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Review Article | Open Access | Int. J. Agric. Vet. Sci., 2022; 5(5), 116-129 | doi: 10.34104/ijavs.023.01160129

Review on the Epidemiology and Public Health Importance of Camel Tuberculosis

Moges Abate Aklilu Mail Img ,
Daniel Tamirat WeldeMariam* Mail Img ,
Shahana Akter Shanta Mail Img ,
Md. Samiul Islam Mail Img ,
Aklema Akter Mail Img

Abstract

Camel (Camelus dromedarius), Camels are an important livestock in Ethiopia and are raised in Somali, Afar, and Oromia (Kereyu, Borena, and Guji). They are used for various purposes such as transport, drafting power, ploughing land, festivals, and rivalry as in dashing. The pastoral community utilizes their products such as milk and meat. However, they are also, susceptible to various diseases which can affect their health. One of the major diseases that affect camels is tuberculosis. Camel tuberculosis is a persistent disease that is characterized by the improvement of granulomas inside the breathing tract and associated lymph nodes. The mycobacteria are discharged from those granulomas and might contaminate different prone animals Camel tuberculosis is a chronic disease that is characterized by the development of granulomas in the respiratory tract and related lymph nodes. The mycobacteria are discharged from these granulomas and can contaminate other susceptible animals. Camel tuberculosis is a chronic disease that affects the respiratory system and the lymph nodes of the infected animals. It can also pose a public health risk in areas where people consume raw camel milk or have close contact with camels. The disease is caused by different types of mycobacteria, such as Mycobacterium caprae, Mycobacterium tuberculosis, and Mycobacterium bovis. The diagnosis of camel tuberculosis can be based on clinical signs, history, tuberculin skin tests, post-mortem examinations, bacteriological and molecular methods. Public awareness and control measures are needed to reduce the transmission of the disease and its economic impact. 

INTRODUCTION

Camels are an important livestock in Ethiopia and play a significant role in the livelihood of pastoral and agro-pastoral communities. They are known for their resilience to harsh climates and are often used for transportation, draft, ploughing land, festivity and rivalry as in dashing (Yirda et al., 2020). Accor-ding to the Babege et al. (2021), approximately 35 million camels exist worldwide,with the majority of them living in Somalia, Niger, Kenya, Ethiopia,Chad  Mali,  Pakistan and Mauritania. These five countries that border each other - the Somalia, Kenya, Sudan, Ethiopia, and Djibouti - have 84% of the camels in Africa and more than half of the global camel population (Mwinyihija and Mekonnen, 2016). 

Climate change is partly responsible for the expan-sion of camel rearing areas, especially in Africa (Faye et al., 2012). Important domestic animal species that are specifically adapted to arid and semiarid regions of Asia and Africa include camels (C. dromedaries) (Faraz, 2020). According to the Babege et al. (2020) 1.42 million heads of the dromedary camels are raised in arid and semi-arid areas of Ethiopia, with the majority of these animals living in the east of the nation regions (Babege et al., 2021). Camels are the main source of income for numerous communities who raise camels in various ecozones around the world (Faraz et al., 2019). 

In Ethiopia, different pastoralist communities keep camels for various purposes, producing milk and meat, for instance (Faraz et al., 2019). Camel milk is an important source of income and food security for the pastoralists and the traders involved in the camel milk value chain in Ethiopia. Camels are well adapted to the dry and harsh environments where other livestock species struggle to survive (Madalcho et al., 2019; Faraz et al., 2021). The management system of camels in Ethiopia is mainly traditional and extensive, relying on natural pastures and water sources (Woldearegay et al., 2015). The pastoralists move seasonally with their animals to access water and pasture resources (Nori, 2005). The average camel herd size per household varies from a few heads to several hundreds, with females constituting more than 75% of the herd. Male camels are usually sold early for slaughter or as pack animals. Female camels can reproduce up to 25 years of age, producing eight to ten calves in their lifetime. Camels occupy practically all fringe drier lowland areas that generally fall below 1,500 meters above sea level (Bediye et al., 2018). The majority of pastoralists rely on camels as a resource and as the foundation of the pastoral economy. They utilized camels for agriculture or land plows (Bediye et al., 2018). The camel used pastoral communities as a source of meat, milk, and income for food security, as well as for other functions including transporta-tion, entertainment, celebration, and competition as in hustling and splendor arise in East Africa., the Middle East and South Asia (Gader and Alhaider, 2016). In recent years, camels have become one of the national export animals for Ethiopians (Kasaye et al., 2013; Saikat et al., 2020).

