Tuberculosis is one of the most important infectious diseases of cattle in Nigeria and Africa. This study aimed at determining the prevalence of tuberculosis, based on post-mortem meat inspection and Zeihl-Neelson Stain in slaughtered cattle. A total of 2207 cattle, consisting 1004 males and 1203 females were examined for gross TB lesions. The overall positives out of 2207 cattle examined were 212 with a prevalence of (9.6%, 95%CI = 6.7-13.8). Based on sex 97(9.7%, 95%CI = 8.2-12.7) males were positives while 115(9.5%, 95%CI = 8.1-12.9) females were positives. The chi-squire (x2) test of significance based on sex shows the difference was not statistically significant at (P<0.05). This study found that breed and age of cattle examined were statistically associated with prevalence of bovine tuberculosis lesions in slaughtered cattle (P<0.05). In conclusion, this study highlight the importance of bovine tuberculosis and it public health implications in cattle in the study area in particular. Measures for control are also suggested.
Bovine tuberculosis, predominantly caused by Mycobacterium bovis infection, is one of the most important infectious diseases of livestock. In Africa, bovine tuberculosis (BTB) has received scant attention, and many countries including Nigeria have no control or eradication policy. It has been estimated (Anon, 1994; Thion 1995; Awar-Ndukum et al., 2005) that nearly 85% of cattle and 82% of the human population in the continent live in areas where the disease is prevalent or only partially controlled. An increased risk of infection for humans exist in these communities due to close contact between people and their livestock and consumption of untreated milk as part of the societies characteristics (Unger et al., 2003) in countries where pasteurization of milk is rare and BTB in cattle is common, 10% to 15% of human TB cases may be caused by M. bovis (Ashford et al., 2001). The current HIV/AIDS epidemic, especially in areas where BTB is prevalent in domestic and wild animals, poses an additional serous public health threat (Cosivi et al., 1995; Daborn et al., 1996; Demelash et al., 2009) as TB is the most frequent opportunistic disease associated with HIV infection (Cosivi et al., 1998).
In Nigeria, BTB is considered an endemic disease, has been reported in many regions (Alhaji, 1976; Ayawale, 1986; Shehu, 1988; Cadmus et al., 2004; Abubakar, 2007) with prevalence ranging from 2.5% to 14%. Despite the documented endemicity of BTB in Nigerian cattle, information on the disease epidemiology in animals and humans is largely scanty. Due to inadequate surveillance system, lack of diagnostic facilities (Abubakar et al., 2012), inadequate financial resources and qualified manpower and lack of prioritization from government, there is no national data on the distribution of bovine tuberculosis. This has made the quantification of economic and public health impact of the disease difficult. Nonetheless, it may not be difficult to project the enormous loses BTB could inflict on the countries livestock economic, given the high prevalence of the disease reported in several places. In a country confronted with challenges of increasing human population, the control of BTB must be given special attention in poverty alleviation through improved livestock productivity. Moreover, with increased incidences of TB/HIVAIDS co-infection in the country and high risk of exposure of the population to zoonotic TB, the documentation of adequate information on BTB in cattle is a prerequisite for intervention strategies. Definitive diagnosis of Mycobacterium bovis infection often requires isolation and identification of the causative agent from tissue specimens (Corner, 1994). Furthermore, several new laboratory procedures have been introduced as an aid in the diagnosis of the infection (Asseged et al., 2004). However, because of technical problems and cost, they have not come into widespread use in veterinary diagnostic laboratories (Cadmus et al., 2006). Therefore, in countries like Nigeria, implementation of detailed necropsy examination of carcasses at slaughter houses continues to be an important step in surveillance of BTB.
The main aim of this study was to describe the magnitude and distribution of gross TB lesions compatible with tuberculosis in slaughtered cattle in Borno State, Nigeria.
The study was performed between 2011 and 2012 in Borno State, Nigeria. The State is located in the arid zone with an area of about 69,436 km2and lies within latitude 10-130N and longitude 12-150E and lies within the savannah region of Nigeria. The area falls in the tropical continental north with dry month of between 4-8month (October to May) followed by a short (4month) rainy season (late June to early October) (Iioeje, 1981). Borno state is located within the North Eastern corner of Nigeria and has boundaries with Chad to the North East, Cameroon to the East and Adamawa to the South West. According to the 2006 census, the population of the state is estimated to be 4,558,668.
