Seroprevalence study of swine brucellosis and knowledge of pig traders and dressers at slaughter facilities in Temeke Municipality of Dar es Salaam, Tanzania
C Simon, E D Karimuribo1 and B M Kessy2
Livestock Department - Temeke Municipal Council, P.O. Box 46343, Dar es Salaam, Tanzania
cleophasshayo@gmail.com
1 Department of Veterinary Medicine and Public Health, Faculty of Veterinary Medicine
Sokoine University of Agriculture, P. O. Box 3021, Morogoro, Tanzania.
2 Department of Veterinary Surgery and Theriogenology, Faculty of Veterinary Medicine, Sokoine University of Agriculture
P.O. Box 3020, Morogoro, Tanzania
Abstract
A cross sectional study was carried out between December 2013 and January 2014 to establish seroprevalence of swine brucellosis in pigs slaughtered at five pig slaughter facilities in Temeke Municipality located in Dar es Salaam city, Tanzania. The study also assessed knowledge and practices of pig traders, dressers and pork inspectors with respect to swine brucellosis. A total of 414 serum samples collected at five purposively selected slaughter facilities were screened using Buffered Plate Agglutination Test (BPAT) and Standard Plate Test (SPT). All positive reactors to BPAT and SPT were confirmed by Rivanol test. Overall, the seroprevalence of swine brucellosis was 0.7% (95% C.I=0.2-2.1) (3/414 pigs screened) based on Rivanol test results. Three positive reactor pigs recorded at Mchicha Tazara (1) and Keko A (2) pig slaughter facilities were traced to originate from Singida (2) and Simiyu (1) regions. It was further established that the majority of pigs slaughtered in Temeke originated from Manyara (36.0%), Dodoma (21.7%) and Singida (18.6%) regions. The majority of pig traders (66.7%) and pig dressers (94.4%) had limited knowledge on occurrence of swine brucellosis.
To the best of our knowledge this is a systematic study which has reported for the first time the seroprevalence of swine brucellosis in pig herds transported for slaughter in towns in Tanzania. Findings of this study indicate that swine brucellosis is prevalent albeit at low levels amongst slaughtered pigs. There is therefore a need to strengthen disease surveillance as well as adopting appropriate disease control measures in the country including sensitization of the public on the public health importance of swine brucellosis.
Key words: BPAT, Brucella, public health, Rivanol, SPT
Introduction
Brucellosis is a major zoonotic disease of public health affecting domestic animals, wildlife and humans (OIE 2009a). According to OIE, it is the second most important zoonotic disease in the world after rabies and it is common in countries that do not have good standardized and effective public health and domestic animal health programs (Kunda et al 2005; Abubakar et al 2011). The aetiological agent of brucellosis in pigs is Brucella suis (biovars 1, 2 or 3) which is a small non-motile coccobacillus or short rods facultative intracellular Gram-negative bacteria. Brucellosis caused by B. suis biovar 1 and 3 causes a severe disease in human similar to the one caused by B. mellitensis (Corbel 2006; Meirelles-Bartoli et al 2012; Rahman et al 2012). Pigs can get infection by consuming contaminated feed, water and during mating with infected pigs. Environment contaminated with reproductive organs discharges or aborted materials especially where different stock species are kept increases the risk of infection between pigs (Megid et al 2010).
Infection in pigs results in irregular oestrus, abortions, stillbirths, small litters and birth of weak piglets. Infected swine tissues have high concentration of B. suis organisms as compared with cattle (Meirelles-Bartoli et al 2012). This may have a serious implication in pigs and personnel dealing with pigs. Due to the long duration of human illness and its convalescence, brucellosis is perceived as an important socio-economic as well as a medical problem. Its clinical presentation in human confuse with other diseases like malaria and typhoid (Corbel 2006; Kunda et al 2007; WHO 2013).
Brucellosis can be controlled by test and slaughter. Diagnostic approaches include the use of widely acceptable serological screening tests like the Rose Bengal test (RBT) and the Buffered Plate Agglutination Test (BPAT). These tests use Brucella abortus antigen for serological testing of antibodies against all smooth Brucella species i.e. B. mellitensis, B. abortus, and B.suis due to cross reactivity caused by lipopolysaccharide or membrane proteins shared (Paulo et al 2000). It is recommended that positive reactor samples should be confirmed using an established confirmatory and/or complementary test such as Enzyme-Linked Immunosorbent Assay (ELISA), Fluorescence Polarisation Assay and Rivanol (OIE 2009b; Poester et al 2010; Montasser et al 2011). Culture remains the gold standard while DNA probes or polymerase chain reaction (PCR) methods can be used to demonstrate the agent in various biological samples.
