Effect of reactor retention on the spread of brucellosis in Jersey cattle and buffalo herds

Herd and individual animal prevalence of bovine brucellosis with associated risk factors on dairy farms in Haryana and Punjab in India

Herd and individual animal prevalence along with associated risk factors of bovine brucellosis was assessed on dairy farms located in 22 districts in Haryana and Punjab of India. Examination of 4,580 female animals of 119 dairy farms by Rose Bengal test and enzyme-linked immunosorbent assay revealed that an overall herd prevalence was 65.54% (78/119) and individual animal prevalence was 26.50 % (1,214/4,580). Herd prevalence in Haryana was 62.79% which was not significantly different (P = 0.4208) from Punjab (72.72%). Individual animal prevalence was 34.15% in Punjab which was significantly higher (P < 0.0001) than Haryana (22.34%). Prevalence of brucellosis on dairy farms was detected in 20 of the 22 districts, of which 12 districts were in Haryana and 8 in Punjab. Risk factors such as species of animals, age of animals, herd size, awareness of dairymen for brucellosis, entry of a purchased animals on the farm, abortion on farm, use of calving pens, type of breeding, and type of farming were analyzed. The study indicated that the odds ratio (OR) was significant with risk factors of species (OR = 1.63; 95 %CI = 1.40-1.90; P < 0.0001), age (OR = 0.22; 95%CI = 0.17-0.29; P < 0.0001), awareness of brucellosis among dairymen (OR = 21.65; 95%CI = 2.63-178.04; P = 0.0042), entry of purchased animal on the farm (OR = 9.16; 95%CI = 2.38-35.18; P = 0.0012), abortion in animals (OR = 5.57; 95%CI = 1.92-16.10; P = 0.0015) and on cow farm (OR = 3.43; 95 %CI = 1.33-8.82; P = 0.0105). While the OR was insignificant (P > 0.05) with risk factors of herd size, use of calving pen on farms, type of breeding and on buffalo and mixed type of farms.

Estimation of receiver-operating characteristic curves to determine accuracy of a competitive enzyme-linked immunosorbent assay for the serodiagnosis of Brucella infection in domestic water buffalo (Bubalus bubalis) and cattle

OBJECTIVE

To estimate receiver-operating characteristic (ROC) curves for a competitive ELISA (c-ELISA) that is used in serodiagnosis of brucellosis in water buffalo and cattle, to determine the most appropriate positive cutoff value for the c-ELISA in confirmation of infection, and to evaluate species differences in c-ELISA function.

SAMPLE POPULATION

Sera from 4 herds of cattle (n = 391) and 4 herds of water buffalo (381).

PROCEDURE

Serum samples were evaluated for Brucella-specific antibodies by use of a c-ELISA. On the basis of previous serologic test results, iterative simulation modeling was used to classify animals as positive or negative for Brucella infection without the use of a gold standard. Accuracy of c-ELISA for diagnosis of infection was compared between cattle and water buffalo by comparison of areas under ROC curves.

RESULTS

A positive cutoff value of 30% inhibition for c-ELISA yielded sensitivity and specificity estimates, respectively, of 83.9 and 92.6% for cattle and 91.4 and 95.4% for water buffalo. A positive cutoff value of 35% inhibition yielded sensitivity and specificity estimates, respectively, of 83.9 and 96.2% for cattle and 88.0 and 974% for water buffalo. Areas under ROC curves were 0.94 and 0.98 for cattle and water buffalo, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

ROC curves can be estimated by use of iterative simulation methods to determine optimal cutoff values for diagnostic tests with quantitative outcomes. A cutoff value of 35% inhibition for the c-ELISA was found to be most appropriate for confirmation of Brucella infection in cattle and water buffalo.

Comparison of serologic tests for detection of Brucella infections in cattle and water buffalo (Bubalus bubalis)

OBJECTIVE

To estimate sensitivity and specificity of 4 commonly used brucellosis screening tests in cattle and domestic water buffalo of Trinidad, and to compare test parameter estimates between cattle and water buffalo.

ANIMALS

391 cattle and 381 water buffalo.

PROCEDURE

4 Brucella-infected herds (2 cattle and 2 water buffalo) and 4 herds (2 of each species) considered to be brucellosis-free were selected. A minimum of 100 animals, or all animals > 1 year of age, were tested from each herd. Serum samples were evaluated for Brucella-specific antibodies by use of standard plate agglutination test (SPAT), card test (CT), buffered plate agglutination test (BPAT), and standard tube agglutination test (STAT). A Bayesian approach was used to estimate sensitivity and specificity of diagnostic tests without the use of a gold standard, assuming conditional independence of tests.

RESULTS

Sensitivity and specificity estimates in cattle, respectively, were SPAT, 66.7 and 98.9; CT, 72.7 and 99.6; BPAT, 88.1 and 98.1; and STAT, 80.2 and 99.3. Corresponding test estimates in water buffalo, respectively, were SPAT, 51.4 and 99.3; CT, 90.4 and 99.4; BPAT, 96.3 and 90.7; and STAT, 75.0 and 98.8. Sensitivity of the CT and specificity of the BPAT were different between cattle and water buffalo with at least 95% probability.

CONCLUSIONS AND CLINICAL RELEVANCE

Brucellosis serologic test performance varied by species tested, but BPAT had the highest sensitivity for screening cattle and water buffalo. Sensitivity and specificity of more than 2 screening tests can be estimated simultaneously without a gold standard by use of Bayesian techniques.