A study on molecular epidemiology of bovine tuberculosis in man and cattle in
Tanzania was carried with two components. The first component was based on field
investigation of tuberculosis in cattle and man in Arusha region, in the north and in
the Usangu Plains in the Southern Highlands of Tanzania. The second component
involved laboratory analysis of mycobacterialstrains acquired from field study by
both conventional and molecular biology techniques.
In field work, a total of 6383 cattle were tuberculin tested, and 911 (14.3%) were
classified as reactors. 841 of 6383 cattle examined were destine for slaughter and 225
(26.8%) were found to have visible lesions. A total of 1719 pooled lymph node
samples collected from slaughter cattle in the study area (Arusha n=1068 and the
Usangu Plains n=651) were cultured and 4.0% yielded mycobacteria. 80 of the
samples from the Usangu Plains came from cattle classified as reactors (Table 3.9),
while samples from Arusha had no accompanying tuberculin test results. Among the
isolates 72.6% were classified as M. bovis and the rest as atypical mycobacteria. Of
the 805 milk samples cultured (14% were from reactor cattle), only two (0.3%)
yielded M. bovis, the remaining 36 isolates were atypical mycobacteria (Table 3.10).
Its only two isolates of atypical mycobacteria which came from reactor cattle.
Regarding human specimens, a total of 53 lymph node biopsies were submitted for
culture and 21 (39.6%) were positive for mycobacteria. Six isolates were identified as
M. bovis, and the remaining 15 were M. tuberculosis. Of 96 sputum samples which
were collected, mycobacteria species were recovered from 23 but only one (4.3%)
was classified as M. bovis. Sixteen (69.1%) isolates were identified as M.
tuberculosis, and the rest were atypical mycobacteria. Epidemiological data revealed
that M. bovis was more prevalent in people with cattle contact than in other
occupations (Table 3.13)
The IS986 and mtpAQ multiplex PCR developed in the course of this study was able
to differentiate M. bovis from M. tuberculosis. DNA fingerprinting of all the strains
cultured was carried out using restriction fragment length polymorphism (RFLP) and
spoligotyping techniques. The copy number of IS986 amongst strains of M. bovis
from cattle ranged from one to six, while those from man had five to 15. There was
similarity of DNA fingerprints among some of the strains from cattle and man as
determined by the three typing techniques (Figures 6.2, 6.5 and 6.9). M. tuberculosis
strains were found to belong to three clusters by IS986 RFLP, with one cluster
containing over 60% of the strains.
Intersegment PCR, a molecular typing technique developed in the current study was
able to differentiate strains but the results were influenced by the concentration of
template DNA. A DNA fragment apparently found only in M. bovis and absent in M.
tuberculosis and other mycobacteria was identified by the RAPD PCR techniques.
This fragment was cloned, sequenced and its DNA sequence was found to match a
M. tuberculosis cosmid, which also matched rfbE gene of Yersinia enterocolitica.
Specificity testing revealed hybridization to M. tuberculosis as well.
The findings of the above studies have showed the existence of M. bovis infection in
man and cattle in Tanzania. The study has also shown the zoonotic importance of
infection in the two populations which necessitates a veterinary/medical approach to
the control of the disease in Tanzania. Furthermore, it has been shown that molecular
biology techniques are essential epidemiological tools in studies of zoonotic
conditions such as tuberculosis. The study was unable to find a specific DNA element
for M. bovis. This observation concurs with others which have found 100%
homogeneity between species of the M. tuberculosis complex.