Leptospirosis in cattle is caused by the organisms collectively referred to as Leptospira Hardjo (Leptospira borgpetersenii type hardjobovisand Leptospira interrogans type hardjoprajitno).
Leptospira Hardjo causes milk drop in cattle and has been associated with infertility, abortion and the birth of weak calves with a reduced survival rate. Most cases of abortion occur during the second half of pregnancy, in the period from five months to full term.
A sudden drop in milk yield occurs two to seven days after infection of susceptible cows. The udder becomes soft and flabby with colostrum-like secretions or blood-tinged milk in all quarters. Signs may be mild and go undetected but some cows become lethargic and stiff with a fever and reduced appetite. Abortion may occur three to 12 weeks following infection with most abortions occurring during the last three months of pregnancy. Infection may also produce premature and weak calves.
Antibiotic treatment of milk-drop cases is recommended to reduce excretion of leptospires and zoonotic risk. A single intramuscular injection of streptomycin/ dihydrostrepomycin at 25mg/kg will eliminate infection from most cattle.
Approximately 75% of UK cattle have been exposed to Leptospira hardjo, for which they are the “maintenance host”, which means that after infection they harbour the bacteria in their kidneys for months, even 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 overall costs of disease caused by leptospirosis average out at £68-£106 / cow in an affected herd. Or in terms of cost per litre of milk, this works out at a loss of 0.91-1.41ppl.
Control of Leptospira Hardjo in cattle herds relies upon a combination of management decisions to reduce risk of infection, strategic antibiotic treatment, and vaccination. The primary course of immunisation consists of two injections four weeks apart followed by annual boosting. Vaccination should prevent urine shedding following exposure and will protect against milk drop and abortion.