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Journal of Clinical Microbiology, January 2004, p. 431-434, Vol. 42, No. 1
0095-1137/04/$08.00+0 DOI: 10.1128/JCM.42.1.431-434.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Molecular Epidemiology of Disease Due to Mycobacterium bovis in Humans in the United Kingdom
Andrea L. Gibson,1* Glyn Hewinson,2 Tony Goodchild,2 Brian Watt,3,
Alistair Story,4 Jacqueline Inwald,2 and Francis A. Drobniewski1
Mycobacterium Reference Unit, Health Protection Agency, and Department of Microbiology, Guy's, King's and St Thomas' School of Medicine, King's College Hospital (Dulwich), East Dulwich Grove, London, SE22 8QF,1
Veterinary Laboratory Agency, Weybridge, New Haw, Surrey KT15 3NB,2
Scottish Mycobacteria Reference Laboratory, Royal Infirmary, Little France, Edinburgh EH16 4SA,3
HPA, Communicable Disease Surveillance Centre, Colindale, London NW9 5EQ, United Kingdom4
Received 2 May 2003/
Returned for modification 13 June 2003/
Accepted 12 September 2003

ABSTRACT
Mycobacterium bovis is the causative agent of bovine tuberculosis,
with a wide host range. Fifty human
M. bovis isolates were typed
using spoligotyping and variable number tandem repeats (VNTR).
Fifteen of these spoligotypes have not yet been recorded in
cattle. The predominant spoligotype in humans and cattle was
subdivided by VNTR.

