July 25, 2016

Key Features of Leptospirosis in Dogs

Many domestic and wild animals, especially rodents, serve as chronic, asymptomatic carriers of Leptospira, and excrete the bacteria in their urine.
By Nicola M. Parry, BVSc, MRCVS, MSc, DipACVP
Leptospirosis is a zoonotic bacterial disease, caused by pathogenic serovars of Leptospira. It represents a global veterinary and public health problem. Many domestic and wild animals, especially rodents, serve as chronic, asymptomatic carriers of Leptospira, and excrete the bacteria in their urine. As is the case in humans, dogs become infected either directly through contact with the urine of infected animals, or indirectly through contaminated water or soil. In the United States, dogs with leptospirosis are more likely to be living near an outdoor water source, swimming or drinking from an outdoor water source, or indirectly exposed to wildlife.
 
Dogs are hosts of L. interrogans serovar Canicola and shed it into the environment. However, since the introduction, in the 1960s, of the bivalent antileptospiral vaccine that protects against serovars Canicola and Icterohaemorrhagiae, cases of infection in the United States have more frequently been associated with other serovars such as Grippotyphosa and Pomona—however, prevalent serovars may differ according to geographical region.
 
In dogs, leptospirosis manifests similarly to the disease in humans. Nevertheless, although dogs can develop a variety of clinical signs, the signs of acute leptospirosis usually reflect acute kidney injury and liver impairment; fever can occur early in the disease and can be accompanied by pain (typically caused by inflammation in one or more organs or tissues), reluctance to move, weakness, and a stiff gait; icterus and bleeding may also occur in some dogs (bleeding may or may not be associated with disordered hemostasis). Pulmonary hemorrhagic syndrome has also emerged as a severe manifestation of acute leptospirosis in dogs; although its pathophysiology is poorly understood, affected dogs develop severe intra-alveolar hemorrhage (in the absence of disordered hemostasis) that is associated with high mortality (up to 70%). Less commonly, cardiac, pancreatic, intestinal, ophthalmologic, and dermatologic manifestations have also been reported; abortion and infertility may also occur.

In dogs with acute onset of kidney disease and azotemia, antemortem diagnosis is usually based on high antibody titers as detected by the microscopic agglutination test (MAT). Because MAT results may be negative in the first week of illness, clinicians should perform acute and convalescent phase antibody testing, two weeks apart. Polymerase chain reaction assays may also be used to assist in the diagnosis.
 
Although the optimal treatment for leptospirosis remains unknown, it is typically treated using antibiotics, as well as supportive care, as indicated (for kidney or liver injury, for example). According to the 2010 American College of Veterinary Internal Medicine Small Animal Consensus Statement on Leptospirosis, “[t]he recommended treatment for optimal clearance of the organism from renal tubules is doxycycline”, given orally at a dose of 5 mg/kg every 12 hours for 14 days. Clinicians should not wait to obtain results of diagnostic tests, but should initiate treatment in any dog in which leptospirosis is suspected.
 
Currently available vaccines are effective against leptospirosis and clinicians should educate owners about the benefits of vaccinating their dogs against leptospirosis, in particular in reducing both the risk of morbidity and mortality associated with infection, as well as the risk of disease transmission to humans. In dogs at risk for leptospirosis (many clinicians consider all dogs to be at risk if they go outdoors), experts recommend annual vaccination with vaccines containing all four leptospiral serovars (Grippotyphosa, Pomona, Canicola, and Icterohaemorrhagiae). Additional preventive measures include reducing exposure of dogs to possible sources of infection (such as standing water), and reducing contact with wild animals (such as rodents) and farm animals.
 
Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.

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