First isolation of Mycobacterium tuberculosis from suspected cases of bovine tuberculosis in rural abattoirs in Chad

Abstract

Background

Tuberculosis is a zoonotic disease affecting domestic ruminants, human worldwide and caused by Mycobacterium bovis that belongs to Mycobacterium tuberculosis complex. In Chad, tuberculosis caused by Mycobacterium bovis was previously isolated from both suspected patients and domestic ruminant carcass.

Objectives

The objective of our study is to assess the multispecies feature of causative agents of tuberculosis infection in domestic ruminants destined to human consumption.

Methods

In 2012, a cross-sectional study was conducted in 7 abattoirs in southern Chad. Bacteriology and molecular typing were performed on collected lesions.

Results

Samples were taken on suspected lesions carcass from local cattle breeds as 234 Arabic, 91 Fulani, 1 Bogolodje and 1 cross breeds. Among them, 25 were defined as “total seizures” and 302 others as “partial seizures”. These lesions were majority within the age group from 3 to 12 years old. Mainly Mycobacterium bovis strains were isolated from 42 suspected bovine carcasses. Mycobacterium tuberculosis strain was isolated from a female Fulani 6 years old. However, 112 of these carcass were males and 215 females and sex has significant influence on tuberculosis infection in cattle (p = 0, 04, OR = 1, 7 IC OR 95%: 1,039 − 3,089). Thus, females were twice as likely to be at risk as males and ten (3%) suspected cattle carcass were due to Non Tuberculosis Mycobacteria infection.

Conclusion

As previously show by other studies performed in Chad, causatives agents of lesions suspected in abattoir as tuberculosis lesions are usually diverse. However, M.bovis was confirmed in bovine carcass but M.tuberculosis was also isolated.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11250-026-04949-3.

Introduction

Tuberculosis (TB) is a chronic disease in animal and is mainly caused by Mycobacterium bovis (M.bovis) which is a member of M.tuberculosis complex. The disease affects domestic animals and wildlife, then could be transmitted to human or vice versa (Boukary et al. 2011). Bovine tuberculosis is the cause of large economic losses in the livestock, precisely in countries under development like Chad. Cattle could be also infected or be receptive to Non-Tuberculosis Mycobacteria (NTM) such as M.avium which is responsible of a benign and curable respiratory infection in human population (Ngandolo Bongo Nare Richard et al. 2021). In animals, such infection could be leads to lesions erroneously defined as tuberculosis lesions in slaughterhouses. However, tuberculosis is not curable in animal and the only solution in farms, is to detect periodically infected cattle using standard skin test followed by farms sanitation as it’s done in developed countries in order to limit the disease spreading from one area to another. In Africa which farming system is mostly based on transhumance characterized by a seasonal mobility of animals as main strategy for grazing and watering, national and cross-border animal disease surveillance is not feasible and chronic animal disease as bovine tuberculosis could be for a long time endemic in farms in which usually old females were retained for dairy purpose and consequently are the most infected (Ngandolo et al. 2009). In case of dairy production fall, these animals are usually sold for slaughter purpose and their carcasses or offal can be detected as “partial” or “total” seizures in abattoirs causing an important economic loss. Therefore, TB has a negative impact on national economy and population’s health in Sub-Saharan countries (Mohamed 2020).

