Brucellosis is caused by bacteria of the genus Brucella and remains as a major zoonosis world wide. The disease is characterized by abortion, retained placenta and to lesser extent, orchitis and infection of accessory sex glands in males. Brucellosis is not a sustainable disease in humans. The source of human infection always resides in domestic or wild animal reservoirs. The disease is prevalent in the most countries of the world. Although many countries have eradicated Brucella abortus from cattle, in some areas Brucella melitensis has emerged as a major cause of infection in this species as well as in sheep and goats because of much focus on eradication of bovine brucellosis rather the ovine and caprine brucellosis. New Brucella strains or species may emerge and existing Brucella species adapt to changing social, cultural, travel and agricultural environment. Brucella suis is also emerging as an agent of infection in cattle, thus extending its opportunities to infect humans. Marine mammal brucellosis, due to two new proposed Brucella species i.e. B. cetaceae and B. pinnipediae, represents a new zoonotic threat for humans. Pathogenicity is related to production of lipopolysaccharides containing a poly N-formyl perosamine O chain, Cu-Zn superoxide dismutase, erythrulose phosphate dehydrogenase, stress-induced proteins related to intracellular survival and adenine and guanine monophosphate inhibitors of phagocyte functions. Protective immunity is conferred by antibody to lipopolysaccharide and T-cell-mediated macrophage activation triggered by protein antigens. Diagnosis still centers on isolation of the organism and serologic test results, especially enzyme immunoassay. Species and biovars should be identified by phage lysis, and by cultural, biochemical and serological criteria. Polymerase chain reaction (PCR) can provide both a complementary and biotyping method based on specific genomic sequences.
Brucellosis is caused by members of genus Brucella. These are small, non-motile, aerobic, facultative intracellular, gram-negative coccobacilli that can infect many species of animals and man. Six species are recognized within the genus Brucella: Brucella abortus, Brucella melitensis, Brucella suis, Brucella ovis, Brucella canis, and Brucella neotomae (Alton et al., 1988: Corbel et al., 1920). This classification is mainly based on the difference in host preference and in pathogenicity. Distinction between species and biovars is currently performed by differential laboratory tests ((Alton et al., 1988: Corbel et al., 1920). Although it has been proposed that the Brucella species should be grouped as biovars of a single species based on DNA-DNA hybridization studies (Verger et al., 1985) and on the comparison of the genome of B. melitensis (DelVecchio et al., 2002) and B. suis (Paulsen et al., 2002), the current classification of Brucellae in species, according to differences in host preference and in pathogenicity should be preferred (Cloeckaert et al., 2001: Moreno et al., 2002). The main pathogenic species worldwide for domestic animals are B. abortus, responsible for bovine brucellosis; B. melitensis, the main etiologic agent of small ruminant brucellosis; and B. suis responsible for swine brucellosis. These three Brucella species may cause abortion in their hosts and because of the presence of brucellosis in a herd/flock of a region or a country results in imposition of international veterinary regulations on animal movements and trade, which result in huge economic losses (Crawford, 1990: Anonymous, 2003). B. ovis and B. canis are responsible for ram epididymitis and canine brucellosis respectively. For B. neotomae only strains isolated from desert rats have been reported. Brucella strains have also been isolated from a great variety of wildlife species such as bison (Bison bison), elk (Cervus elaphus), feral swine and wild boar (Sus scrofa), fox (Vulpes vulpes), hare (Lepus capensis), African buffalo (Syncerus caffer), reindeer (Rangifer tarandus tarandus), caribou (Rangifer tarandus groenlandicus), chamois (Rupicapra rubicapra) and ibex (Capra ibex) and wildlife has to be considered as a reservoir for zoonotic brucellosis (Rhyan, 2000: Godfroid,2002). The broad spectrum of Brucella isolates has recently been enlarged to marine mammals. A number of recent reports describe the isolation and characterization of Brucella strains from a wide variety of marine mammals (Foster et al., 2002). Though it has been eradicated in many developed countries in Europe, Australia, Canada, Israel, Japan and New Zealand (Geering et al., 1995), still it remains an uncontrolled problem in regions of high endemicity such as the Africa, Mediterranean, Middle East, parts of Asia and Latin America (Refai, 2002). From public health view point, brucellosis is considered to