Leptospirosis

In adult cattle, sheep and goats the first sign is often abortion, stillbirth or weak newborns, or a sudden drop in milk with thick, yellow, blood-tinged milk and little udder inflammation; calves and lambs show fever, jaundice, red urine and anaemia. Pigs mainly show late abortion and mummified fetuses. Horses may abort or develop recurrent uveitis years later. Dogs begin with fever, lethargy, muscle pain and reluctance to move, then signs of kidney injury (vomiting, altered urination), jaundice, bleeding, and in pulmonary haemorrhage syndrome fast breathing and coughing blood. At necropsy kidneys are swollen and mottled and the liver enlarged.

Leptospirosis is caused by pathogenic spirochaetes of the genus Leptospira, which include more than 300 serovars in 30 serogroups. The bacteria enter through mucous membranes or damaged skin, spread in the bloodstream while evading innate immunity, and invade tissues by binding endothelial cadherin and loosening the vascular lining. The main damage is acute tubulointerstitial nephritis and liver dysfunction; vascular injury leads to haemorrhage, including pulmonary haemorrhage in dogs, and haemolysis in young ruminants. Organisms then persist in the kidney and the male and female genital tract, so infected animals shed them in urine for months or years. Disease is milder in the host species that maintains a serovar (for example Hardjo in cattle) and more severe in incidental hosts.

Pathogenic leptospires occur on every continent except Antarctica and are most common in warm, humid, marshy areas, peaking in the rainy season in the tropics and in summer and autumn in temperate regions. Each serovar has maintenance hosts: cattle carry Hardjo, pigs Pomona, and rodents, especially brown rats, are key reservoirs for dogs. Transmission is through urine-contaminated water, soil and feed, direct contact, bites, venereal and placental routes; the organisms survive for months in stagnant water or wet soil. Chronic carriers shed for years. Leptospirosis is zoonotic, although the risk of dogs infecting people appears low with basic precautions.

WOAH groups the differentials by presentation: other causes of sudden milk drop, such as acute viral infections or loss of drinking water; other causes of combined liver and kidney failure; and other causes of reproductive loss, such as brucellosis, neosporosis, Q fever and bovine viral diarrhoea in cattle, and chlamydiosis and toxoplasmosis in sheep. In dogs, leptospirosis should be considered in any acute kidney injury, especially with liver dysfunction or pulmonary haemorrhage. Confirmation uses paired MAT titres showing a four-fold rise, or PCR on blood and urine.

Kidneys, liver, blood vessels, lungs, uterus and placenta, fetus, mammary gland, male genital tract, eyes (uvea), meninges

Serovar-specific vaccines for cattle (Hardjo), pigs (Pomona) and dogs, given yearly to dogs; rodent control, safe drinking water, keeping animals from contaminated ponds, quarantine and testing of new stock, sanitation in breeding areas.

With treatment about 80% of dogs survive even with kidney involvement; pulmonary haemorrhage syndrome carries up to 70% mortality. Up to 40% of cows may abort in newly infected herds. Survivors may stay carriers or develop chronic kidney disease.