Mycobacteria and zoonoses among pastoralists and their livestock in south-east Ethiopia

Globally, tuberculosis (TB) causes millions of deaths per year. Ethiopia ranks seventh among the world’s 22 countries with high tuberculosis burden. Mycobacterium tuberculosis (M. tuberculosis) is the most common cause of human TB, but an unknown proportion of cases are due to M. bovis. Although cattle are considered to be the main hosts of M. bovis, isolations have been made from many other livestock and wildlife species and transmission to humans constitutes a public health problem. BTB became rare in human and cattle in developed countries as the result of milk pasteurization and test and slaughter policy. A Test and slaughter control option is difficult to apply in developing countries due to high cost of implementation. TB caused by M. bovis is clinically indistinguishable from TB caused by M. tuberculosis and can only be differentiated by laboratory methods. A considerable amount of suspected human TB and TB like-lesions specimens in animals were identified as non-tuberculous mycobacteria (NTM) in numerous reports. Conventional diagnostic laboratory methods are not accurate enough to identify NTM from Mycobacterium tuberculosis complex (MTC). Polymerase chain reaction (PCR) based molecular techniques are appropriate methods to differentiate NTM from MTC.
BTB is endemic in Ethiopian cattle in central highlands and the situation is not well known in pastoral areas. Further more a zoonotic link of M. bovis was not documented in Ethiopia.
Limited information is available on the status of brucellosis and Q-fever in livestock of southeast Ethiopian pastoralists. In the present study we investigate the presence of zoonotic transmission of tuberculosis at the human-livestock interface and assess the status of brucellosis and Q-fever in pastoral livestock of southeast Ethiopia in Oromia and Somali Regional States.
Comparative intradermal tuberculin test (CIDT) was conducted in 894 cattle from Dhuko, Sirba, Arda-Bururi and Siminto pastoral association (PA) in Oromia and Hayadimtu, Bifatu, Melkalibe and Bakaka PAs in Somali region. In addition 479 camels and 518 goats were included from the same PAs in Somali region. The test results were interpreted based on the Office Internationale des Epizooties (OIE) recommended 4 mm and a recently suggested 2 mm cut-off for the CIDT test in cattle and >4 mm was used for camels and goats. The individual animal prevalence of tuberculin reactors was 4.0% (95% CI= 2.7-5.3%) and 5.4% (95% CI= 3.9-6.8%) when using the 4 mm and the 2 mm cut-off, respectively. BTB prevalence was 0.4% (95% CI= -0.2-1.0%) and 0.2 %( 95% CI=-0.2-0.6%) in camels and goats, respectively. In Somali region prevalence of avian PPD reactors in cattle, camels and goats were 0.7% (95% CI= 0.2-2.0%), 10.0 %( 95% CI= 7.0-14.0 %) and 1.0% (95% CI= 0.3-4.0%), respectively, whereby camels had an odds ratio (OR) of 16.5 (95% CI=5.0- 55.0) when compared to cattle. As compared to Somali regions high prevalence of BTB reactor cattle were from Oromia region with some hot spot PAs; Arda-Bururi and Siminto in Oromia and Hayadimitu in Somali region and risk factors to be further investigated. The high proportion of camel reactors to avian PPD needs further investigation of its impact on camel production.
Sputum and fine-needle aspirate (FNA) specimens were collected from 260 patients with suspected pulmonary TB and from 32 cases with suspect TB lymphadenitis, respectively. In parallel, 207 suspected tuberculous lesions were collected from livestock slaughtered at abattoirs. Specimens were processed and cultured for mycobacteria; samples with acid-fast stained bacilli were further characterized by molecular methods including genus and deletion typing as well as spoligotyping. Non-tuberculous mycobacteria (NTM) were sequenced at the 16S rDNA locus. Culturing and molecular typing of acid-fast bacilli collected from humans yielded 174 (67%) and 9 (28%) mycobacterial isolates from sputum and FNA, respectively, of which 161 were characterized as M. tuberculosis, three were M. bovis, and the remaining 10 were typed as NTMs. Similarly, a yield of 40 (23%) mycobacterial isolates was recorded from tuberculous lesions of livestock animals, including 24 M. bovis and 4 NTMs from cattle, 1 M. tuberculosis and 1 NTM from camels, and nine NTMs from goats. Isolation of M. bovis from humans and M. tuberculosis from animal confirmed transmission between livestock and humans in the pastoral areas of southeast Ethiopia.
Simultaneous surveys of brucellosis and Q-fever were conducted in animals tested for tuberculin skin test. Sera were collected from all livestock tested for BTB to assess the status of brucellosis and Q-fever in pastoral livestock of study area. A total of 1830 animals comprising 862 cattle, 458 camels and 510 goats were screened initially with Rose Bengal test (RBT) for brucellosis. All RBT positive and 25% of negative animals were further tested using ELISA. These comprise a total of 460 animals (211 cattle, 102 camels and 147 goats). Besides, sera from a total of 368 animals (180 cattle, 90 camels and 98 goats) were tested for Q-fever using ELISA kit. The sero-prevalence of brucellosis in RBT tested animals was 1.4% (95% CI= 0.8, 2.6%), 0.9% (95% CI= 0.3, 2.7%) and 9.6% (95% CI =5.2, 17.1) in cattle, camels and goats, respectively. Twelve percent (12.0%) of negative camel sera were positive for ELISA. Thus, ELISA is more sensitive than RBT in the present study. The sero-prevalences of Q-fever were 31.6% (95% CI=24.7-39.5%), 90.0% (95% CI= 81.8-94.7%) and 54.2% (95% CI= 46.1-62.1%) in cattle, camels and goats, respectively. Both brucellosis and Q-fever are prevalent in the study area. High seropositivity of Q-fever in all livestock species tested and higher seropositive in goats for brucellosis implies risks of human infection by both diseases. Thus, warrant further study of both diseases in animals and humans in the area.
The simultaneous study of mycobacteria in humans and livestock, and other zoonoses in the present study demonstrates an added value of a “One Health” approach of closer cooperation of human and animal health sectors in Ethiopian pastoralists