be an occupational disease that mainly affects slaughter-house workers, butchers and veterinarians. Transmission typically occurs through contact with infected animals or materials with skin abrasions. Symptoms in human brucellosis can be highly variable, ranging from non–specific, flu-like symptoms (acute form) to undulant fever, arthritis, orchitis and epididymitis (Plummet et al., 1998). The Brucella may enter the body through digestive tract, lungs or mucosal layers and intact skin. Then it may spread through blood and the lymphatic system to any other organ where it infects the tissues and causes localized infection (Lapaque et al., 2005). The organism is able to escape phagocytic killing through inhibiting the phagosome-lysosome fusion and reproducing inside macrophages (Young, 2005). After a variable incubation period ranging from less than one week to several months, non-specific systemic symptoms such as fever, headache, malaise, night sweats and arthralgia follows, resembling flu like disease. During the early stage of the disease, patients are frequently bacterimic that has a continuous pattern, making circulating Brucella easily detectable by blood culture. Once in the blood stream, the organism is seeded to multiple organs/systems, especially those rich in reticuloendothelial tissue, such as liver, spleen, skeletal and hematopoietic system (Greenfield et al., 2002). There are so many factors that can affect the prevalence of brucellosis in various species of livestock. Prevalence of brucellosis can vary according to climatic conditions, geography, species, sex, age and diagnostic tests applied.
Several synonyms of brucellosis have been known like Malta fever, undulant fever, Rock of Gibraltar fever and Bang’s disease. The disease has very old history, as organisms resembling Brucella had been detected in carbonized cheese from the Roman era. Brucellosis was first recognized as a disease affecting humans on the Island of Malta in the early 20th century. Though its distribution is worldwide, yet brucellosis is more common in countries with poorly standardized animal and public health programme (Capasso, 2002). The Brucella remains a major source of disease in humans and domesticated animals worldwide. Although reported incidence and prevalence of the disease vary widely from country to country, bovine brucellosis caused mainly by B. abortus is still the most widespread form. In humans, ovine/caprine brucellosis caused by B. melitensis, is by far the most important clinically apparent disease. The disease has a limited geographic distribution, but remains a major problem in the Mediterranean region, western Asia, and parts of Africa and Latin America. Recent re-emergence in Malta and Oman indicates the difficulty of eradicating this infection (Garcia carrillo, 1990). Sheep and goats and their products remain the main source of infection, but B. melitensis in cattle has emerged as an important problem in some southern European countries, Israel, Kuwait and Saudi Arabia. B. melitensis infection is particularly problematic because B. abortus vaccines do not protect effectively against B. melitensis infection; the B. melitensis Rev.1. vaccine has not been fully evaluated for use in cattle. Thus, bovine B. melitensis infection is emerging as an increasingly serious public health problem in some countries. A related problem has been noted in Mexico and some South American countries,where B. suis biovar 1 has become established in cattle (Baumgarten, 2002: Luna-Martinez, 2002: Samartino, 2002). Moreover, in some areas of these countries, cattle are now believed to be more important than pigs as a source of B. suis biovar 1 infection for humans, because B. suis biovar 1 is capable of colonizing the bovine udder as B. melitensis does (Corbel, 1997). Variable prevalence of this disease has been reported in sheep and goats. Bio varieties of Brucella vary with respect to geographic region. B. melitensis biovar 1 from Libya, Oman and Israel and Br. melitensis biovar 2 from Turkey and Saudi Arabia have been isolated. Br. melitensis biovar 3 is the most commonly isolated species from animals in Egypt, Jordan, Israel, Tunisia and Turkey (Refai, 2002). Br. abortus biovar 1 in Egypt, biovar 2 in Iran, biovar 3 in Iran and Turkey and biovar 6 in Sudan have been reported (Halling and Boyle, 2002). The routes of infection are multiple i.e, food-borne, occupational or recreational, linked to travel and even to bioterrorism. New Brucella strains or species may emerge and existing Brucella species adapt to changing social, cultural, travel and agricultural environment (Godfroid et al., 2005). The incidence of reactors in newly established cattle farms may be more than 30%, however, the highest rate (72.9%) of infection till now has been reported in the Palestinian