D1981.PDF

Rev. sci. tech. Off. int. Epiz., 2001, 20 (2), 630-639
Tracing movement of African buffalo
in southern Africa
W. Vosloo (1), A.D.S. Bastos (2), A. Michel (1) & G.R. Thomson (3)
(1) Onderstepoort Veterinary Institute, Private Bag X05, Onderstepoort 0110, South Africa
(2) Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
(3) Onderstepoort Veterinary Institute, Private Bag X05, Onderstepoort 0110, South Africa; present address:
Organisation of African Unity/Inter-African Bureau for Animal Resources (OAU-IBAR), P.O. Box 30786,
Nairobi, Kenya
Summary
Genetic characterisation of two pathogens, namely foot and mouth disease (FMD)
virus and Mycobacterium bovis, isolated from African buffalo (Syncerus caffer) in
southern Africa was used to determine the origin of buffalo in situations where the
source of infection was obscure. By determining the phylogenetic relatedness of
various FMD virus isolates using partial sequencing of the main antigenic
determinant, VP1, the origin of buffalo moved illegally to the non-endemic region
of South Africa was traced to the Kruger National Park (KNP) where FMD is
endemic in the buffalo population. Comparative analysis of the ‘genetic
fingerprints’ of bovine tuberculosis isolates from buffalo and cattle has aided in
tracing the original source of infection of buffalo populations in the KNP.
Furthermore, these analyses have assisted in tracing the origin of infected animals
that have been moved to other parts of South Africa.
Keywords
African buffalo – Bovine tuberculosis – Foot and mouth disease virus – Southern Africa –
Traceability.
Introduction
The use of techniques that enable analysis of the genomes of
infectious agents combined with statistical methods for
deriving relationships between them is being used increasingly
to advance the understanding of the epidemiologies of a
number of important livestock diseases (13, 22, 27, 29, 34, 48,
61, 66). The previously painstaking and often unreliable
process of determining the origin of infections such as foot and
mouth disease (FMD) and classical swine fever (CSF) that
suddenly appeared in new locations can now be a rapid and
reliable process, if adequate background data are available (28).
Infectious agents, and ribonucleic acid (RNA)-containing
viruses in particular, are able to mutate rapidly. This can result
in geographically separated populations evolving
independently, allowing representatives of such separated
microbial populations to be identified (so-called topotypes)
(7, 12, 25, 42, 53, 65). Subsequent spread of these topotypes
to new locations can therefore be traced by genome analysis.
Thus, for example, the recent intra- and intercontinental spread
of the pan-Asian O topotype of FMD virus, which has caused
serious epidemics in locations as far apart as the Indian
subcontinent, South-East Asia, South Africa and the United
Kingdom, is well known (40, 54).
This approach is being used increasingly for other important
infections of animals, some of which are discussed here.
However, these techniques provide another possibility that was
not originally anticipated, namely the use of genome analysis of
infectious agents to identify the origin of animals that harbour
them. The rate at which the genomes of infectious agents
mutate is several orders of magnitude faster than the rate of
mutation of mammalian genomes (33). This means that
differentiable mutations occur much faster than in the
mammalian hosts. Therefore, the identification of the probable
origin of animals may be possible by studying the infectious
agents harboured by animals where more usual methods for
animal identification have failed. This method is particularly
useful where particular populations of animals have been
isolated for relatively long periods of time, e.g. within wildlife
reserves or on closed-herd farms. So far, the infectious agents
that have been used are principally those that are potentially
pathogenic, because information on these agents is usually
more detailed than that on non-pathogenic agents. However,
Rev. sci. tech. Off. int. Epiz., 20 (2)
providing that the distribution of the genotypes that constitute
the population of a particular agent is known, a wide variety of
micro-organisms could be employed.
