Introduction

• Cause:
  • Leptospiral serovars of major importance in cattle are Hardjo and Pomona (host-adapted species).
  • Serovars Icterohaemorrhagiae, Grippotyphosa and, less commonly, Bratislava , and Canicola (non host-adapted strains) are occasionally implicated.
• Diagnosis: Serum Microscopic agglutination test (MAT) titers of ≥1/400; paired serum 3-4 weeks apart tested by antibody ELISA or MAT.
• Dark field microscopy using urine samples.
• FAT/IHC/PCR on fetal tissues.
• Bulk milk antibody ELISA.
• Treatment:  
  • Streptomycin, tetracycline, oxytetracycline, procaine benzylpenicillin, amoxicillin, ceftiofur, tilmicosin, or tulathromycin.
  • Leptospires also are highly susceptible to erythromycin, tiamulin, and tylosin, although these antibiotics cannot be relied on to remove the renal carrier state.
• Prognosis: Good for host adapted species, guarded for non host-adapted species.
• Zoonosis.

Pathogenesis

Etiology

• Caused by bacteria from the genus Leptospira:
  • There are multiple serovars of leptospirosis, with the ones affecting cattle being:
    • L. borgpetersenii serovar Hardjo.
    • L. interrogans serovar Hardjo.
    • L. Pomona.
  • Leptospira borgpetersenii serovar Hardjo is the most common serovar of leptospirosis affecting cattle worldwide:
    • Cattle are the maintenance host for Hardjo.
    • It is endemic in many cattle populations with resultant low to moderate levels of disease.
  • Leptospira interrogans serovar Hardjo is less common than borgpetersenii and is associated with more severe outbreaks of disease:
    • Serological methods cannot distinguish between both strains of Hardjo.
  • Leptospira Pomona is not as prevalent worldwide and is not as adapted to cattle as Hardjo, resulting in more severe forms of disease.
  • With less commonly implicated serovars, all of which are non host-adapted, disease is more severe:
    • These serovars include:
      • Icterohaemorrhagiae.
      • Grippotyphosa.
      • Bratislava.
      • Canicola.
• After infection with Hardjo, cattle harbor the bacteria in their kidneys for months to years, excreting many leptospires in their urine so acting as a reservoir of infection for other cattle
• Both dairy and suckler cattle can be affected.
• The main source of infection is the carrier animal; water/feed that has been contaminated with infected urine can also be important.
• The organisms gain entry to the body though the membranes of the eyes, nose, mouth, and even the skin, especially if it is injured.
• Infected animals also commonly shed Hardjo in placental fluids and milk.
• In addition, some Leptospira serovars, such as Hardjo, can be transmitted venereally.

Predisposing factors

General

• Risk factors for Hardjo infection in cattle have been reported to include large herds, open herds, contract rearing or rearing of dairy heifers away from the main herd, access to contaminated water sources, co-grazing with sheep (potential maintenance host), and use of natural breeding.

Pathophysiology

• Dissemination of leptospires is probably a result of motility of the organism. 
• Virulence factors have not been well described; however, it has been postulated that pathogenic leptospires release haemolysins, sphingomyelinases, and phospholipases. 

Timecourse

• The incubation period is generally 7 to 14 days but ranges between 2 and 30 days.
• Hardjo abortion can occur anytime from 3 weeks to 3 months post-infection.

Epidemiology

• Some animals excrete Leptospira continually for a short time and then stop, others shed intermittently for life.
• Transmission is greatest in grazing cattle.
• Carriers can stop or reduce shedding when fed a concentrate diet or a diet that results in an acidic urine.
• The organism can persist in the environment for up to 4 months given sufficient moisture.
• Leptospira do not tolerate drying, exposure to sunlight or extremes in pH or temperature well.
• Spread occurs most rapidly in wet seasons on low lying areas.

Diagnosis

Treatment

Prevention

Outcomes