The probability of M. bovis transmission is more likely to occur between animals, particularly those in close contact such as herd animals (Grange & Collins 1987). Humans can also be infected by M. bovis from contact with infected animals or animal products and the likelihood of infection and disease, as with human forms of TB are exacerbated by crowding and stress (Figueroa-Munoz & Ramon-Pardo 2008). The transmission of M. bovis between humans or from humans to animals is very rare. Although the occurrence of M. bovis in humans is relatively minor compared to the burden from M. tuberculosis as far as we know, there is concern that the HIV and AIDS pandemic may have magnified this risk.

Transmission of M. bovis at the livestock-wildlife or human-animal interface occurs essentially because of overlap in their territories (Aranaz et al. 2004). Encroachment of wildlife sanctuaries by humans in Tanzania has increased the likelihood of this interaction and infection. Specifically, boundary regions areas in protected areas are used increasingly for grazing of livestock and agriculture and this corresponds with areas where the remaining population of wildlife has been concentrated by this land-use pressure (Etter et al. 2006). Factors as source of infection and transmissions of M. bovis include persistence of M. bovis in infected animals after death and survival of M. bovis in the environment (Aranaz et al. 2004).

It is not only domestic animals that can experience pathology from M. bovis, but a wide range of wild animal species in Africa, including lion (Panthera leo), buffalo (Syncerus caffer), wildebeest (Connochaetes taurinus), kudu (Tragelaphus strepsiceros), bushbuck (Tragelaphus scriptus), topi (Damaliscus lunatus) and a number of others (Cleveland et al. 2005). These animals can be a source of infection for livestock and humans (Aranaz et al. 2004) and in Tanzania, a classic example is the illegal hunting of resident and migratory herbivores in protected areas (Loibooki et al. 2002; Magige et al. 2008; Sinclair & Arcese 1995). The transmission of bovine tuberculosis from wildlife to humans in such cases is by direct contact between infected animals and hunters, either via aerosol contamination when the carcass is opened, through entry of organisms via cuts in the skin or through the alimentary system (Fanning & Edwards 1991; Georghiou et al. 1989; Robinson et al. 1988).

Tuberculosis in man is generally characterised by loss of weight, weakness, poor appetite, http://www.emedicinehealth.com/script/main/art.asp?articlekey=58790 cough, and night sweats. Mycobacterium tuberculosis is the most common cause of human TB, however an unknown proportion of cases occur due to M. bovis (Acha & Szyfres 1987) at least partly because it is impossible to distinguish tuberculosis infection caused by M. bovis from M. tuberculosis from clinical signs alone. Bovine tuberculosis (BTB) is often subclinical; when present, clinical signs are not specifically distinctive and are characterised by weakness, anorexia, emaciation, dyspnoea, enlargement of lymph nodes, and cough, particularly with advanced tuberculosis (OIE 2009). Pathologically, BTB is characterised by the formation of granulomas (tubercles) that are usually yellowish and either caseous, caseo-calcareous or calcified and are sometimes encapsulated (De Lesle et al. 2002). However, in disseminated cases, multiple small granulomas may be found in numerous organs such as female genitalia (http://www.cfsph.iastate.edu). Mycobacterium bovis may present as extra pulmonary tuberculosis often as cervical lymphadenitis (Kleeberg et al. 198`4; Mfinanga et al. 2004). Based on this premise, M. bovis may present either as pulmonary TB (47%) or extrapulmonary cases (53%), whereas M. tuberculosis presents as 82% pulmonary and 18% extrapulmonary cases (Owendidactic.org, n.d.). Currently, M. bovis accounts for only 1% of all human TB in developed countries as compared to 10% in the developing world (Etchechoury et al. 2010). According to a WHO report (2010), there was a significant increase (116.6%) of extrapulmonary cases of TB reported in Tanzania between 1995 and 2009, which is suggestive of an emerging M. bovis epidemic, however, information on the contributions of M. bovis infection to extra pulmonary cases is very limited and it is possible that these extra cases may also be HIV-related (Amanfu 2006). The survey conducted by National Tuberculosis and Leprosy Program, Tanzania (NTLP) in 2009 reported that 20.994 (37.2%) out of 64.417 TB patients in Tanzania were co-infected with HIV. According to the World Bank (2010) report on development indicators, the prevalence of HIV (% of population aged 15−49) in Tanzania is 5.6%.