This paper will focus on the use of FMD viruses and
Mycobacterium bovis to determine the probable origin of African
buffalo (Syncerus caffer) using specific examples. These animals
are a valuable resource in southern Africa where their status as
one of the ‘big-five’ game species makes them highly sought
after for both hunting and eco-tourism. Unfortunately, these
buffalo can maintain the three South African Territories (SAT)
types of FMD viruses, Theileria parva (the causative agent in
southern Africa of Corridor disease [CD]) and M. bovis (which
causes bovine tuberculosis), making the animals potentially
dangerous for domestic cattle with which they may come into
contact. For this reason, the prices paid for buffalo differ,
depending on whether or not the animals are infected with
these agents (which they may harbour without apparent ill
effect). In 1998, breeding animals that were infection-free were
valued above US$16,500 each, whilst FMD-infected buffalo
were valued at between US$500 and US$1,000. Those infected
with T. parva were worth between US$4,300 and US$7,200
(64). At that time, the population of buffalo in South Africa was
estimated at 31,500, of which 67.1% were in sub-populations
infected with FMD viruses and T. parva (Kruger National Park
[KNP]), 25.2% were infected with T. parva only (HluluweUmfolozi Game Reserve [HUP]) and 7.7% were free from
infection with these agents (referred to locally as ‘disease-free’)
(64).
The buffalo populations in HUP and KNP are also the only
populations in South Africa known to be infected with M. bovis.
Bovine tuberculosis (BTB) is becoming a significant problem in
wildlife world-wide (11, 14, 15, 19, 47, 55) and has severely
affected nature conservation and ecotourism in South Africa
(35, 36, 37). Since the mid-1980s, BTB has become established
as an important disease of wildlife in the major game reserves
of South Africa (18, 26). African buffalo serve as effective
maintenance hosts because of their relatively high susceptibility
to M. bovis, herd structure and characteristic behavioural
patterns (49). Once a buffalo herd becomes infected with
M. bovis, the prevalence can exceed 90% (49). Under these
conditions, spill-over of the infection to other species occurs
and has been demonstrated in a number of species, such as
lion, kudu, leopard, cheetah, baboon (9, 35), hyaena, genet and
bushpig (D.F. Keet and D. Cooper, personal communication).
Furthermore, infected buffalo pose a threat to cattle, and
therefore also their owners, when the fences separating
livestock and wildlife areas are breached.
In South Africa, buffalo from FMD- and CD-infected herds may
be moved only within veterinary control areas that are
registered with the Directorate of Veterinary Services,
Department of Agriculture and that comply with the fencing
regulations for premises holding buffalo (Animal Disease Act
1984, Act No. 35). Most African buffalo in the KNP become
631
infected with the three SAT-type FMD viruses at an early age.
Following initial sub-clinical infection, a high proportion
become carriers of the disease (58). Single buffalo can maintain
the virus for five years or longer in the oesophageo-pharyngeal
region, while an isolated herd of buffalo was shown to maintain
infection for up to twenty-four years (17). These carriers can,
albeit rarely, infect susceptible livestock, notably cattle, after
direct and prolonged contact between the two species (16, 24,
32, 63).
In persistently infected African buffalo, SAT-type FMD viruses
have a mutation rate of between 1.54 x 10–2 and 1.64 x 10–2
substitutions per nucleotide per year in the region coding viral
protein 1 (VP1) (63). Furthermore, SAT-type viruses evolve
independently in different regions (7, 39, 62), in accordance
with the topotype concept (53). This localised, yet highly
variable evolution of FMD viruses is useful for tracing the origin
of epizootics and has previously been applied to demonstrate
interspecies transmission under both experimental (24, 63) and
natural conditions (6, 23).