Camel milk has been used as a treatment for various diseases in many cultures. According to a study, people living in Babilie and Kebribeyah districts, Jijiga Zone of the Somali Regional State used camel milk as treatment for gastritis, asthmatics, stomach discomfort, HIV, hamot (kar), tuberculosis, fever, urinary problems and hepatitis. Additionally, camels graze on a variety of plant species, and therapeutic active ingredients from these plant species are released into the milk, which is used to treat a variety of illnesses like jaundice, malaria, constipation, to clear the stomach, postpartum care for women, to detoxify snake venom, and diarrhea (Dibessa, 2020). The pastoralists thought camel milk to be readily available medication for various sicknesses due to the presence of various bioactive components in camel milk. These bioactive components have been found to have antimicrobial, antiviral and anti-infla-mmatory properties. The milk is also rich in many nutrients that are important for overall health. Camel milk is comparable to full cows milk in terms of calories, protein, and carbohydrates. Additionally, it has a lot of antioxidants, which guard against cell damage and the development of major illnesses including cancer, the diabetes, and heart disease (Dibessa, 2020). Camel milk has become incre-asingly popular in many countries due to its nutria-tional content and potential health benefits. Accor-ding to  (Abrhaley and Leta, 2018).  children prefer camel milk over other dairy animals milk due to its taste and nutritional value. Camel milk has a lactose concentration of 4.8%, which is comparable to that of human mothers milk and is easily assimilated by those who are lactose intolerant. 

This makes it a fantastic substitute for those with cows milk allergies (Gebremichael et al., 2019). In addition, the culinary and cooking practices, as well as the palate for meat, in the several African and Arabian countries have evolved toward camel meat due to its medicinal benefits, the availability and affordability. Camel meat is leaner than beef and contains more protein than chicken. It is also prosperous in vitamins and minerals such as iron, zinc and vitamin B12 (Bekhit and Farouk, 2013). Camel farming is an important source of income for many people in Ethiopia. According to data available from the Ethiopian tax and income authority, live animal trading accounted for 70% of profit, while meat exports accounted for the remaining 30% . During the Ethiopian financial year (July 2010-June 2011), the Ethiopia earned USD 211.1 million by exporting 16,877 tons of meat and 472,041 head of live animals. Camels accounted for 13% of the total number of traded live animals and 25% of the total revenue generated (Mamo, 2019).

In Somali area, camel milk sale was the main source of income. There are various camel milk assortment focuses selling milk in nearby towns and urban areas of the Somali district of Ethiopia, just as traded to the neighboring nation of Soma (Yohannes Mehari and Gebru, 2006). In addition, in Meiso (Oromia) lowlands of Ethiopia, the majority of pastoralists (78%) had been selling camel milk  (Tegegne et al., 2013). Tuberculosis affects Old World Camelids (OWC) including Dromedaries and Bactrian camels (Miller et al., 2015). Camel tuberculosis is common (Kinne et al., 2006a) reported a higher TB preva-lence of 13% in camels in Kazakhstan, while (Kinne et al., 2006b) reported a similar prevalence of 10% in Ethiopian abattoirs based on the diagnosis of macroscopic lesions in otherwise healthy drome-daries (Mamo et al., 2011). A bacterial disease that affects both people and animals, tuberculosis is persistent. It is distinguished by the progressive development of particular granulomatous tubercle lesions in the tissues that are afflicted. The disease affects all age groups of susceptible hosts and is accountable for more deaths throughout the world than any other bacterial disease today (Shitaye et al., 2006; Gole and Hamido, 2020).

In this African country, the bacterium that causes TB in humans appears to infect animals more often than the one that affects cattle does humans. Therefore, effective control measures are highly necessary be-cause in Ethiopia there is the largest number of pastoral population in which their life is dependent on livestock and consumed raw animal products such as milk and meat daily. This kind of situation makes people more likely to contract zoonotic ill-nesses like tuberculosis. To estimate the risk and burden of camel tuberculosis transmission in pastoral area and other animals, the first step is to determine its prevalence. Even though tuberculosis has long been reported in different pastoral areas, there is no sufficient information on the prevalence, public health importance and its control measures in the Ethiopia at the national level (Ayana and Dibessa, 2020).

The aims of this paper are -

1) To discus the zoonotic impotrance of camel tuberculosis 

2) To highlight some possible approaches for the Camel tuberculosis control and prevention

Camel Tberoculosis

The genus Mycobacterium of the family Myco-bacteriaceae includes non-motile and non-sporing acid-fast rods of various lengths (Teshome, 2021). Mycobacteria possess a waxy coat that makes it difficult for the hosts defence mechanisms to destroy them and results in a slow chronic disease (Thacker et al., 2011). The following species are grouped in the MTC: M. tuberculosis, M. canettii, M. africanum, M. bovis, M. pinnipedii, M. caprae and M. microti (Djelouadji et al., 2011). 

