Leptospira borgpetersenii serovar hardjo type hardjo-bovis
Leptospira borgpetersenii serovar hardjo type hardjo-bovis is a thin, spiral-shaped, tightly coiled spirochete. It is the most common cause of bovine leptospirosis in the U.S. In addition, hardjo-bovis is one of the more important of the most common serovars because cattle are maintenance hosts. Leptospires are transmitted to cattle via maintenance hosts and incidental hosts. Maintenance hosts are a constant source of infection and typically do not show clinical signs. As silent-carrier animals, they maintain the bacteria and transmit leptospires to other animals. Transmission is efficient, with incidence of infection relatively high. Maintenance hosts can be carriers for months, years or even a lifetime.
In the case of hardjo-bovis, the sole maintenance host is cattle. As such, only cattle transmit the bacteria, infecting each other and other animals (sheep and humans). Transmission can even occur in utero, resulting in maintenance host calves being born. Carrier animals—maintenance hosts—shed leptospires in urine, reproductive fluids and uterine discharges, thus contaminating pastures, drinking water and feed.
Incidental hosts do not carry the bacteria and are only infected for a short period. Once incidental hosts are removed from exposure to a maintenance host, the disease is not perpetuated.