In South Africa, genome typing of M. bovis isolates by restriction
fragment length polymorphism (RFLP) has been useful for
tracing the origin of individual infected animals as well as in
investigating the transmission of BTB within and between
animal species (44). Generally, RFLP analysis is an accepted
method for characterising strains of Mycobacterium tuberculosis
and the closely related M. bovis (20, 46, 56, 60). The most
commonly used marker is the insertion sequence IS6110. Gel
patterns are produced with fragments generated by treatment
of bacterial deoxyribonucleic acid (DNA) with restriction
endonucleases. This provides information on both the number
of insertions and the relative sites of insertion within the
genome. In studies on human tuberculosis, epidemiologically
unrelated isolates have a high degree of polymorphism of the
IS6110 RFLP gel pattern, while epidemiologically related
isolates have identical or similar (one band variation) patterns
(60). Furthermore, the IS6110 gel patterns of M. tuberculosis
have sufficiently high degrees of stability to allow
epidemiologically valid studies to trace outbreaks of
M. tuberculosis strains with high copy numbers of IS6110 (45,
57). In strains with only a few copies of this insertion sequence,
including M. bovis, the accuracy and discriminatory power of
strain classification must be increased by including an
additional genetic marker, such as the highly repetitive
polymorphic guanine- and cytosine-rich repeat sequence
(PGRS) (2, 21, 51) in the analysis.
This paper expands on this theme by detailing a case that
demonstrated the usefulness of sequencing data of the main
antigenic determinant of FMD virus, to determine the
geographical origin of FMD-infected buffalo moved illegally.
This case also illustrates the accuracy with which illegally
moved buffalo can be traced. Furthermore, the authors
describe the potential use of RFLP analysis for M. bovis isolates
from infected buffalo, to trace the origin of these animals.
632
Rev. sci. tech. Off. int. Epiz., 20 (2)
Materials and methods
Study area and background case details: foot
and mouth disease
In August 1998, seven juvenile African buffalo were
transported to a farm in the Potgietersrus district in the
Northern Province of South Africa (Fig. 1). The buffalo, which
were sold as ‘disease-free’ animals, were allegedly purchased
from a farm in the Free State Province. Both farms are outside
the FMD control area. Suspicion was raised when only
photocopies of movement permits were presented. The buffalo
were immediately quarantined and serum and probang
samples collected for serological screening and virus isolation.
As soon as infection with FMD virus was confirmed, the buffalo
were destroyed and intensive serological surveys conducted in
the area surrounding the purported source farm to ensure that
the disease had not spread from the buffalo to other susceptible
animals in the vicinity. For comparative purposes, SAT-3 viruses
recovered from FMD-infected buffalo populations in South
Africa, Zimbabwe and Zambia were also selected. These
included viruses from the KNP in South Africa, Chikwarakwara
and Gona-re-zhou in southern Zimbabwe, Hwange National
Park in western Zimbabwe, Matusadona National Park, the
Urungwe Safari Area in northern Zimbabwe and Kafue
National Park in Zambia.
Virus isolation
Primary porcine kidney (PK) cells were inoculated with 10%
suspensions of ground tissue and secretions recovered from
probang samples or lesions and studied for the development of
cytopathic effect (CPE). The viruses recovered were typed by
enzyme-linked immunosorbent assay (ELISA) (50).
Serology
Antibodies to FMD virus SAT 1, 2 and 3 were measured using
a liquid phase blocking ELISA (30).
Molecular characterisation methods
The C-terminal half of the 1D (VP1) region of the FMD virus
genome was amplified and sequenced using primers developed
for molecular epidemiological studies of SAT-type viruses in
southern Africa, as described previously (3). Nucleotide
sequences were generated by direct sequencing of the purified
polymerase chain reaction (PCR) product, after which the data
were aligned (31) and used to infer a phylogeny (41). The
phylogenetic analysis methods employed followed those
advocated for genetic resolution of FMD viral relationships
based on partial VP1 sequence data (43).
Study area and background case details: bovine
tuberculosis
The following discussion focuses on two separate outbreaks of
BTB in which molecular typing was useful in identifying the
origin of disease.