Authority (Shuaibi,1999). It is interesting to note that the second highest prevalence (71.42%) of brucellosis has been reported in mules from Egypt (Anonymous, 2007a). Invariably, all domestic animals suffer from this disease. Brucellosis in buffaloes has been reported from Egypt (10.0%) and Pakistan (5.05%). Since cattle are found throughout the world, prevalence of brucellosis (0.85 to 23.3%) in cattle has been reported from a wide range of countries. In camels, brucellosis has been reported from Arabian and African countries (0.0- 17.20%), where the disease also occurs in buffaloes, equines and swine. The countries with the highest incidence of human brucellosis include, Saudi Arabia, Iran, Palestinian Authority, Syria, Jordan and Oman. Bahrain is reported to have no incidence (Refai, 2002). The percent prevalence of bovine brucellosis has been reported to decrease in Ireland and Italy during the year 1999-2000 but there had been a trend towards a significant increase in Azores (Jacques and Kasbohrer, 2002). B. canis can cause disease in humans, although this is rare even in countries where the infection is common in dogs (Ross et al., 1994). Precise information on prevalence is lacking, but B. canis has been recorded in the United States, Mexico, Argentina, Spain, China, Japan, Tunisia, and other countries. The recent isolation of distinctive Brucella strains, tentatively named Brucella maris, from marine animals in the United Kingdom and the United States extends the ecologic range of the genus and, potentially, its scope as a zoonosis (Ross et al., 1994: Ewalt et al., 1994).
The disease can be found in any season of the year. The epidemic peak occurs from February to July and is closely related to the months associated with delivery and abortion in animals (Shang et al., 2002). In humans, prevalence of the disease is high (39.5%) in summer season (Salari et al., 2003). Notifications of human brucellosis, which are mandatory in Italy, reach a peak between April and June. However, considering the standard incubation period of 2-4 weeks and the fact that lamb slaughter is traditionally at a peak during the Easter period, it might be expected that occupational exposure would result in a peak of human cases between March and May. The observed peak between April and June could be related to the production and consumption of fresh cheese, starting just after lamb slaughter (De-Massis et al., 2005).
Sex and Age Wise Prevalence
There are controversial reports regarding the prevalence of brucellosis in relation to sex of animals, as some of the research workers reported significantly higher prevalence in females than in males (Hussein et al., 2005), whereas MacMillan et al. (1982) were of the view that Br. abortus causes intermittent bacterimea in the mares but not in the stallions. The relatively higher incidence reported among human females than males might be due to more involvement of females in handling of livestock. These females may be highly exposed to the risk of infection through direct contact with animals, consumption of raw milk and milk products. Moreover, risky practices in rural areas such as skinning of stillborn lambs and kids, as well as crushing the umbilical cord of newborn lambs and kids with teeth can also be contributing factors (Hussein et al., 2005). However, some reports indicate that Brucella antibody titers are not associated with sex (Muma et al., 2006). The antibody titer against Br. abortus appears to be associated with age, as low prevalence in young stock has been reported than the adults (Ahmed and Munir, 1995b). Kazi et al. (2005) reported higher prevalence of infection in animals more than 4 years of age compared to younger animals. It appears that the high prevalence of brucellosis among older cows might be related to maturity with the advancing age. Thereby, the organism may have propagated to remain either as latent infection or it may cause clinical manifestation of the disease (Kazi et al., 2005). Brucellosis is essentially a disease of the sexually mature animals, the predilection site being the reproductive tract, especially the gravid uterus. Allantoic factors including erythritol, possibly steroid hormones and other substances stimulate the growth of most of the Brucellae (Radolf, 1994). The tropism of Brucella to the male or female reproductive tract was thought to be by erythritol, which stimulates the growth of the organism, but Brucella has also been found in the reproductive tract of animals with no detectable levels of erythritol (Anonymous, 2007b). Erythritol, a sugar alcohol synthesized in the ungulate placenta and stimulates the growth of virulent strains of Br. abortus, has been credited with the preferential localization of this bacterium within the placenta of ruminants (Smith et al., 1962).
