Phenotypic characterization of Brucella strains isolated from livestock in Nigeria
Introduction
Brucellae are Gram-negative, facultative intracellular bacteria that can infect many animal species and man (Corbel, 1997, Young, 1995). Brucellosis is recognized as an important zoonotic disease worldwide resulting in heavy economic losses to the livestock industry and posing serious human health hazards (WHO, 1986, Acha and Szyfres, 1980). Six species are recognized within the genus Brucella: Brucella abortus, Brucella melitensis, Brucella suis, Brucella ovis, Brucella canis and Brucella neotomae (Corbel and Morgan, 1984). This classification is based mainly on host specificity and differences in pathogenicity (Alton et al., 1988). The main pathogenic species worldwide are B. abortus, responsible for bovine brucellosis; B. melitensis, the main aetiological agent of ovine and caprine brucellosis and producing the most severe infection in humans; B. suis, responsible for swine brucellosis. B. ovis and B. canis cause ovine epididymitis and canine brucellosis, respectively. The isolation of B. neotomae, the only strain from desert wood rats has been reported (Clavareau et al., 1998). Brucella species and their biotypes are currently distinguished by differential tests based on serotyping, phage typing, dye sensitivity, CO2 requirement, H2S production and metabolic properties (Alton et al., 1988).
Nigeria has a livestock population of 18.4 million cattle, 14.5 million sheep, 25.5 million goats, 6.9 million pigs, 18,000 camels and 0.24 million horses (Anon, 1994). The economic impact and public health significance of uncontrolled incidences of brucellosis in this livestock population will be undoubtedly significant.
The history, epidemiology, prevalence, socio-economic impact, and suggestions for the control of the disease in livestock and human population in the country have been reviewed (Ocholi et al., 1993, Halle and Ajogi, 1997). Brucellosis is an endemic disease in the animal population in Nigeria (Eze, 1985). Studies in various parts of the country indicates that the disease is widespread particularly in ranches, livestock breeding centers and dairy farms where prevalence is ranging between 3.7 and 48.8% (Esuruoso and Hill, 1972, Esuruoso and Van Blake, 1972, Esuroso, 1974, Esuruoso, 1974) and between 0.4 and 26% in the traditional nomadic Fulani herds (Nuru and Dennis, 1975, Eze, 1978; Falade and Shonekan, 1981, Ocholi et al., 1996). All these investigations were based on serological surveys. There are few reports available based on the isolation of Brucella from cattle (Eze, 1978, Bale and Kumi-Diaka, 1981), goats (Falade, 1981), sheep (Okoh, 1980) and horses (Oladosu et al., 1986) but there is no current information to confirm these. Current work on the isolation of brucellae from Nigerian livestock is required in order to elucidate the epidemiology of this disease and to provide information which may be helpful in planning control programme.
The prevailing species and biotypes of Brucella commonly associated with infections among Nigerian livestock have not been established. An important step to this is to undertake widespread isolation of Brucella among the various livestock species in the country.
Reports from the field indicate that abortion is a common feature among livestock in Nigeria but cases are not always subjected to detailed laboratory investigations (Okoh, 1980).
The aim of this study was to isolate Brucella from aborting animals and to undertake the characterization of such isolates by conventional typing methods.
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Collection of samples
Samples of aborted fetuses, milk from cattle, sheep, goats, pigs, dogs and horses from brucellosis positive herds, hygroma fluid from cases of hygroma and vaginal swabs from recently aborting animals or animals that had history of abortion were collected from Plateau, Adamawa, Taraba, Bauchi, Kaduna, Kano, Borno, Sokoto, Nassarawa and Kogi states of Nigeria (Table 1).
Cultural isolation
Culturing of the samples was performed according to the technique described by Alton et al. (1988): Primary isolation of Brucella
Results
A total of 25 strains of Brucella were obtained from 830 culture samples collected. Isolates were obtained from both milk and vaginal swabs from each of the two sheep that aborted. Six isolates were obtained from hygroma fluid, 12 from milk, 2 from aborted fetuses and 5 from vaginal swabs (Table 2).
All the isolates showed the following common characteristics typical of the genus Brucella: Non-motile, Gram-negative cocobacilli, and oxidase and catalase positive. They grew aerobically even on
Discussion
Knowledge and understanding of the prevailing species and biovar of Brucella infecting the livestock is crucial to the necessary steps required for the formulation of policies and strategies for the control of brucellosis in an animal population. This work adds to the knowledge of the epidemiology of brucellosis in Nigeria and may therefore serve that purpose.
Reports from various areas of Nigeria reveals that animal brucellosis is widely distributed in the country. There is a pattern of low,
Acknowledgements
The World Bank-assisted National Agricultural Research Project (NARP) — National Veterinary Research Institute (NVRI) Programme, supported this work. We thank the Director, NVRI for the support. We wish to thank Mrs. J.A. Stack and Mrs. L.L. Perrett of the FAO/WHO Collaborating Centre for Brucellosis Reference and Research, Veterinary Laboratories Agency, Weybridge, UK for supplying the Monospecific antisera and Brucella phages used for typing the Brucella isolates.
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