Tuesday, August 26, 2014

Canine Leptospirosis:Growing in Effect and Threat

Leptospirosis is a serious threat to our pets, leading to liver and kidney disease, yet many pet owners are totally unaware of the disease and risks. In addition, it can be prevented through the vaccination of your pet. Here is an excellent, detailed article about this disease so you can have a better understanding.

Canine leptospirosis: Growing in effect and threat

By Pedro Paulo Diniz, DVM, PhD

Assistant Professor in Small Animal Internal Medicine

Western University of Health Sciences, Pomona, CA

Despite advances in prevention, the zoonotic disease leptospirosis is not only widespread but growing within the US canine population. The multitude of clinical signs and lack of an accurate in-clinic diagnostic tool make early diagnosis of this disease a great challenge. As a consequence, 1 in 5 dogs die because of complications associated with the infection.1,2,3

The delay in suspecting the infection is the major cause of death by canine leptospirosis.

The number of seropositive dogs in the US has increased over 600% in 7 years

Leptospirosis is considered an emerging infectious disease worldwide.2 While national numbers of infected dogs are not currently available, one large study with over 33,000 samples detected a 6-fold increase in seropositive dogs between 2000 and 2007, following an increase in sample testing by 5 times during the same period.4 The increase in testing reflects the veterinary community’s greater awareness regarding the risk of infection.

The more you test for canine leptospirosis, the more you may find in your area.

Not restricted to rural and wet environments anymore

Rainfall and flooding are important factors associated with canine leptospirosis, since unvaccinated dogs can become exposed to contaminated water and wet soil. Regions with increased rainfall and frequent flooding, such as the Northeast, Midwest, Gulf Coast, and Washington state, are endemic areas of canine leptospirosis.4,5,6 However, canine leptospirosis is present throughout the contiguous United States, even in areas of low precipitation. In fact, hot spots of canine leptospirosis were identified in Colorado, central California, and central Texas, among other regions.5 The leptospirosis season has 2 distinct annual peaks: during the spring (March until May) caused by increased rainfall and standing water/flooding, and during the fall (November and December) caused by higher activity of wildlife reservoir hosts.4 However, canine exposure is documented year-round.

Even more startling, though historically associated with rural environments and contact with livestock, recent studies have demonstrated that urban areas have twice the risk for dog infection than rural areas, regardless of the dog’s age, sex, and breed.7,8 Some of the causes include the smaller proportion of vaccinated city dogs (decreased “herd immunity”) and the active presence of reservoirs for the pathogen. 

Risk factors for canine leptospirosis include access to marshy areas and standing water, contact with rodents and wildlife, and living in urban areas.

The fact that the 2 most frequent Leptospira serovars in the US (L. grippotyphosa and L. pomona)9 have wildlife reservoirs (raccoons, skunks, opossums, deer) suggests that wildlife plays a key role in the transmission of the disease in urban and periurban environments. Raccoons have been identified as major reservoirs of the pathogen in the US. In Colorado, 1 in 3 raccoons in urban and suburban areas shed spirochetes in their urine.9 In addition, up to 90% of inner-city rats carry and shed Leptospira spp.; consequently, indoor dogs with access only to backyards and local parks are also at risk of infection.

Indoor dogs, living in both urban and suburban areas, even with limited outdoor access, are at a similar risk of infection to dogs in rural areas.

Am I missing leptospirosis cases?

Anorexia, fever, depression, vomiting, and diarrhea are frequent signs of canine leptospirosis. In addition, azotemia, elevated liver enzymes, thrombocytopenia, isosthenuria, and proteinuria are common laboratory findings.1,2,3 However, several other diseases may cause similar signs and findings, including hepatic, renal, and vector-borne diseases. In fact, positive tests for vector-borne diseases serve as a marker of exposure to wildlife and should increase clinician awareness of possible exposure to leptospires.10

Signs of canine leptospirosis

Typical: lethargy, fever, anorexia, vomiting, diarrhea, polyuria, polydipsia, dehydration, icterus
Atypical: abdominal pain, stiffness, posterior paresis, respiratory signs, oculonasal discharge, uveitis

Unfortunately, the majority of cases do not simultaneously show all typical signs, with many cases presenting single or few atypical laboratory abnormalities such as coagulopathy, hypoalbuminemia, or glycosuria or clinical signs such as uveitis, cardiac manifestations, intussusceptions, or neurologic and respiratory signs.1,2,10 Between 43% and 70% of dogs with leptospirosis have abnormal lung patterns on thoracic radiographs (interstitial lung pattern).10,11 In addition, it is believed that hepatic infection almost always occurs in conjunction with azotemia; however, a recent study documented 14% of dogs presenting only hepatic involvement, with no azotemia or proteinuria.10 In order to prevent veterinary staff and client exposure to this zoonotic pathogen, clinicians should suspect canine leptospirosis in the presence of any typical or atypical clinical signs or laboratory findings. 

The lack of typical signs does not rule out the suspicion of canine leptospirosis.