A total of 23,351 cattle’s were slaughtered while 2207 were examined for bovine TB lesions between 2011 and 2012 based on judgemental or purposive sampling technique (non-probability/convenience) as described by (Abubakar, 2016). The study was carried out from 10 major abattoirs/slaughter houses that supply meat to the public in Borno state. Epidemiological data such as age, sex, and location of lesion were observed from each carcass. These carcasses were examined visually for changes in colour, (pale yellow or gray) or morphology and then palpated before incision from the surrounding tissues.
The chi-square (x2) was used to calculate the expected values with their appropriate degrees of freedom (df). The calculated chi-squire values were compared with the tabulated chi-squire values to specify the level of significance or association between variables, (P<0.05) regarded as significant. Prevalence with appropriate confident interval was calculated using Minitab version 16 for this study
The result of post-mortem meat inspection conducted in 10 abattoirs/slaughter houses within the study area is presented in (Table 1).
Table 1: Prevalence of BTB in males and females, based on gross TB Lesions in slaughtered cattle in Borno state
|Sex||Cattle Examined||Positive||Negative||Prevalence(95% CI)||(P-Value)|
A total of 23,385 cattle were slaughtered between March 2011 and November 2012 in Borno state, out of which 2207 were examined, 212 were positive with a prevalence of (9.6%; 95%CI = 6.7-13.8). The prevalence of BTB in male and female cattle examined is presented in (Table 1). A total of 2207 cattle, consisting 1004 males and 1203 females were examined for TB lesions. Out of the males examined 97 were positive with a prevalence of (9.7%; 95%CI = 8.2-12.7). On the other hand, out of the females examined 115 were positive with a prevalence of (9.5%; 95%CI = 8.1-12.9). The chi-squire (x2) test of significance in the occurrence of BTB lesions between males and females shows the difference was not statistically significant (P<0.05).The four major breeds of cattle examined for TB lesions in the state were Bunaji (White Fulani), Rahaji (Red Bororo), Wadara and Sokoto Gudali. The prevalence of BTB lesions among the major breed of cattle examined is presented in (Table 2). Out of the 2207 cattle examined 843, 531, 475 and 358 were Bunaji, Rahaji, Wadara, and Sokoto Gudali breeds of cattle respectively.
Table 2: Prevalence of Bovine tuberculosis among breeds of cattle’s, based on gross TB lesions in slaughtered cattle in Borno state
|Breed||Cattle Examined||Positive||Prevalence (95% CI)||(P-Value)|
|Sokoto Gudali||358||32||8.9 (6.1-12.2)|
Out of the Bunaji cattle examined, 73 were found to be positive with a prevalence of (8.7%; 95%CI = 7.1-10.5). For the Rahaji breed examined, 57 were positive with a prevalence of (10.7%; 95%CI = 8.2-13.7). For the Wadara breed examined, 50 were positive with a prevalence of (10.5%; 95%CI = 7.9-12.8) while for the Sokoto Gudali breed examined, 32 were positive with a prevalence of (8.9%; 95%CI = 6.1-12.2). There was a significant differences between the breeds of cattle examined at (P<0.05). The prevalence of BTB lesions among different age groups based on TB lesions in slaughtered cattle is presented in (Table 3).
Table 3: Prevalence of Bovine tuberculosis among different age groups of cattle examined, based on gross TB lesions in slaughtered cattle in Borno state
|Age||Cattle Examined||Positive||Prevalence (95% CI)||(P-Value)|
|>4 – 6yrs||1237||97||7.8 (5.3- 11.4)|
The ages of cattle examined were classified in to three groups (≤4yrs, >4yrs – ≤6yrs and >6yrs). Out of 2207 slaughtered cattle examined at post-mortem meat inspection for BTB lesions, 115, 1237 and 855 were between the ages of ≤4yrs, >4 – ≤6yrs and >6yrs respectively. In the age group of ≤4yrs, 5 were positive giving a prevalence of (4.3%; 95%CI =3.1-7.8), in the group >4 and ≤6yrs 97 were positive with a prevalence of (7.8%; 95%CI = 5.3-11.4) and for those that were over 6yrs, 110 were positive with a prevalence of (12.9%; 95%CI = 9.8-15.2). There was a significant differences between the ages of cattle examined at (P<0.05).
The distribution of TB lesions in different organs of affected cattle shows that the lungs had the highest number of TB lesions with 141(66.5%), followed by lymph nodes with 50(23.6%) while liver, intestines, and spleen were 11(5.2%), 7(3.3%) and 3(1.4%) respectively (Table 4).
