Epizootic bovine abortion

Definition

An infectious disease of cattle characterized by late-term abortion, stillbirth, or birth of weak calves, caused by the bacterium Pajaroellobacter abortibovis (formerly classified within the order Rickettsiales). The pathogen is transmitted by the soft tick Ornithodoros coriaceus, which acquires infection during blood-feeding on infected cattle and maintains the bacterium transovarially. The disease occurs enzootically in parts of the western United States, particularly California, where the tick vector and wild deer hosts coexist with cattle operations.

Etymology

From Greek epizōon ('upon an animal') + Latin bos, bovis ('ox, cattle') + Latin abortio ('miscarriage, untimely birth'); the term distinguishes outbreaks in animal populations from human epidemics.

Example

Ranchers in the foothills of the Sierra Nevada often experience epizootic bovine abortion in heifers moved to tick-infested rangeland for the first time; control relies on excluding cattle from vector habitat or acaricide treatment rather than vaccination, as no commercial vaccine exists.

Synonyms

• foothill abortion
• Pajaroellobacter abortion

Related Terms

• vector-borne disease
• Ornithodoros
• Transovarial transmission
• enzootic
• tick-borne pathogen
• Rickettsiales
• veterinary entomology

Usage Notes

The term 'epizootic' emphasizes outbreak occurrence in animal populations and contrasts with 'enzootic,' which describes stable, baseline presence. 'Foothill abortion' is common in western U.S. veterinary practice but is avoided in formal scientific contexts due to geographic imprecision. Diagnosis requires fetal tissue examination; serology of the dam is unreliable. The vector tick Ornithodoros coriaceus is also called the 'pajaroello tick' or 'deer bed tick,' reflecting its association with deer resting sites.