Of these, M. tuberculosis, M. bovis, M. pinnipedii, M. caprae, and M. microti have been isolated from the camelids (Damene et al., 2020). The name “Tuberculosis” comes from the nodules, called the ‘tubercles, which form in the lymph nodes of the affected animals (Pasick et al., 2015). So that Tuberculosis (TB) is, a chronic, reportable granulo-matous zoonosis caused by Mycobacterium tuber-culosis complex and affects many animal species including camels (Dibessa, 2020).

MTBC is defined as a complex of seven distinct bacterial species named M. tuberculosis, M. canettii, M. africanum, M. pinnipedii, M. microti, M. caprae and M. bovis (Riojas et al., 2018). But, importantly, differ in physiological characteristics, virulence and host range. Mycobacterium tuberculosis, M. Africa-num and M. canettii are principally pathogenic in humans. Mycobacterium bovis and M. microti are the causative agents of TB in animals, and can be transmitted to humans (Mostowy et al., 2005).

Etiology of Tuberculosis in Camel

Two members of Mycobacterium are Mycobac-terium bovis and Mycobacterium tuberculosis cause tuberculosis in cattle and other domestic animals (Erler et al., 2004). Some of atypical Mycobacteria rarely causing TB in camels are M. kansasii, M. aquae, M. aqua var. ureolyticum, M. microti, M. fortuitum and M. smegmatis. The atypical spices of Mycobacterium cause disease in camel when it becomes immunocompromised (Mamo et al., 2011). 

Along with three atypical Mycobacteria (M. kansasii and M. microti) discovered TB in a small llama herd on the border of England and Wales, the four major Mycobacteria, M. bovis, M. tuberculosis, M. avium, and M. avium sups Para tuberculosis, have been isolated from new world Camelids (Kinne et al., 2006).

Source of the contamination and means of the Transmission

Granulomas, which are clumps of immune cells that isolate hazardous substances in the body and are most commonly found in the lungs and accom-panying lymph nodes, where the mycobacteria spread and infected additional susceptible people, are what characterize the disease (Dibessa, 2020). In close-contact groups of animals, respiratory sprea-ding is the most important mode of disease trans-mission. When an infected host coughs or sneezes, releasing M. bovis into the air, an uninfected host inhales it directly, resulting in infection or conta-mination (Francis, 1971). Inhaled air, milk, urine, nasal discharge, vaginal discharge, and discharges from exposed peripheral lymph nodes are all sources of microorganisms. Evident infection disseminators are gross lesions that link with the airways, skin, or intestinal lumen. Animals may have active myco-bacterium in their nasal and bronchial mucus prior to the onset of any sickness symptoms. Excretion of the organism starts in experimentally infected animals around ninety days after infection (Teshome, 2021). When an infected animal is put into a herd of camelids that is not already diseased, tuberculosis can spread between the herds (Alvarez et al., 2012). Animals with pulmonary lesions exhale bacteria that non-infected animals may breathe in and become infected as a result (Dubie et al., 2015). Due to their frequent interaction with their domesticated animals, pastoralists are particularly susceptible to zoonotic illnesses, which are diseases that can spread from animals to humans (Desta, 2016). In Ethiopia, the main ways that camels can infect people are by drinking raw milk and  eating under oocked meat from sick animals, and by breathing in the air near them. For several underdeveloped nations where pasteurization is uncommon and where people live close to their livestock, these potential risk risks are especially concerning (Gumi et al., 2012).

Epidemiology

Mycobacterium tuberculosis is a chronic and the contagious disease that affects people and animals worldwide. Camelids, such as the dromedaries, are susceptible to TB and can act as reservoirs of the infection for other species (Pesciaroli et al.,  2014). In Ethiopia, TB is endemic in most regions and poses a serious threat to public health and animal welfare. On the epidemiology of TB specifically relevant to camelids in Ethiopia, there is, however, insufficient available data. The available studies suggest that the distribution of TB in camelids varies greatly between regions and depends on the diag-nostic methods used. Members of the tuberculosis bacteria complex are the primary causes of tuber-culosis in camelids. Direct or indirect contact with infected items or animals can spread the disease.The lack of the established and trustworthy diagnostics makes camelid TB diagnosis difficult (Alvarez et al., 2012). In order to better diagnose and control TB in camelids and comprehend its effects on both human and animal health in the Ethiopia, further study is required (Wernery and Kinne, 2012). Worldwide, people, wild, domesticated, and confined animals are all susceptible to tuberculosis. Since 1888, drome-daries have been associated with tuberculosis (TB). There are significant regional and national variations in the geographic distribution (Kasaye et al., 2013). The incidence of camel tuberculosis  is very low in most European countries, as well as in the United States, Canada, Japan, and New Zealand, with less than 0.1% of the animals infected. Some countries, such as Australia, Denmark, Sweden, Norway, and the Finland, have declared themselves free of this disease. 