In Chad, microbiological studies related to TB biology were performed since 2000 and had highlighted the presence of M.bovis strains in cattle. However, suspicion of TB in cattle is often reported and M. bovis strains were isolated from bovine carcass. Otherwise, until now, no national plan or strategy including testing lived animals using standard skin test, followed by systematic farms sanitation and slaughter of infected cattle in order to control the disease spread in both human and animal population was not yet established (Diguimbaye Colette 2004, Ngandolo et al. 2009). In contrast, nowadays, in developed countries, M. bovis is mostly eliminated due to effectiveness of control measures. However, because of the existence of some wildlife animals which are acting as reservoirs for bovine tuberculosis, M. bovis continue to circulate from one farm to another (Gamatie et al. 2011). The persistence of M. bovis infection in European farms had suggested the hypothesis of the foreign origin of the disease and had urged the emergency of the molecular M. bovis mapping in the world. Thus, three important clonal strains were mapped during the two first decades of the 2000s as African 1 (Borna Müller et al. 2009), African 2 (Berg Stefan, Garcia-pelayo and Müller 2011) and European 1 (Smith Noel et al. 2011).The African 1 clonal strain was firstly described and is dominant in Mali, Cameroon, Chad and Nigeria, then the African 2 clonal strain was specific to Ouganda, Burundi, Tanzania and Ethiopia; showing a natural regional mapping of the two strains in Africa between West, Central and East parts of the continent. The European 1 clonal strain which is widely spread in New Zealand, Corea, Algeria, and South Africa, was suspected to be introduced in Africa during the colonial period (Smith Noel et al. 2011). At the continent level, the movement of animal from one country to another due to the seasonal transhumance could be one of the causes of the spreading of each clonal strain to bordering countries as is the case in Cameroon, Chad and Nigeria when addressing to the African 1 clonal strain. Those three countries are sharing the same grazing and watering area around Lake Chad and epidemiologically have to be the same in terms of animal diseases epidemiology feature.

However, Chad is an agro pastoral country with an important livestock estimated livestock to 94 million animals (Republique du Tchad 2015), the national animal diseases surveillance system is now facing many issues related to the lack of qualified human resources on the field and in the national laboratory in charge of animal diseases diagnostic. The present study which was performed by the Institut de Recherche en Elevage pour le Développement (IRED), the national laboratory in charge of animal diseases diagnostic in Chad, aims to demonstrate the multi species feature of causative agents of tuberculosis infection in domestic ruminants destined to human consumption in addition to what have been done so far in order to perceive a clear overview on the zoonotic disease epidemiology within this group of animals.

Materials and methods

Sample size

Our sample size was estimated based on the previous tuberculosis prevalence in cattle provided by (Ngandolo et al. 2009) in southern Chad. Thus, the estimated sample size for the present study was fixed at 320 when the prevalence of 14% of bovine tuberculosis suspicion at a slaughterhouse was considered and the Confidence Level of 99% was fixed using the online OpenEpi Software Version 3. However, the availability of the carcass and offal to be inspected depended on many factors such as the demand and supply in terms of need for meat from livestock in the surveyed cities during our data collection period. During the collection period all suspected cases on organs were collected.

Study sites

From June to September 2012, a cross sectional study was conducted, then epidemiological data and biological samples were collected in the frame of the health surveillance of meat and offal intended for the human consumption in seven (07) slaughterhouses based in southern Chad. Specially, these data and samples lesions were from carcass and offal suspected as infected by TB in Guelendeng, Bongor, Kelo, Moundou, Doba, Koumra and Sarh (See Map at last page of the manuscript with different cities, Fig. 1). Abattoirs located in these cities are often named as “slaughter areas” because of their non-formal structures and are based between 150 Km and 752 Km from N’Djamena the capital city where is located the national veterinary laboratory at the Institut de Recherche en Elevage pour le Developpement (IRED).

Fig. 1.

Study site differents cities. (source Ngandolo et al. 2021)

Networking and sampling process

A data collection network was established including partners from communities such as private motorcycles taxi association based in each city and inter urban bus agencies as a channel for transportation of samples from field to N’Djamena. Thus, each partner involved in the network was first trained on basic knowledge related to management and transportation of infectious materials according to the IATA good practices. In order to maintain the collected samples at + 4 °C before their transportation to IRED, workers in abattoir had closely collaborated with local staff from district hospitals which are well equipped in terms of cold chain to keep cool the collected samples before their transportation to IRED.

