Stott, Jeffrey L. Department of Veterinary Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, California.
- Economic impact
- Disease transmission
- Tick vector
- Disease etiology
- Animal models
- Characterization of the etiologic agent
- Links to Primary Literature
- Additional Readings
Foothill abortion, or epizootic bovine abortion (EBA), is an economically devastating disease that has a limited geographical distribution. The disease is believed to have existed in California since the 1920s, and it became recognized as a significant deterrent to maximum calf production in California in the early 1950s. Pregnant beef cattle that were grazed in the summer months for the first time on foothill and mountainous terrain were at the greatest risk, aborting fetuses late in gestation or giving birth to weak calves that often succumbed to the infection (Fig. 1). The pathology of the disease was characterized in the early 1960s. Affected fetuses often exhibit an extensive ascites (an abnormal accumulation of serous fluid in the abdominal cavity, resulting in an obviously enlarged abdomen), petechial (small, round, red–purple) hemorrhages on mucous membranes (nostrils, nose, and gums), a swollen liver, petechial hemorrhages in the thymus, and enlarged organized lymphoid tissues (including the spleen and lymph nodes) [Fig. 2]. Microscopically, the disease is characterized by proliferation of lymphocytes and mononuclear phagocytes, acute vasculitis, and focal-necrotizing lesions that can appear as pyogranulomas in lymph nodes and the spleen. The thymus presents with unique lesions that are characterized by atrophy of cortical thymocytes and infiltration of macrophages; these are pathognomonic (distinctively characteristic) of foothill abortion. In general, the classical and primary diagnosis of foothill abortion is based on the unique gross and microscopic presentation of the fetus, the history of the dam (whether she had been grazed in the foothill or mountainous regions of California in the summer and during pregnancy), and abnormally high levels of immunoglobulins in the blood. Naïve (previously unexposed) dams infected between gestational days 85 and 125 routinely generate fetuses having characteristic gross and histologic lesions. Dams infected late in gestation (generally at more than 150 days) are likely to produce healthy calves, whereas the effect of infection early in pregnancy has not been established.
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