Tanzania has the third largest domestic stock population in Africa (after Ethiopia and Sudan). According to the Ministry of Livestock Development and Fisheries (MLDF) national census conducted in 2007/2008, the total numbers were 18.5 million cattle, 13.1 million goats, 3.6 million sheep and 53 million poultry. The livestock production system is a pastoral and agro-pastoral system, where movement of animals searching for pasture and water is unrestricted. The presence of large numbers of livestock in traditional settings and where animals are kept in close contact with little veterinary service contributes to spread of disease. Previous studies conducted in pastoral communities in the Arusha region found that a history of TB in the family, drinking raw milk, eating raw animal products, poor ventilation and having poor knowledge concerning transmission of tuberculosis were risk factors for M. bovis infection and disease (Mfinanga et al. 2004).

The diagnosis of TB in cattle in Tanzania is done by tuberculin skin testing (TST), meat inspection in abattoirs and rarely by bacteriological or molecular techniques The commonly used diagnostic test for human TB in primary health centres and hospitals is microscopic examination and culture, and speciation are not done routinely (Mfinanga et al. 2004). Although meat is recommended to be abbatoir-inspected before entering markets, proper meat inspection is not effectively carried out due to the inadequacy of the veterinary service sector as a result of the withdrawal of public veterinary services. In addition, the recommended test and slaughter policy, a disease control program based on slaughter of positive reactors animals, is not properly implemented (see Figure 1) despite our knowledge that this policy has successfully reduced the prevalence of bovine tuberculosis (Michel et al. 2009). It is only Algeria, Burkina Faso, Cameroon, Morocco, Namibia and South Africa out of 48 countries in Africa that apply a test-and slaughter policy as a control measure and consider bovine tuberculosis as a notifiable disease (Cosivi 1998). The lack of public finances are obstacles in the control of bovine tuberculosis in many countries. In Tanzania, lack of clear policies on how bovine tuberculosis can be controlled and the failure of health authorities to recognise M. bovis as cause of tuberculosis hinder the control of the disease (Kazwala et al. 2006).

Few studies have confirmed M. bovis in humans in Tanzania (Kazwala et al. 2001; Mfinanga et al. 2004), however, there is a body of evidence for M. bovis infection in man and a description of the relationships between M. bovis isolates found in humans and cattle. In their study, Kazwala et al. (2001) found that M. bovis isolates from man had a 70% – 80% genetic relatedness to those found in cattle, arguably suggesting an infection and evolutionary relationship between them. Mycobacterium bovis infection in man has also been reported in other countries in Africa including Nigeria, Zaire and Egypt (Cosivi 1998; Idrisu et al. 1977; Idigbe et al. 1986; Nafeh et al. 1992).

This paper aims to review the current situation of M. bovis infection in animals and discuss the zoonotic importance of M. bovis in Tanzania. The paper also highlights the burden of tuberculosis, risk factors for infection, communities’ knowledge on prevention of the disease and challenges to its control in order to safeguard the human and animal population in Tanzania.

Reports from several studies that have been conducted in various districts have reported M. bovis infection in livestock as well as wildlife. The prevalence of presumed M. bovis infection determined by using a single intradermal comparative tuberculin test (SICTT) was 1.7% (n = 181) and 0.4% (n = 259) in Kibaha and Morogoro respectively (Mdegela et al. 2004) (Table 1). Durnez et al. (2009) reported a prevalence of 2.4% (n = 728) M. bovis infection in cattle from 49 herds belonging to extensive and intensive management systems. The prevalence of M. bovis infection reported by this study was in same range as demonstrated previously in the same region by Shirima et al. (2003). According to Kazwala et al. (1996), the highest prevalence of 13.3% M. bovis infection was reported in the Southern Highlands and larger herds of cattle had a higher rate of bovine tuberculosis. The prevalence of M. bovis infection in cattle in other parts of the country are as follows: Shinyanga, Mwanza, Bukoba: 0.2% in intensively managed farms (Jiwa et al. 1997), Rift valley districts (Babati, Hanang, Mbulu and Karatu) 0.93% (Kazwala et al. 2001), Manyara region 0.9% (Cleveland et al. 2007).

The prevalence of M. bovis in cattle has been reported to be higher in intensive systems than in pastoral production systems (Shirima et al. 2003). However, in contrast, Durnez et al. (2009) reported a higher prevalence of bovine tuberculosis in the extensive than in an intensive system. Husbandry practices in the country could contribute to the difference in prevalence of M. bovis infection in extensive and intensive systems. Free movement of animals, overcrowding in communal grazing areas and watering points might contribute to its spread.

