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.