Ante and post mortem processing

On arrival at the abattoirs, socio-demographic data such as “sex”, “age” and “breeds” were recorded from each animal destined to be slaughtered by a veterinarian. However, Ante mortem inspection consisted to visually appreciate the lived animal overweight (as bad, average and good), the level of hypertrophy of the inguinal and prescapillary lymph nodes (normal, hypertrophied, very hypertrophied) and the animal breathing rate. These parameters collected on lived animals had guided to detect typical tuberculosis lesions on carcass and offal during post mortem inspection sessions in accordance with the guide of good practices of inspection of red meats established by the Ministry in charge of livestock and Animal Production in Chad (Republique, 2011). Thus, during the post mortem diagnostic sessions, all granulomatous lesions on liver, lung, ganglion were collected in sterile flacons and stored at + 4 °C in a cooler, then sent to district hospitals before their transportation to IRED in N’Djamena for laboratory processing.

Laboratory processing

Bacteriology diagnosis was performed as described by (Diguimbaye Colette 2004). Thus, collected samples were decontaminated and sowed on specific Middle brook broth 7H9 medium is a liquid medium containing pyruvate or glycerol. For each sample, 0.5 ml were sowed on medium and stored at 37 °C in an incubator for eight weeks. Cultures were check for growth of mycobacteria each week, and then in case of culture turbidity, smear was made up and coloured using Zhiel nelson method. The coloured smears were observed at microscopy under oil immersion at objective 100 for Fast Acid Bacilli (AFB) identification AFB are colored in red while the background stains blue, this technique is used for detection of AFB during microscopy. A specimen of 1.5 ml of all positive cultures were inactivated using heat killing block machine in order to inactivate the mycobacteria and obtain DNA that will be used for further molecular typing. Thus, Genus typing method was used for typing mycobacteria from Mycobacterium gender and members of the Mycobacterium tuberculosis complex, then RD4 and RD9 Deletion typing methods, respectively for the characterization of Mycobacterium bovis and Mycobacterium tuberculosis species as described in the protocol (Berg 2008). To characterize the genus and Mycobacterium tuberculosis complex species, six differents primers were used and the specific gene for genus 16 S rRNA was targeted with two primers. These primers are: (These primers were used in our previous study done in the same site in Chad and paper was published in 2021 (Bongo et al. 2021), validated by Veterinary laboratory agency in United Kingdom)

MYCGEN-F (5’-AGA GTTTGATCCTGGCTCAG – 3’) and MYCGEN-R (5’- TGC ACAACGGCCACAAGGGA-3’) to determine the genus of mycobacteria.

Others primers for variable region of 16 S rRNA gene for Mycobacterium intracellular.

MYCINT-F (5’-CCT GGCTTAGCATGTCTTTA-3’) and Mycobacterium avium MYCAV-R (5’-ACC AGAAGACATGCGTCTTG − 3’) and two others primers identified species of complex tuberculosis target the MPB70 gene which is specific to mycobacteria belong to complex M.tuberculosis, TB1-F (5’-GAA CAATCCGGAGTTGACAA − 3’) and TB1-R (5’-AGC ACGCTGTCAATCATGTA-3’).

The first step of the molecular typing method include the preparation of Mix solution using different reagents which include the Master Mix solution, the Taq polymerase, and the concerned or specifics primers in a 50 µl Eppendorf tube as below (Table 1).

Table 1.

Preparation of Mix with different reagents and primers during genus typing

Reagents	Volume for one reaction in µl
Manufactured Qiagen free water (Cat N° 129114 and Lot N° 142315905)	6.2 µl
Master Mix contains DNA polymerase, dNTPs, MgCl2 and buffer	10 µl
Primers (06)	0.3 µl of each
DNA	2 µl
Total	20 µl

The next step is the amplication with the following program:

• Starting denaturation: 95 °C for 10 min,

• Denaturation: 95°C for 1 minute......(35 cycles)

• Annealing 61 °C for 2 min......(35 cycles)

• Elongation: 72 °C for 0.5 min......(35 cycles),

• Final elongation:72 °C for 10 min and

• Hold at 4 °C +∞.

