FACTS ON LEPTOSPIROSIS
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Canine Leptospirosis, United States, 2002-2004

Summary

A study by Moore et al, conducted as part of a larger project supported by the Centers for Disease Control and Prevention and published in Emerging Infectious Diseases, recorded the significant increase in positive Leptospira microscopic agglutination tests (MAT) for 23,005 dogs across the United States from 2002 to 2004.1
Study Design

The results of all Leptospira MATs for dogs from January 2002 through December 2004 were obtained electronically from Antech Diagnostic Veterinary Laboratory (Los Angeles, CA, USA). Antech provides laboratory services to >18,000 US veterinary hospitals. The seven Leptospira serovars included in the MATs were L. canicola, L. grippotyphosa, L. icterohaemorrhagiae, L. hardjo, L. pomona, L. autumnalis, and L. bratislava. MAT results for each serovar were reported as the highest dilution of serum (1:100, 1:200, 1:400, 1:800, 1:1,600, 1:3,200, 1:6,400 or ≥1:12,800) at which ≥50% agglutination of organisms occurred when compared with a control suspension.

Calculation of seropositivity was performed separately by using cutoff titers of ≥400, ≥800, or ≥1,600. The percentage of seropositive MATs was calculated by state and year.

During the study, 23,005 serum samples were submitted for a leptospirosis MAT, and ≈23,000 tests were performed for the L. canicola, L. grippotyphosa, L. icterohaemorrhagiae, L. hardjo, and L. pomona serovars. Laboratory testing for serovars L. autumnalis and L. bratislava was initiated in 2003 and ≈11,600 tests were performed for each of these 2 serovars.

Clinical Syndromes and Signs of Canine Leptospirosis

Syndrome Symptomology

Peracute

Massive leptospiremia causing shock, often fatal, with few premonitory signs

Acute

INITIAL: pyrexia, shivering, generalized muscle tenderness

SUBSEQUENT: vomiting, rapid dehydration, shock, icterus

Subacute

Fever, anorexia, vomiting, dehydration, thirst, conjunctivitis, rhinitis, tonsillitis, coughing, dyspnea, reluctance to move

Chronic

RENAL FUNCTION: progressive deterioration accompanied by weight loss, polyuria, polydipsia, anorexia, vomiting

HEPATIC FUNCTION: possible liver failure accompanied by inappetance, weight loss, ascites, icterus, hepatoencephalopathy

Results1

The portion of positive leptospirosis MATs for the 23,005 dogs increased significantly from 2002 to 2004. No consistent or distinct geographic pattern for positive MAT results was observed in the study (Figure 1), but seropositivity was greater in the Midwest, Southcentral, and Northwest regions of the United States.

Moderately strong positive correlation in seropositivity (r= 0.59-0.72) was present between serovars L. autumnalis, L. pomona, L. grippotyphosa, and L. bratislava with the strongest correlation between serovars L. autumnalis and L. pomona. This suggests that cross-protection to L. autumnalis could be induced by current bacterins that lack this antigen.

Key Learnings

Leptospirosis may be more common than previously understood. The proportion of positive Leptospira MATs increased significantly from 2002 to 2004 — highest for serovars L. autumnalis, L. grippotyphosa, L. pomona, and L. bratislava, in that order.

Leptospirosis is everywhere. The seroprevalence of leptospirosis, according to this study, is increasing nationwide, but especially in the Midwest, Southcentral, and Northwest regions of the United States.

L. autumnalis and L. pomona are closely related — serologic lab tests may cross-react and (in the author’s opinion) may cross-protect.

Veterinary practitioners and public health officials need to be aware of the potential change in the ecologic environment and circulating endemic strains for this zoonotic organism.

Canine vaccines (like the Vanguard 4-Way Leptospira vaccines from Pfizer Animal Health) are available with serovars L. grippotyphosa and L. pomona as well as the traditional serovars L. canicola and L. icterohaemorrhagiae.




 

Figure 1. Canine leptospirosis microscopic agglutination test results shown as the percentage, by state and year, from 2002 to 2004. A test was considered positive if the titer for any serovar was ≥400 for L. autumnalis, L. bratislava, L. canicola, L. grippotyphosa, L. icterohaemorrhagiae, L. pomona, or L. hardjo serovars.


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1 Moore G, Guptill LF, Glickman NW, et al. Canine leptospirosis, United States, 2002-2004. Emerg Infect Dis 2006;12:501-503.

 


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