Leptospirosis

Shawn Kearns, DVM, DACVIM
angell.org/internalmedicine
internalmedicine@angell.org
617-541-5186

Disease description

Epidemiology

Leptospirosis is a disease caused by infection with an aerobic, filamentous, gram-negative, motile spirochete (bacteria) of the genus Leptospira. The main species affecting dogs in the United States are L. interrogans and L. kirshchneri. (1) Leptospira species are made up of over 250 serovars (antigenically distinct organisms in the same species) that are divided into serogroups (antigenically-related serovars that may cross-react on antibody detection methods). Of the twenty serogroups identified, approximately 10 are considered pathogenic in dogs. The most common serogroups and their reservoir hosts include Canicola (dog), Icterohaemorrhagiae (rat), Grippotyphosa (raccoon, skunk, marsupials), Pomona (cow, pig), Hardjo (cow), Bratislava (rat, pig, horse), and Autumnalis (mouse). (2, 3) These seven are the groups typically evaluated on titer testing. Prevalence of groups varies by geographic region. In contrast to dogs, few cases of clinical leptospirosis have been reported in cat and seroprevalence is variable based on regions examined. (2, 4)

Leptospiral organisms prefer warm, moist, alkaline environments. They are more likely to be found in stagnant or slow-moving water. Incidence of infection increases in late summer to fall (July-November) and after flooding or heavy rainfall. (2, 5, 6) Environmental flooding can saturate the soil with organisms, prevent evaporation of contaminating animal urine, and prolong survival of organisms in surface water. Leptospira spp. can remain viable for months in moist environments under optimal conditions even though they cannot replicate outside the host body. Leptospira spp. remain in the environment through infection of reservoir hosts who maintain a carrier state, often without clinical illness.

Leptospirosis has been documented throughout the United States with pockets of increased prevalence in certain areas including Virginia, West Virginia, the west coast and around the Great Lakes region. (7) Other studies have shown an increased prevalence in the northeast, Midwest and south central areas of the United States. (8) Prevalence studies do not always take into account recent rainfall or flooding which may alter prevalence season to season. Exposure to livestock and wildlife, crowded kennels, rodent exposure in urban environments, houses on large lots, deciduous forest land, increased precipitation, and temperature have been noted as risk factors for exposure and/or infection. (5, 7, 9)

Signalment

Although any breed can be affected, herding dogs, hounds, working dogs, and mixed breed dogs are at greatest risk due to increased environmental exposure. (6, 10) However, other studies have shown 40-50% of dogs to be of small or intermediate breeds. (11, 12, 13) Dogs of any age are at risk, but the lowest seroprevalence has been reported in dogs >10 years. (14) Younger dogs (<6 months of age) are more likely to have severe clinical signs and severe hepatic involvement compared to adult dogs. (15)

Transmission

The primary mode of transmission in animals is through contact with infected urine or through indirect transmission via exposure to water sources, soil, food or bedding that is contaminated with infected urine or tissue. Transmission via venereal or placental transfer, bite wounds or ingestion of tissues is much less common.

Pathophysiology

Leptospires penetrate mucous membranes, wet or macerated skin, and broken skin, after which they enter the blood stream and quickly multiply. Organisms attach to endothelial cells and cause vasculitis, vascular leakage, hemorrhage, and inflammation. The bacteremic phase can last for up to 10 days. (16) Organisms then spread and replicate in many organs. Within the kidneys, organisms penetrate the renal capillaries and enter the interstitium. Leptospires are found within proximal renal tubular cells and tubular lumen, leading to organisms being shed in the urine. Leptospires can persist in the kidneys and be shed in the urine for weeks to months without treatment. Kidney swelling can impair renal perfusion and decrease glomerular filtration. Endothelial damage also leads to ischemic injury within the kidney. The lipopolysaccharide (LPS) component of the outer envelope of leptospires activates macrophages, stimulates neutrophil adherence, causes platelet activation, and stimulates the release of pro-inflammatory cytokines. (2) Infection with serogroups Canicola, Bratislava, and Grippotyphosa are more commonly associated with renal dysfunction.

