Leptospira interrogans (gram-negative spirochetes with bent or hooked ends)

Leptospirosis is common in other less developed parts of the world due to poor sanitation but is also of a concern here in the United States with exposure from our domestic pets.

Leptospires do not replicate outside of an animal host and human-human transmission is rare. Leptospires are transmitted between animals by direct or indirect contact. Direct transmission occurs through contact with infected urine, venereal and placental transfer, bite wounds, or ingestion of infected tissues. Indirect exposure occurs with exposure to contaminated water sources, soil, food, or bedding. Spirochetes can survive in the environment with ambient temperatures, slow moving water, and alkaline pH. Rats are the most common source of infection to humans worldwide. In the United States, dogs> livestock > rodents > wild mammals are the most significant source to humans. Leptospires penetrate mucous membranes or abraded skin and multiply rapidly once inside the vascular system. They spread and further replicate in the kidneys, liver, spleen, CNS, eyes, and genital tract. Leptospires can persist in the renal tubules without causing disease and can be excreted in the urine for very long periods of time.

Dogs

Clinical signs depend on the age and immunity of the host and virulence of the infecting serovar. Most Leptospira infections are subclinical. Young animals are more severely affected than adults. Clinical signs of infection include fever, generalized muscle tenderness, shivering, inappetence, vomiting, diarrhea, hepatic disease, icterus, (icterus) petechial and ecchymotic hemorrhages, leukocytosis, thromboctyopenia, increased serum urea and creatinine, and acute renal failure. Reluctance to move and paraspinal hyperesthesia can result from muscular or meningeal inflammation.

kidney from a dog infected by leptospirosis

Impairment of renal function can result in a decreased glomerular filtration rate caused by kidney swelling and decreased renal blood perfusion. Leptospiral toxins can cause severe hepatic dysfunction and chronic active hepatitis, causing increased ALT, ALP, and LDH and bilirubinuria. Clinical infection is very rare in cats.

Diagnosis: is made with dark field microscopic examination of the urine, culture from the blood or urine, histopathology and serology with the microscopic agglutination test that is serovar specific.

leptospires in renal tubules

Treatment: Supportive therapy depends on the severity of infection and the presence of renal or hepatic dysfunction. Fluid loss and electrolyte imbalances must be corrected and hemorrhages may be controlled by plasma or whole blood transfusion. Oliguria or anuria should be treated with rehydration and osmotic diuretics if necessary. Antibiotics help reduce fever and inflammation and inhibit the multiplication of the organism. Penicillin and its derivatives are the antibiotics of choice for treating leptospiremia but they do not eliminate the carrier state.

Prevention includes elimination of the carrier state in wild animal reservoirs and subclinically infected domestic animals. A vaccine has been developed for dogs, which protects the dog from clinical disease but does not prevent the dog from shedding the organism in the urine.

Leptospirosis can occur sporadically or epidemically in human populations. It has an incubation period of about 10 days. Infection occurs through mucosal contact with water contaminated with the urine of infected animals. Human leptospirosis can take an icteric (10%) or anicteric (90%) form. In Weil’s disease (icteric form) caused by L. icterohaemorrhagiae, clinical signs include: fever, conjunctivitis, rash, diarrhea, petechiae, hepatomegaly, renal tubular damage, immune-mediated meningitis.

Nonicteric leptospirosis appears like a flu-like illness with intense headaches, myalagia, fever, chills and weakness followed by leukocytosis, conjuncitval effusion, a rash and meningitis.

Diagnosis: Identifying the organism on dark field examination of the patient’s blood constitutes the diagnosis. Culture requires several weeks. A more rapid diagnosis can be made with the DOT-ELISA test.

Treatment: Humans should see their physicians for diagnosis and treatment.

Prevention: The majority of infections are in people who engage in water sports or have occupational exposure to wildlife or domestic animal hosts (veterinarians). Contaminated urine is very infectious for people and other animal species. Contact with urine on mucous membranes or skin abrasions should be avoided. This can be done by using latex gloves when handling urine. Healthy vaccinated dogs with leptospiruria and no other signs of leptospirosis have been the source of infection in people.

electron microscopy of leptospires

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