3.1 Descriptive study of animal population
The study included 60 (75.94%) goat farms and 19 (24.1%) sheep farms; among them a total of 277 (77.59%) goat samples and 80 (22.41%) sheep blood samples tested for brucellosis. The median herd size of the goat and sheep farms were 48 and 100, respectively. The median age of goat and sheep were 1.5 and 2 years, respectively. The individual species wise herd characteristics of goat and sheep are depicted in table 1. About 17.65% (12/68) sheep were either purchased from nearby herds or brought from India, and 61% (105/172) of the goat were introduced from the neighboring districts or abroad. The median age of the sheep owner was 45, and that of the goat farms was 35. Only 55 of the sheep herd were registered while 90% of the sheep herd were registered. A Terai indigenous community maintained most of the sheep herds, and that was one of the sources of their livelihood.
Sero-prevalence of goat and sheep population
Of the total of 80 sheep samples tested, 12 (15%; 95% CI: 8.79–24.41), and among 277 goat samples tested 3 (1.1%; 95%CI: 0.37–3.14) were seropositive to Brucella. The brucellosis was detected only in female goats, but in the sheep populations, higher proportion of males 18.75% (3/16) were positive to Brucella than female 14.1% (9/64). The local goats, such as Khari, were positive to Brucella. Lampuchre breed is indigenous sheep that has the highest burden of disease. The detailed illustrations of the sex-wise and breed wise comparison of seroprevalence of Brucella among goats and sheep are described in table 1.
Table 1:Comparison of seroprevalence of Brucella among goats and sheep by sex and breed wise classification
Variables
|
Category
|
Total number (%)
|
RBPT positive (%)
|
ELISA positive (%)
|
Overall Prevalence (95%CI)
|
Species
|
|
|
|
|
|
Goat
|
Male
|
65 (18.21)
|
0.00
|
0.00
|
1.1% (0.37-3.14)
|
|
Female
|
212 (59.38)
|
1.81% (5/277)
|
1.1 % (3/277)
|
|
|
|
|
|
|
Sheep
|
Male
|
16 (20)
|
18.75 % (3/16)
|
18.75 % (3/16)
|
15% (8.79-24.41)
|
|
Female
|
64 (80)
|
12.5% (8/64)
|
14.1% (9/64)
|
Breeds
|
|
|
|
|
|
Breed of Goat
|
Local
(Khari, Terai)
|
135 (48.74)
|
2.22 % (3/135)
|
2.22 % (3/135)
|
1.1% (0.37-3.14)
|
|
Exotic
(Boer, Jamunapari)
|
142 (51.26)
|
1.41 % (2/142)
|
0.00
|
|
|
|
|
|
|
Breed of Sheep
|
Lampuchre
|
75(93.75)
|
14.67% (11/75)
|
16% (12/75)
|
15% (8.79-24.41)
|
|
Baruwal
|
5 (6.25)
|
0.0
|
0.00
|
Univaraible regression analysis
The bivariate analysis of the sheep and goat data was depicted in Tables 2 and 3, respectively. The sheep of age greater than 1.5 years had significantly 3.29 higher odds of brucellosis than the sheep of age ≤ 1.5 years (OR = 4.29, 95%CI: 1.16, 20.63, p = 0.0406). There were significantly higher odds of brucellosis among sheep herd size of >100 than the sheep herds of ≤100. The sheep that had parity greater than 1.5 were 4.11 more likely to be detected with brucellosis compared to sheep ≤ 1.5, but the result was statistically borderline significant (OR = 4.11, 95%CI: 0.98, 21.29, p = 0.055).
On the other hand, there were some empty cells in the two by two contingency tables in the goat bivariate analysis. Correction was made with the addition of 0.5 and calculated the odds ratios [22, 27–28] (Table 3). In bivariate analysis, the goats that were taken for grazing had significantly higher odds (OR = 14.5, 95% CI: 1.1, 283.9, p = 0.003) of detecting brucellosis compared to goats stall-fed at farms (Table 3).
Multivariable logistic regression analysis
The variables that qualified from the sheep data for multivariable analysis (p<0.20) were age category, gender, common grazing system, disinfection process applied at the farm entry point. Parity was dropped from the model because it had a higher correlation with the age category (r = 0.63). Similarly, for the goat data, the same sets of the variables were included in final firth multivariable logistic regression based on the cut off criteria of p<0.20.
In the multivariable regression analysis, sheep of older age (>1.5 years) had significantly higher odds OR = 6.39, 95%CI: 1.23, 54.67, p = 0.046) of Brucella compared to the younger sheep (≤1.5 years) (Table 4).
On the other hand, none of the variables were identified as the significant risk factors for the brucellosis in goat population after firth logistic regression [27]. But, the goats from the frequent grazing herds had higher odds (OR = 8.81, 95%CI: 0.44, 174.56) of Brucella than goats from isolated herds. However, the finding was at borderline level of significance (p<0.153) (Table no 5).
Table 2: Univariable analysis results of potential risk factors associated with sero-positivity of sheep population against Brucella spps.