The liver is the second main organ affected by leptospires. Hepatic dysfunction can occur from damage by leptospiral toxin with subsequent centrilobular necrosis, bile duct occlusion, fibrosis, and chronic hepatitis. (2, 3) Hepatitis may be granulomatous or lymphoplasmacytic/neutrophilic in type. One study of 10 dogs with leptospirosis demonstrated chronic hepatitis without clinical evidence of prominent renal involvement. (17) Acute liver failure without renal involvement may also occur. (18) Serogroups Icterohaemorrhagiae and Pomona are more associated with hepatic involvement. (2, 19)

Pulmonary abnormalities can occur secondary to the effects of the leptospiral toxin on lung tissue, and from fluid exudation secondary to vasculitis. (2) Leptospiral pulmonary hemorrhagic syndrome (LPHS) is increasingly recognized in dogs with acute leptospirosis. (20) Intra-alveolar hemorrhage in the absence of marked inflammatory cell infiltrate has been documented. LPHS is associated with high mortality rates (up to 70%). (21, 22)

Bleeding abnormalities from abnormal primary or secondary hemostasis can also occur. Vasculitis, thrombocytopenia and disseminated intravascular coagulation all may play a role in bleeding diatheses. Thrombocytopenia may result from platelet consumption, adhesion and aggregation due to stimulated vascular endothelium, increased platelet consumption due to immune causes, hemophagocytic syndrome, or a combination of factors. In one study of 35 affected dogs, 14 (40%) were hypercoagulable, 7 (20%) were hypocoagulable and 40% had a normal profile. In this same study, 23% of dogs were considered to have DIC but this did not influence prognosis. The mortality rate was lower, however, in patients that were hypercoagulable versus those that were hypocoagulable. (23)

Anti-leptospiral IgM antibodies are detected in the first week of infection, increasing rapidly early in infection. Anti-leptospiral IgG antibodies increase to detectable levels approximately 2 weeks after infection. These principles can help understand pitfalls of testing (below).

History/Physical Examination Findings

Leptospirosis can manifest as peracute, acute, subacute, or chronic disease. Young patients tend to have more severe clinical signs compared to older patients. Clinical signs are often non-specific or relate to the primary target organs damaged. Gastrointestinal signs (vomiting, decreased appetite, diarrhea), lethargy, polyuria, and polydipsia are most commonly noted in the history. Pulmonary, ocular and central nervous systems signs are less common. Exam findings are often due to dehydration and/or hypovelemia but some patients may have just fever, PU/PD or myalgia as the initial presenting complaint.

Complete Blood Count:

As with historical and exam findings, CBC changes are non-specific. Changes may include a leukopenia during the leptospiremic phase and may be followed by leukocytosis, with or without a left shift. Anemia (up to 63%) and thrombocytopenia (up to 58%) may also be present or develop during the disease course. (1, 11, 24) Those infected with serogroup Pomona may be more likely to be thrombocytopenic.

Biochemistry Panel

Most (87-100%) dogs with leptospirosis are azotemic but the azotemia can vary quite a bit in severity. Electrolyte abnormalities (hyponatremia, hypochloremia, hypokalemia, hyperkalemia, hypophosphatemia, and/or hyperphosphatemia), as well as metabolic acidosis are commonly present. Hypokalemia may be due to both renal and gastrointestinal loss, however leptospiral glycolipoprotein also directly inhibits expression and functions of the tubular Na+-K+-ATPase. (11) Hypoalbuminemia was also a common finding in one study. (19) More severe azotemia has been noted with Serogroup Pomona. (24)

Hepatic disease is usually less severe than renal disease, with increased hepatic enzymes (ALT, ALP, AST, bilirubin) often occurring up to a week after the onset of azotemia (25). Hepatic disease may also be noted in the absence of renal disease. (19) Elevation of ALP is usually greater than the increase in ALT activity. In one study, 80% of dogs with leptospirosis had increased liver enzyme activities, and 69% were hyperbilirubinemic. (11) Chronic hepatitis (granulomatous) without prominent renal involvement has also been reported (17), however, proving a prior infection may be difficult in many patients.

