Seroprevalence and molecular detection of bovine brucellosis and leptospirosis in Assam
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Date
2022-09
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College of Veterinary Science, Assam Agricultural University, Khanapara Campus
Abstract
Brucellosis and leptospirosis are neglected zoonotic disease prevalent throughout the world. Bovine brucellosis is predominantly caused by Brucella abortus. Leptospirosis in bovine is mainly caused by Leptospira serovars under the serogroup Sejroe. Both the diseases share some common clinical signs and symptoms and cause severe economic losses. The present study was undertaken to estimate the seroprevalence of bovine brucellosis and leptospirosis and diagnose both the diseases by molecular detection of Brucella and Leptospira organisms in clinically suspected and seropositive cases. The study was carried out in Assam during August 2021 to July, 2022.
In this study, a total of 1013 cattle serum samples were collected from 11 districts of Assam viz. Tinsukia, Lakhimpur, Dhemaji, Sonitpur, Nagaon, Kamrup-M, Barpeta, Udalguri, Kokrajhar, Dhubri and Cachar, and screened for Brucella antibodyby Rose Bengal Plate Test (RBPT) and Indirect-enzyme Linked Immunosorbent Assay (i-ELISA) to estimate the seroprevalence of the disease. To detect seroprevalence of leptospirosis, a total of 512 cattle serum samples were collected from 7 districts of Assam viz. Dhemaji, Bishwanath, Nagaon, Kamrup-M, Bongaigaon, Kokrajhar and Dhubri, and tested by i-ELISA for Leptospira antibody. A total of 41 serum samples were found to be positive for Brucella antibody by both the tests with a seroprevalence rate of 4.04% and 19 out of 512 serum samples were found to be positive for Leptospira antibody by i-ELISA with a seroprevalence rate of 3.71%. Higher seroprevalence of brucellosis was recorded in female (4.60%) than in male animals (2.16%). Similarly, higher seroprevalence of leptospirosis was recorded in female (4.53%) than in male animals (1.45%). Age wise seroprevalence of brucellosis was found to be highest in animals of 2.1 to 5 years (1st to 3rd lactation) of age(6.32%) followed by animals of 5.1 years and above (4th lactation onwards) age group (2.90%). In case of leptospirosis, animals of 5.1 years and above (4th lactation onwards) age group showed highest seroprevalence (7.47%) followed by animals of 2.1 to 5 years (1st to 3rd lactation) of age (4.14%).
In both brucellosis and leptospirosis, higher seroprevalence rate i.e., 6.54% and 4.33%, respectively was recorded in crossbred than in local cattle (1.07% and 2.97%, respectively). In case of brucellosis, animals reared in organised farms showed higher seroprevalence (8.94%) than the animals reared in semi-organised (3.08%) and backyard farms (1.63%). On the other hand, in case of leptospirosis, animals reared in backyard farms showed higher seroprevalence (7.20%) than the animals reared in semi-organised (2.63%) and organised farms (2.47%). In relation to animal health status, the seroprevalence of both the diseases were found to be highest in clinically ill animals with 40.90% for brucellosis and 8.18% for leptospirosis than apparently healthy animals i.e., 3.22% for brucellosis and 3.06% for leptospirosis. Again, among clinically ill animals, seropositivity for brucellosis was highest in animals with history of abortion (66.66%) followed by animals with retention of placenta (50.0%) and repeat breeding (33.33%). Similarly, in case of leptospirosis, highest seroprevalence was found in animals with history of abortion (33.33%) followed by animals with retention of placenta (25.0%) and repeat breeding (13.33%).
In this study, both Brucella and Leptospira antibodies could be detected in 5 out of 512 serum samples screened by i-ELISA specific for both the diseases with a seropositivity rate of 0.976%.
For molecular detection of brucellosis, 41 seropositive (32 apparently healthy and 9 clinically ill) and 23 clinically suspected (seronegative) samples (whole blood, aborted foetus, placenta, vaginal swab) were tested by Brucella genus specific PCR. Out of these, 9 clinical samples (39.13%) from seronegative cases and 4 samples (9.75%) from seropositive cases were found to be positive for Brucella genomic DNA in Brucella genus specific bcsp31 PCR. Overall, out of 64 samples examined, Brucella genomic DNA could be detected in 13 number of samples with a positivity rate of 20.31%. All 13 Brucella DNA were confirmed as Brucella abortus by multiplex PCR (AMOS). For molecular detection of leptospirosis, 19 seropositive (15 apparently healthy and 4 clinically ill) and 33 clinically suspected (seronegative) samples (whole blood, aborted foetus, placenta, vaginal swab and urine) were tested by Leptospira lipL32 gene PCR. Out of 33 clinically suspected (seronegative) samples, Leptospira DNA could be detected in 6 number of samples with positivity rate of 18.18%. Leptospira DNA could not be detected from seropositive samples. As a whole, out of 52 samples, Leptospira DNA could be detected in 6 sample with an overall positivity rate of 11.53%.