In Tanzania pig keeping provides an opportunity as an income generating activity but is faced with a number of production constraints such as availability of quality feeds, prevalence of diseases like helminths and abortions (Karimuribo et al 2011). In recent years, there has been increased concentration of human population in urban and peri-urban areas (Kunda et al 2005). Urbanisation and population growth in Temeke has increased demand for food and quality protein source like pork. Since most pigs are kept in villages, pig traders purchase them from keepers, collect and pool them into one pen managed by pig trader temporarily (10-14 days) before being transported to Temeke where they fetch high price.
There is scarcity of research information on the prevalence and factors associated with swine brucellosis in Tanzania. The present study aimed at establishing swine brucellosis seroprevalence and assess knowledge of pig traders and dressers at slaughter facilities in Temeke Municipality of Dar es Salaam, Tanzania. The study also attempted to document sources of pigs slaughtered in Temeke Dar es Salaam as well as practices of managing such pigs which might influence the occurrence of brucellosis in pigs. It was anticipated that findings from this study would help to guide further research and necessary intervention for improved pig production industry.
Materials and methods
Study area
The study was conducted in Temeke Municipal Council of Dar es Salaam city which lies between Latitude 6° 48' and 7° 10' South of equator, and between Longitude 39° 33' and 40° East of Greenwich meridian. Temeke Municipality is composed of 30 administrative wards and 120 streets. It has total area of 786.5 km2 and was selected as a representative of Municipalities of Dar es Salaam city. Five out of eight purposively selected slaughter facilities in Temeke were used during this study.
Study design and sampling strategy
A cross sectional study was conducted between December 2013 and January 2014 to establish the magnitude of swine brucellosis in pig slaughter facilities in this survey. Pigs in the slaughter facilities were used as sources of pigs to be sampled. Each pig slaughter facility was visited once each time a new consignment of pigs arrived for slaughter until when required sample size was met. The maximum sample size was calculated according to formula by Naing et al (2006) [i.e. n = Z2 p(1-p)/d2 ] where n= total number of pigs sampled to detect at least one infected animal at 95% confidence interval (Z statistic value =1.96), p= expected prevalence (p) of 50% at 5% precision (d). The prevalence of 50% (0.5) was used in this case to get maximum sample size as prevalence of the disease has not been established.
Purchased pigs from the pig keepers were identified by putting identification marks (shaved marks) right at the time of purchasing. Each pig was accompanied by information related to age, sex, identification mark, and management in the herd obtained through structured interview. Each time when new batches of pigs were received in the slaughter facilities holding pen, proportional contribution of each facility was calculated to establish the number of pigs to be picked for sampling from each facility. The identification marks of each pig present in respective slaughter facility were recorded in pieces of papers, folded, put in a box, mixed and each time a piece of paper was randomly picked without replacement. Respective pigs for each identification mark read from the randomly picked piece of paper were bled to get blood samples. A total of 414 samples were proportionally collected from the five pig slaughter facilities based on the established average number of pigs present in the holding pens as indicated in Table 1.
| Table 1: Number of pigs proportionally sampled from each slaughter facility holding pen | |||
|
Facility name |
Sex |
Total number |
|
|
Males |
Females |
||
|
Mchicha Tazara |
70 |
102 |
172 |
|
Keko A |
31 |
63 |
94 |
|
Keko B |
24 |
52 |
76 |
|
Mama Jack and Nuru |
14 |
9 |
23 |
|
Mbagala Charambe |
18 |
31 |
49 |
|
Total |
152 |
262 |
414 |
Structured interview to pig keepers, pig traders, dressers and pork inspectors
A questionnaire comprising of closed ended type questions was used to collect information from 115 purposively selected pig keepers who had pigs for selling to pig traders. Data collection approach employed face-to-face interview of pig keepers which was conducted by 21 pre-trained pig traders from the source regions of Pwani, Dodoma, Katavi, Manyara, Simiyu and Singida. Individual pig information recorded were sex, age and the identification mark (either existing or marked by pig traders before being transported to Temeke-Dar es Salaam. Herd-related information recorded by pig traders included: herd size (small (≤ 10 pigs), medium (11-20 pigs) or large (≥ 21 pigs), feed sources (purchasing of readymade feed, buy ingredients and compound, use of green leafy material from the farm), pig management system (intensive or semi-intensive), history of buying new pigs (within the past one year), sharing of boars, contact with wild pigs, presence of other livestock species in the farm, reproductive health issues like abortion and still birth, handling and disposal of placenta or aborted foetuses. Data collection from 21 pig traders, 19 dressers and seven pork inspectors was carried out by the researcher (CS) using face-to-face interviews. A close-ended questionnaire was used to collect information on knowledge and practices in respect to risks and preventive measures taken by pig slaughter facility personnel against swine brucellosis.