First case
Matusadona
Chizarira
Hwange
Gona-re-zhou
Potgietersrus
Barberton
Free State
Hluhluwe
-Umfolozi
Northern Cape
In 1990, the first case of BTB in African buffalo was diagnosed
in the southern part of the KNP, from which location the disease
spread in a northerly direction. Infected cattle may have been
the origin of the epidemic; according to official reports of the
Directorate of Veterinary Services, tuberculous cattle had been
identified on various farms south of the KNP in the period
between 1955 and 1987 (38). Circumstantial evidence pointed
to the involvement of a specific farm (Farm A) in the Barberton
district of Mpumalanga Province where cattle had reportedly
mingled and shared grazing with buffalo during the 1950s and
1960s (Fig. 1). The farm was subsequently depopulated in
1992. Isolates of M. bovis from several cattle from Farm A and
buffalo from the KNP were analysed by RFLP in 1997.
Second case
KNP: Kruger National Park
Fig. 1
Map of southern Africa indicating the regions mentioned in the
text, including large game parks
Before tuberculosis infection was diagnosed in the HUP (the
second largest game reserve in South Africa), buffalo from this
conservation area were used to stock other game parks and
private farms in various parts of the country. In two of these
operations, buffalo were diagnosed with tuberculosis six
months after translocation from the HUP (P. Morkel and
N.P.J. Kriek, personal communication). In both cases, the
633
Rev. sci. tech. Off. int. Epiz., 20 (2)
buffalo were moved to properties in the Northern Cape
Province (Fig. 1). Traceback of the origin of this infection was
considered crucial for two principal reasons. Firstly, if the
buffalo had carried the infection at the time of leaving the HUP,
this implied that the single (negative) intradermal tuberculin
test performed before translocation was insufficient to ensure
effective movement control. Alternatively, the buffalo could
have contracted the infection after reaching their various
destinations, in which case the unidentified source of infection
could still pose a risk to the remaining wildlife populations in
the new conservancies.
Bacterial culture and restriction fragment
length polymorphism analysis
Mycobacterium bovis was cultured from tissue samples
submitted for routine diagnosis and processed as described
previously (8). Subcultures of the primary isolates in either
10 ml of 7H9 Middlebrook broth or on Löwenstein-Jensen
medium with pyruvate were treated with a final concentration
of 0.2M glycine on the penultimate day of incubation. Isolation
of DNA was performed as described by van Soolingen et al.
(59). For hybridisation with the IS6110 and PGRS probes,
1.5 µg of DNA was digested with PvuII and AluI respectively.
Electrophoresis and DNA transfer to a nylon membrane was
performed as described by Skuce et al. (56). The entire region
encoding IS6110 was amplified by PCR using a digoxigenin
(DIG)-labelled primer (56). Prehybridisation, hybridisation and
detection were performed according to the instructions
supplied by the manufacturer of the DIG-labelled probes. DIGlabelled DNA molecular weight marker VII was used on one
central and both outer lanes as an external marker. The DNA
patterns generated with the IS6110 probe were analysed using
commercial software (similarity coefficient of Dice, unweighted
pair group method with arithmetic averages [UPGMA],
maximum tolerance 1.2%), while the PGRS fingerprints were
analysed manually.
cluster within four distinct genetic lineages (I-IV) (Fig. 2), that
correspond with geographically discrete sampling localities (4).
These genetic lineages correspond to the following
geographical regions:
– lineage I: southern Zimbabwe and South Africa
– lineage II: Botswana and western Zimbabwe
– lineage III: Zambia
– lineage IV: northern Zimbabwe.
Within lineage I, five discrete genotypes are discernible,
labelled A-E (Fig. 2). Genotype A comprises viruses exclusively
from Chikwarakwara (100% bootstrap support), genotype B
contains viruses from two different buffalo herds occurring
within the Gona-re-zhou National Park. Included within the
latter genotype is a virus obtained from a buffalo from Hwange
Results
Foot and mouth disease
Serology and isolation of foot and mouth disease virus
Sera obtained from 1,295 cattle, 784 sheep and one buffalo in
the vicinity of the source farm in the Free State Province were
negative for the three SAT-types (results not shown). Serum
samples recovered from the seven juvenile buffalo indicated the
presence of antibodies to the three SAT-types with high titres
against SAT-3 (results not shown). SAT-3 FMD viruses were
isolated from three of the seven buffalo allegedly moved from
the Free State to the Potgietersrus area.