A study by Kazwala and colleagues (2006) reported the similarity of M. bovis isolates from different geographical locations, which was attributed to migration of cattle as well as sale to local communities. Uncontrolled movement of cattle together with a decline in service of public sector in the provision of veterinary services impeded disease control programs in Tanzania. The withdrawal of a public veterinary service forced livestock keepers to take the responsibility of treating their own livestock in order to fill this vacuum (ftp.fao.org/docrep/fao).

In Tanzania, M. bovis infections have been confirmed in a number of wildlife species including buffalo (Syncerus caffer), African civet (Civettictis civetta, n = 1), lion (Panthera leo), wildebeest (Connochaetes taurinus), topi (Damaliscus lunatus) and lesser kudu (Tragelaphus imberbis) (Table 2). Of particular note, M. bovis has been recovered from apparently healthy wildebeest that did not show lesions at post-mortem (Cleveland et al. 2005). These reports are not comprehensive surveys and little information is available on the disease status in wildlife. Analysis of serum samples by using Enzyme Immunoassay (EIA) detected M. bovis antibodies in 4% of Serengeti lions, 6% (n = 17) buffalo (Syncerus caffer) in Tarangire and 2% (n = 41) wildebeest in the Serengeti (Cleveland et al. 2005). It is important to note that the WHO recently issued a statement on the unreliability of serology to diagnose TB and these results are thus at best likely to be a significant underestimate and quantitatively inaccurate.

Human tuberculosis due to M. bovis is mostly the result of transmission from cattle to man and in many cases results into extrapulmonary manifestation (Cosivi 1998; Daborn et al., 1997; Kazwala et al. 2001; Mfinanga et al. 2004; Amanfu et al. 2006; Munyeme & Munang’andu 2011). It has been suggested that M. bovis infection in man increases proportionately to the total number of TB cases and that HIV is a major factor for development of active TB disease (Cosivi 1998). In developing countries M. bovis infection in humans is also increasing due to the lack of control and diagnostic measures, and pasteurisation of milk (Etter et al. 2006). Thus there is every reason to be seriously concerned that the HIV pandemic will result in an increase of human tuberculosis due to M. bovis, and a greater degree of transmission of infection to other humans and to animals could well occur. Information on cross transmission of M. bovis infection between livestock, wildlife and man in Tanzania is limited. This situation is similar to that of other developing countries where M. bovis infection in man is almost certainly underreported (Cosivi et al. 1998; Munyeme & Munang’andu 2011) due to the lack of diagnostic facilities to distinguish tuberculosis caused by M. bovis and M. tuberculosis.

In Africa, consumption of raw fresh milk and improperly cooked or raw meat, and the attitude of some communities which regard bushmeat (poached or hunted wildlife) as a cheap source of protein, represents one of the major risk factors for humans with respect to infection with M. bovis (Aranaz et al. 2004; Etter et al. 2006). Kazwala et al (1998) found that out of 805 milk samples that were collected, 31 (3.9%) were positive for mycobacteria. In this study, atypical mycobacteria represented with 87% of the positive samples, however, 6.5% contained M. bovis. Whilst these samples represent a minority of the positives, the results show that raw milk is a threat to public health. Moreover, Durnez et al. (2009) reported a high prevalence of M. bovis and recovered atypical mycobacteria isolates from milk samples in and around Morogoro, Tanzania, and concluded that the populace, especially cattle owners in an extensive system, should be educated concerning bovine tuberculosis. The high level presence of atypical mycobacteria in milk also poses a danger to immunocompromised individuals, especially HIV and AIDS patients.

Mfinanga et al. (2004), in their study in the Arusha region, northern Tanzania, investigated 457 biopsy specimens, of which 65 (14.2%) were positive on culture for mycobacteria. In this study, the proportion of atypical mycobacteria was 31 (47.7%) compared to 7 (10.8%) M. bovis, and 27 (41.5%) M. tuberculosis. They concluded that atypical mycobacteria were more common than M. tuberculosis and therefore HIV and raw milk are major risk factors identified for M. bovis and non-tuberculous mycobacterial adenitis.