Test Based Prevalence
No single serological test is appropriate in all epidemiological situations and all have their limitations especially when it comes to screening individual animals (Nielsen et al., 2006). Consideration should be given to all factors that impact on the relevance of the test method and test results to a specific diagnostic interpretation or application. In epidemiological units where vaccination with smooth Brucella is practised, false-positive reactions may be expected among the vaccinated animals because of antibodies cross-reacting with wild strain infection. The main serological test used for diagnosis of brucellosis is the Rose Bengal Plate Test (RBPT), which has very high (>99%) sensitivity but low specificity (Barroso et al., 2002). As a result, the positive predictive value of this test is low and a positive result is required to be confirmed by some other more specific test like serum agglutination test (SAT) and ELISA. However, the negative predictive value of RBPT is high as it excludes active brucellosis with a high degree of certainty. The SAT is recommended for collection of quantitative information on immune responses. It is the most frequently used confirmatory serological test and has become the standard method for the diagnosis of the brucellosis. The sensitivity and specificity of the SAT test are 95.6 and 100.0%, respectively, while that specificity of the ELISA is 45.6% (Memish et al.,2002). Brucella has also been isolated from a variety of wildlife species such as bison, elk, African buffalo, reindeer, caribou, feral swine, wild boars, foxes and hares (Davis, 1990). Anti-Brucella spp. antibodies were detected by tube agglutination test, ELISA and immunoblotting in 53% serum samples of Pacific bottlenose dolphins (Tursipa aduncus) from the Solomon Islands (Tachibana et al., 2006). Ribeiro et al. (2003) tested fistulus withers secretions from three horses by the plate agglutination test (PAT), SAT, buffered RBPT and 2-mercaptoethanol test (2-MET), and compared the results with standard agglutination test. Titers were higher in the PAT, SAT and 2-MET and positive reaction was observed in RBPT. B. abortus was isolated from the secretion of fistulous withers, collected from one animal. These results suggest that the modified tests may be used as alternative test to diagnose brucellosis in horses with fistulous withers. Ocholi et al. (2004a) isolated Brucella from aborted fetuses, hygroma fluid, milk and vaginal swabs obtained from aborting cattle, sheep, goats, pigs and horses. A total of 25 isolates, obtained mainly from cattle, sheep and horses, were biotyped. All strains belonged to one species, Br. abortus biovar 1. Ocholi et al. (2004b) isolated Br. abortus from a horse which had carpal bursitis. In a subsequent study, Ocholi et al. (2005) examined serum and milk samples from ewes for Brucella, a total of seven isolates of Brucella were obtained from milk samples and vaginal swabs collected from aborting ewes. All isolates were identified and bio-typed as Br. abortus biovar 1.