However, the bovine tuberculosis is widespread in almost all African countries (Dubie et al., 2015). A study conducted in an abattoir in Eastern Ethiopia identified M. Bovis as the agent responsible for Tb in the dromedary camels. Out of 398 carcasses examined, 33 (8.3%) were positive for camel Tb according to (Beyi et al., 2014). It was discovered in eastern Ethiopia in order to describe its frequency and isolate M. bovis as the causal organism from affected camels. A study which conducted  on   276 pastoral camels which slaughtered at abattoir of east of Addis Ababa show that 14 camels with lesions suggestive of tuberculosis infection, indicating a 5% prevalence in this area. A tissue impression smear from a lesioned camel was AFB-positive in only four cases out of 14, and from 14 samples only one  samples was confirmed to have MTBC by PCR (Rhodes et al., 2015). In a study conducted on 906 camels from two pastoral regions of Southern and Eastern  Ethiopia, 91 camels were  suspected tuber-culosis lesions, indicating a 10% prevalence. from those which have liesion symptom were 31camels, 31 (34 percent) with acid fast Bacilli (AFB) positive mycobacterial isolates from cultured. A PCR test for Mycobacterium detected 21 positive camels out of 31, but only two of them had MTBC and were the identified as M. bovis (Dibessa, 2020).

In these two Ethiopian studies, the low recovery rate of a positive causal agent (i.e., M. bovis) from the majority of lesioned camels may be attributable to a poor culture for non-MTBC mycobacteria, and it also reveals the range of mycobacteria that cause mycobacterial illnesses in the camels. The M. terrae complex, M. fl avescens, M. brasiliensis, M. chelo-nae, and M. avium have been identified as the responsible parties by recent 16S rDNA sequencing of these non-MTBC mycobacteria (Mamo et al., 2011). The probable link between non-MTBC and MTBC in camel mycobacterioses in Ethiopia has also been demonstrated in other investigations conducted in slaughterhouses. A thorough post-mortem investigation of 293 OWCs from eastern Ethiopia shows that TB lesions are significantly correlated with female dromedaries, with a probable incidence of 12.3% (36/293). Mycobacteria were found in 61% of the lesions examined in a research on camels with gross lesions. Only three of the isolates were identified as M. tuberculosis by mole-cular characterisation, while the bulk (15/22) were non-MTBC (Gumi et al., 2012; Zerom et al., 2013). Camels from Metehara and Borana have been found to have 9.82 percent camel TB at Akaki abattiors. Camels from Metehara and Borana have a high prevalence, with 9.6% and 10.94%, respectively, from Metehara and Borana. According to Jibril et al. (2019), out of 387 camels tested with the single intra-dermal comparative the cervical tuberculin (SICCT) test, 38 (9.82 percent) were positive for tuberculin reaction. Similarly, other studies have reported abattoir-based prevalence of camel tuber-culosis of 10.4% in Akaki (Jibril et al., 2016), 5.1% in Dire Dawa (Gumi et al., 2012a), and 3.1% in Southern Ethiopia (Gumi et al., 2012). In addition, some authors have found camel tuberculosis pre-valence of 5.1% and 3.1% in Akaki and Eastern Ethiopia, respectively (Beyi et al., 2014; Kasaye et al., 2013). 

In Ethiopia, M. bovis and M. tuberculosis have been isolated from tissue lesions of dromedary camels (Zerom et al., 2013). Moreover, M. pinnipedi, M. caprae, and M. microti have been identified from camelids as the members of the MTBC (García-Bocanegra et al., 2010; Manual, 2008). According to Kinne et al. (2006) and Zerom et al. (2013) non-tuberculous mycobacteria (NTBC) such M. kansasii, M. aquae, M. fortuitum, and M. smegmatis are also responsible for causing camel TB. In southern Ethio-pia, M. tuberculosis strains have also been found in camels (Gumi et al., 2012) from camels in Eastern Ethiopia (Zerom et al., 2013) and  from goats in Afar and from pigs in Ethiopia (Arega et al., 2013).

Risk Factors

In accordance with Mamo et al. (2011) the tuber-culosis-causing agent is susceptible to all types of animals, including humans, physical conditions, sex, and age groups. In conventional domesticated animal raising systems, The way livestock are kept and managed, such as mixing different animal species and sharing water sources, can increase the risk of M. bovis spreading among animals, from animals to humans, from humans to animals, and from humans to humans (Gumi et al., 2012). Camels with TB were more common in the youngest and oldest age groups. Similar findings have been reported in cattle, especially in older animals with TB (Munyeme et al., 2009). This might be because older animals have weaker immune systems. Younger camels might have more lesions because their immunity is not fully developed (Menzies and Neill, 2000). Also a pathogen risk factor: the causative organism is heat, desiccation, and many disinfectants resistant; M. bovis pathogenicity is related to its capacity to survive and reproduce in the host macrophages. Housing, sharing a shelter with humans, and animal stocking intensity are all environmental risk factors (Quinn et al., 2003). The consumption of raw milk (as opposed to pasteurized milk) is a common practice in the Ethiopia that increases the risk of zoonotic TB transmission from infected animals to humans. M. bovis is the main agent of zoonotic TB and it can be found in unpasteurized milk and other dairy products. Moreover, the inhala-tion of aerosols from cattle to humans (or vice versa) can also be a potential source of infection (Romha and Ameni, 2018). Another factor that contributes to the spread of zoonotic TB is the low level of aware-ness among pastoralists. They often value the nutria-tional and medicinal benefits of raw milk and do not boil it before the consumption. They also have limited knowledge about milk-borne diseases (Wako, 2015).