The finding that atypical mycobacteria are common was confirmed in a study by Durnez et al. (2011), in Morogoro, Tanzania, where 7.3% of 645 terrestrial small mammals sampled in cattle farms were positive for atypical mycobacteria. A high proportion of the atypical mycobacteria were recovered in insectivores as opposed to rodents. Insectivores feed on insects that spend most of their time in the ground. The recovery of atypical mycobacterium from this source is not surprising perhaps, since mycobacteria are well known environmental and soil dwelling microbes. What is important in this work is that Durnez et al. (2011) established a direct correlation between the proportion of atypical mycobacterium in reacting and non-reacting tuberculin farms, complicating the interpretation of tuberculin skin testing (TST) results.

Mycobacterium bovis is one of the well-known causative agents of human extra-pulmonary tuberculosis. This situation prevails in Tanzania, where an early study (Daborn et al. 1997), showed that seven out of nineteen lymph node biopsies from suspected extra-pulmonary tuberculosis patients were infected with M. tuberculosis and four with M. bovis. In most developing countries, the extent of human tuberculosis due to M. bovis and the frequency of M. bovis extra-pulmonary tuberculosis is not known (Chen et al. 2009; Cosivi 1998). However, between 1995 and 2009, the number of reported extra-pulmonary TB cases increased from 6195 to 13 417 in Tanzania (WHO 2010, see Table 3), which is in all likelihood an underestimate (Kazwala et al. 2001). The available literature shows that M. bovis infections are correlated with people who keep large numbers of cattle (Kazwala 1996) and most cases of extra-pulmonary TB were found in regions with a high proportion of cattle to humans (Kazwala et al. 1993). A WHO (2006) zoonotic survey reported the following extr-apulmonary cases in several regions with a high population of cattle in Tanzania; Arusha (30%), Mbeya (28.1%), Iringa (27.3%), Shinyanga (19.8%), Mara (19.7%), Dodoma (19.4%) and Mwanza region (10.8%). A study conducted by Mfinanga et al. (2004) found that a disproportionately high number of mycobacterial adenitis was found in subsistence farmers and livestock keepers in Arusha and Mbeya region which is suggestive of cross transmission of M. bovis.

A high proportion of cattle are kept in traditional settings in rural areas where knowledge regarding M. bovis infection is generally minimal (Mfinanga et al. 2004). According to Pušić et al. (2008), the persistence of bovine tuberculosis is mostly linked to the traditional extensive breeding system and free-ranging cattle.

Mycobacterium bovis is resistant to pyrazinamide, one of the four first line TB antibiotics and prognosis is often poor (WHO 2010). Given this scenario, it is not surprising that multidrug-resistant strains (MDR) of M. bovis have been detected in the USA (Bouvet et al. 1993) and Spain (Guerrero et al. 1997; Rivero et al. 2001).

A study conducted in Tanzania reported genetic relatedness of M. bovis isolates in man to those found in cattle (Kazwala et al. 2006). These authors found one strain of M. bovis from a human patient in Arusha region that had the same genotype as M. bovis from cattle within the same geographical area.

Consumption of raw fresh milk is also a risk factor for bovine tuberculosis. Mdegella et al (2004) and colleagues in their study in Morogoro and Kibaha districts concluded that despite the low prevalence of tuberculosis in milk in the study herds, milk consumers are at high risk of being infected with the disease and insisted that farmers should be educated about the risk of bovine tuberculosis and associated health risks. Mfinanga et al. (2003) in their study on the role of livestock keeping in tuberculosis trends in pastoral communities in Babati, Hanang, Mbulu and Karatu districts in the Arusha region, found that all ethnic groups possessed habits and beliefs that increased the risk of being infected with both bovine and human tuberculosis.

In their study, Mdegella et al. (2004) found that 14% of milk samples (n = 109) were positive for atypical mycobacteria. In addition, Mfinanga et al. (2004) found that several activities, including handling animals and animal products, specifically milking, herding cattle and goats, hunting, slaughtering, handling skins and hides, moving cow dung and plastering walls with dung or mud, might increase risk of zoonotic tuberculosis.

A single comparative intradermal tuberculin test (SCITT) survey conducted in different farming systems in the eastern zone of Tanzania found that bovine tuberculosis occurred both in intensive and pastoral farming systems, with significantly higher prevalence in the intensive system than in pastoral systems (Shirima et al. 2003). This could be attributed to husbandry practices in especially dairy cattle that are confined indoors, where close contact between animals and lack of ventilation increase chances of disease transmission. However, this is contrary to results presented by Durnez et al. (2009) in a more recent study, who showed that M. bovis infection in extensive farming systems was higher than intensive systems. The contradiction of infection rate in different farming systems could be explained by considering the management practices of each farming practice, or that systems have changed over time. In the extensive system, free movement of cattle which share grazing land and watering points facilitate disease transmission. Poor animal housing and drainage systems designs in intensive farm systems and water supply are key elements that could play a big role in diseases transmission (Pool 1945).