Mechanisms of Pathogenicity
Virulent Brucella organisms can infect both nonphagocytic and phagocytic cells. The mechanism of invasion of nonphagocytic cells is not clearly established. Cell components specifically promoting cell adhesion and invasion have not been characterized and attempts to detect invasin genes homologous to those of enterobacteria have failed. Within nonphagocytic cells, Brucellae tend to localize in the rough endoplasmic reticulum. In polymorphonuclear or mononuclear phagocytic cells, they use a number of mechanisms for avoiding or suppressing bactericidal responses. The S-LPS probably plays a substantial role in intracellular survival, as smooth organisms survive much more effectively than non-smooth ones. Compared with enterobacterial LPS, S-LPS has many unusual properties: a relatively low toxicity for endotoxin sensitive mice, rabbits and chick embryos; low toxicity for macrophages; low pyrogenicity and low hypoferremia-inducing activity. It is also a relatively poor inducer of interferon (and tumor necrosis factor) but, paradoxically is an effective inducer of interleukin 12 (Zhan and Cheers, 1995: Caron et al., 1994). S-LPS is the main antigen responsible for containing protection against infection in passive transfer experiments with monoclonal and polyclonal antibodies. The protection is usually short term and incomplete, however, the elimination of virulent Brucella depends on activated macrophages and hence requires development of Th1 type cell-mediated responses to protein antigens (Dubray, 1987). An important determinant of virulence is the production of adenine and guanine monophosphate, which inhibit phagolysosome fusion, degranulation and activation of the myeloperoxidase- halide system and production of tumor necrosis factor (Caron et al., 1994). The production of these inhibitors is prevented in pur E mutants, which are substantially attenuated in consequence. Cu-Zn superoxide dismutase is believed to play a significant role in the early phase of intracellular infection (Bricker et al., 1990). However, conflicting results have been reported and this role needs to be confirmed. Survival within macrophages is associated with the synthesis of proteins of molecular weight 17, 24, 28, 60 and 62 kDa. The 62 kDa protein corresponds to the Gro EL homologue Hsp 62, and the 60 kDa protein is an acid-induced variant of this. The 24 kDa protein is also acid induced, and its production correlates with bacterial survival under acidic conditions (<pH4). The 17 and 28 kDa proteins are apparently specifically induced by macrophages and correlated with intracellular survival (Lin and Ficht, 1995). Another stress-induced protein, HtrA, is involved in the induction of an early granulomatous response to B. abortus in mice and is associated with a reduction in the levels of infection during the early phase. Howevr, it does not prevent a subsequent increase in bacterial numbers and htrA-deficient mutants ultimately produce levels of splenic infection similar to those given by wild-type B. abortus (Tatum et al., 1994). Similarly, recA-deleted mutants produce a lower initial spleen count than recA-positive strains but still establish persistent infection (Tatum et al., 1993). The role of iron-sequestering proteins or other siderophores in the pathogenesis of brucellosis is still unknown. In general, the low availability of iron in vivo restricts microbial growth. However, high iron concentrations promote the killing of Brucella, probably by favoring production of hydroxylamine and hydroxyl radical. The mechanisms of pathogenesis of Brucella infection in its natural host species and in humans are still not completely understood, and further studies are needed.
Bioterrorism and its potential for mass destruction have been subjects of increasing international concern. Production costs of biological weapons are low and aerosol dispersal equipment from commercial sources can be adapted for biological weapon dissemination. As far as brucellosis is concerned, inhalation of only a few organisms is sufficient to cause a significant likelihood of infection. In a theoretical model of a bioterrorist attack and in the absence of an intervention program for 100000 persons exposed, a B. melitensis cloud would result in 82,500 cases of brucellosis requiring extended therapy, with 413 deaths (Kaufmann et al., 1997). The economic impact of such a brucellosis bioterrorist attack would cost $ 477.7 million per 100 000 persons exposed (Kaufmann et al., 1997). The severity of this disease, lack of vaccines suitable for use in man and frequent failure of clinical laboratories to correctly identify isolates led to the investigation of Brucella as an agent for bioterrorism. Before 1954, when Britain was focusing on anthrax, brucellosis was the first microorganism chosen by the United States to develop as a weapon. This microorganism could be effectively disseminated in four pound bombs (Yagupsky and Baron, 2005). Indeed, the American military weaponized B. suis in 1954, however, changing global politics resulted in abandonment of these efforts following the biological and toxic weapons convention in 1972. Brucellae are not difficult to grow and disperse and transmission to humans may result in prolonged illness and long-term sequelae (Yagupsky and Baron, 2005). Aerosol or food contamination could be the sources of dispersion. This microorganism has the advantage of being debilitating without being fatal. The infective dose for these organisms is very low, if acquired via the inhalation route. It has been estimated that 10-100 organisms are sufficient to constitute an infectious aerosol dose for humans. Therefore, diagnostic laboratory testing should be integrated with epidemiological investigation when assessing potential covert biological terrorism events to rule out false-positive laboratory findings. In addition, support systems should be established to facilitate early recognition of rare and unusual emerging infectious diseases (CDC, 2000).
