Seroprevalence and bacteriological study of canine leptospirosis in Tehran and its suburban areas

ABSTRACT

To determine the seroprevalence of canine leptospirosis in Tehran and its suburban areas, 300 blood samples were collected from dogs referred to the Small Animal Teaching Hospital of Faculty of Veterinary Medicine at University of Tehran, Iran, between October 1998 and October 2000. Following separation of sera, they were kept at -30 °C until the time of laboratory examinations at Razi Institute. All referral cases were selected from the non-vaccinated dogs against leptospirosis. They were 3 months to 11 years old. All of the sera were examined by microscopic agglutination test [MAT] and indirect fluorescent antibody [IFA] techniques in serial two-fold serum dilutions from 150 to 11600. A titer of 1100 or more was considered positive. All sera were examined against 16 serogroups of live leptospiral antigens as recommended by world health organization [WHO]. Seroepidemiological analysis in this study indicated that 93 out of 300 [31.0%] serum samples were positive against one, two or three leptospiral serogroups of canicola [9.0%], icterohaemorrhagiae [5.7%], grippotyphosa [3.7%], canicola+grippotyphosa [3.3%], canicola+icterohaemorrhagiae [3.0%], grippotyphosa+icterohaemorrhagiae [0.7%] and canicola+icterohaemorrhagiae+grippotyphosa [5.7%] using MAT at a titer of 1100 or more. No leptospiral organism was isolated from 93 urine samples of reacted dogs in this study. Seventeen out of 93 [18.3%] reacted dogs showed clinical symptoms of leptospirosis. The rate of positive reaction was 36.9% [31 out of 84] in farmer dogs and 31.0% [67 out of 216] in urban dogs. The rate of positive reaction was 42.3% [60 out of 142] in male and 34.4% [54 out of 158] in female dogs. The statistical analysis using McNemar test, however showed no significant difference between urban and farmer as well as between male and female dogs in this study [p=0.076]. The prevalence rate of reacted dogs examined by IFA technique at 1100 dilution of serum samples was 34.3% [103 out of 300]. The same rate using MAT was 31.0% [93 out of 300]. The proportion of reacted dogs examined by IFA technique was the same as that examined by MAT at a titer of 1400 or more. If MAT is considered as the gold standard test for diagnosis of leptospirosis, then the IFA at a titer of 1100 or more would have a sensitivity of 95%, a specificity of 92%, a false positive rate of 8% and a false negative rate of 5%. In conclusion, with the given sensitivity and specificity of IFA technique, we suggest it as a supportive diagnostic procedure to be used for detection of canine leptospirosis in the field. To prevent and control of canine leptospirosis as a potential zoonotic disease in Iran, use of potent vaccines against the three major serogroups of canicola, icterohaemorrhagiae and grippotyphosa in all urban [pet] and farmer [shepherd] dogs older than 3 months is highly recommended