Molecular Epidemiology of Brucellosis in Egypt, Diagnostic Procedures, Proteomics and Pathogenesis Studies

Wareth, Gamal GND

Brucellosis is a zoonotic disease occurring worldwide in animals as well as in humans leading to huge economic losses. The infection is caused by Gram-negative bacteria of the genus Brucella. The disease is a very common in developing countries, but is often neglected. In Egypt, brucellosis was reported in a scientific report for the first time in 1939. Since then the disease emerged and remained endemic at high levels among ruminants, particularly in newly established large intensive breeding farms. The disease is prevalence nationwide in all farm animal species, in carrier hosts e.g. rats and in the environment. Serological investigations within the national surveillance program give indirect proof for the presence of brucellosis in cattle, buffaloes, sheep, goats and camels. Even though serologic assays for brucellosis are a well-established procedure but most of the corresponding studies still miss scientific standards. B. melitensis bv 3 and B. abortus bv 1 are the predominant isolates in Egypt and have been isolated from farm animals and Nile catfish. The epidemiologic situation of brucellosis in Egypt is complicated and needs clarification (Chapter 1). The disease is characterized by high morbidity but low mortality. However, the disease mainly transmitted via direct contact with infected animals, the most common way of infection is ingestion of contaminated milk or milk products and meat. DNA of B. melitensis was detected in milk samples that collected from apparently healthy animals’ produces milk for human consumption by molecular assays. The shedding of Brucella spp. especially the highly pathogenic species B. melitensis in milk poses an increasing threat to consumers and this is of obvious concern (Chapter 2). In endemic countries like Egypt, transmission of host specific Brucella spp. to nonpreferred hosts may occur due to the mixed rearing of farm animals. The interspecies transmission of B. melitensis from small ruminants to cattle and buffalo was reported. It is worth mentioning that, B. abortus DNA was identified in serum samples collected from aborted ewe and goats by real time PCR. This study is the first record on brucellosis caused by B. abortus in small ruminants in Egypt. Interestingly that, both B. abortus and B .melitensis. DNA was detected in one ovine serum. These results should be taken in consideration during implementation of control measures (Chapter 3). Among the 11 known Brucella spp., B. melitensis is the most virulent one and is the major causes of abortions in small ruminants. It causes also the severe form of human brucellosis. While, B. abortus infectious occurs in cattle preferably among cows. These two species having similar genomes, while are differences in host specificity and display different proteomes. A comprehensive identification of immunodominant proteins of these two species using antibodies present in the serum of naturally infected ruminants provided insight on the mechanism of their infection in different hosts. A number of heat shock proteins, binding proteins, enzymes, and hypothetical proteins were identified using western immunoblotting and MALDI-TOF MS/MS in both B. abortus and B. melitensis. Brucellae appear to express these proteins mainly for their survival in the host system during infection (Chapter 4). Diagnosis of brucellosis is still challenging in animals and humans and is based mainly on serology and isolation of Brucella. All serological tests have limitations concerning specificity and sensitivity. Cross-reactivity with other Gram-negative bacteria and within the species of the genus is the major hindrance for the specific serological diagnosis of brucellosis. The present study suggest a number of new immunogenic protein candidates of B. abortus and B. melitensis that had immunoreactivity against only sera collected from cattles, buffaloes, sheep and goats, respectively. Among of them five proteins, (Dihydrodipicolinate synthase, glyceraldehyde-3-phosphate dehydrogenase, lactate malate dehydrogenase, amino acid ABC transporter substrate-binding proteins, and fumarylacetoacetate hydrolase domaincontaining protein 2) have prominent immunogenic features. They may be cloned, purified and expressed in recombinant form to be used as specific antigen in serodiagnosis of brucellosis in the future. These proteins can be used to replace the classical LPS antigen preparation in Brucella serodiagnosis, will help to specify the causative species and will reduce false positive reactions resulting from cross-reaction with other Gram-negative bacteria (Chapter 5). Brucellae are intracellular stealthy pathogens causing disease in humans and in a wide range of domestic and wild animals. Rapid multiplication and cytoarchitectural damages induced in liver, kidney, lung, spleen, gastrointestinal tract, spinal meninges, yolk sac and chorioallantoic membrane after egg inoculation of B. microti in chicken embryos demonstrated the proliferation and pathogenicity of B. microti. This study provides the first results on the multiplication of the mouse pathogenic B. microti in chicken embryos and describes gross and histopathology associated with the infection. Our results suggest that, even though chicken are no mammals, they are useful tools to study the pathogenesis, pathogen interactions and immunopathology of brucellae (Chapter 6).




Wareth, Gamal: Molecular Epidemiology of Brucellosis in Egypt, Diagnostic Procedures, Proteomics and Pathogenesis Studies. Freie Universität Berlin, Fachbereich Veterinärmedizin 2015.


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