Pathogenesis

Camel tuberculosis (TB) is a persisting infectious disease caused by Mycobacterium bovis or Myco-bacterium tuberculosis, which can affect the res-piratory system, lymph nodes, and other organs of camels (Mohamed, 2019). The pathogenesis of camel TB is not well understood, but it is believed to involve inhalation or ingestion of the bacteria, followed by multiplication and dissemination within macrophages (Gumi et al., 2011). The bacteria can evade the host immune response by inhibiting phagosome-lysosome fusion, modulating cytokine production, and inducing granuloma formation (Abebe, 2019). The clinical signs of camel TB may include weight loss, coughing, dyspnea, lympha-denopathy, and abscesses (Khan  et al., 2013). 

Camel TB poses a significant threat to the health and productivity of camels in Ethiopia, as well as a potential zoonotic risk to humans who consume camel milk or meat (Gutema  et al., 2019). Accor-ding to the distribution of TB lesions in the bodily organs of camels, lungs and related lymph nodes accounted for 57.14% of lesions, retropharyngeal lymph nodes for 28.57%, and mesenteric lymph nodes for 14.29% (Kasaye et al., 2013). By using this process, mycobacteria are able to live, grow, and finally destroy phagocytes. In order to move from cell to cell, M. marinum, a close relative of M. TB and M. bovis, may break through the phagosomes and enter the cytoplasm (Stamm et al., 2003). Then, more phagocytes come in to ingest the growing amount of tubercle bacilli. A granuloma, a tiny collection of cells, forms. Large numbers of phago-cytes build up as a result of the diseases cellular reactions, and eventually macroscopic lesions called tubercles appear. After 10-14 days, the hosts macro-phages acquire cell-mediated immunity (CMI) responses and become more capable of eliminating the intracellular bacteria. T lymphocytes, which are involved in cell-mediated immunity (CMI), secrete lymphokines that are messenger proteins produced by lymphocytes. These lymphokines attract, immo-bilize, and activate more mononuclear cells from the blood at the locations where harmful mycobacteria or their products are present (Thoen et al., 2006). 

The presence and enlargement of macrophages in the difficult-to-access channels between the reticular cells of the lymph node assist the growth and deve-lopment of the granulomatous lesion in the node. In certain cases, the lung and the thoracic nodes are both impacted because some of the mycobacteria that have been engulfed are still in the lung. Primary lesions may grow big and solid and frequently localize in a node or nodes (Thoen et al., 2006).

Clinical Findings

Camel Tuberculosis is a serious and contagious disease that affects camelids, such as llamas and alpacas. It is caused by bacteria from the Mycoba-cterium tuberculosis species, which can infect the respiratory tracks and other organs. Camelids with TB may `not show any signs of illness or may only have mild symptoms, such as changes in behavior, reduced appetite, weight loss, coughing or difficulty breathing. Some camelids may die suddenly without any warning. TB can be transmitted to camelids by contact with infected cattle or wildlife, or through contaminated materials (Crawshaw et al., 2013). Therefore, it is important to test camelids for TB regularly and to examine any dead animals for signs of TB lesions. The most common organs affected by TB in camelids are the lungs and the lymph nodes near the lungs. The lesions caused by TB can be very severe and extensive, and may not be detected until the animal is dead. The lesions are white or creamy and caseous.the clinical signs in camelids include wasting, anorexia, and respiratory distress, enlarge-ment of superficial lymph nodes, recumbence and eventually death (Twomey et al., 2010). The most common organs affected by tuberculosis are the lungs and their related lymph nodes. The infection can cause multiple or single lesions in the bile ducts or lungs that can merge into large areas of dead tissue, sometimes involving the entire lung lobes. Healthy camelids have small and hard-to-detect lymph nodes. However, tuberculous affected lymph nodes are often very large and have many white, cream or yellowish foci of dead tissue. In severe cases, the whole node may be replaced by one big lesion (Jibril et al., 2018). The lung damage may be so extensive that it is surprising that the animal did not die sooner (Crawshaw et al., 2013). In humans, the common symptoms of active lung TB include, cough with sputum and sometimes with blood, chest pains, weakness, weight loss, fever, and night sweats (Bazzano and Yan, 2020).

