ReviewImportance of identification and typing of Brucellae from West African cattle: A review
Introduction
In Africa, livestock development is continuously being challenged by several constraints among which are many parasitic, viral and bacterial infectious diseases. Brucellosis is one of the major bacterial infectious diseases, affecting domestic animals in many developing countries (Akakpo and Bornarel, 1987, Corbel, 1997, Wastling et al., 1999, McDermott and Arimi, 2002). In sub-Saharan Africa, bovine brucellosis remains the most widespread form of the disease in livestock (Akakpo and Bornarel, 1987, Corbel, 1997, McDermott and Arimi, 2002, Bronsvoort et al., 2009). It is responsible for considerable economic losses through its negative impacts on livestock production including late term abortion, birth of weak calf, retention of placenta, metritis, infertility, orchitis or epididymitis with or without sterility and hygroma. Brucellosis is caused by slow-growing, small, Gram negative, cocco-bacilli bacteria composing the genus Brucella. These bacteria are facultative intracellular pathogen which can be transmitted to a susceptible host mostly by direct contact, ingestion or via aerosol. When transmission occurs, lymphatic tissues, blood and other tissues and organs of the host are invaded, with a particular tropism for the reproductive tract (Olsen and Tatum, 2010). On the basis of pathogenicity, host preference and phenotypic characteristics, six species of Brucella are commonly listed: Brucella (B.) neotomae (desert rat), B. canis (dogs), B. suis (pigs), B.ovis (rams), B. melitensis (sheep, goats) and B. abortus (cattle) (Osterman and Moriyon, 2006). Besides these six common species of Brucella, some strains were newly reported like B. ceti and B. pinnipediae identified in marine mammals, B. microti in the common vole (Microtus arvalis), in wild red fox (Vulpes vulpes) and in soil and B. inopinata in human (Ewalt et al., 1994, Foster et al., 1996, Clavareau et al., 1998, Scholz et al., 2008, Scholz et al., 2010, Tiller et al., 2010, Banai and Corbel, 2010, Nymo et al., 2011). Based on their cultural morphology, serotyping and biochemical characteristics, these species may be sub-divided into sub-types (also known as biovars, or biotypes) (Alton et al., 1988).
In cattle, the disease is mainly caused by one of the seven biovars of B. abortus (1, 2, 3, 4, 5, 6, and 9) but also occasionally by biovars of B. melitensis and B. suis (Corbel, 2006, OIE, 2009, Fretin et al., 2012). Among species encountered in cattle, B. suis (biovars 1 and 3) and B. melitensis can cause disease in human, with more severe cases related to B. melitensis (Acha and Szyfres, 2003, Corbel, 2006). In addition to these common zoonotic species, newly reported strains of Brucella in marine mammals were also alleged to have a zoonotic potential but further investigations are still needed (Godfroid et al., 2005).
For a better understanding of its epidemiology in cattle, prevalence of brucellosis has been investigated throughout the years in Africa (Akakpo and Bornarel, 1987, Mangen et al., 2002). Besides these investigations, species and biotypes infecting cattle have also been investigated. By providing information on the actual evidence of the presence of the disease-causing agent, identification and typing of strains are relevant in the “one health” perspective. They are also useful for a better knowledge of the disease epidemiology, for managing outbreaks, for identification of appropriate antigens for testing and for setting up efficient preventive and control measures (Crawford et al., 1979, Ica et al., 2008, Saegerman et al., 2010, Godfroid et al., 2010). Since infected animals and particularly infected cattle may be sources of human brucellosis, knowledge on prevailing strains in these hosts may supply information that can be used to assess potential threats for public health at national and/or at regional levels.
The aim of this review was to determine strains of Brucella reported in cattle from West Africa in order to provide a summary of species and biovars reported in that sub-region of Africa, determine geographical distribution of strains, identify samples used for typing and discuss potential implications on public health.
Section snippets
Study area
The area of concern in this review included West African countries. West Africa is one of the four major regions of sub-Saharan Africa. It covers almost one fifth of the geographical area of the whole continent with 5,112,903 km2 and comprised of members of the Economic Community Of West African States (ECOWAS) (Fig. 1). Four main climatic zones are encountered from south to north in this area namely, humid, sub-humid, semi-arid and arid zones (McDermott and Arimi, 2002). West Africa is an
Results
A total of 15 studies reporting results of identification and/or typing of Brucella in cattle were gathered by the literature search (Table 1). Results published by Chambron (1965), were not expressed according to recommendations of the Subcommittee on Taxonomy of Brucella of the International Committee on Systematic Bacteriology on classification of Brucella and were not included in this review. Bale and Kumi-Diaka (1981) erroneously encoded H2S production for two Nigerian isolates among the
Samples and typing methods of Brucella in West Africa
The primary objective of this review was to provide an overview on strains of Brucella reported in cattle in West African epidemiological context through a literature search aiming to be as exhaustive as possible. Data collected through this review were based on both conventional phenotypic and/or genotypic characteristics. Phenotypic identification of Brucella at biovar level using bacteriological methods commonly consisted in a combination of morphological, cultural and biochemical
Conclusion and perspectives
Data on species and biovars of Brucella in cattle remain crucial for a better understanding of the epidemiology of bovine brucellosis in the West African sub-region. This review summarized available published data of decades of typing in cattle since 1960s but cannot be assumed to be exhaustive of strains actually present in 2012 in that region. At least, the proposed summary provided indication of the presence of Brucella sp. and gave a global and updated map of disease-causing agents of
Conflict of interest statement
None of the authors of this paper has a financial or personal relationship with other people or organizations that could inappropriately influence or bias the content of the paper.
Acknowledgements
The authors would like to thank the Institute of Tropical Medicine of Antwerp, the University of Liege (UREAR-ULg) for academic support. We would also like to thank Dr David Shamaki and his colleagues, from National Veterinary Research Institute, Vom, Nigeria and Ms Sylvie Courtault and Marie-Estelle Esnault from Institut de Recherche Agronomique (INRA), Tours, Nouzilly, France for helping us during the literature search.
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