INTRODUCTION
Mycobacterium bovis has a wide host range, infecting many domestic
and wild animals. Although occurring relatively rarely,
M. bovis can also infect humans. In the United Kingdom, only about 1%
of clinically diagnosed cases of tuberculosis (TB) that are
subsequently proven bacteriologically are attributed to
M. bovis,
but in the developing world,
M. bovis is still a cause for concern
(
6). The resurgence of bovine TB in cattle in the United Kingdom
is raising concerns that transmission from cattle to humans
might be a serious public health issue. It is therefore important
to be able to quickly identify where rates of
M. bovis in cattle
are high and pose a potential risk of transmission to humans.
M. bovis was once a major source of TB in humans in the United
Kingdom but was almost eradicated after the introduction of
control measures to reduce bovine tuberculosis in cattle together
with the pasteurization of milk for human consumption. The majority
of bovine TB cases in the 1980s and early 1990s presented either
in the elderly or in those who had been infected abroad and
returned or migrated to the United Kingdom (
13). Many animals,
such as badgers, foxes, ferrets, and deer (
1,
3,
9), are believed
to act as vectors for transmission to livestock, and some have
also been associated with transmission to humans (
8,
16,
18).
Enhanced surveillance of
M. bovis infections in humans was initiated
in 1998. However, in 2001 a revised system which allows more
timely collection of data was introduced (
4,
5). Advances in
molecular typing have provided tools to enhance our knowledge
of
M. bovis dissemination. Restriction fragment length polymorphism
using the insertion sequence IS
6110 is considered to provide
the best discrimination of
M. tuberculosis isolates. However,
M. bovis isolates from cattle usually have a single copy of
IS
6110 (
7); therefore, alternative techniques such as spacer
oligonucleotide typing (spoligotyping) and variable number tandem
repeats (VNTR) have been used successfully in discriminating
between strains of
M. bovis (
1,
7,
11,
12,
15,
17).
This study examines the molecular epidemiology of M. bovis cases within the United Kingdom using two molecular typing techniques and compares the typing patterns obtained to those prevalent in United Kingdom cattle today.
All available viable M. bovis isolates (50 isolates) from humans diagnosed in the United Kingdom between 1997 and 2000 were identified; 40 were recovered at the Mycobacterium Reference Unit, London, and 10 were recovered at the Scottish Mycobacteria Reference Laboratory, Edinburgh. DNA was extracted by using a quick extraction method (19). Briefly, one colony was removed using a 1-µl loop and placed in 150 ml of water. An equal volume (150 ml) of chloroform was added, and the mixture was vortexed and then boiled at 80°C for 20 min to kill the cultures.
Spoligotyping was performed using the method described by Kamerbeek et al. (15), and VNTR was performed using the method described by Frothingham and Meeker-O'Connell (11). The size of each exact tandem repeat at each locus (A to E) was determined by running the PCR product on an agarose gel containing size markers (100-bp ladder; Promega, Southampton, United Kingdom) (20-bp ladder; Sigma-Aldrich, Dorset, United Kingdom). Deletion typing was carried out on a strain with a spoligotype not typical of M. bovis, using the method described by Brosch et al. (2). Seven regions of difference (RD) were examined: RD 4, 7, 8, 9, 10, 12, and 13. The Hunter-Gaston index (HGI), which is based on the probability of two unrelated strains from a test population being placed into different typing groups, was calculated to determine the discriminatory power of each typing method alone and in combination (14).
Epidemiological information was obtained from internal laboratory records at the Mycobacterium Reference Unit and Scottish Mycobacteria Reference Laboratory and from existing surveillance data held at the Health Protection Agency Communicable Disease Surveillance Centre.
Spoligotyping of the 50 human M. bovis isolates produced 25 individual spoligotypes (Fig. 1) and had an HGI of 0.90. Thirty-two isolates were divided into seven clusters, A to G (Fig. 1). The spoligotypes were compared with M. bovis spoligotypes from a bank of over 15,000 cattle isolates collected from all over the United Kingdom held at the Veterinary Laboratory Agency (VLA) and dating between 1987 and 2002. The largest cluster of human M. bovis isolates (15 isolates, 30%) had been seen in cattle before and was sequentially numbered type 9 (international type SB140; http://www.Mbovis.org) at the VLA. Type 9 is the most frequently seen spoligotype of M. bovis (over 30% of all isolates have this spoligotype) isolated from cattle and has a wide geographical range in the United Kingdom (10).
Human type 9 isolates were seen across the United Kingdom, suggesting
that transmission between cattle and humans might occur. Interestingly,
15 of the human
M. bovis spoligotypes had not been seen at the
VLA in isolates from cattle. When these 15 types were compared
to the international spoligotype database, only 2 were recognized.
The first was isolated in Argentina, the second was isolated
in Australia, and the remaining 13 spoligotypes were all unique
to the United Kingdom. In the majority of these cases, it is
likely that disease was due to reactivation of a past infection
that had been acquired prior to milk pasteurization rather than
to primary infection, because 72.3% of the patients were over
the age of 50. (Fig.
2). Therefore, these 13 unique spoligotypes
may reflect
M. bovis strains circulating in the United Kingdom
over 50 years ago.
M. bovis spoligotypes do not usually contain spacers 39 to 43;
however, one spoligotype from the panel contained spacers 40
to 43, which are more commonly seen in
M. tuberculosis. Phenotypic
and biochemical tests demonstrated that this isolate had typical
M. bovis characteristics; it was microaerophilic, TCH (thiophen-2-carboxylic
acid hydrazide) negative, and pyrazinamide resistant, and it
grew better on pyruvate than glycerol Lowenstein-Jensen slopes.
Deletion analysis was performed to ascertain the identity of this strain. The strain contained RD 4, 12, and 13 but lacked RD 7, 8, 9, and 10, indicating that this strain is actually M. Africanum and not M. bovis.
VNTR typing alone produced 18 different patterns and had an HGI of 0.85. Combining spoligotyping with VNTR vastly improved the level of discrimination, producing 34 different types and a very high HGI of 0.96. Furthermore, VNTR was very useful in subdividing type 9 spoligotypes, separating the group into six subtypes (Table 1).
Epidemiological information showed that the study population
was widely distributed across the United Kingdom, had an average
age of 58.7 years, and had approximately equal proportions of
males and females (21:17). Where ethnicity was known (a total
of 15 patients), 14 patients were white and 1 was of black-African
origin and was originally from Nigeria but had lived in the
United Kingdom since 1996. This person had a unique spoligotype;
therefore, it is possible that she was infected in Nigeria before
arriving in the United Kingdom. Of interest, 59% (13 of 22)
of cases had some contact with a farm, ranging from having a
Saturday job milking cows, to living on a dairy farm as a child,
to being a farmer (now retired). One spoligotype cluster represents
an outbreak on a farm in Gloucester. Two siblings (a 20-year-old
male and a 17-year-old female) living on their parents' farm
became infected with
M. bovis. The brother occasionally helped
his father on the farm by restraining the cattle and would often
be sprayed with nasal mucus. Cattle infected with
M. bovis of
the same spoligotype had been detected on the farm in previous
years. Transmission from cattle to human is thought to have
occurred by the inhalation of infected aerosols from cattle.
The brother is thought to have subsequently infected his sister,
as she had no contact with the cattle but was also diabetic
and pregnant, i.e., immuno-compromised. This is thought to be
the first case of human-to-human transmission since 1990 (R.
M. M. Smith, F. Drobniewsky, A. L. Gibson, J. D. E. Montague,
M. N. Logan, D. Hunt, R. G. Hewinson, R. L. Salmon, and B. ONeill,
unpublished data).
It is important to monitor bovine tuberculosis in humans, especially in those who are at high risk of primary infection, such as agricultural and abattoir workers, and to identify any transmission between animals and humans. A combination of spoligotyping and VNTR is an efficient discriminatory tool for the molecular surveillance of M. bovis and also addresses the problem of analyzing isolates with single copies of IS6110. The combined VNTR and spoligotyping approach is of value in typing M. tuberculosis isolates. Further improvements in these techniques might produce a combined system capable of high discrimination for all M. tuberculosis complex isolates in humans or other mammals.

ACKNOWLEDGMENTS
This work was funded by the Department for Environment, Food,
and Rural Affairs and supported by the Health Protection Agency,
formerly the Public Health Laboratory.

FOOTNOTES
* Corresponding author. Mailing address: Mycobacterium Reference Unit, Health Protection Agency, Dulwich Hospital, East Dulwich Grove, London SE22 8QF, United Kingdom. Phone: 0208 693 1312. Fax: 0207 346 6477. E-mail:
andreagibson78{at}hotmail.com.

Present address: Silverburn House, by Penicuik, Midlothian, EH26 9LF, United Kingdom. 

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Journal of Clinical Microbiology, January 2004, p. 431-434, Vol. 42, No. 1
0095-1137/04/$08.00+0 DOI: 10.1128/JCM.42.1.431-434.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
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