The molecular epidemiology of Mycobacterium bovis infections in Tanzania.

A molecular epidemiological study to determine the zoonotic importance of bovine tuberculosis was carried out in Tanzania. Specimens from human cases of tuberculosis as well as from slaughtered cattle were collected from regions with a high proportion of extrapulmonary tuberculosis. In order to determine the similarity of strains from the two sources, molecular typing techniques, namely RFLP and spoligotyping, were used to determine the genetic profile of the strains involved. The results of pTBN12 typing of M. bovis from cattle and man has shown a rather heterogeneous population of this species spread all over Tanzania, assuming that the present sample is representative. There were 13 different pTBN12 RFLP types encountered. The genetic relatedness between the pTBN12 RFLP patterns indicated a high degree of relatedness (86%) between the dominant pTBN12 genotypes existing in Tanzania. There were 13 different spoligotypes found in this study, whose genetic relatedness was also high (79%). DNA profiles were also confirmed by IS986 RFLP, which revealed that strains have 1-13 copies of IS986. Geographically, there was overlap between pTBN12 RFLP and spoligotypes amongst strains isolated from various parts of Tanzania. The diversity of the RFLP and spoligotype patterns observed in Tanzania probably reflects the extensive internal movements of cattle belonging to pastoralists. The evidence of overlap between DNA fingerprints of M. bovis from cattle and man has once more highlighted a need for synergy of veterinary and medical policies in the control of tuberculosis in Tanzania and probably in other developing countries.

Isolation of Mycobacterium bovis from human cases of cervical adenitis in Tanzania: a cause for concern?

SETTING: Pastoralist communities in the Northern and Southern zones of Tanzania. DESIGN: Observational study. OBJECTIVES: To determine the involvement of Mycobacterium bovis in tuberculosis cases presenting at tuberculosis (TB) clinics in rural areas in these zones. METHODS: A total of 149 tuberculosis cases identified on the bases of clinical manifestation were sampled. Appropriate specimens were cultured on two Löweinstein Jensen slants with respectively glycerol and pyruvate added. Forty-one isolates were cultured and subjected to biochemical typing. RESULTS: Overall, 31 (70.5%) of the mycobacterial isolates recovered from all forms of tuberculosis were identified as M. tuberculosis, seven (16.0%) were identified as M. bovis, and six (13.6%) were other mycobacterial species. There was a significantly higher isolation rate (P < 0.05) of M. bovis among strains recovered from extra-pulmonary (26.8%) than pulmonary tuberculosis samples (4.3%). CONCLUSION: Based on these findings, it is imperative that M. bovis be considered as a pathogen of concern to people living in rural areas of Tanzania. Further work is required to establish a zoonotic link between cattle and the people in these communities who rear them.

Risk factors associated with the occurrence of bovine tuberculosis in cattle in the Southern Highlands of Tanzania.

A study was conducted in the Southern Highlands of Tanzania to determine the prevalence of bovine tuberculosis and the risk factors associated with the occurrence of the disease in cattle of different categories and in different climatic zones. The overall prevalence of the disease was 13.2%, and 51% of the herds tested contained reactor cattle. Assessment of risk factors was based on comparisons of the reactivity of the cattle in the single comparative intradermal tuberculin test (SCITT). Older cattle were more affected by the disease than yearlings and calves (p<0.0001). There were significant differences between male and female cattle (p<0.05) and between cattle with exotic blood compared to indigenous Short Horn Zebu (SHZ) cattle (p<0.05). The castrated bulls, often used for draught power, were more frequently (p<0.01) affected than the entire bulls, mainly used for breeding. Reactivity to tuberculin did not appear to be influenced by the reproductive status of the animal. The reactivity to tuberculin of pregnant cattle was not significantly different from that of the rest of the cows (p>0.05). However, significantly more (14.6%) lactating cattle reacted in the SCITT than did non-lactating cows (12.0%) (p<0.05). There was a highly significant difference (p<0.001) between reactivity in the SCITT among cattle grazing in the hot and dry lower lands (14.0%) and that in those grazing in the cool and wet highlands (8.7%).

Isolation of Mycobacterium species from raw milk of pastoral cattle of the Southern Highlands of Tanzania.

A study to determine the secretion of Mycobacterium spp. in milk from indigenous cattle was carried out in pastoral cattle reared in the Southern Highlands to Tanzania. The study was aimed at elucidating the dangers associated with milk-borne zoonoses in a society where milk is normally consumed raw. Out of 805 milk samples, 31 (3.9%) were positive for mycobacteria. There was a preponderance of atypical mycobacteria (87%) whereas only two isolates (6.5%) were confirmed as M. bovis. Atypical mycobacteria included: M. terrae (n = 7), M. fortuitum (n = 2), M. flavescens (n = 13), M. gordonae (n = 1) and M. smegmatis (n = 4). Although the number of M. bovis positive samples was low, the habit of pooling milk may still pose great public health dangers to milk consumers in this part of the world. Moreover, isolation of atypical mycobacteria should also be considered to be a danger to human health in countries such as Tanzania, where the number of people with lowered immunity due to HIV infection is on the increase.

