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1 GENERAL INTRODUCTION 1.1 Introduction and Background 1 CHAPTER I GENERAL INTRODUCTION 1.1 Introduction and background Brucellosis is a collective term that refers to the disease syndromes caused by bacteria of the genus Brucella, characterised by epizootic abortions, chronic endometritis, infertility, arthritis, orchitis or chronic infections in domestic animals. In humans the disease is characterised by septicaemia which manifests itself as recurrent fever, and localised chronic infections. Brucella spp. are Gram-negative, coccobacillary, aerobic and facultative intracellular bacteria. There are nine distinct species which include: Brucella abortus (B. abortus), B. melitensis, B. suis, B. canis and B. ovis, B. neotomae, B. microti, B. ceti and B. pinnipedialis (Garritty et al., 2005; Foster et al., 2007; Scholz et al., 2008). Each of these brucellae have preferred natural hosts that include cattle (B. abortus); goats and to a lesser extent sheep (B. melitensis); pigs (B. suis); dogs (B. canis) and sheep (B. ovis) respectively (Quinn et al., 1999). B. ceti and B. pinnipedialis have cetaceans (whales and dolphins) and seals (pinnipeds) respectively, as their preferred natural hosts (Garritty et al., 2005; Foster et al., 2007). B. neotomae that was originally isolated from a desert wood rat (Neotoma lepida) is believed to be non-pathogenic for cattle, sheep, goats and pigs (Garritty et al., 2005), while B. microti has been recently isolated from a vole, Microtus arvalis (Scholz et al., 2008). 2 The most important brucelloses in domestic animals are caused by B. abortus, B. suis and B. melitensis (Blood and Radostits, 1989). Four species, B. abortus, B. suis, B. melitensis and B. canis are associated with systemic disease in humans, and are thus recognized as zoonotic pathogens of public health significance (Quinn et al., 1999). Brucellosis in humans is an occupational disease for shepherds, veterinarians, farmers, abattoir workers and laboratory personnel who handle infected animals and contaminated animal products (Moyer and Holocomb, 2005). In addition, B. abortus and B. melitensis are important food-borne pathogens that may be acquired by consuming raw milk and milk products such as soft cheese (Leclerc et al., 2002; Kuplulu and Sarimehmetoglu, 2004). B. melitensis is the most virulent species for humans and accounts for the majority of cases of human brucellosis (Leclerc et al., 2002). Among the animal brucelloses, bovine brucellosis, caused by B. abortus biovars is the most important disease in many countries around the world due to its economic importance (McDermott and Arimi, 2002; Nicoletti, 1980; Silva et al., 2000; Taleski et al., 2002). The disease is characterised by abortion “storms” in pregnant cattle (Blood and Radostits, 1989) especially in naïve herds that are intensively managed (Bishop et al., 1994) and is thus a major contributor to low calf crop in cattle farming. Occasionally, in cows, there is a decrease in milk yield and low reproductive efficiency due to high incidences of retained placenta (Blood and Radostits, 1989; Walker, 1999). In affected bulls, orchitis and epidydimitis are typical presentations of the disease (Bishop et al., 1994) with subsequent decline in fertility even though libido is retained (Kumi-Diaka et al., 1980). Other causes of economic loss in areas where brucellosis is 3 endemic are due to the direct costs incurred by farmers when trying to control the disease (Nicoletti, 1980). The prevalence and incidence of bovine brucellosis vary considerably between herds, areas and countries (McDermott and Arimi, 2002). The disease has been reported to occur in most countries in Africa (Chukwu, 1985; Faye et al., 2005) including the sub- Saharan region (McDermott and Arimi, 2002). The disease has been reported to be endemic in some farming areas in Zimbabwe (Mohan et al., 1996). Together with bovine genital campylobacteriosis, brucellosis was established to be the most important cause of abortion and infertility in cattle in Zimbabwe during the 1970s (Swanepoel et al., 1975). The disease was originally perceived to be more important in dairy than in beef cattle (Manley, 1969), but was later established to be equally important in both cattle farming sectors (Swanepoel et al., 1976). The prevalence of bovine brucellosis is believed to be low in communal areas due to the extensive nature of cattle rearing although only very few studies have been conducted in this sector (Madsen, 1989). However, the establishment of smallholder dairy schemes in communal areas using cattle purchased from commercial sector (Madsen, 1989), coupled with the subsequent restocking of communal cattle through purchases of commercial cattle has a possible influence on the dynamics of bovine brucellosis in communal areas. It is noteworthy that in most of these communal areas, mixing of cattle from different villages is likely due to sharing of grazing areas, water points and communal dip tanks used for control of ticks and tick borne-diseases. The practice of mixing cattle herds been reported to be an important risk factor for transmission of Brucella spp. (McDermott and Arimi, 2002). 