodies within the erythrocyte. Following the initial appearance of the marginal body, the number of red cells which becomes parasitized will double every 24 hours for up to 10 or 11 days. At this time the animal will die from anemia or gradually improve as new red blood cells are produced. Convalescence usually requires 30 to 60 days.