Determinants
|
Total no of sheep
|
Brucella positive
|
Brucella negative
|
Odds ratio (OR)
|
95% CI
|
P value
|
Animal Origin
|
|
|
|
|
|
|
Purchased
|
12
|
3
|
9
|
2.19
|
(0.85, 2.21)
|
0.32
|
Home Breed
|
68
|
9
|
59
|
Ref
|
|
|
Age (median=1.5 years)
|
|
|
|
|
|
|
>1.5
|
37
|
9
|
28
|
4.29
|
(1.16, 20.63)
|
0.041*
|
<=1.5
|
43
|
3
|
40
|
Ref
|
|
|
Herd size (median= 100)
|
|
|
|
|
|
|
>100
|
24
|
7
|
17
|
4.2
|
(1.19,15.91)
|
0.026*
|
<=100
|
56
|
5
|
51
|
Ref
|
|
|
Parity (Median=1 year)
|
|
|
|
|
|
|
>1
|
24
|
6
|
18
|
4.11
|
(0.98,21.29)
|
0.055
|
<=1
|
40
|
3
|
37
|
Ref
|
|
|
Gender
|
|
|
|
|
|
|
Male
|
16
|
3
|
13
|
1.41
|
(0.28,5.53)
|
0.646
|
Female
|
64
|
9
|
55
|
Ref
|
|
|
Common Grazing herds
|
|
|
|
|
|
|
Yes
|
74
|
12
|
62
|
2.6
|
(0.12, 49.16)
|
0.154
|
No
|
6
|
0
|
6
|
Ref
|
|
|
Repeat breeding
|
|
|
|
|
|
|
Yes
|
11
|
3
|
8
|
2.94
|
(0.62,2.63)
|
0.199
|
No
|
53
|
6
|
47
|
Ref
|
|
|
*P value<0.05 means statistically significant
Table 3: Univariable analysis results of potential risk factors associated with sero-positivity of goat population against Brucella spps.
Determinants
|
Total no of goats
|
Brucella Positive
|
Brucella Negative
|
Odds Ratios (OR)
|
95% CI
|
P value
|
Animal orgin
|
|
|
|
|
|
|
Purchased
|
105
|
2
|
103
|
1.2
|
0.11, 26.11
|
0.87
|
Home bred
|
172
|
1
|
171
|
Ref
|
|
|
Age (median=2 years)
|
|
|
|
|
|
|
<=2
|
194
|
3
|
191
|
3.1
|
0.16, 59.74
|
0.12
|
>2
|
83
|
0
|
83
|
Ref
|
|
|
Herd size (median= 48)
|
|
|
|
|
|
|
<=48
|
140
|
3
|
137
|
7
|
0.36, 136.8
|
0.06
|
>48
|
137
|
0
|
137
|
Ref
|
|
|
Parity (Median=1)
|
|
|
|
|
|
|
<=1
|
113
|
3
|
110
|
6.5
|
0.33, 127.2
|
0.04*
|
>1
|
102
|
0
|
102
|
Ref
|
|
|
Gender
|
|
|
|
|
|
|
Female
|
211
|
3
|
209
|
2.19
|
0.112, 42.9
|
0.34
|
Male
|
65
|
0
|
65
|
ref
|
|
|
Grazing system
|
|
|
|
|
|
|
Yes
|
92
|
3
|
89
|
14.5
|
1.1, 283.9
|
0.01*
|
No
|
185
|
0
|
185
|
Ref
|
|
|
Disinfection at the farm entry point
|
|
|
|
|
|
|
No
|
135
|
3
|
132
|
7.5
|
0.39, 147.1
|
0.06
|
Yes
|
142
|
0
|
142
|
Ref
|
|
|
Repeat breeding
|
|
|
|
|
|
|
Yes
|
42
|
1
|
41
|
2.1
|
0.18, 23.28
|
0.29
|
No
|
171
|
2
|
169
|
Ref
|
|
|
Table 4: Multivariable analysis results of risk factors (p<0.05) associated with sero-positivity of sheep population against Brucella spps.
Determinants
|
Category
|
Coefficient
|
Standard Error
|
Odds ratio (OR
|
95% CI
|
P value
|
Age (median=1 year)
|
>1.5
|
1.86
|
0.9309
|
6.39
|
(1.23, 54.67)
|
0.04*
|
|
<=1.5
|
|
|
|
|
|
Herd size (median=100)
|
>100
|
-1.5016
|
0.9176
|
4.49
|
(0.03, 1.29)
|
0.09
|
|
<=100
|
|
|
|
|
|
|
|
|
|
|
|
|
*P value<0.05 means statistically significant
Table 5: Multivariable analysis results of risk factors (p<0.05) associated with sero-positivity of goat population against Brucella spps
Determinants
|
Category
|
Coefficient
|
Standard Error
|
Odds ratio (OR)
|
95% CI
|
P value
|
Age (median=1 year)
|
>1.5
|
0.98
|
1.55
|
2.66
|
(0.13, 55.69)
|
0.53
|
|
<=1.5
|
|
|
|
|
|
Herd size (median= 48)
|
>48
|
1.4112
|
1.559
|
4.10
|
(0.19, 87.01)
|
0.36
|
|
<48
|
|
|
|
|
|
Grazing System
|
Yes
|
2.1757
|
1.524
|
8.81
|
(0.44, 174.56)
|
0.15 a
|
|
No
|
|
|
|
|
|
a: This variable is a borderline significant and could be a potential risk factor