Genetic characterisation of foot and mouth disease
viruses
Nucleotide sequence determination and phylogenetic analysis
based on partial VP1 sequences revealed that SAT-3 viruses
Fig. 2
Neighbour-joining tree (Jukes and Cantor method) based on
partial VP1 gene nucleotide sequence data, depicting genetic
relationships of SAT-3 foot and mouth disease viruses from
southern Africa
Bootstrap values based on 1,000 replications and ≥ 95% are indicated
in bold. Viruses recovered from illegally-moved buffalo are indicated in
bold and italic. The major phylogeographical lineages are indicated as
I-IV, in accordance with previously identified SAT-3 buffalo topotypes
(4), whilst lineage I genotypes are denoted A-E. Genotype A contains
viruses from Chikwarakwara; genotype B contains viruses from two
different herds in the Gona-re-zhou National Park; genotype C contains
viruses from the buffalo found at Potgietersrus; genotype D contains
viruses from the northern Kruger National Park (KNP) and genotype E
contains viruses from the southern parts of the KNP. Lineage II contains
viruses from Botswana and western Zimbabwe; lineage III viruses from
Zambia, while lineage IV contains viruses from northern Zimbabwe
634
National Park (ZIM/11/94), which was translocated to southern
Zimbabwe two years prior to the animal being sampled
(E.C. Anderson, personal communication). Genotype C is
representative of the Potgietersrus buffalo in question, whilst
genotype D consists of northern KNP viruses. These northern
KNP viruses are distinct from those occurring in the southern
part of the game park (genotype E). The viruses recovered from
the three juvenile buffalo from Potgietersrus shared over 99%
sequence identity across the region sequenced, suggesting a
common source of infection. Furthermore, these buffalo viruses
were most closely related to SAT-3 type viruses recovered from
buffalo in the Langtoon Dam area in the northern half of the
KNP (Fig. 2), as described in a previous study (5). Because
genotypes C and E are more closely related to each other than
to other lineage I viruses (60% bootstrap support), the most
likely origin of the former genotype viruses is the northern part
of the KNP. Therefore, the buffalo had clearly not originated
from the Free State Province where FMD has not occurred for
more than 100 years. The movement permits were
subsequently demonstrated to be illegal and investigations
indicated that the source farm had no records of the seven
juvenile buffalo.
Rev. sci. tech. Off. int. Epiz., 20 (2)
Genetic characterisation of bovine tuberculosis
First case
Molecular typing of M. bovis isolates from domestic cattle from
Farm A (TB871) and wild animal species: buffalo (TB1795,
TB435, TB428, TB442, TB643, TB664), lion (TB571), baboon
(TB600) and kudu (TB1773) from the KNP, demonstrated that
all isolates shared an identical gel pattern, indicating that the
BTB infection in wildlife in the KNP had probably originated
from that farm (Fig. 3). Mycobacterium bovis isolates from cattle
on Farm A and wildlife in the KNP had identical fingerprint
patterns using both the IS6110 (Fig. 3) and PGRS (results not
shown). The single kudu isolate from a locality close to Farm A
(TB636) was unrelated to any of the other isolates.
Second case
Buffalo that were translocated from the HUP to the Northern
Cape and showed clinical signs of BTB after movement, had
identical RFLP patterns to other isolates from the HUP
(TB1006, TB1042, TB1044) (Fig. 3). This was a clear
indication that the buffalo were sub-clinically infected at the
time of movement and that the skin test had failed to detect that
infection.