For identification of M. bovis, M. tuberculosis species, the following primers sequences used during deletion typing method are:

• RD4- FlankFW 5´ - CTC GTC GAA GGC CAC TAA AG − 3´;

• RD4- FlankRev 5´ - AAG GCG AAC AGA TTC AGC AT − 3´;

• RD4- InternalFW 5´ - ACA CGC TGG CGA AGT ATA GC − 3´;

• RD9- FlankFW 5´ - AAC ACG GTC ACG TTG TCG TG − 3´;

• RD9- FlankRev 5´ - CAA ACC AGC AGC TGT CGT TG − 3´;

• RD9- InternalRev 5´ - TTG CTT CCC CGG TTC GTC TG − 3´;

The mix used for the deletion typing method (Table 2) to identify species within the Mycobacterium tuberculosis complex group as M.bovis or M.tuberculosis is the following (Berg 2008).

Table 2.

Preparation of Mix with different reagents and primers during deletion typing

Reagents	Volume for one reaction in µl
Manufactured Qiagen free water (Cat N° 129114 and Lot N° 142315905)	7.1 µl
Master Mix contains DNA polymerase, dNTPs, MgCl2 and buffer	10 µl
Primers (RD4, RD9 FlankRev, FlankFW, InternalFW )	0.3 µl of each
DNA	2 µl
Total	20 µl

Eighteen (Emma et al. 2019) µl of the mixed solution was distributed in different 50 µl Eppendorf tube in which was added 2 µl of each extracted DNA destined to be amplified. Both, Genus typing and deletion typing regimens using the Eppendorf thermocyler machine and was performed as bellow:

• Starting of denaturation : 95 ° C for 15 min,

• Denaturation: 95 °C for 1 min (35 cycles)

• Annealing: 55°C for 0.5 min (35 cycles)

• Elongation: 72 °C for 1 min (35 cycles)

• Final elongation: 72 °C for 10 min

• Hold: 4 °C + ∞

The PCR products were submitted to the electrophoresis migration process using a gel prepared with 2% of agarose and 120 V was used as migration power provided by a BioRad machine. Band sizes with ladder (RD9- 396 pb for M.tuberculosis and RD4 InternalFW + RD4- FlankRev: 446 pb for M. bovis).

Data management and statistical analysis

Field data and laboratory outcomes were double registered in a secured data base set up using Microsoft ACCESS™ Software. They were transferred to STATA 13 software for analysis purpose by using intermediate software named STATA / transfer. All these registered data were analyzed and the results are presented below.

Results

Characteristics of samples

During this period suspected tuberculosis samples were collected on 327 animals slaughtered.

In abattoir, 327 suspected animals were slaughtered for consumption purpose and inspected, they come from local breed as follows: 234 bovines from Arabic breed, 91 bovine from Fulani breed, one from bogolodjé breed and one from cross breed. One hundred twelve (112) are males and two hundred fifteen (215) are females and the majority of seizures were in age range from three (Ngandolo et al. 2009) to twelve (Berg 2008) years old with three hundred and seven (307) of partial seizures and twenty-five (Diguimbaye-djaibé Colette et al. 2006) of total seizures (Table 3).

Table 3.

Distribution of TB suspicion cases by age, sex, breed and type of seizure (%)

Age group	Sex		Cattle breed				Type of seizures
	M	F	Arabe	Mbororo	Bogolodjé	others	Partial	Total
0,5–3,5	5	9	11	3	0	0	15	0
3,6–6,5	52	57	74	34	1	0	100	12
6,6–9,5	40	66	81	25	0	0	103	4
9,6–12,5	9	55	45	18	0	1	56	8
≥ 12,6	6	28	23	11	0	0	33	1
Total	112 (34.25%)	215 (65.74%)	234 (71.55%)	91(27.82%)	1 (0.30%)	1 (0.30%)	302(92.35%)	25 (7.64%)

Bacteriological and molecular characteristics of TB strains

In the laboratory, bacteriology diagnosis was performed on specific media and 73 carcasses (21%) were infected by different types of mycobacteria from Mycobacterium genus. Using genus typing multiplex PCR technique in order to have bacteria belong to genus Mycobacterium in one hand and bacteria of Mycobacterium tuberculosis complex in other hand. This gave 53 bacteria belong to complex tuberculosis and after the RD4 and RD9 deletion technique was performed with bacteria belong to Mycobacterium tuberculosis complex and gave 42 cases of M.bovis and one case of infection by M.tuberculosis. This human strain (M.tuberculosis) was isolated on a prescapilar lymph node one cattle in transhumant herd from Fulani breed which is a female with six age year old (Table 4). Also, infection by non-tuberculosis mycobacteria was about 3% (10/327) on abattoir suspicion.

