Tuberculosis causes over 2million deaths annually and is rapidly increasing in sub-Saharan African countries, fuelled by the concurrent HIV-epidemic. The achievements of the Millenium Development Goals with regard to tuberculosis are far behind its objectives. In the last four years, we established the first tuberculosis laboratory capable of cultivating mycobacteria in Chad, which is a high incidence country. Colleagues in Tanzania, have been engaged with studies on Mycobacterium bovis in animals and man for a past decade, have been able to isolate albeit few M. bovis from human cases of tuberculous cervical adenitis. We have now established the molecular tools and collaborative network to address the question of the importance of bovine tuberculosis in the human tuberculosis epidemic, fostered by HIV/AIDS in different parts of Africa. The highest risk groups are individuals with concomitant HIV/AIDS infection. In Africa, the proportion of M. bovis in human TB is not known and is under-reported because diagnostic laboratories don’t search for it systematically. Consumption of raw milk, poorly heat-treated meat and close contact with infected animals represent the main sources of infection for humans. In many industrialized countries bovine tuberculosis was eliminated by state compensation for tested and slaughtered animals. In most developing countries this is not possible and alternative ways, even livestock vaccination are (re)-investigated to reduce transmission. Better knowledge of molecular epidemiology and the spectrum of host interactions are pre-requisites for the development of surveillance and may open ways for possible control.
The aim of this project is to assess trans African population based patterns of molecular epidemiology of M. bovis and host susceptibility in cattle to understand zoonotic tuberculosis within the concept of “one medicine”. Specifically, the objectives are: 1) To identify East-West African spatial patterns of genetic drift and its overlap with imported strains: 2) To address the genetic variability of different cattle populations or breeds and associations between genetic markers and M.bovis infections; 3) To assess the importance and risks M. bovis derived zoonotic tuberculosis in human tuberculosis.
Research questions and approaches:
1) What is the molecular genetic population structure of African bovine tuberculosis and to which extend is it intermixed with imported strains? Can we demonstrate a direction of spread of bovine tuberculosis in Africa? Can we identify a limit of spread of M. bovis in West Africa?. A network involving partners in Tanzania, Chad, Nigeria, Mauritania, Mali, Senegal and Morocco provides access to livestock herds and carcasses in abattoirs (population based samples) to isolate and characterize M. bovis strains. The molecular characterization will be done by Direct Repeat (DR) and Variable Numbers of Tandem Repeat (VNTR) typing to define region specific clades and their relationship. In depth characterization will be done by single nucleotide polymorphisms (SNP) and chip hybridisation methods. Cluster analysis combined with representative disease frequency will be used to estimate and interpret proportions of reactivation and recent transmission in livestock and spill over to humans depending on different livestock systems and risk factors for human infection. Spatial geographical analysis of DR and VNTR patterns will be investigated by principal component analysis to identify trends of spread of M. bovis across Africa.
2) Is there an association between polymorphisms of microsatellite genetic markers in cattle and the different levels of severity of the infection (genotype-phenotype relationships)? What is the molecular genetic similarity / diversity of bovines susceptible or infected by M.bovis in different countries of the continent? In collaboration with the Institut für Nutztierwissenschaften (INW, ETH Zürich), this part will analyse genetic structure, characterise diversity levels within and relationships between infected cattle populations from 6 geographic regions, using selected microsatellite genetic markers. An association study will be conducted to estimate the frequency (effect) of microsatellite markers (haplotypes) on the severity of M.bovis infection in different breeds of cattle.
3) What is the importance of specific risk factors of M. bovis in the human tuberculosis epidemic
Medical teams will collect fine needle aspirates of cervical lymph nodes of suspected extra pulmonary tuberculosis patients for cultivation in Tanzania, Chad and Mauritania in the framework of a case-control study. Allele patterns of human and animal isolates will be correlated to identify homologous strains. Human behaviour and related livestock systems will be analysed for all human M. bovis cases to identify risks of exposure.
Expected results are: 1) Determine trends of spread and possible origins of M. bovis in Africa and its interaction with imported strains; 2)Genotypic variation of hosts’ susceptibility to M. Bovis within-breed and a between-breed and possible genetic similarities between different geographic regions within Africa at molecular level. 3) Identify determinants and risk factors of spill over of M. bovis to humans, 4) Geographical site specific transmission intensity to develop options to prevent human infection and control in livestock; 5) Provide the basis for functional genomic assessments.
