Updates on leptospirosis (Proceedings)
Leptospirosis is a re-emerging disease worldwide. Leptospirosis is caused by multiple serovars of Leptospira interrogans or by Leptospira kirschneri serovar grippotyphosa. It is a filamentous, motile bacteria. Each serovar is maintained by one or more natural hosts. Clinically important serovars and their normal hosts for North America include canicola (dog), ictero-haemorrhagiae (rat), grippotyphosa (vole, raccoon, skunk, opossum), pomona (cow, pig, skunk, opossum), hardjo (cow), bratislava (rat, pig, potentially horse), and potentially autumnalis (mouse). Host-adapted species do not usually develop disease from the serovar they carry, but infection in an incidental host can cause severe disease.
Transmission and pathogenesis
The primary method of transmission is via water contaminated with urine, although urine-contaminated soil, bedding and food are also routes of exposure. Exposure to urine, blood, or saliva can also transmit disease. The organism prefers a warm, moist, alkaline environment, and is more likely to be present in stagnant or slow moving water. The organism can persist for several months in an appropriate environment. An increase in incidence is common following periods of flooding or heavy rainfall. Peak incidence in dogs is from July-Nov. Adult large breed male dogs with access to outdoors are more likely to contract leptospirosis.Organisms can penetrate mucus membranes, wet or macerated skin, or intact skin. They replicate in various organs, preferentially including the kidneys, liver, spleen, central nervous system, eyes, and genital tract. The incubation period is usually 5 to 7 days but may vary. Antibody production appears around day 7-8 and the organism is cleared from most organs except the kidneys. The organism replicates and persists in the renal tubular epithelial cells, causes shedding for weeks to months following infection is antibiotics are not used to eliminate organisms from the kidney.
Leptospirosis may present as a peracute, acute, subacute, or chronic disease. Peracute disease is associated with massive leptospiremia, and death occurs with few premonitory signs. Definitive diagnosis is difficult during this stage, but it appears to be uncommon. The initial signs of acute disease are typically pyrexia, shivering, and muscle tenderness. These signs are subsequently followed by signs of vomiting, dehydration, shock, tachypnea, and coaguation defects. These patients die before kidney or liver failure occur. Serology would be negative due to the short time frame from exposure to death.
Subacute disease is the most commonly recognized form of leptospirosis. The signs affect multiple body systems, and include fever, anorexia, dehydration, injected mucus membranes, and petechial and ecchymotic hemorrhages. Musculoskeletal manifestations include reluctance to move, paraspinal hyperesthesia, stiffness, arthralgia, and myalgia. Conjunctivitis, uveitis, or meningitis may be present. Gastrointestinal signs can be quite profound, and include vomiting, diarrhea, and intussusception. Common signs of renal involvement include initial polydipsia and polyuria, which can progress to oliguria or anuria. Less severe cases may have massive polyuria. Swollen, painful kidneys may be present. Icterus occurs from intrahepatic cholestasis and hepatic necrosis. Respiratory signs may include rhinitis, tonsillitis, cough, dyspnea, and interstitial pneumonia.
Survivors of the acute or subacute form of leptospirosis may develop chronic renal or hepatic disease. The chronic renal disease is characterized by interstitial nephritis with fibrosis. In the liver, chronic active hepatitis with inflammation and fibrosis may lead to hepatic failure.
Young dogs (< 6 months) seem to have more severe clinical signs and are likely to have more severe liver involvement than adult dogs. Subclinical infection without any clinical signs can occur.