Table 4.

Distribution of bacteria strains by age and sex after RD4 and RD9 deletion

Age	sex		Mycobacteria strains			Total
	Male	Female	M.tuberculosis	M.bovis	NTM
0,5–3,5	1	2	0	3	0	3
3,6–6,5	7	8	1	15	4	20
6,6–9,5	8	2	0	11	3	14
9,6–12,5	3	6	0	9	1	10
≥ 12,6	1	4	0	5	2	12
Total	20	22	1	42	10	53

Statistical analysis

With STATA software, logistic regression was also performed to see the association or to have link between variables outcomes (mycobacteria infection) and socio demographics variables (sex, age). Statistical significance was set up at p-value of 0.05 with level of 95% and Odds ratio give the strength of association between variables outcomes and sex or age. Infections due to M.bovis are equal in males (20 strains) and females (22 strains). In summary, the real infection due to M.bovis is 12.84% (42/327) in cattle. These infections due to mycobacteria strains were highlighted in age group of 3 to 12 year old. Multivariate analysis done with outcomes variables and explanatory variables prove that there is a significative difference for the sex (p = 0, 04, OR = 1, 7, IC OR 95%: 1,039 − 3,089) means that females are approximately twice at risk to be infected than males.

Discussion

Chad is an agro pastoral country with a livestock of more than 90 million heads, and farmers are living closely with their livestock in remotes areas (Republique du Tchad 2015). Since 2000, through the joined Swiss Tropical Institute (actual Swiss TPH)–LRVZ (actual IRED) program entitled «Health of Nomadic People and their cattle», some research works were conducted in Chari Baguirmi and Kanem provinces in line with the epidemiology of tuberculosis in human and animal populations (Montavon et al. 2013). The objective of these studies were first to reveal the presence of Mycobacterium bovis in both hosts as cause of the zoonotic tuberculosis. However, the first finding had revealed the presence of Mycobacterium bovis in cattle but not in human population (Diguimbaye Colette et al. 2006).This first program allowed the capacity building of the first national laboratory unit based at IRED and able to isolate, then perform the molecular characterization of mycobacteria strains harvested from both animal carcass (or offal) and human suspected patients samples as the first tools to highlight the importance of the “One Health” approach at the national level (Ngandolo Bongo Nare Richard et al. 2021). As evidence, the first research work in line with the molecular characterization and drug resistance testing of Mycobacterium tuberculosis strains isolated from Chadian patients has been performed in this laboratory (Diguimbaye Colette et al. 2006). These outcomes were at the origin of the motivation which led the researchers involved in the implementation of the project on the health of nomadic people and their cattle to set up the African Bovine Tuberculosis Network (BTB Network) in 2007. This network gave birth to the Afrique One Consortium in collaboration with other African and European research groups as a group of African specialists on the theme of the epidemiology of Mycobacterium bovis in Africa; whose achievements are the description of the clonal M. bovis strains named respectively African One (Borna Müller et al. 2009), African two (Berg Stefan, Garcia-pelayo and Müller 2011) and European One (Smith Noel et al. 2011).

The current work was conducted in the frame of the Afrique One Consortium research activities, especially during the Afican Science Partnership for Intervention Research Excellence (ASPIRE) phase in link with its approach to generate a critical mass of young generation of scientists as “One Health” specialists in Africa. In fact, in line with our objectives, in same study conducted in 2012 in health centers in southern Chad, data and samples were used from tuberculosis suspected patients in the same areas and the study has demonstrated the zoonotic aspect of M. bovis (Ngandolo Bongo Nare Richard et al. 2021). However, the current research work has highlighted the zoonotic feature of M. tuberculosis in cattle as one of the causes leading to tuberculosis suspected lesions in Chadian slaughterhouses. These two findings have demonstrated the need of the implication of a multidisciplinary platform involving different sectors in the control and elimination pathway of the human tuberculosis in Chad.