The clinical picture in brucellosis can be misleading and cases in which gastrointestinal, respiratory, dermal, or neurologic manifestations predominate are not uncommon (Santini et al., 1994). Because unusual cases with atypical lesions continue to be reported, diagnosis needs to be supported by laboratory tests. Blood culture is still the standard method and is often effective during the acute phase; the lysis concentration method gives the best results. Automated incubation detection methods are effective, but allowance should be made for the relatively slow growth of the organism (Solomon and Jackson, 1992). Presumptive identification is made on the basis of morphologic, cultural and serologic properties. Confirmation requires phage typing, oxidative metabolism or genotyping procedures. Reliance should not be placed on gallery type rapid identification systems as these have misidentified Brucella as Moraxella phenylpyruvica, with serious consequences for laboratory staff (Luzzi et al., 1993).
Brucellosis in animals may be suspected if abortions occur in late pregnancy (usually third trimster) in a herd, particularly in the light of history of past infection or introduction of new animal which usually leads to storm of abortions. A confirmatory diagonosis is made on the basis of isolation of Brucella from abomasal contents of aborted foetus, uterine or vaginal exudates by bacteriological culture and inoculation in guinea pig or mice. In bovines herd survillence tests, such as abortus ring test (ABR), milk ring test (MRT) can be used 3-4 times a year on pooled milk samples to detect most infected herds. Individual animal testing is done by tests like standard tube agglutination tests (STAT), which is most widely used. Simple spot agglutination tests like Card test and Rose Bengal Plate Test (RBPT) employ stained Brucella antigens. Of these RBPT is most popular for screening individual animals. CFT is most realible test with a relative insensitivity to antibodies produced following S-19 vaccination. Supplementary tests include enzyme immune essay (EIA). Another useful variation for EIA is Dot-immunoassay which can be used to screen large number of individual animals. Other promising tests which are currently not in routine use include indirect hemolysis test (IHLT), hemolysis in gel test, radial immune diffusion test and anamnestic test. Use of skin delayed hypersensitivity (SDTH) test in addition to serological test has been suggested to significantlt improve the diagonosis of brucellosis.
In humans diagonosis is based on epidemiological, clinical and laboratory findings. The confirmatory diagonosis can only be made by isolation and identification of the organism from the patient. The most suitable specimen is blood taken during high temperature. However, live biopsy and bone marrow aspirates from iliac crest or sternum can also be processed. In serology, a paired serum sample showing four fold or more rise in antibody titre is indicative of acute brucellosis. The commonly used tests include STAT, 2-mercaptoethanol test (2-MET), Coombs or anti-globulin test (AGT) and CFT. Of these STAT is most commonly used test. Newer tests include ELISA and PCR which appears to be more promising and rapid and sensitive.
