Leptospira icterohaemorrhagiae is a thin, spiral-shaped Leptospira bacterium. Leptospires are transmitted to cattle via maintenance 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 L. icterohaemorrhagiae, the maintenance host is the rat. As such, only rats transmit the bacteria, infecting each other and other animals (cattle and pigs). Cattle are incidental hosts and do not carry the bacteria and are only infected for a short period. Once incidental hosts are removed from exposure to a maintenance host (infected rats), the disease is not perpetuated.
Leptospirosis is one of the most important and costly contributors to reproductive loss in the beef and dairy industries.
The most common cause of bovine leptospirosis in the U.S. is Leptospira borgpetersenii serovar Hardjo type hardjo-bovis. Although, Leptospira icterohaemorrhagiae is not the most common cause of bovine leptospirosis, it is important to control and help prevent the disease.