Pathology

The use of pathology to diagnose camel tuberculosis was unusual in Ethiopia because there were few studies on this disease in camels. Some researchers conducted a tubercle lesion epidemiology assess-ment using abattoirs in various pastoral districts of Ethiopia (Dibessa, 2020). A postmortem exam-ination was conducted after the previously men-tioned operation (Mamo et al., 2011). Under a bright light source, tissues from the lung and lymph nodes including the sub-mandibular lymph node, retro-pharyngeal lymph node, trachea-bronchial lymph node, cranial and caudal mediastinal lymph node were thoroughly investigated. Externally, the lobes of the left and right lungs were examined and felt. Then, using sterile surgical blades, each lobe is divided into slices that are roughly 2 cm thick to aid in the discovery of lesions. Similar to this, lymph nodes were examined for the existence of visible lesions by cutting them into thin sections (approxi-mately 2 mm thick). Under a bright light source, the sliced surface was inspected for abscess and tubercle lesions (Asseged et al., 2004; Mamo et al., 2011). The prevalence and economic impact of camel TB in Ethiopia are not well studied, but some reports indicate that it is a common and important problem in pastoral regions where camels are kept for milk, meat, and transportation. A cross-sectional study conducted on 906 slaughtered camels in two abattoirs found that 10.04% of them had gross TB lesions, mainly in the abdominal organs(Mamo et al., 2011). Another study that examined 31 myco-bacterial isolates from camels with TB lesions identified two strains of Mycobacterium caprae, one of which was new and designated as SB1953, and 19 strains of non-tuberculous mycobacteria (Dibessa, 2020. These findings suggest that camel TB in Ethiopia is caused by a variety of mycobacteria, some of which may have different sources of infection, transmission routes, and pathogenicity. The diagnosis of camel TB is challenging due to the lack of standardized and validated tests for this species. The intradermal tuberculin test and the P22 ELISA have been used as screening tools, but their sensitivity and specificity are unknown (Infantes et al., 2020). The isolation and identification of the causative agents require sophisticated laboratory techniques that are not widely available.

The pathological prevalence of camel TB was 10.04% based on the presence of gross lesions, which were more common in females and in certain lymph nodes and lung lobes. Out of the camels with visible TB lesions, 34% showed the mycobacterial growth. The mycobacteria were identified as mem-bers of the M. tuberculosis complex using multiplex PCR, RD4-based PCR, and spoligotyping (Jibril et al., 2018). Camels with macroscopic lesions that ranged from hard white, grey, or yellow nodules with a dry and solid necrotic center to thin-walled suppurative abscesses were considered postmortem positive (Kinne et al., 2006). Each camels lymph nodes, including those in the parotid, mandibular, retropharyngeal, tracheobronchial, mediastinal, pres-capular, prefemoral, mesenteric, superficial inguinal, and supramammary regions, were carefully in-spected for tuberculous diseases and excised. Addi-tionally examined were the lungs, liver, mammary gland, kidneys, and other organs (Beyi et al., 2014).

Diagnosis 

The process of diagnosing tuberculosis in animals involves two steps: ante-mortem and post-mortem examinations. Ante-mortem tests include the single intradermal comparative tuberculin skin test, which uses purified protein derivatives (PPD) from M. bovis and M. avium to detect skin reactions, and the interferon-gamma (IFNγ) test, which measures the immune response to mycobacteria. However, these tests have limitations in terms of sensitivity and specificity, especially for camelids. Serological tests, which detect antibodies against mycobacteria, have shown promising results but need further validation . These tests can help identify infected animals before they show clinical signs, which are often nonspecific and may include respiratory distress, weight loss, lymph node enlargement and death. Post-mortem diagnosis is based on the observation of character-istic lesions in the organs, histopathology and bac-terial culture . This is the only definitive way to con-firm tuberculosis infection in camelids. Camel tuberculosis is a chronic and conta-gious disease that can affect different organs and cause various symp-toms depending on where the infection is located. It can be confused with many other diseases, so it is important to use reliable diagnostic methods to con-firm it. The most common diagnostic methods for camel tuberculosis are the tuberculin skin test and the identification of the bacteria in samples from infected animals (Kasaye et al., 2013). 

Other methods that can be used to diagnose camel tuber-culosis are microscopic examination of stained samples, bacterial culture, the molecular techniques, spoilgotyping, histopathology and serological tests. However, none of these methods can provide the accurate diagnosis in all cases, and some of them still need to be the validated (Beyi et al., 2014). Therefore, more research is needed to develop better diagnostic tools for camel tuberculosis.