Elevated creatine kinase has been reported in ~43% of cases of leptospirosis associated with myositis. (26)

Urinalysis:

Results from urinalysis usually are non-specific and consistent with tubular damage. Changes may include hyposthenuria, glucosuria, proteinuria, and hyperbilirubinuria. Proteinuria is variable but in one report ranged from 0.15 to 7.34 as determined by a urine protein:creatinine ratio. (19) Sediment examination can reveal red blood cells, white blood cells, and granular casts.

Diagnostic Imaging

Radiography

Pulmonary involvement has been reported in dogs with leptospirosis with thoracic radiograph abnormalities noted in up to 70% of cases. (11, 19, 22) As radiographic changes may be seen without clinical signs of respiratory distress (11, 19), thoracic radiographs are recommended as part of the initial diagnostic plan for patients suspect to have leptospirosis. Clinical signs of respiratory disease may develop over the course of the disease progression even if not apparently initially. Interstitial to nodular alveolar densities, or alveolar consolidation may be seen on thoracic radiographs. (11) Patients with LPHS typically have abnormalities that initially appear bilaterally in the caudal-dorsal lung fields. (21) LPHS is thought to be have an immune-mediated basis in people and is associated with a high mortality. This syndrome is more commonly seen in Europe. (22)

Ultrasonography

Ultrasound changes are noted in 85-100% of dogs but are non-specific in nature. Changes detected in the kidneys include renomegaly, pyelectasia, increased cortical echogenicity, perinephric effusion, reduced corticomedullary definition, and a medullary band of increased echogenicity (medullary rim sign). (2, 21, 25, 27) In one study of 35 dogs with leptospirosis, 100% had increased cortical echogenicity. (28) Changes seen in other abdominal organs include hypoechogenicity of the pancreas, pancreatic enlargement, thickening of the gastric and intestinal walls, splenomegaly with a mottled splenic echotexture, hepatic hypoechogenicity, gallbladder mucocele, biliary wall thickening, biliary sludge, and lymphadeomegaly. (1, 21, 28) None of these changes are considered specific for leptospirosis, however.

Clotting Tests

Patients with leptospirosis may be hypo or hypercoagulable so coagulation testing results can be variable. Prolongation of PT and aPTT have been reported in 6-50% of dogs. (1, 29) Elevated fibrinogen, d-dimer and fibrinogen degredation products has been reported as well as decreased antithrombin III activitiy. (23) The exact pathophysiologic mechanisms of bleeding in dogs and humans is not well understood but is suspected to be due to hepatic failure, disseminated intravascular coagulation, and/or direct vascular damage from the spirochetes.

Leptospirosis Specific Testing

Two main categories of diagnostic testing are available: tests that detect bacteria directly and those that detect antibodies directed against Leptospira spp. Direct testing via culture or visualization via dark field microscopy are rarely used in clinical practice due to low sensitivity and for cultures, a long incubation time.

Polymerase Chain Reaction (PCR) Assay

Detection of bacterial DNA using polymerase chain reaction (PCR) is the most commonly used direct testing. Direct testing is most useful prior to antibiotic administration and early in the course of the disease when bacterial numbers are highest in blood and urine. Blood is the sample of choice during the first week of infection since organism numbers are highest in blood at that time. After ~10 days of infection, organisms are found in greater numbers in urine. If the time of infection is unknown, which is most common, both blood and urine should be submitted to reduce the chance of false-negative results. (1) Samples should be obtained prior to starting antibiotic therapy due to high chance of a false negative after starting antibiotics. (30) PCR assays may detect organisms in subclinical carriers and should be considered in patients that may present with only mild signs such as non-azotemic polyuria and polydypsia. (2) Recent vaccination can interfere with real-time PCR detection of leptospires. (21) Current commercial PCR assays do not determine the infecting serovar. This generally does not impact management, however information on infecting serovars improves our understanding of epidemiology and is important for vaccine development. In asymptomatic dogs, a positive PCR could indicate a chronic carrier state but prevalence varies by regions. Unfortunately there are limited studies evaluating the performance of these assays. One blood-based PCR assay had a sensitivity of 86% in the first 6 days of infection but this drops to 34% at day 7.

