Evaluation of temporal and regional variations in canine leptospirosis in the United States

Hu Suk Lee, Purdue University

Abstract

Leptospirosis is an important cause of disease in dogs. Some previous studies of pre-2000 data have identified male, large breed, outdoor dogs of herding or working groups to be at an increased risk for this infection. Recent epidemiological studies suggest that this presenting signalment may be changing. This dissertation includes three epidemiological studies of canine leptospirosis in the United States using data from university veterinary teaching hospitals [Veterinary Medical Database (VMDB)] and private practitioner submissions to a commercial diagnostic laboratory [IDEXX]. The first study evaluated the temporal changes, by decade, in the signalment of dogs diagnosed with leptospirosis from 1970 through 2009. A total of 1,091 cases of leptospirosis were diagnosed among the 1,659,146 dogs examined from the 26 veterinary teaching hospitals in the VMDB. The results show that the VMDB hospital prevalence of leptospirosis in dogs, after a marked reduction in the 1970s and low rates in the 1980s, has increased beginning in the 1990s. Hospital prevalence significantly increased in dogs between 2 and 9.9 years old and in male dogs in the 1990s and 2000s, with the greatest increase seen in dogs weighing <15 pounds in the 2000s. These changes may reflect changes in exposure risk for dogs and>/or failure to receive the appropriate Leptospira vaccination. The second study was to evaluate the seasonal differences of leptospirosis seroprevalence in dogs for four regions [north-east (NE), mid-west (MW), south-central (SC), and California-southern west coast (CS)] using data from IDEXX Laboratories Inc. between 2000 and 2010. Of the total tested samples from the 11-year period, 7.80% (3,503 / 44,916) were considered seropositive at a titer ≥ 1:1,600. Significantly higher seropositive rates occurred in November and December in the MW and NE regions and in December only in the SC region. High/higher monthly rates also indicative of seasonality were observed earlier in the calendar year for both CS and SC regions. The understanding of seasonal patterns may help veterinarians in formulating and ranking lists of differential diagnoses for their patients, and can help in the evaluation of the risk of Leptospira exposure. The third study was to evaluate the seasonal differences of specific Leptospira serovars in dogs and to identify spatial clustering of each serovar based on serological tests in the United States. The results of MATs for canine serum samples between 2006 and 2010 were obtained from IDEXX Laboratories Inc.. A total of 2,473 serum samples were considered to be sero-positive (any titers ≥ 1:1,600) among 30,503 dogs tested between 2006 and 2010 (8.10%; 95% CI: 7.80-8.42). Overall, the seasonal plots showed that seroprevalence (%) all serovars except for Canicola was increased between August and December compared to other months. Overall (any titers ≥ 1:1,600), primary and secondary spatial clusters were identified in central Texas and north-central Colorado between 2008 and 2010, respectively. The primary cluster was associated with the spatial clustering of serovars Autumnalis, Grippotyphosa and Pomona. The secondary cluster in north-central Colorado was associated with the serovar Bratislava. Seasonality and spatial clusters of each serovar were demonstrated based on the serology results. Due to the limitations of antibody testing, further study will be needed for evaluation of seasonality of Leptospira infection through bacterial culture with vaccination history and clinical signs in dogs.

Degree

Ph.D.

Advisors

Moore, Purdue University.

Subject Area

Public health|Epidemiology|Veterinary services

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