Brucellosis in humans can be prevented by eradication of this disease form the animals. The exercise of hygienic precautions to limit exposure to infection through occupational activities and the effective heating of dairy products and other potentially contaminated foods. Vaccination now has only a small role in the prevention of human disease, although in the past, various preparations have been used, including the live attenuated B. abortus strains 19-BA and 104M (used mainly in the former Soviet Union and China), the phenol insoluble peptidoglycan vaccine (formerly available in France) and the polysaccharide protein vaccine (used in Russia). All had limited efficacy (Corbel, 1997) and in the cases of live vaccines, were associated with potentially serious reactogenicity. Subunit vaccines against brucellosis are still of interest. The live vaccines have provoked unacceptable reactions in individuals sensitized by previous exposure to Brucella or if inadvertently administered by subcutaneous rather than percutaneous injection. These will probably require a combination of detoxified lipopolysaccharide- protein conjugate and protein antigens such as the L7/L12 ribosomal proteins presented in an adjuvant or delivery system favoring a Th1 type immune response. pur E mutants of B. melitensis appear safe in animals (Crawford et al., 1996) and may have potential application as human vaccines if their safety and efficacy is confirmed in clinical trials. New vaccines have been evaluated for use in animals, including the B. suis strain 2 live vaccine given either orally or parenterally. This vaccine has proved inferior to the Rev.1. strain for the prevention of B. melitensis infection in sheep and goats and ineffective against B. ovis infection in sheep. B. abortus strain 19 still appears to be as effective as any for the prevention of B. abortus infection in cattle. However, the RB51 strain of B. abortus, an R mutant used as a live vaccine has been licensed in the United States. This does not interfere with diagnostic serologic tests, but in laboratory trials, its efficacy appeared comparable with that of strain 9. Similar rfb mutants of B. melitensis and B. suis are under development for the prevention of ovine/caprine and porcine brucellosis. Substantial progress has been achieved in understanding the molecular basis of the genetics of Brucella and the pathogenesis of the infection. However, further progress is needed, especially in relation to diagnostic procedures and therapy. An effective and safe vaccine against human brucellosis is also some way in the future.
From the above discussion, it can be concluded that brucellosis is one of the world’s major zoonotic problems. Nearly all animal species are susceptible. The disease caused by various Brucella species renders heavy economic losses. Various factors such as climatic conditions, geography, species, sex and age of the host have been reported to affect its prevalence. Brucellosis is not a sustainable disease in humans. The source of human infection always resides in domestic or wild animal reservoirs and the routes of infection are multiple: food-borne, occupational or recreational, linked to travel and even to bioterrorism. B. melitensis is the most important zoonotic agent, followed by B. abortus and B. suis. In regions where human brucellosis is endemic, there is a great need for high-level recognition that animal and human health are inextricably linked and that the veterinary and public health sectors share the common goal of protecting, promoting and improving the health and well being of human populations. To date, no human vaccine exists and the long duration and high cost of treatment of human brucellosis reduce the efficacy of the therapy. Therefore, the development of a human vaccine should be treated as a priority. Due to the lack of vaccine and to the burden associated with the disease management in man, the actual challenge remains to eradicate animal brucellosis. Besides the implementation of sound proficient eradication, surveillance and vigilance programs, the changing nature of the disease due to the changing animal husbandry and farming systems also has to be taken into account. There is a huge reservoir of B. suis biovar 2 in wildlife in Europe: hares and wild boars have been reported to be widely and sustainably infected and spill over to outdoor reared domestic pigs and cattle has occurred. B. suis biovar 2 is peculiar in many aspects. A significant characteristic is that this particular biovar is not an important pathogen for humans, in contrast to B. suis biovars 1, 3 and 4. In the USA, there is a B. abortus reservoir in bison and elk that causes a threat to bovine brucellosis eradication programs (Rhyan et al., 2001). Thus, wildlife should always be carefully monitored in order to prevent the re-emergence of brucellosis from the wildlife reservoir (Rhyan, 2000). B. melitensis has regularly been isolated from cattle in contact with infected sheep and goats in Mediterannean countries and represent a major zoonotic threat (Anonymous, 2003). This challenges the preferred animal host speciation of brucellae. In the context of bioterrorism, it is of crucial importance to be able to discriminate quickly between true brucellosis and other diseases appearing in the differential diagnosis of brucellosis, among which are infections due to cross-reactive bacteria in brucellosis serology, like YO9 (Gourdon et al., 1999). New Brucella strains or species may emerge and existing Brucella spp. adapt to changing social, cultural, travel and agricultural environments. Hence, the global animal and human brucellosis picture will, in essence, always remain incomplete and regular updates are required.
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