Microscopic Agglutination Test (MAT)

The MAT has been the most commonly used test for leptospirosis in animals. The highest dilution of serum that agglutinates 50% of leptospiral organisms is the titer reported, with agglutination being triggered by both IgM and IgG antibodies. The magnitude of circulating IgM specific to leptospiral lipopolysaccharide plays a major role in the agglutination of leptospires in MAT but these do not usually appear until ~day 8 post infection. This may help explain negative results earlier in the course of disease along with a lag in IgG production. (32) In addition, the highest titer does not always correlate with the infecting serovar and there may be considerable variability in results among different laboratories.

A single positive titer of ≥1:800 to a serogroup not covered by vaccination is suggestive of infection in a dog with compatible clinical signs. One study showed that a single MAT titer of ≥1:800 had a sensitivity of 22-67% depending on the diagnostic laboratory, and a specificity of 69-100%. Paired titers taken 2-4 weeks apart that show a four-fold increase are also suggestive of active infection. While antibiotic therapy may blunt the antibody response, the 4-fold titer increase is often still present. The sensitivity of MAT testing increases to 100% when using paired titers with a specificity of 70-100%. Due to serologic cross-reactions among serovars, antibody response does not predict the infecting serovar. (2, 33)

Vaccination can interfere with interpretation of titers, however post-vaccinal titers tend to be low and generally decline over 4 months. (33) Ongoing exposure to field strains of leptospires may contribute to higher titers, especially to non-vaccinal strains. (1)

ELISA

IgM antibodies generally rise during the first week of infection with a maximum value around 2 weeks. IgG is produced in large quantities 1-3 weeks after infection. Due to these differences, the IgM ELISA test is more sensitive at detecting early infection compared to MAT. (2) The point-of-care tests are based on these antibodies and are used more frequently now.

Point-of-Care Tests

Point-of-care tests have been developed that detect Leptospira-specific antibodies in canine sera. (29) The SNAP Lepto (Idexx) detects antibodies against the LipL32, an abundant membrane protein of Leptospira. When MAT titers were ≥ 1:800, there was agreement found between MAT and SNAP Lepto in 83.2% of cases. (33) The highest agreement was found when MAT was > 1:3200 but titers of this magnitude are often not seen until a couple of weeks into the course of the disease. (35) In clinical practice, the SNAP lepto was positive in 15/22 dogs that were confirmed to have leptospirosis but also identified 20/131 (15%) as a false positive. (34) Vaccinal antibodies are detected with the SNAP lepto and positives from vaccination have been seen up to 1 year post-vaccine. (34)

The WITNESS® Lepto detects IgM antibodies using whole cell extracts from L. kirschneri sv Grippotyphosa and L. interrogans sv Bratislava. In one study, the sensitivity was 98% and specificity 93.5% compared with diagnosis obtained via MAT. Another study of acute clinical cases found a sensitivity of 75% compared to only 24% for MAT in dogs that were later diagnosed by a rise in MAT titer or positive PCR. Twenty-four percent of dogs tested post vaccination had cross reactive antibodies at 12 weeks. (32)

There are two reports comparing the three main antibody tests currently available (single MAT, Witness Lepto and SNAP Lepto). In a study of 89 dogs the sensitivities for the three tests were 70.3% (MAT), 86.5% SNAP Lepto, 78.9% Witness Lepto while specificity was 10%, 97.6%, and 75% respectively. A four-fold rise in MAT was used for the final diagnosis. In another study of 32 dogs experimentally infected, the WITNESS® Lepto (Zoetis) identified seroconversion in all dogs by day 10 while MAT identified seroconversion in 30/32 dogs by day 14 post infection. The SNAP® Lepto (Idexx) test detected seroconversion in 3 dogs during the first 14 days. (32) Sensitivity was 98% and specificity was 93.5% for WITNESS® Lepto when compared to MAT. Differences in the sensitivity for these tests may be related to sample timing after infection and/or the infecting serovar, which is usually not known at the time of testing.