Treatment

First lines of drugs for TB therapy are streptomycin, isonized (INH), ethambutol and rifampin. Second line drugs are pyrazinamide, paraminosalicylic acid, kanamycin, cyclosserine, caperomycin and ethiona-mide. Because of resistance often develops under single drug regime a combination is commonly used. Because of the public health hazards inherent in the retention of TB animals, anti-tuberculous chemo-therapy of animals  is discourage (Teshome, 2021). Many countries require reporting of tuberculosis cases in animals and have laws to prevent this disease by killing the infected ones. Giving anti-Tb drugs to sick animals is usually not done, but some captive wild animals have received them. After the detection of Tb in two Bactrian camels kept in a zoo, prophylactic treatment of the remaining 17 camels was attempted using isoniazid incorporated into pelleted feed at a dose of 2.4 mg/kg, fedad libitum (Oevermann et al., 2004).

Control and Prevention 

Ethiopian pastoralists rely on Dromedary camels for milk, meat, and profit since they can tolerate the harsh climate of the countrys several regions. Tuberculosis (TB) affects dromedary camels causing morbidity and mortality in these animals (Jibril et al., 2018). National control programs are frequently focused on intradermal tuberculin testing, but these programs are unlikely to be successful because to the limits of this test in camelids; therefore, a combi-nation of ante mortem assays could improve the sensitivity of herd testing. The infection can be controlled by eliminating infected animals and preventing further spread  in the herd, but it will not be eliminated until the infection is controlled in wildlife hosts, which are reservoirs of the disease (Thoen et al., 2006). To control the disease effect-tively, it is necessary to understand how the infection spreads within the ecological system that includes both domestic and wild animals (Renwick et al., 2007). Some preventative measures include paste-urizing milk, culling sick animals and organs during meat inspections, and employing efficient disease management techniques (Dibessa, 2020). It also helps to regularly clean and sanitize polluted loca-tions, food troughs, and water sources. Poorly man-aged cattle are more susceptible to tuberculosis than well-managed cattle (Kiros, 1998). With hot 5% phenol or an equivalent cresol as phenols (2-5%), hypochlorite (1-5%), alcohol (often 70% ethanol), formaldehydes and iodophores (3-5%), and glutara-ldehyde (Zahra), food and water troughs should be thoroughly cleaned and disinfected. 

Public Health importance of Camel Tuberculosis

One of the most dangerous infectious diseases for humans in the globe is tuberculosis (TB). In 2010, Tb was estimated to have caused an estimated 8.8 million new cases, a 128 population/year global incidence rate, and 1.5 million fatalities (WHO, 2012). The current increasing incidence of this infection in humans, particular in immune com-promised human, has given renewed interest in the public health importance of M. bovis, especially in developing countries like Ethiopia (Radostitis et al., 2007). Camel tuberculosis (TB) is a zoonotic disease caused by Mycobacterium bovis and Mycobacterium tuberculosis, which can infect humans and animals. Camel TB is a major public health concern in the Ethiopia, where camels are widely used for milk production, transportation, and meat consumption. Camel TB poses a serious threat to the health and livelihoods of camel keepers and consumers, as well as to the national economy and food security. 

According to the World Health Organization (WHO), the Ethiopia ranks among the 30 high TB burden countries in the world, with an estimated incidence of 164 cases per 100,000 population in 2019 (WHO, 2012). The prevalence of camel TB in Ethiopia is not well known, but some studies have reported rates ranging from 1.4% to 15.6% based on bacterio-logical and molecular methods. Camel TB can be transmitted to humans through direct contact with infected animals or their products, such as milk and meat. However, the extent of human exposure and infection by camel TB in the Ethiopia is largely unknown (Teshome, 2021). Camel TB is also a potential threat to wildlife conservation, as camels share habitats and water sources with wild animals, such as antelopes, gazelles, and hyenas. Camel TB could spill over to these species and cause outbreaks that could affect their population dynamics and biodiversity. Moreover, camel TB could compromise the efforts to control bovine TB in cattle and other domestic animals, as camels can act as reservoirs and sources of infection (Mamo et al., 2009). Dromedary camels are important livestock animals that provide meat and milk for human consumption. They are found mainly in the Middle East and Africa, where they number around 30 million. Camels are well adapted to harsh and dry environments, but they also face various health risks. They can be infected by and transmit pathogens that cause diseases in humans and other animals, such as MERS, bruce-llosis, camelpox, and Rift Valley fever (Zhu et al., 2019). The transmission of infectious zoonotic illnesses between animals and humans is generally facilitated by intimate contact between them. "Those diseases and infections that are naturally communi-cated between vertebrate animals and man," according to the World Health Organization (WHO). People who live close to animals, especially in developing countries, are at risk of getting zoonotic TB, which is a type of TB caused by Mycobacterium bovis. This bacterium can infect many animals, but cattle are the main source of human infection. People can get zoonotic TB by drinking raw milk or eating raw meat from infected animals, or by breathing in the bacteria from animal droppings or carcasses. Zoonotic TB is hard to diagnose and treat because it needs special tests and drugs that are often not available. Zoonotic TB can affect the lungs and other organs of the body. It is a serious public health problem for people who depend on livestock for their livelihood (WHO, 2017). Camel tuberculosis, like bovine tuberculosis, has a major zoonotic impact, particularly in nomadic populations who consume raw camel milk and animal products. Prevalences of 5-10% were recorded in slaughtered camels based on gross pathology (Mamo et al., 2009).

