Volume 15, Number 12—December 2009
Mycobacterium bovis and M. tuberculosis in Goats, Nigeria
To the Editor: Documentation of possible tuberculosis (TB) in goats in Nigeria was reported by Ojo (1) on the basis of gross lesions without culture confirmation. Livestock owners in Nigeria normally graze cattle and goats together, and this practice poses a high risk for transmission of bovine TB among these animals (1). This practice is especially a threat to goats in Nigeria because several reports have described bovine TB in cattle in Nigeria (2–5). However, reports of diagnosis of TB in goats in Nigeria are lacking.
Molecular epidemiologic techniques such as deletion typing and spoligotyping have been used to characterize members of the Mycobacterium tuberculosis complex (MTC) and to provide information on transmission of mycobacterial diseases between animals and humans (6). However, because of limited resources and lack of expertise, these techniques are not commonly used in most developing nations such as Nigeria, where TB is endemic (3).
Because slaughterhouses provide excellent opportunities for detecting diseases of economic and public health importance, we investigated the presence of mycobacteria in slaughtered goats with lesions suggestive of TB. The investigation was conducted at the Bodija Municipal Abattoir in Ibadan in southwestern Nigeria over a period of 6 months. Slaughtered goats were obtained from local herds and herds in northern Nigeria. A total of 10,389 male and female goats of 2 breeds (West African Dwarf and Red Sokoto) and 1–2 years of age were slaughtered; 1,387 were inspected for gross lesions of TB.
Of 1,387 animals screened, 62 (4.47%) had lesions suggestive of TB in the liver, lungs, and mesenteric lymph nodes. Five (0.36%) goats were confirmed positive by culture as described (2). Deletion typing (6) with the RD9 deletion was used to distinguish M. tuberculosis from other members of the MTC. Those isolates with a deletion in this region were further investigated with primers specific for RD4. This reaction distinguishes between M. bovis, M. caprae, and other members of the MTC. Spoligotyping was performed as described (7) to type an M. tuberculosis isolate from a goat after identification of this bacterium by deletion typing.
We isolated 4 strains of M. bovis and 1 strain of M. tuberculosis from the goats (Table). Spoligotyping identified the M. tuberculosis isolate as belonging to the East African Indian (EAI)–5 family in the SpolDB4 database. All M. bovis isolates were M. bovis bovis, not M. bovis caprae, according to their deletion typing profile (6). One M. bovis isolate was obtained from a male goat; the 3 remaining M. bovis isolates and the M. tuberculosis isolate were obtained from female goats.
Epidemiologic inferences can be made from the results of our study. First, M. bovis, which is naturally found in cattle, was isolated from 4 slaughtered goats. Although M. bovis caprae was the M. bovis variant most frequently isolated from goats in some areas (8), in our study, only M. bovis bovis was isolated. This finding is consistent with results reported by Crawshaw et al. (9), and suggests transmission from cattle, rather than transmission from the goat reservoir. Second, because the infected goats were adult females, infection may be transmitted to their offspring. Third, M. tuberculosis was isolated from a goat. Its presence in this goat may have been caused by direct transmission from humans because this bacterium may be a natural pathogen of humans.
Transmission caused by close cohabitation of goats and humans with advanced TB may occur, given the endemic nature of TB in humans in Nigeria (10). TB cases caused by EAI strains have been found in humans in southwestern Nigeria (4; S.I. Cadmus et al., unpub. data), a finding that supports zoonotic transmission of this organism from humans to goats. However, different lineages of M. tuberculosis may vary in host range, and EAI genotype strains may be adapted to human and animal hosts. Conversely, human-to-animal transmission of M. tuberculosis has been reported in Nigeria relative to infection in cattle (3,4). Thus, confirmation of TB in goats supports the possibility of risk for TB transmission between humans and animals in Nigeria.
This study should be interpreted in the context of its limitations. Because the sources of the animals were unknown, we could not determine whether the organisms were imported from a neighboring country (3). In addition, we lacked information on the breed and condition of the animals. However, we have identified M. tuberculosis and TB in goats in Nigeria. Additional studies of other slaughterhouses in Nigeria are needed to confirm our results.
We thank the students at the abbatoir for assistance during meat inspection.
This study was supported by the MacArthur Foundation/University of Ibadan, Nigeria.
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Table of Contents – Volume 15, Number 12—December 2009
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Simeon I. Cadmus, Department of Veterinary Public Health and Preventive Medicine, Faculty of Veterinary Medicine, University of Ibadan, Ibadan, Nigeria