Zoonotic tuberculosis due to Mycobacterium bovis in developing countries.

The World Health Organization (WHO) estimates that human tuberculosis (TB) incidence and deaths for 1990 to 1999 will be 88 million and 30 million, respectively, with most cases in developing countries. Zoonotic TB (caused by Mycobacterium bovis) is present in animals in most developing countries where surveillance and control activities are often inadequate or unavailable; therefore, many epidemiologic and public health aspects of infection remain largely unknown. We review available information on zoonotic TB in developing countries, analyze risk factors that may play a role in the disease, review recent WHO activities, and recommend actions to assess the magnitude of the problem and control the disease in humans and animals.

The zoonotic importance of Mycobacterium bovis.

The zoonotic importance of Mycobacterium bovis has been the subject of renewed interest in the wake of the increasing incidence of tuberculosis in the human population. This paper considers some of the conditions under which transmission of M. bovis from animals to humans occurs and reviews current information on the global distribution of the disease. The paper highlights the particular threat posed by this zoonotic disease in developing countries and lists the veterinary and human public health measures that need to be adopted if the disease is to be contained. The association of tuberculosis with malnutrition and poverty has long been recognized and the need to address these basic issues are as crucial as specific measures against the disease itself.

Epidemiology of Mycobacterium bovis infection in animals and humans, with particular reference to Africa.

The epidemiology of Mycobacterium bovis infection in animals and humans is described, together with a review of available reports on the distribution and prevalence of this mycobacteriosis in Africa. The significance of these reports is considered, with particular emphasis on the potential zoonotic importance of bovine tuberculosis as a cause for public health concern in Africa. Published data describing tuberculosis in Europe in the 1930s and 1940s show that bovine tuberculosis was considered to be a significant zoonosis: M. bovis was responsible for more than 50% of cervical lymphadenitis cases in children. Despite the paucity of information on M. bovis infection in Africa, there is sufficient evidence to suggest that it is widely distributed and is found at significantly high prevalence in some populations of animals. Some epidemiological conditions for the spread of M. bovis infection between animals and humans are very similar in Africa today to those in Europe in the 1930s, with the added and potent impact of the epidemic of human immunodeficiency virus infection. The public health threat of tuberculosis in Africa requires urgent investigation through collaborative veterinary/medical research programmes.

The epidemiology of Mycobacterium bovis infections in animals and man: a review.

Tuberculosis is primarily a respiratory disease and transmission of infection within and between species is mainly by the airborne route. Mycobacterium bovis, the cause of bovine-type tuberculosis, has an exceptionally wide host range. Susceptible species include cattle, humans, non-human primates, goats, cats dogs, pigs, buffalo, badgers, possums, deer and bison. Many susceptible species, including man, are spillover hosts in which infection is not self-maintaining. In countries where there is transmission of infection from endemically infected wildlife populations to cattle or other farmed animals, eradication is not feasible and control measures must be applied indefinitely. Possible methods of limiting spread of infection from wildlife to cattle including the use of vaccines are outlined. The usefulness of DNA fingerprinting of M. bovis strains as an epidemiological tool and of BCG vaccination of humans and cattle as a control measure are reviewed. The factors determining susceptibility to infection and clinical disease, and the infectiousness of infected hosts and transmission of infection, are detailed. Reports of the epidemiology of M. bovis infections in man and a variety of animal species are reviewed. M. bovis infection was recognised as a major public health problem when this organism was transmitted to man via milk from infected cows. The introduction of pasteurization helped eliminate this problem. Those occupational groups working with M. bovis infected cattle or deer, on the farm or in the slaughter house, are more likely to develop pulmonary disease than alimentary disease. In recent years, tuberculosis in farmed cervidae has become a disease of economic as well as public health importance in several countries. Nowadays, the human immunodeficiency virus (HIV) is associated with a greatly increased risk of overt disease in humans infected with Myobacterium tuberculosis. It is believed this increased risk also occurs in the case of M. bovis infections in humans.

HIV/AIDS and its implications for the control of animal tuberculosis.

The HIV/AIDS pandemic is associated with a number of opportunist mycobacterial infections, principally tuberculosis and disease due to the avian tubercle bacillus, Mycobacterium avium. Tuberculosis occurring early in the course of HIV infection is usually caused by M. tuberculosis. However some cases are due to the bovine tubercle bacillus, M. bovis, which, in turn, is transmissible from man to animals, principally by the aerogenous route although the majority of cases in man are non-pulmonary. These two mycobacterial species may be differentiated by means of a set of simple tests. The quality and quantity of information on the world-wide distribution and prevalence of bovine and human tuberculosis due to M. bovis is not uniform. There is a notable paucity of information from the tropics but available reports suggest that there are significant levels of bovine tuberculosis. If correct, this information has serious public health implications in the light of the current HIV/AIDS epidemic. Urgent investigation is required so that appropriate control measures can be instituted where indicated and possible. The avian tubercle bacillus is a very common opportunistic pathogen in the late stage of AIDS but infection leading to disease is extremely rare in healthy, HIV-negative persons. Because of its widespread environmental distribution, infection by this pathogen cannot be prevented.