Table 4: Distribution of Bovine tuberculosis lesions in different organs of slaughtered cattle in Borno state
|Organs||Location of TB- lesions||Percentage (%)|
The detection of 9.6% prevalence from BTB among slaughtered cattle has serious epidemiological and public health importance. This poses great danger of contracting the disease by the public especially abattoir workers and herdsmen. It further confirms that control measures are either not in place or inadequately applied, because in countries where control of bovine TB is in place, detection of lesions at the abattoir during meat inspection is usually very minimal (Corner, 1990). This finding, also agrees with an earlier suggestion that, abattoir monitoring could be an essential element in the national bovine tuberculosis campaign and the most effective means of detecting residual infection in herds especially in countries that have achieved control of the disease (Corner, 1990). The association between the disease and sex of cattle examined for gross TB lesions was not statistically significant at (P<0.05). This is in agreement with previous studies in Africa and Nigeria (Omer et al., 2001; Teklu et al., 2004; Asseged et al., 2004; Cleaveland et al., 2007; Abubakar et al., 2012).Variation among breed of cattle examined for susceptibility to bovine tuberculosis has been documented (Alhaji, 1976; Kazwala et al., 2001; Ameni et al., 2006) and was supported by our findings that Bunaji breed of cattle was less likely to develop BTB lesions than the other breeds of cattle. We however, suggested that further studies needed to be carried out to elucidate genetic variations in the breeds to tuberculosis resistance within different ecotypes/genotypes of zebu cattle. The preponderance of BTB cases observed in older cattle, as reported in the present study, is in agreement with previous findings (Bonsu et al., 2000; Cleaveland et al., 2007; Abubakar et al., 2012) and may partly explain the importance of longetivity and prolonged exposure to the pathogen, added to the possible reactivation of latent infections in old and stressed animals (Cleaveland et al., 2007). The results from this study showed that 66.5% of the gross lesions that were found to be grossly positive from BTB were from the lungs. This agrees with earlier studies where it was found that 70-90% of TB suspected lesions were found in the lungs and lymph nodes of the head or thoraxic cavity (Lepper, 1973; Neill et al., 1994; Palmer et al., 2002a; Philips, et al., 2003; Abubakr, 2007; Abubakar, 2010). It further suggested that the most common route of transmission was through aerosol (Table 4).
This study underscores some inadequacies and lack of thoroughness among the veterinary staff carrying out meat inspection to detect carcasses with gross tuberculous lesions, implying that large proportion of tuberculosis infected carcasses were passed undetected and meat approved for human consumption. The most probable explanation for the failure of standard meat inspection to correctly detect tuberculous lesions could be the manner of examination (Corner, 1994) and incompetence of meat inspection personnel. Shitaye et al. (2007) argued that post-mortem meat inspection for detection of BTB lesions in particular depended on the work load, time and diligence of the inspector conducting the examination. Furthermore, indiscipline such as coming late to work by meat inspectors and lack of meat inspection training could be other reasons for inefficiency of the service as most of the personnel lacked adequate trainings in the area of meat inspection. However, it was also not uncommon that when veterinary staff inspect meat, condemn and seize infected meat and meat products for disposal, some pathological lesions were missed completely due to lack of unassisted command on the part of the veterinary staff over the rough behaviours of butchers and meat traders. Over time and with repeated meat inspections, butchers acquire ample knowledge about the nature of pathologies that can lead condemnation of meat just from observing the activities of the veterinary staff. Unruly butchers could obstruct inspection of their carcasses or hide gross TB lesions. Similar findings have been reported by Cadmus and Adesokan (2009) and Abubakar et al. (2012), that pathological cases including those due to zoonosis in slaughtered animals were missed due to uncooperative attitudes of butchers in ensuring thorough meat inspection.
Conclusion and Recommendation
From this study, 9.6% prevalence of a sample of 2207 cattle examined for gross TB lesions in Borno state, Nigeria in Sahel part of northern Nigeria were found to be compatible with bovine tuberculosis. Control could only be achieved when all susceptible domestic species are considered together and intergovernmental co-operation is initiated to prevent cross-border spreads. Proper abattoir hygiene, proper post-mortem meat inspection and clean handling of milk and meat before consumption are necessary to prevent infection in humans. However, this study indicates that a widespread and detailed epidemiological study is needed to ascertain the true extent of tuberculosis in Nigerian livestock before initiation of a control program.
The authors acknowledged the contribution of National Bovine TB project in the Department of Veterinary Medicine, Ahmadu Bello University, Zaria, Nigeria and State Government for providing all the logistics used in this study.