In a European study comparing WITNESS® Lepto and Test-it^TM Leptospira Canine IgM lateral flow assay, a diagnosis of leptospirosis would have overlooked in 21.4% (MAT) and 24% (Point of Care) of true positives if convalescent testing had not been performed. (36)

Given the zoonotic potential and the potential reversibility of acute kidney injury, obtaining a definitive diagnosis is important. As such, at Angell we would typically recommend a combination of testing for patients. If antibiotic therapy has not been instituted, we generally recommend both a PCR based test (typically blood and urine) as well as antibody testing (Witness Lepto) +/- MAT titers. If a point-of-care test is positive, with no vaccinal history, this would be highly suggestive of disease. If a point-of-care test is positive with any vaccinal history, paired MAT titers are considered unless a positive PCR test returns.

Treatment/Management/Prevention

Specific Therapy

Based on the 2010 ACVIM Consensus Statement on Leptospirosis, doxycycline at 5 mg/kg PO or IV q 12 hrs for 2 weeks is the treatment of choice as it will eliminate the renal carrier state, unlike penicillins. The true optimal duration of therapy remains unknown at this time. If doxycycline is not tolerated, ampicillin or penicillin G can be used but dose reduction should be considered in azotemic patients. Although test samples should be collected prior to antibiotic therapy (ideally), treatment should not be withheld while waiting for the results of testing.

Supportive Therapy

The mainstay of supportive therapy is correcting fluid and electrolyte imbalances, providing anti-nausea and anti-vomiting treatments, and providing nutrition. Supportive therapies for the liver are also administered as needed, such as antioxidants (e.g. SAMe) and choleretics (e.g. ursodeoxycholic acid). Other therapies will be dependent on the severity of clinical signs (i.e. oxygen support if respiratory signs). If a patient is suspected to be oliguric, anuric, experiencing signs of fluid overload, or having a progressive rise in renal values, referral for dialysis should be considered. Though the overall survival for acute kidney injury with or without dialysis treatment is only ~50%, infectious etiologies, including leptospirosis have a much better survival rate (~80-90%). (37, 38) Recovery of adequate renal function usually occurs within 2-4 weeks of starting dialysis and some patients may only need 1-3 treatments before polyuria occurs. Early hemodialysis in humans has been associated with increased survival and shorter hospital stays in humans. Per the consensus statement, renal replacement therapy should be considered in patients with inadequate urine output developing volume overload, hyperkalemia, BUN > 80mg/dL, or signs of uremia that are not responsive to medical management.

Patients with LPHS may require oxygen therapy or even mechanical ventilation. Studies in humans with LPHS show improved outcome after cyclophosphamide and plasma exchange. Studies are needed in dogs to determine the benefit of other therapies.

Monitoring

Patients presenting with signs of acute kidney injury with or without liver involvement require intense monitoring. Blood work is most often monitored daily to watch for any progression of azotemia, development of hepatic involvement and to ensure stable electrolytes. For dogs with acute leptospirosis, biochemistry profiles are evaluated every 24 hours. Monitoring for oliguria, anuria and fluid overload is accomplished primarily through quantitative urine output (indwelling urinary catheter) versus fluid intake as well as serial body weight measurements. Dogs with non-oliguric renal failure may be severely polyuric so more precise measurement of ins and outs is warranted to ensure adequate replacement of these fluid losses.