Extensive husbandry practices are widespread and cattle move from one place to another searching for grazing and watering points. This situation is exacerbated during drought, when nomadic tribes move and establish temporary settlements in areas where grazing land and water are available. Bovine tuberculosis could be eradicated at the national level if attention is given at policy level. According to Collins (2006), the success of a national eradication programme, include a clear identification of the goals, of the policies that guide actions and of the sequences of actions that are required within the programme to accomplish these goals. Eradication is possible if movement of cattle is controlled, if there is compulsory testing of all cattle within specified intervals, if positive reactors are removed (slaughtered in a controlled manner), if compensation is provided to farmers for all positive reactors, if compulsory identification is done, and if there is establishment and maintenance of disease free areas, and sufficient funds and manpower to fulfil the task are provided (http://www.pathobiologics.org/ivphc/ref/MCCRINDLE_SHANGAI_2006.pdf). However, this has been impossible for most developing countries because of cost implications. In The Netherlands and Australia, eradication of bovine tuberculosis was successfully achieved due to the practical involvement of farmers as stakeholders (Collins 2006). However, the success of bovine tuberculosis eradication programmes in developed countries was achieved at a time when herds were smaller, and the intensity and demands of production were lower (Collins 2006).

The presence of maintenance hosts in wildlife populations also impede bovine tuberculosis eradication programs (Etter et al. 2006). White et al. (2008) reported that the presence of multiple hosts for bovine tuberculosis complicate control measures not only because of resistance variation between the different host species but also because of ecological and behavioural differences. The African buffalo is a known maintenance host of bovine tuberculosis. Aerosol transmission of M. bovis within buffalo herds is favoured by their social behaviour (Michel et al. 2006) and can be transferred to domestic cattle by intermingling. Globally, the presence of wildlife maintenance hosts threatens M. bovis eradication programs (Etter et al. 2006). In Tanzania, the National policy on control of wildlife diseases in protected areas is to leave nature to take its own course. There are very few circumstances where treatment or intervention occurs or is allowed. Wildlife immunisation is not allowed in National Parks, Game Reserves and Game Controlled Areas. In circumstances where bovine tuberculosis control in wildlife is not practised and communities around protected area conduct illegal bush hunting in wildlife areas, the risk for cross-transmission of diseases to livestock and humans remain very high.

According to Cross and Gertz (2006) vaccination could potentially control bovine tuberculosis, but combining vaccination and culling of infected animals is a more attractive management option. This is perhaps of little importance for TB control at this stage, since there is no evidence that vaccination against TB would be successful, even if attempted. Furthermore, vaccination of cattle against bovine tuberculosis or improvement in tuberculosis testing procedures will have no effect on wildlife tuberculosis prevalence (Kao et al. 1997). In Britain, culling of a maintenance host of bovine tuberculosis, the badgers (Meles meles), increased the prevalence of bovine tuberculosis in the cattle population because of ecological and social disturbances of the badger populations (White et al. 2008). Thus, the reduction of transmission risk between species is not a simple matter.

However, a reduction of or minimising contact between wildlife and livestock could serve as a priority for future management of the disease in Tanzania. Collins and Grange (1983) reported that ‘it is axiomatic that no control measures against transmissible diseases can be totally effective unless all reservoirs of the causative agent can be eliminated’. As in other parts of the world, the challenge facing the control of tuberculosis is the lack of an effective vaccine. The current TB vaccine, M. bovis Bacille Calmette-Guérin (BCG) provides little or no protection against pulmonary tuberculosis in cattle and man (Hogartha et al. 2005). Nevertheless, bovine tuberculosis could be controlled if there are sound control measures such as regular skin testing and removal of reactors, meat inspection in abattoirs, restriction of cattle movements (Pušić et al. 2008).

The authors would like to thank the Southern African Centre for Infectious Diseases Surveillance (SACIDS) funded by the Welcome Trust for support. Prof Mark Rweyemamu, The Director SACIDS is acknowledged for his ideas and encouragement in writing of the manuscript. The SACIDS Collaborative institutions in the United Kingdom (Royal Veterinary College and London School of Hygiene and Tropical Medicine) through London International Development Centre (LIDC) are also acknowledged for their support during a stay in the UK.

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