A Sero – Prevalence Study of Bovine Brucellosis

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Published on International Journal of Agriculture & Agribusiness
Publication Date: May 17, 2019

Kindalem Bayew Wassie
Animal Health Department Head in Janamora Wereda Livestock Development Office
Janamora, Ethiopia

Journal Full Text PDF: A Sero – Prevalence Study of Bovine Brucellosis (Study in Bahir Dar Town).

Abstract
A cross sectional study was conducted from January, 2019 to April, 2019 in Bahir Dar town with a sero-prevalence study of bovine brucellosis. Out of 35 farms in which the survey was conducted breed of animals, herd size of the farm, production system and breeding system of the farms were investigated as a risk factor for the prevalence of abortion. All risk factors have no statistically significance for the prevalence of abortion in this study. The relationship of risk factors with the prevalence of abortion is provided in Table 1. In the table 1 in case of breed category local, cross, exotic and mixed breed has the prevalence of 8.6%, 20%, 0% and 5.7% respectively. From this breed cross breed is the highest prevalence. The total prevalence of the breed is 12/35 (34.3%). In the case of herd size <10, 10-20, and >20 category has the prevalence of 17.1%, 8.6% and 0% respectively. From the herd size category animals that <10 has the highest prevalence when it compared to others. In case of production system Intensive, Semi-intensive and Extensive system has the prevalence of 20%, 14.3% and 5.7% respectively. From these systems intensive production system has the better prevalence rather than semi-intensive and extensive system. From breeding system natural mating has the prevalence of 11.4% which is the highest prevalence when compared to others. Out of a total 406 serum samples tested 20 were positive in Rose Bengal Plate test with an overall prevalence of 4.9%. The relationship between breeds and bovine brucellosis is provided in Figure 1. The maximum prevalence was recorded in cross breeds 10/406 (2.5%) while minimum prevalence was observed in exotic breeds 3/406 (0.7%). The Sero-prevalence rate of bovine brucellosis between different parity groups of ≤2 calved, 2-5 calved and ≥5 calved cows was also investigated. The highest sero-prevalence was recorded in cows calved ≥5 calves (2.9%) and the lowest sero-prevalence recorded in cows’ calved ≤2 calves (0.5%).

Keywords: Bahir Dar, Breed, Cattle, Bovine Brucellosis, Breeding System.

1. INTRODUCTION
Livestock plays an important role in Ethiopian agriculture. The sector has been the focus of a breadth of analysis by experts, development partners and others that reflect a range of perspectives. The reports reaffirm that livestock continues to be a significant contributor to economic and social development in Ethiopia at the household and national level. On a national level, livestock contributes a significant amount to export earnings in the formal market (10 percent of all formal export earnings, or US$ 150 million per annum) and the informal market (perhaps US$ 300 million per annum). Moreover, livestock accounts for 15 to 17 percent of total GDP, and 35 to 49 percent of agricultural GDP. At the household level, livestock contributes to the livelihood of approximately 70 percent of Ethiopians [1]. One of the infectious diseases which are a major constraint for animal production is brucellosis. Brucellosis is a highly contagious, zoonotic and economically important bacterial disease of animals worldwide. The economic and public health impact of brucellosis remains of concern in developing countries [2]. Brucellosis results from infection by various species of Brucella, a Gram negative, facultative intracellular coccobacillus or short rod in the family Brucellaceae [3].
Brucellosis is an infectious bacterial zoonotic disease caused by member of genus Brucella. The disease affects both animals and human resulting in a serious economic loss in animal production sector and deterioration of public health. The disease is primary reproductive disease clinically characterized by abortion in the last trimester and retained placenta in the female whereas orchitis and epididymitis with frequent sterility occur in male. The means of transmission in both female and male are through ingestion and direct or indirect contact with excretion of the organisms in uterine discharge and milk of infected animals [4].
Brucellosis is an important, zoonotic disease that leads to considerable morbidity resulting in significant loss of working days across the globe and thus perpetuates poverty. The disease is presented as an acute or persistent febrile illness with a diversity of clinical manifestations [5]. Various synonyms have been used for human brucellosis including Malta fever, Rock fever of Gibraltar, Cyprus or Mediterranean fever, intermittent typhoid and most frequently, undulant fever [6]. The incubation period varies between 14 and 120 days [7]. Primary clinical manifestations of brucellosis among livestock are related to the reproductive tract. In highly susceptible non-vaccinated pregnant cattle, abortion after the 5th month of pregnancy is cardinal feature of the disease [8].
Retention of placenta and metritis are common sequels to abortion [9]. Females usually abort only once, presumably due to acquired immunity. In general, abortion with retention of the placenta and the resultant metritis may cause prolonged calving interval and permanent infertility. In humans, the disease is characterized by a multitude of somatic complaints, such as fever, sweating, anorexia, malaise, weight loss, depression, headache and joint pains and is easily confused with malaria and influenza [10].
Humans can become infected indirectly through contact with infected animals or by animal products consumption. The disease is rare in industrialized nations because of routine screening of domestic livestock and animal vaccination programs. Clinical disease is still common in the Middle East, Asia, Africa, South and Central America, the Mediterranean Basin, and the Caribbean [11]. Brucellosis can be a serious economic disease. Losses due to abortion or stillbirths, irregular breeding, loss of milk production and reduced human productivity are some of the economic consequences of the disease. The reduced human productivity can hardly be measured in medical care [12]. The Centre for Disease Control and Prevention lists Brucella as a possible bio-terrorist agent. However, it has never been successfully used in this manner. The centre also classifies B.abortus, B.melitensis and B.suis as “agents of mass destruction” and as category B organisms [13].
In Africa, brucellosis is considered to be one of the most serious disease problems facing the veterinary profession. The high prevalence is due to close human-animal contacts, food consumption customs and the fact that many countries have not yet started control or eradication schemes. Brucellosis is perhaps the most widespread and economically important disease in tropical and sub-tropical regions. The direct loss of meat (as a result of abortion, infertility and weight loss) in infected herds of cattle was estimated to be 15% while that of milk (reduced milk production) was 20%. In Ethiopia, brucellosis is one of the infectious diseases, which causes reduced productivity as reported by few studies [14].
The diagnosis of brucellosis depends on serological testing and on the isolation and identification of the infecting Brucella species. Care should be taken during collection and transportation of specimens, which should be processed in a biohazard cabinet [15]. Treatment is unsuccessful because of the intracellular sequestration of the organisms in lymph nodes, the mammary gland, and reproductive organs. Brucella species are facultative intracellular bacteria that can survive and multiply within the cells of the macrophage system. Treatment failures are considered to be due not to the development of antimicrobial resistance but rather to the inability of the drug to penetrate the cell membrane barrier. Control programs have employed two principal methods: vaccination of young or mature animals and the slaughter of infected and exposed animals, usually on the basis of a reaction to a serological test [8]. The General objectives of this cross-sectional study are;
a. To know the sero-prevalence of Bovine Brucellosis in Bahir Dar town.
b. To know the risk factors and their effect associated with the disease occurrence.
c. To give recommendations for the stakeholders on prevention and control of the disease.