Otherwise, a bovine experimental infection with M. tuberculosis isolates (M.tuberculosis H37Rv and M. tuberculosis BTB1558) isolated in Ethiopia in 2008 has shown that both M.tuberculosis strains caused reduced gross pathology and histopathology in cattle compared to M. bovis (Villarreal-Ramos et al. 2018). The main question is to understand for how long these infected cattle were kept in the experimental station after the natural infection with these two strains compare to those infected in a farm under a normal condition; then sent for human consummation after a stamping out process and suspected as tuberculosis infection cases in a slaughterhouses. Thus, in Chad, most of the animals to be slaughtered were usually among the old females (Ngandolo et al. 2009). During our study, the isolated M. tuberculosis strain was harvested from a female of approximately six years of age showing that, most of females slaughtered at abattoirs in Chad are in stamping out process (Ngandolo et al. 2009). This M. tuberculosis strain was isolated from a prescapilar lymph node in which the suspected lesion has shown the same aspect with those caused by M. bovis and isolated from another cow during the same study.

However, in United States, three probable cases of human-to-cattle MTBC transmission have occurred since 2013 (Lombard et al. 2021) and in Africa, both M. bovis and M. tuberculosis were isolated from environment usually frequented by both cattle and wildlife animals (Ameni et al. 2013), (Emma et al. 2019). Other studies done with samples collected from slaughtered animal coming from known farms had highlighted that, M. tuberculosis confirmed by polymerase chain reaction using primers targeting regions of difference (RD4, RD9) on the genomes had shown that no detailed epidemiological investigation was carried out on the respective farms to confirm or link humans as sources of tuberculosis transmission to cattle (Motlatso et al. 2017). Thus, even in our case, if the isolated strain is not from human source, the evidence of cross transmission of M. tuberculosis from human to animal and vice versa or from environment to animal is possible knowing that M. tuberculosis is the main causative agent of tuberculosis in human and M.bovis commonly causes tuberculosis in animals (Motlatso et al. 2017). In Kenya during a study done using tuberculosis suspected gross lesions collected from two abattoirs, after laboratory diagnosis, it has demonstrated that from 64 carcass suspected as AFB positive, the molecular characterisation of the isolated strains had shown presence of M.bovis (19/64) and M. tuberculosis (2/64) confirming the frequency of M. bovis is the main causes of tuberculosis in cattle among M. tuberculosis complex isolated from suspected carcass in African slaughterhouses, showing also that, M. tuberculosis is involved in the suspected gross lesions in cattle (Stephen et al. 2012, Faїza Belakehal 2021).Our work had described a relatively same situation by isolating one M. tuberculosis strain (1/73) compared to M. bovis (42/73) from the whole stained AFB cases. However, the study performed in Algeria using gross lesions collected from abattoirs in which it was demonstrated that using RD9 deletion typing when analysing 60 isolated strain, all belonged to M. tuberculosis complex group is an confused situation in which M. bovis proportion has to be clearly sorted out (Faїza Belakehal 2021). Otherwise, our findings rose up several other aspects of the complexity of the animal tuberculosis epidemiology in the Chadian context that are important to be addressed in line with such outcomes highlighted in the world.

