Leptospirosis

Dr Stephanie Leeder

What is leptospirosis?

Leptospirosis is a zoonotic bacterial disease caused by the motile spirochetes of the leptospira species

How does infection occur:

Leptospires can penetrate intact mucosal surfaces or abrasions in the skin, leading to a bacteremia, which lasts for up to 10 days. Bacteria then are able to invade tissues such as the kidney and liver and are then shed in the urine. Antibody levels are typically low in the first week of infection and then quickly rise.

What are the clinical findings?

Clinical signs of infection are non-specific including fever, vomiting, and poor appetite. Other signs may include jaundice, ocular inflammation, or dyspnea from pulmonary hemorrhage.

Leptospirosis in dogs can manifest with signs of vasculitis, AKI, and/or hepatic injury. These findings are variable based on the infecting strain and host immune response.

What diagnostic tests are available:

Diagnostic tests fall into 2 groups; those that detect the bacteria directly and those that detect antibodies directed at the bacteria.

The first group includes culture, dark field microscopy, or PCR. This group of tests are most useful early in the course of disease and before antibiotic treatment. Antibody testing is done by microscopic agglutination test (MAT). Because antibody titers may be low or negative initially, acute and convalescent testing is recommended.

Which diagnostic should I use?

Dark field microscopy: Rarely used due to high levels of false negatives and false positives

Bacterial culture: Technically difficult and incubation times can take up to several months. However culture is the only way to definitively diagnose the infective serovar.

PCR: commonly performed on blood AND urine BEFORE antibiotics. Tissue samples may also be used. it is recommended that whole blood is submitted for PCR within the first 10 days of illness and urine after the first week of illness, corresponding to the bacteremic and bacteriuric phases of disease. False negatives can occur if bacterial numbers are low. Vaccination will not interfere with this test.

Sensitivity and specificity of the assays will vary by region and laboratory however one study reported a high specificity of 99.5 % and a sensitivity of 86%on blood samples in the first 6 days of infection, but this dropped to 34% after 7 days of infection.

MAT Testing: This is the traditional reference test for the diagnosis of lepto. Negative MAT results are not uncommon during the first week of
infection, and sensitivity of a single acute MAT is only 50%; however, this improves to 100% when paired samples are assessed, with specificity ranging between 70% and 100%.

Consensus recommendations for the diagnosis of leptospirosis in dogs with appropriate clinical signs include PCR of both blood and urine before the administration of antibiotic therapy and paired MAT titers.

How is leptosporisis treated?

Specific treatment involves oral or IV antimicrobials. When leptospirosis is strongly suspected then treatment should be initiated as soon as possible after initial diagnostic blood and urine samples are collected. Antimicrobial treatment recommendations include either oral doxycycline or IV
penicillin derivatives (such as ampicillin) if the patient is too ill for oral medications. If penicillin is initially used then it is recommended that treatment then be changed to doxycycline for 2 weeks, in order to eliminate the carrier phase of the organism.

For more information, get in touch with the team at SASH.