Leptospirosis is a zoonotic disease of worldwide distribution affecting most mammalian species. Since dogs can shed leptospires in their urine without showing clinical signs of disease, this can lead to exposure of humans. The control of leptospirosis therefore is important not only from an animal, but also a public health perspective.¹ However, the role of companion animals in the epidemiology of leptospirosis cannot be reduced to that of simple vectors. They may contribute significantly to the elimination of small rodents from the immediate home environment and serve as sentinels, indicating the presence of leptospires in specific locations.²

Awareness of the disease and its current manifestations, high clinical suspicion in severely affected areas, and good understanding of the significance and the limitations of available diagnostic tests are essential for a satisfactory management of the disease. Furthermore, careful attention to established safety protocols and basic hygiene rules should avoid endangering the treating staff and the dog owners.

When to Suspect Leptospirosis?

The infection of dogs with leptospires causes a wide spectrum of organ manifestations with injury to the kidney, liver, vasculature, blood, and lung.² The resulting clinical picture can vary markedly between affected individuals and geographic areas, and it tends to shift over time depending on prevailing serovars or strains.

In a recent study describing 298 confirmed cases over a 10-year period in Switzerland,² the authors could demonstrate markedly increasing incidence during that time period and show that canine leptospirosis should therefore be considered a re-emerging disease also in areas of temperate climates. Although these cases represent only the tip of the iceberg, incidence rates as high as 22 cases/100,000 dogs/year were reported in an area with an estimated human incidence of approximately 0.05 cases/100,000 humans/year. This canine incidence is close to incidence rates reported for humans in tropical regions or during epidemic outbreaks.

In most reports, acute kidney injury (AKI) remains the dominating manifestation of acute canine leptospirosis and it should therefore probably be the main cause of suspicion. Particularly in endemic areas, every dog with AKI should be treated as suspect for leptospirosis and undergo diagnostic testing, receive early antibiotic therapy, and be labeled as such to avoid disease transmission. The local epidemiology of canine leptospirosis should dictate other groups at risk that could include dogs with liver failure or severe respiratory failure suggestive of pulmonary hemorrhage. The signalment of the dog may increase the suspicion for certain groups such as hunting dogs, but the disease should never be ruled out based on a more sedentary life style (home dog), a certain age class (puppies), or certain breeds (toy breeds) that intuitively may seem unlikely to be exposed. All dogs at any age, gender, or breed have been reported to be affected.

Diagnostic Tests: Strengths and Limitations

Since leptospirosis is a potential zoonosis and a severe disease with high mortality, a reliable confirmation of a clinical suspicion is important both from a public health perspective and in order to provide timely and adequate care to the affected dogs.

A positive culture of biological samples is the definitive proof of infection, but culturing leptospires is difficult and rarely available. Identification of leptospires in the fresh urine with darkfield microscopy has poor sensitivity and specificity. The main test available for direct detection of leptospires in biological samples is the PCR. The detection of leptospiral DNA is supposed to be very specific and its analytical sensitivity very high. However, its use under clinical conditions including animals treated with antibiotics and of uncertain duration of clinical signs has raised serious doubts on its diagnostic sensitivity.³ Pre-analytic conditions concerning sampling, preparation, and shipping also need to be clearly evaluated.

Testing for antileptospiral antibodies via the microscopic agglutination test (MAT) is currently the most useful diagnostic tool available. However, it is important to realize that all antibody tests lack sensitivity in early sampling, time being needed for the production of antibodies. Most studies indicate a diagnostic sensitivity around 50% for sampling at the time of initial presentation, hence the need for confirmatory testing 1–2 weeks later.³ This rule is also valid for IgM assays that suggest an earlier detection of Leptospira-specific antibodies. Most data from these tests being based on late samples suggest "unrealistic" sensitivities and specificities > 95%. Under clinical conditions, however, these assays also indicate an antibody testing blind period at presentation and a possible false-positive period postvaccination.

How to Proceed with a Suspect Case?

It is essential that every suspicion of leptospirosis be confirmed or ruled out whenever possible. Although final confirmation often comes late, the dog's final status is important to evaluate the risk associated with a particular environment, the choice of an adequate vaccination protocol, the risk of residual renal disease, and for our knowledge of the local epidemiology.