In central African sub region, mainly in Chad, the isolation of M. tuberculosis strain from cattle is the first through the current work. However, during our study, most frequent strains (42/73) were composed by M. bovis species which were in 3, 6 to 12, 5 years old group without any influence of sex showing that both female and males stamped out from herds and sent for slaughter were all at risk for tuberculosis even the study has done in rural abattoirs compare to previous such research done in Chad. However, isolation of non-tuberculosis mycobacteria (NTM) causing gross lesions in cattle has been highlighted in our previous work in Chad (Diguimbaye Colette et al. 2006, Ngandolo et al. 2009) as described by other authors worldwide as reported in Rwanda by isolation of non-tuberculosis mycobacteria 12.0% (36/300) (Ntivuguruzwa et al. 2021) and even as described in South Africa with isolation from a cow (Motlatso et al. 2017). In the current work, the ratio of the isolated NTM was 13.70% (10/73) compare to other mycobacteria causing gross lesion suspected as tuberculosis lesion in slaughtered cattle. Non-tuberculosis mycobacteria are known to be predominant in environment and both animal and human populations are supposed to be exposed to them (Zulu et al. 2021). In our previous studies in Chad, NTM were harvested from both animal and human populations (Diguimbaye Colette et al. 2006) and recent scientific evidence has shown the importance NTM as traditional environmental organisms which are pathogenic in animal and human populations (Zulu et al. 2021). These findings prove the limit of controlling bovine tuberculosis in herds using comparative tuberculin test in the African context (Ngandolo et al. 2009) on the one hand knowing that NTM are cross reacting with M. bovis tuberculin; and on the other hand, they sort out the limit of tuberculosis treatment in human when it is well known that most of them are resistant to the actual molecules used to treat tuberculosis in human (Thumamo et al. 2022). However, as in Chadian herds, both cattle and small ruminants are living in the same farms and isolation of mycobacteria strains from these species will be important in order to well appreciate the epidemiology of mycobacteria infections in the context of farming system in the Sahel.

Multivariate analysis show that tuberculosis infection could be due to sex variable (p = 0, 04 OR = 1, 7 IC OR 95%: 1,039 − 3,089),this is in concordance with study done in Chad (Diguimbaye-djaibé Colette et al. 2006) but different to study done in Cameroon where sex has no influence on infection (p = 0.52) (Awah-Ndukum et al. 2012). Females were twice as likely to be at risk as males; that could be due to livestock systems where females are long time maintained in the herd for breeding or the physiologic stage of pregnant females which are exposed them to some disease when immunity decreases.

The most seizures and isolation of M.bovis concern old animals (3 to 12 years old) as mentioned studies carried out in Chad (Ngandolo et al. 2009) and Cameroon (Awah-Ndukum et al. 2012) where old animals have presented more suspected lesions than young, this could be due that TB is a chronic disease.

The study allows knowing genetic profile of causatives agents of lesions suspected in abattoir as tuberculosis lesions circulating in south of Chad which are suspected as tuberculosis infection and also highlights existence of M.tuberculosis strain in cattle for the first time in the country in domestic ruminants in general destined to human consumption. The study also revealed presence of BTB in cattle in southern Chad and other environmental bacteria involved in the tuberculosis suspicion and some risks factors.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

Conceptualization: L. Didi, Ngandolo Bongo Richard, Colette Diguimbaye. Data Curation: L. Didi, Ngandolo Bongo Richard. Formal Analysis: L. Didi, Ngandolo Bongo Richard, Philippe Koné. Funding Acquisition: Bassirou Bonfoh, Jakob Zinstagg, Colette Diguimabye. Investigation: L. Didi, Ngandolo Bongo Richard, Tadio Sylvain. Methodology: L. Didi, Ngandolo Bongo Richard, Philippe Koné, Alembedji Baba, Rianatou. Project Administration: Colette Diguimbaye, Ngandolo Bongo Richard. Ressources: Colette Diguimbaye, Ngandolo Bongo Richard. Software: L. Didi, Ngandolo Bongo Richard, Philippe Koné. Validation: Ngandolo Bongo Richard, Colette Diguimbaye, Bassirou Bonfoh. Writing – Original Draft Preparation: L. Didi, Ngandolo Bongo Richard. Writing – Review & Editing, Ngandolo Bongo Richard, Bassirou Bonfoh.

Data availability

Our dataset generated and analyzed during the study are available at IRED laboratory from the corresponding author on reasonable request and are not public.

Declarations

Statement of animal rights

Not applicable.

Conflict of interest

Authors certify that there is no conflict of interest with any financial, personal, or other relationships related the manuscript.