Definitive diagnosis: the challenge continues despite advances

To date, no in-clinic assay is available for rapid diagnosis of canine leptospirosis, with the microscopic agglutination test (MAT) still being the most used diagnostic tool.1,2,3 While initial antibody titers of 1:800 in non-vaccinated dogs and 1:1600 in vaccinated dogs strongly support exposure, detection of a 4-fold increase in convalescent antibody titers is still the gold standard. Convalescent MAT titers are required for diagnosis in approximately half of the cases.10 Antibody titers do not correlate with disease severity and cannot accurately determine the serovar involved. In addition, MAT results from different diagnostic laboratories may diverge, due to the lack of standardization among labs.12

                  Figure. The diagnostic strategy for canine leptospirosis combines PCR and serology

Polymerase chain reaction (PCR) assays are a sensitive and specific tool for early detection, but they should be performed from both blood and urine samples of sick dogs.1 PCR better detects leptospiremia in the first 2 weeks post-infection and better detects leptospiruria after that period. PCR is the tool of choice for detecting urinary shedding because serology poorly predicts Leptospira shedding in dogs.13 PCR should be preferentially used in combination with serology.3 In addition, a negative PCR never rules out infection.

MAT and PCR testing can be effectively used to diagnose lepto, but the highest MAT titer does not confirm the involved serovar. Negative PCR does not rule out infection.

Vaccines are safe and effective and should be used

The fact that over 60% of the cases of leptospirosis in dogs are caused by serovars not present in bivalent vaccines (L. grippotyphosa and L. pomona) demonstrates the importance of using a vaccine against at least 4 serovars.4

In the largest study of its kind, 1.2 million dogs in the US were evaluated and found the current Leptospira vaccines were not associated with an increased risk of adverse effects within 3 days of vaccine administration.14 That study determined that young-adult, small-breed dogs that receive multiple vaccines in one office visit are at the greatest risk of adverse effects, independent from what type of vaccine is used. Therefore, a reduction in number of vaccines administered at the same visit for this population of dogs is advised.

The real paradigm shift in the last 30 years is that indoor dogs living in urban and suburban areas, even with limited outdoor access, are at a similar risk of infection to dogs in rural areas in contact with livestock and stagnant water. Veterinarians should be aware of this trend when determining a dog’s risk of exposure in order to define the best prophylactic strategy.

The cost of vaccination and risk of adverse effects largely outweigh the cost of therapy and risk of death by canine leptospirosis.

Recommended literature

1.  Sykes JE, Hartmann K, Lunn KF, Moore GE, Stoddard RA, Goldstein RE. 2010 ACVIM small animal consensus statement on leptospirosis: diagnosis, epidemiology, treatment and prevention. J Vet Intern Med. 2011;25(1):1–13.
 2.  Greene CE, Sykes JE, Moore GE, et al. Leptospirosis. In: Greene CE, ed. Infectious Disease of the Dog and the Cat. 4th edition. St. Louis, MO: Elsevier Saunders; 2012:431–447.
 3.  Sykes JE. Leptospirosis. In: Sykes JE, ed. Canine and Feline Infectious Diseases. St. Louis, MO: Elsevier Saunders: 2014;474–486.
 4.  Gautam R, Wu CC, Guptill LF, Potter A, Moore GE. Detection of antibodies against Leptospira serovars via microscopic agglutination tests in dogs in the United States, 2000–2007. J Am Vet Med Assoc. 2010;237(3):293–298.
 5.  Gautam R, Guptill LF, Wu CC, Potter A, Moore GE. Spatial and spatio-temporal clustering of overall and serovar-specific Leptospira microscopic agglutination test (MAT) seropositivity among dogs in the United States from 2000 through 2007. Prev Vet Med. 2010;96(1–2):122–131.
 6.  Moore GE, Guptill LF, Glickman NW, Caldanaro RJ, Aucoin D, Glickman LT. Canine leptospirosis, United States, 2002–2004. Emerg Infect Dis. 2006;12(6):501–503.
 7.  Alton GD, Berke O, Reid-Smith R, Ojkic D, Prescott JF. Increase in seroprevalence of canine leptospirosis and its risk factors, Ontario 1998–2006. Can J Vet Res. 2009;73(3):167–175.
 8.  Raghavan R, Brenner K, Higgins J, Van Der Merwe D, Harkin KR. Evaluations of land cover risk factors for canine leptospirosis: 94 cases (2002–2009). Prev Vet Med. 2011;101(3–4):241–249.
 9.  Duncan C, Krafsur G, Podell B, et al. Leptospirosis and tularaemia in raccoons (Procyon lotor) of Larimer Country, CO. Zoonoses Public Health. 2012;59(1):29–34.
 10.  Tangeman LE, Littman MP. Clinicopathologic and atypical features of naturally occurring leptospirosis in dogs: 51 cases (2000–2010). J Am Vet Med Assoc. 2013;243(9):1316–1322.
 11.  Kohn B, Steinicke K, Arndt G, et al. Pulmonary abnormalities in dogs with leptospirosis. J Vet Intern Med. 2010;24(6):1277–1282.
 12.  Miller MD, Annis KM, Lappin MR, Lunn KF. Variability in results of the microscopic agglutination test in dogs with clinical leptospirosis and dogs vaccinated against leptospirosis. J Vet Intern Med. 2011;25(3):426–432.
 13.  Harkin KR, Roshto YM, Sullivan JT, Purvis TJ, Chengappa MM. Comparison of polymerase chain reaction assay, bacteriologic culture and serologic testing in assessment of prevalence of urinary shedding of leptospires in dogs. J Am Vet Med Assoc. 2003;222(9):1230–1233.
 14.  Moore GE, Guptill LF, Ward MP, et al. Adverse events diagnosed within three days of vaccine administration in dogs. J Am Vet Med Assoc. 2005;227(7):1102–1108.