2. MATERIALS AND METHODS
2.1. Study Area
A cross sectional study was conducted from January, 2019 to April, 2019 in Bahir Dar town with a sero-prevalence study of bovine brucellosis. Bahir Dar is the capital town of Amhara National Regional State, one of the leading tourist destinations in Ethiopia with a variety of attractions in the nearby Lake Tana and Blue Nile River. It is distinctly known for its wide avenues lined with palm trees and range of colorful flowers. The study area is located 578 km northwest of Addis Ababa, 11o37’N latitude and 37o25’E longitude with elevation of 1,840m above the sea level, annual rain fall of 1200-1600 mm and means annual temperature of 29.5°C [16]. The landscape is marked by the presence of Lake Tana, which drains a watershed of about 3,000 km2 and areas adjacent to Lake Tana and Abay River have poor drainage and annual over flooding during the rainy seasons leave pockets of water bodies, which persist during the dry months. The livelihood of the peoples is based on agriculture and 80% of the population practice mixed crop livestock farming system. The region has 10.6 million cattle, 5.7 million sheep, 4 million goats, and 2.1 million equines and 17,400 camels managed under extensive and semi-intensive management system [16]. The current level of contribution of the livestock sector in Ethiopia is below the expected potential. Export of livestock and livestock by products have contributed to the economy of the country by providing foreign exchange earnings accounting about 15% and 40% of all export earnings and export from agriculture exports respectively [17]. But this is much lower than would be expected, given the size of the livestock population in the country [18].

2.2. Study population, sample size determination and sampling methods
Indigenous, cross and exotic breeds of cows which are calved and kept under extensive, semi-intensive and extensive husbandry system were randomly selected from the study area. Exotic breeds in this study indicates animals having >75% exotic blood level.

2.3. Study design
A cross sectional study was carried out in dairy cows on indigenous, exotic and cross-breeds using questionnaire survey and serological test RBPT. Farms and cows for this study were selected randomly. Sample size for serum collection was determined using the groups is according to the result formula given by Thrusfield [19] expected prevalence of 50% at 95% confidence interval a sample size of 384 cows were sampled.

2.4. Study methodology
Simple random sampling method was followed to select both the farms and study animals. Owners were interviewed for the presence of mainly abortion history of their cows, their husbandry system and way of breeding and other parameters. Then blood sample were collected from the cows selected randomly from their cows.

2.5 Collection of Serum Samples
Blood samples were collected from the jugular vein of each selected animals using plain vacutainer tube and needle. Identification of each animal was labeled on corresponding vacutainer tubes and kept over-night at room temperature to allow clotting. At the next day sera were collected from the clot to another tube which animals’ identification were coincided. Serum samples were kept at -20°C at Bahir Dar Regional Laboratory tested using RBPT.