The clinical management of the affected dog necessitates a thorough diagnostic database and especially the characterization of the organs involved since this will guide the specific treatment. Screening for pulmonary hemorrhages with thoracic radiographs and screening for other hemorrhagic complications and DIC with a coagulation panel are particularly important.

Although evidence supporting early antibiotic therapy in dogs with leptospirosis is very sparse, the severe clinical manifestations and the zoonotic risk justify the use of appropriate antibiotics in dogs suspected to have leptospirosis, even before definitive laboratory confirmation.¹ The European Consensus panel recommends to treat these dogs with doxycycline (5 mg/kg q12h or 10 mg/kg q24h) for 14 days. Dogs with gastrointestinal signs should be treated initially with an IV penicillin (e.g., ampicillin 20–30 mg/kg q6–8h, penicillin G 25,000–40,000 U/kg q6–8h or amoxicillin 20–30 mg/kg q6–8h), adjusting the dosage to decreased renal function. It is important that the dogs receive a 14-day course of oral doxycycline when the gastrointestinal signs are under control in order to eliminate renal colonisation.¹ The Consensus panel further recommends the treatment of dogs living with dogs diagnosed with leptospirosis with doxycycline for 2 weeks.

Leptospirosis is considered one of the most important zoonoses worldwide. As such, humans with contact with animals are likely to be exposed to and infected with this potentially life-threatening bacterial infection. Handling of diseased animals certainly represents a risk of transmission, especially through contact with their body fluids. Basic hygiene rules including handwashing before and after treating diseased animals, associated with simple additional measures such as wearing gloves for any contact with suspect animals, and wearing goggles and mask for manipulations generating aerosols (e.g., intubation for anesthesia, cleaning up cages) seem to minimize this risk. A serological survey from the staff of the author's hospital where 50–100 dogs are diagnosed with leptospirosis each year failed to show any serological response and thus significant exposure among the tested individuals.⁴ It has been suggested that the most dangerous dogs for disease transmission might be the healthy carriers. Due to a lack of awareness, the staff is unlikely to take specific precautions with these dogs.

After Recovery

Recovery of renal function can continue for several months after initial stabilization. Some dogs with apparent full recovery and normalization of serum creatinine can, however, have residual parenchymal damage and subsequently develop CKD. The European Consensus panel recommends re-examination no later than one week after hospital discharge and every 1–3 weeks thereafter until clinical stabilization. Further monitoring should be progressively extended to intervals of 1–6 months.⁵

Vaccination

The introduction of bivalent canine vaccines against the serovars Icterohaemorrhagiae and Canicola four decades ago and their worldwide inclusion in the routine vaccination programs seems to have drastically reduced the number of cases diagnosed in most countries. The re-emergence of the disease in diverse geographic areas is probably related at least in part to an escape from the vaccine serovars and a shift to "newer" serovars. The recent changes in available products with expanded quadrivalent vaccines seem to have successfully reduced leptospirosis incidence in the USA, but data are still lacking in other areas. In the meantime, the vaccine with the serovar spectrum covering most closely the prevalent serovars should be used, even if a definitive proof of its efficacy is not available from field studies.

References

1.  Schuller S et al. European consensus statement on leptospirosis in dogs and cats. J Small Anim Pract. In press.

2.  Major A et al. Increasing incidence of canine leptospirosis in Switzerland. Int J Environ Res Public Health. 2014;11:7242–7260.

3.  Kümmerle Fraune C et al. Evaluation of the diagnostic value of serologic microagglutination testing and a polymerase chain reaction assay for diagnosis of acute leptospirosis in dogs in a referral center. J Am Vet Med Assoc. 2013;242:1373–1380.

4.  Barmettler R et al. Assessment of exposure to Leptospira serovars in veterinary staff and dog owners in contact with infected dogs. J Am Vet Med Assoc. 2011;238:183–188.

5.  Kis I et al. Long-term outcome of dogs with acute kidney injury. In: Proceedings from the ACVIM Forum; 2012; New Orleans, LA, USA.