Current Status of  the infection in Ethiopia

Animals in Ethiopia are afflicted with BTB, a condition brought on by bacteria from the Myco-bacterium tuberculosis complex. In Ethiopia, meat inspection at the slaughterhouses, tuberculin skin testing, and occasionally bacterial culture are the major means for detecting BTB (Shitaye et al., 2007). According to a cross sectional study con-ducted on 906 camels slaughtered at Akaki and Metehara abattoirs, the prevalence of camel TB was 10.04% based on pathology and 2.2% based on molecular characterization of the causative agents (Ashenafi et al., 2013). Another study on 276 camels slaughtered at the Dire Dawa abattoir reported a prevalence of 5.07% based on postmortem exam-ination and 1.45% based on culture isolation of M. bovis. Camel TB has public health implications, especially in pastoral areas of Ethiopia where people consume raw camel milk and its products and have close contact with their camels (Zerom et al., 2013) as summarized in (Table 1).

Table 1: Summary of current Status of  the infection in Ethiopia.

CONCLUSION AND RECOMMENDATIONS

Camel tuberculosis is a zoonotic disease caused by the Mycobacterium bovis and M. tuberculosis that affects the health and productivity of camels and poses a public health risk to humans who consume camel milk and meat. The epidemiology and public health importance of camel tuberculosis in Ethiopia are poorly understood due to the lack of reliable data and diagnostic tools. However, some studies have indicated that the prevalence of camel tuberculosis is high in some regions of the Ethiopia, especially in pastoral areas where camels are kept in close contact with other livestock and humans. The transmission of camel tuberculosis is likely to occur through inhalation, ingestion, or direct contact with infected animals or their products. The risk factors for camel tuberculosis include poor husbandry practices, lack of biosecurity measures, co-infection with other diseases, and genetic susceptibility of camels. The clinical signs of camel tuberculosis are nonspecific and may include weight loss, coughing, lymphade-nitis, mastitis, and abscesses. The diagnosis of camel tuberculosis is challenging due to the limitations of the available tests, such as tuberculin skin test, interferon-gamma assay, bacteriological culture, and molecular techniques. The control and prevention of the camel tuberculosis require a coordinated and collaborative approach involving multiple stake-holders, such as camel owners, veterinarians, public health officials, researchers, and policymakers. 

Some of the recommended strategies for controlling camel tuberculosis are:

1) Improving the awareness and knowledge of the camel owners and consumers about the zoo-notic potential and economic impact of camel tuberculosis.

2) Implementing regular screening and surve-illance programs for camel tuberculosis using appropriate diagnostic methods and reporting systems.

3) Applying quarantine and isolation measures for suspected or confirmed cases of camel tuber-culosis and restricting the movement and trade of infected animals and their products.

4) Enhancing the biosecurity and hygiene prac-tices in camel farms and slaughterhouses to prevent the introduction and spread of camel tuberculosis.

5) Promoting the use of pasteurization or boiling of camel milk and proper cooking of camel meat before consumption to reduce the risk of human infection.

6) Supporting the development and evaluation of effective vaccines and therapeutics for camel tuberculosis.

7) Conducting further research on the epide-miology, pathogenesis, diagnosis, treatment & prevention of camel tuberculosis in Ethiopia.

ACKNOWLEDGEMENT

We would like to thanks Dr. Adem Abdella from ours deep heart for his advice and holistic mentoring. One thing that has not been forgotten is our deepest gratitude and thankfulness to  all the providers of literature that spent their time to supply us with the necessary information.

CONFLICTS OF INTEREST

The authors have no conflict of interest.

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Article Info:

Academic Editor 

Dr. Phelipe Magalhães Duarte, Professor, Department of Veterinary, Faculty of Biological and Health Sciences, University of Cuiabá, Mato Grosso, Brazil.

Received

August 16, 2023

Accepted

September 21, 2023

Published

September 29, 2023

Article DOI: 10.34104/ijavs.023.01160129

Corresponding author

Daniel Tamirat WeldeMariam*

Dept. of Veterinary Public Health, Haramaya University College of Veterinary Medicine, Ethiopia

Cite this article

Aklilu MA, Mariam MTW, Shanta SA, Islam MS, and Akter A. (2023). Review on the epidemiology and public health importance of camel tuberculosis. Int. J. Agric. Vet. Sci., 5(5), 116-129. https://doi.org/10.34104/ijavs.023.01160129 

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