4 Zimbabwe is prone to periodic droughts as a result of ephemeral and erratic rainfall patterns. One of the most severe droughts to affect the country occurred during the 1991/92 season and resulted in increased cattle mortalities in smallholder farms in communal areas mainly due to inadequate grazing pasture, water and livestock diseases. This loss of livestock severely affected these farmers whose livelihood is heavily dependent on cattle farming. Cattle are a vital source of milk, meat, income, drought power for land tillage, transport and manure, in addition to their use in numerous social or cultural roles. Therefore, there is a need to enhance the control of important diseases of cattle that include brucellosis, anthrax, foot and mouth disease (FMD), and tick- borne diseases in order to ultimately improve food security to these resource-limited farmers. Brucellosis, bovine tuberculosis, anthrax and other zoonoses acquired through direct contact with animals or from consuming beef and milk are increasingly becoming diseases of public health concern especially in people who are immuno-compromised by HIV/AIDS, prevalent in the Southern African sub-region. After the drought in 1991/92, the government of Zimbabwe, through the Agricultural Rural and Development Authority (ARDA) and in collaboration with other organizations such as the Heifer Project International and Initiatives for Development of Equity in African Agriculture, assisted the smallholder farmers to restock their herds. This was a drought mitigation measure aimed at ensuring food security to communal farmers. During this period cattle of the Bos taurus breeds (both dairy and beef) were purchased from commercial farms and mixed with the Bos indicus in the communal areas. While some efforts were made to purchase animals only from brucellosis-free herds, it was not always feasible to establish the status of these animals before 5 translocation. This introduction of new animals to naïve herds was envisaged to be an important risk factor for transmission of Brucella spp. (McDermott and Arimi, 2002). Since the last national brucellosis survey was conducted in 1987 (Madsen, 1989), it was imperative that new data be generated to establish the current status of bovine brucellosis in some of the areas that restocked their herds. 1.2 Hypothesis The restocking of cattle herds is a risk factor for brucellosis in smallholder dairy farms in Zimbabwe 6 1.3 Aims and Objectives of the study It was previously stated that the prevalence of brucellosis among cattle herds in communal areas in Zimbabwe is generally low, averaging about 3.0 % (Madsen, 1989). This statement and the figure could not be relied upon because of the continuous stocking and re-stocking of cattle which have great impact on the prevalence of brucellosis. Thus, this project was aimed at investigating the epizootology and diagnostic approaches towards brucellosis in dairy cattle reared in smallholder farms in Zimbabwe. The study was formulated to investigate the following specific objectives: 1.3. 1. To establish the prevalence of antibodies against Brucella spp. in individual cattle from smallholder farming areas; 1.3.2 To identify risk factors for Brucella spp. infection in individual cattle and herds from smallholder farming areas; 1.3.3 To establish the prevalence and risk factors for abortions in dairy cattle from smallholder farming areas; 1.3.4 To evaluate the different serological tests used for the diagnosis of brucellosis under the Zimbabwean conditions; and, 1.3.5 To investigate the smallholder dairy herds by culture and isolation of Brucella spp. 1.3.6 To characterize the Brucella spp from Zimbabwe using biochemical profiles and polymerase chain reaction (PCR) technique 7 CHAPTER II REVIEW OF LITERATURE 2.1 General Brucella spp. are small gram-negative aerobic bacteria that appear as short rods or coccobacilli, measuring 0.6 to 1.5µm x 0.5 to 0.7µm in size (Walker, 1999). They do not produce spores and have no flagella or true capsules (Holt et al., 1994) but instead have a rudimentary capsule-like envelope that has been demonstrated by electron microscopy for B. abortus and B. melitensis (Corbel and Brinley-Morgan, 1984; Walker, 1999). Brucella cultures exist either as smooth, non-smooth variants of smooth cells or non-smooth (rough), but cultures are commonly designated either as smooth or rough on original identification (Corbel and Brinley-Morgan, 1984; Alton et al., 1988). Although the structure of their cell wall is not completely elucidated, gross analyses have indicated in different proportions, the presence of proteins, carbohydrates, lipids, muramic acid and 2-keto-3-deoxyoctulsonic acid between the smooth and non-smooth species (Garritty et al., 2005). The external layer of the outer membrane of the cell wall comprises mainly lipopolysaccharides (LPS) interspersed with a variety of proteins and lipids (Garritty et al., 2005). Like other gram-negative bacteria, dominant surface antigents in both smooth and non-smooth strains are linked to the lipopolysaccharides (Corbel and Brinley-Morgan, 1984; Walker, 1999).
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