Leptospirosis

• Leptospirosis is a zoonotic disease caused by infection with pathogenic serovars of Leptospira
• Disease affects virtually all mammals with a range of clinical effects from mild infection to multiple-organ failure and death
• Leptospira are maintained in nature through chronic renal infection of carrier animals such as rats, dogs, cattle, horses, sheep, goats, and pigs
• Dogs and rats are common sources of human infection
• Leptospira are aerobic, gram-negative spirochetes with corkscrew-like motility
• Maintenance hosts serve as reservoirs of infection, often wildlife species and sometimes domestic animals
• Leptospirosis in maintenance hosts characterized by high prevalence of infection, low antibody responses, and persistent infection in kidneys and sometimes genital tract
• Incidental hosts have low prevalence of infection, severe clinical signs, and marked antibody response
• Examples include serovar Grippotyphosa infection in dogs or serovar Icterohaemorrhagiae infection in cattle and swine
• Transmission among maintenance hosts often direct through contact with infected urine, placental fluids, or milk
• Infection of incidental hosts more commonly indirect, by contact with contaminated areas
• Survival of leptospires favored by moisture and moderately warm temperatures
• Leptospires invade the body through mucous membranes or damaged skin
• After incubation period, leptospires circulate in blood and replicate in various tissues for 7-10 days
• Agglutinating antibodies detected in serum coincide with clearance of leptospires from blood and organs
• Leptospires remain in kidneys of incidental hosts for a short period and shed in urine
• In maintenance hosts, leptospires often remain in renal tubules, genital tract, and eyes despite high levels of serum antibody
• Clinical signs depend on host species, strain of Leptospira, and age/physiologic state of the animal
• Subclinical infections common in maintenance hosts
• Incidental hosts show acute, systemic illness with renal or hepatic damage
• Pregnant hosts may result in fetal infection, abortion, stillbirth, or birth of weak neonates
• Diagnosis involves detecting antibodies in blood samples with serum MAT titres >1/100 considered significant
• Gold-standard diagnostic method is bacterial culture
• Treatment with streptomycin/dihydrostrepomycin can eliminate infection in most cattle
• Vaccination is recommended to avoid unnecessary antibiotic use
• Control measures include management decisions, strategic antibiotic treatment, and vaccination in cattle herds
• Primary immunisation consists of two injections followed by annual boosting
• Avoidance of exposure to wildlife and domestic animals that may be maintenance hosts
• Leptospirosis prevention cornerstone is vaccination with polyvalent inactivated vaccines
• Reduce risk of infection, strategic antibiotic treatment, and vaccination are key prevention strategies
• In closed herds, all replacements should be isolated and treated before entry
• Herds with acute infection should consider whole herd antibiotic treatment and vaccination
• Herds with endemic infection should vaccinate with an annual booster
• Replacement heifers should complete vaccination before first service