Blood sampling at slaughter facilities
Collection of blood samples from 414 pigs was carried out by the researcher at each slaughter facility that participated in the study. By the use of a vacutainer needle holder and tube, five millilitres (ml) of blood were aseptically collected from the pig’s vena cava using plain vacutainer tubes (Vacuum tube sterile, Zhejiang Kangsh Beijing). Each serum sample was clearly labeled and left in standing position in a rack within a cool box during sample collection in the field. The collected blood samples were taken to Temeke Municipal Livestock Office the same day for centrifugation with an automatic electric powered centrifuge at a speed of 2500 rotations per minute for 10 minutes to get clear serum. The harvested serum samples were pippeted into sterile cryovials, labeled and stored in a refrigerator at 4ºC for a maximum of seven days after which all sera were shipped to Sokoine University of Agriculture (SUA) laboratory in a cool box with ice packs where they were stored at -20ºC until analysis.
Buffered Plate Agglutination Test (BPAT), Standard Plate Test (SPT) and Rivanol (RivT) tests
All 414 serum samples collected were screened for swine brucellosis using BPAT according to procedures by OIE (2009a). The antigen used was Brucella abortus kindly supplied by the National Veterinary Services Laboratory (NVSL- USA -NVSL 1920 serial number 10-51303 Dayton Avenue Ames IA 50010). The test was performed on a glass plate where 80 microlitre (µl) of serum samples, positive and negative control were pipetted followed by additional of 30µl of antigen. The antigen and sera were hand mixed using a pipette tip in circular manner. The plate was hand rocked twice clockwise and anticlockwise at intervals of four minutes and incubated at room temperature for four minutes. Results were read after eight minutes in a bright light guided by the controls. Any agglutination was recorded as a positive reaction and negative if there was no agglutination.
Standard Plate Test (SPT) was performed according to Alton et al (1975) on each BPAT positive serum sample. Briefly, from each BPAT positive sera and controls, decreasing quantities i.e. 80µl, 40µl, 20µl and 10µl were pipetted onto a glass plate. Thirty microlitre of antigen (NVSL 1920 serial number1-1301, Dayton avenue USA) were placed adjacent to each sera and mixed. The plate was then rocked four times in between four minutes interval and results were recorded after eight minutes.
Confirmation of the positive samples was done using Rivanol test (RivT) which was performed according to the reagent manufacturer instructions (NVSL Dayton Avenue-USA). Briefly 300µl each positive serum sample and controls were pipetted in tubes into which equal volume of rivanol solution were dispensed, mixed and left at room temperature for 5 minutes. The mixture was centrifuged at 1000 rotations per minute (rpm) for five minutes. From the supernatant 80µl, 40µl, 20µl and 10µl were placed onto a glass plate and 30 µl of antigen were added to each and mixed starting from the lowest concentration (10µ) to the highest (80µl). The glass plate was hand rocked four times in between six minutes interval and results read after 12 minutes. Any agglutination was recorded as a positive reaction and negative if no agglutination against their dilution. The cut-off point for positive sample was 1:64
Data analysis
All data were entered and cleared in Microsoft Office TM 2007 Excel sheet and later exported to EPI info TM Version 7.1.1.14 (Centre for Disease Control, Georgia Atlanta USA 2007) for analysis. Descriptive and inferential statistics of the outcome variable were calculated as proportions. The proportions were compared by Chi square test at 95% confidence level to establish any statistical significance.
Results
Characteristics of pigs slaughtered in Temeke
It was found that 103 (89.6%) out 115 pig keepers had small herd size. The herd size ranged from one to 104 pigs. Most pigs were from Manyara, followed by Dodoma, Singida, Katavi and Pwani regions with their percentage contribution as indicated in Figure 1.
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Figure 1. Source areas for the pigs transported for slaughter |
The majority of pigs purchased by pig traders were females which overall constituted 63.3% of all 414 pigs for slaughter as shown in Table 2. This trend of buying more female pigs than boars was practised similarly by pig traders in all six regions where the proportion of female pigs ranged from 58.4% (Manyara region) to 88.0% (Pwani region). Most pigs purchased were of adult size constituting 73.3% of all pigs transported to Temeke Municipality. With exception to Mama Jack and Nuru facility (which received pigs from Simiyu only), other slaughter facilities received slaughter pigs from more than one region (three to four regions per facility) as indicated in Table 2.