2.6 Data management and analysis
All data collected during the study period was checked, coded and entered in to Microsoft Excel spreadsheet and analyzed using SPSS software version 16.0. The prevalence of abortion after 5th month of pregnancy was calculated as the number of farms encountered abortion cases after 5th month of pregnancy divided by the total number of farms studied. The sero-prevalence bovine brucellosis was calculated as the number of Rose Bengal test positive sera divided by the total number of sera samples. Pearson’s chi-square (x2) was used to evaluate the association of different variables with the prevalence of abortion after 5th month of pregnancy and sero-prevalence of bovine brucellosis.

3. RESULT
3.1 Result
Out of 35 farms found in Bahir Dar town the questioner data revealed that there is an overall prevalence of 10.6% (5 farms) abortion. Out of 35 farms in which the survey was conducted breed of animals, herd size of the farm, production system and breeding system of the farms were investigated as a risk factor for the prevalence of abortion. All risk factors have no statistically significance for the prevalence of abortion in this study. The relationship of risk factors with the prevalence of abortion is provided in Table 1.
In the table 1 in case of breed category local, cross, exotic and mixed breed has the prevalence of 8.6%, 20%, 0% and 5.7% respectively. From this breed cross breed is the highest prevalence. The total prevalence of the breed is 12/35 (34.3%). In the case of herd size <10, 10-20, and >20 category has the prevalence of 17.1%, 8.6% and 0% respectively. From the herd size category animals that <10 has the highest prevalence when it compared to others. In case of production system Intensive, Semi-intensive and Extensive system has the prevalence of 20%, 14.3% and 5.7% respectively. From these systems intensive production system has the better prevalence rather than semi-intensive and extensive system. From breeding system natural mating has the prevalence of 11.4% which is the highest prevalence when compared to others.

3.1 Rose Bengal Plate Test Result
Out of a total 406 serum samples tested 20 were positive in Rose Bengal Plate test with an overall prevalence of 4.9%. The relationship between breeds and bovine brucellosis is provided in Figure 1. The maximum prevalence was recorded in cross breeds 10/406 (2.5%) while minimum prevalence was observed in exotic breeds 3/406 (0.7%).
The Sero-prevalence rate of bovine brucellosis between different parity groups of ≤2 calved, 2-5 calved and ≥5 calved cows was also investigated. The highest sero-prevalence was recorded in cows calved ≥5 calves (2.9%) and the lowest sero-prevalence recorded in cows’ calved ≤2 calves (0.5%).
The sero-prevalence rate of bovine brucellosis between different production systems was also investigated. The prevalence of intensive, semi-intensive, and extensive production system is 1%, 1.7% and 2.2% respectively. The highest sero-prevalence was recorded in cows kept under extensive production system (2.2%) and the lowest sero-prevalence recorded in cows kept under intensive production system (1%).
The sero-prevalence rate of bovine brucellosis between different breeding systems was also investigated. The highest sero-prevalence was recorded in cows breed with artificial insemination (3.2 %) and the lowest sero-prevalence was recorded in cows breed with mixed mating (0.7%).
The sero-prevalence rate of bovine brucellosis with the abortion history of cows was also investigated. The highest sero-prevalence was recorded in cows having abortion history after 5th month of pregnancy (2.5%) and the lowest in cows having no abortion history before 5th month of pregnancy (0.5%).

4. DISCUSSION
Bovine brucellosis is mainly characterized by abortion and retained fetal membrane. A total of 35 farms were selected randomly and a study was conducted. Out of 35 farms 5 had abortion history which is an overall herd prevalence of 4.9%. This survey is lower than the finding of Adane [20] who reported 11.8% in Wolaita zone of Southern Ethiopia, Abraha [21] who reported 7.4% in Tigray regional state, Degefa [22] who reported 8.3% in Arsi zone of Oromia regional state and Tadesse [23] who reported 6.8% in North Gondar zone of North-Western Ethiopia. The difference in the report may be due to different factors like husbandry system, agro-climatic condition of the study areas. High abortion rate could be due to exposure to physical exercise, stress long distance to search water point and pasture area and competition for available feed resource and infection. Robert [24] indicated that incidence of abortion more than 2 to 5% should be viewed seriously and efforts should be done to determine its cause.
A total of 406 serum samples were collected from randomly selected animals found in Bahir Dar town and a screening test was conducted using Rose Bengal Plate test and 20 samples were Rose Bengal Test positive. This indicates an overall screening sero-prevalence of 4.9%. This finding is higher than the reports of Yohannes [4] reported that out of 406 samples tested 12(2.96%) samples found RBPT positive 8(1.97%) were confirmed as CFT positive and Shiferaw, [25] with 2.1% in Shoa region.