Despite clinical improvement, laboratory abnormalities may persist for several weeks and require follow up visits to monitor for resolution. While azotemia often will resolve in 10-14 days, hepatic recovery may take longer in some patients. Additionally, chronic kidney disease may develop in up to 50% of patients that survive the acute phase of leptospiremia. (38, 39) Interestingly, a recent report from an area known to be endemic for leptospira, showed that many dogs with chronic kidney disease, and no known prior infection of leptospirosis, were positive on urine PCR. (40) The relationship between chronic kidney disease and leptospirosis in the absence of a known acute infection requires further study.

Prognosis

Leptospirosis is typically very responsive to appropriate antibiotic therapy. Survival rates are reported to be 80-90%. (25) Dogs with pulmonary disease and multi-organ involvement have a poorer prognosis. (1, 21) Infection with serogroup Pomona has also been associated with more severe renal disease and poorer outcomes. (24)

Preventive Measures

Vaccination

Currently a bacterin containing four serogroups (Canicola, Icterohaemorrhagiae, Grippotyphosa, Pomona) is available in North America for prevention of leptospirosis and has been shown to provide protection for up to 1 year. (41) These vaccines are not completely cross-protective against other serovars that can cause disease, so it is still possible to develop post-vaccinal leptospirosis from infection with other serovars. (2, 19) Naturally-occurring leptospirosis has been reported in dogs vaccinated with the original bivalent and the currently available quadrivalent vaccines. (1, 41) However, disease in vaccinated patients is uncommon. Challenge studies for the vaccines show a significant reduction in mortality rates, leptospiremia, and for some leptospiuria. Initial immunization involves 2-3 injections at 2-3 week intervals, with numerous studies demonstrating immunity to challenge infection. Vaccines have been shown to protect against serogroups in the vaccine for at least 6-8 months, and some report protection for 12 months. Vaccines must be administered annually. Although reactions can occur after vaccination with leptospirosis, these vaccines are considered to be no more reactive than other vaccines administered to dogs. (1, 2)

Other Preventative Measures

Other methods of prevention include decreased access to potential sources of infection, such as marshy areas and/or standing water and minimizing wild animal contact by use of fencing and rodent control measures.

Zoonotic Potential

Leptospirosis is a zoonotic disease. People can become infected through occupational or recreational exposure (boating, fresh water swimming). Veterinarians, farmers, animal caretakers, and sewer system workers are at increased risk as are children and immunocompromised people. (42) Dogs with leptospirosis are a potential source of infection for people, so contact with urine from infected animals should be avoided. (42, 43)

All dogs with acute renal failure, including acute on chronic disease, should be managed as leptospirosis suspected until an alternate diagnosis has been made. Organisms are likely present in blood or urine for 2-3 days after antibiotic therapy is started but the exact duration is not known. Protective clothing, gloves, boots and eye protection should be used when handling hospitalized dogs. Cages and runs must be disinfected routinely and warning labels should be placed on cages with patients suspected of disease. Leptospires are sensitive to many disinfectants (e.g. bleach, iodophors, quaternary ammonias) and drying. Pressure washing is not used to clean kennel areas since aerosolization of leptospires can occur. Dogs should not be walked in common areas/hallways nor allowed to urinate in areas used by other dogs. (42) Any urine spills should be cleaned and disinfected immediately and any hair that is urine soaked should be washed. Laundering will inactivate leptospires but protective clothing should be worn by individuals handling the bedding. If a patient passes away, protective measure should continue when handling the body.

Once a patient is discharged, owners should wear gloves and wash hands when contacting their dog’s urine until antimicrobial treatment is completed even though the risk of urinary shedding by the time of discharge is likely low. (1) Patients should still urinate away from standing water, where no other animals or people (especially children), will have access.

Treatment of other dogs in the household that may have been coincidentally exposed to a source of leptospires in the environment is recommended, ideally with monitoring of acute and convalescent titers.

Leptospirosis is considered a reportable disease. The state veterinarian should be contacted with any positive cases.

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