Cattle
Cattle
Cattle
Cattle
Cattle
Kudu
Buffalo
Buffalo
Buffalo
Buffalo
Cattle
Lion
Buffalo
Baboon
Buffalo
Cattle
Cattle
Cattle
Cattle
Cattle
Cattle
Cattle
Kudu
Buffalo
Buffalo
Buffalo
Cattle
TB681
TB631
TB1729
TB1226
TB1302
TB1773
TB1795
TB435
TB428
TB442
TB871
TB571
TB643
TB600
TB664
TB1048
TB709
TB1130
TB999
TB810
TB1057
TB1311
TB636
TB1006
TB1042
TB1044
TB781
Fig. 3
Dendogram based on computer-assisted comparison of IS6110 restriction length polymorphism patterns from Mycobacterium bovis
isolates obtained from different domestic and wildlife species
The animals sampled were: 1) free-ranging wild animals in the KNP: TB435, TB428, TB442, TB1773, TB1795, TB571, TB643, TB600, TB664 and a
domestic cow (TB871) from Farm A; 2) greater kudu (TB636) from a farm in close proximity to Farm A; 3) buffalo from the HUP, including those
translocated to the Northern Cape Province: TB1006, TB1042, TB1044; 4) cattle from different geographical regions within South Africa: TB1226,
TB1302, TB681, TB631, TB1729, TB1048, TB709, TB1130, TB999, TB810, TB1057, TB1311, TB781
635
Rev. sci. tech. Off. int. Epiz., 20 (2)
Discussion
in legal cases involving viral diseases transmitted between
humans (1, 52).
A major driving force in the illegal trade in African buffalo is the
difference in price between ‘clean’ and ‘diseased’ buffalo, which
results from the limited availability of infection-free buffalo and
the increasing demand for animals of this status. Given the role
of this wildlife species in transmitting diseases to livestock, the
trade in African buffalo must be closely monitored to enable
irregularities to be identified rapidly and parties found to be
transgressing laws ensuring disease control brought to justice.
Furthermore, the traceback of possible sources of outbreaks in
domestic cattle is important for more efficient disease control.
The RFLP analysis of M. bovis isolates from the KNP revealed
that the agent probably originated on an adjacent farm on
which infected domestic animals were present. The analysis
also indicated that this particular subtype of BTB is spreading
slowly through the KNP in a northerly direction. The single
kudu isolate from a game farm in close proximity to Farm A
(TB636) (10) shows that more than one genotype of M. bovis is
present in the region, but that only one genotype has spread
into the buffalo populations of the KNP and from this species
into other wildlife species.
Most buffalo in southern Africa occur within wildlife reserves
and have been separated from other sub-populations for many
years. The same applies to the pathogens found in these
animals which have been evolving at a much faster rate than
their hosts, as already explained. The genetic diversity (or lack
thereof) of pathogens isolated in particular situations can
therefore be used to trace the origin of the animals, as long as
an extensive database on these pathogens is available.
Phylogenetic analysis of the SAT-type FMD viruses derived
from African buffalo in southern Africa indicates that viruses
evolve independently in discrete geographic localities and that
in some cases the virus populations are specific to a game park
(4, 6, 62). This provides a powerful tool for tracing the origin
of FMD-infected buffalo, as demonstrated by the fact that a
virus isolated from the Gona-re-zhou National Park in southern
Zimbabwe, was grouped with viruses from the Hwange
National Park in north-eastern Zimbabwe (100% bootstrap
support) (Fig. 2). This grouping was unexpected as the
Hwange National Park viruses had previously been
demonstrated to differ significantly from those isolated in the
south of the country. However, further investigation showed
that buffalo from which the virus was recovered had previously
been moved from the Hwange National Park to Gona-re-zhou.
The genetic characterisation of viruses obtained from buffalo
suspected as having been moved illegally in South Africa in
1998 clearly indicated that these buffalo were likely to have
originated from the northern half of the KNP. Seropositivity of
these buffalo to all three FMD viruses and T. lawrencei further
indicated that the true origin of these animals was a region in
South Africa in which both FMD and CD are prevalent. The
KNP is the only region in South Africa where buffalo are
infected with both FMD and CD. The northern region of the
game park, which has low tuberculosis infection rates, is also
the only part of the game park from which buffalo
translocations to adjoining privately-owned game farms in the
FMD control area have been permitted in recent years. This
circumstantial evidence clearly demonstrates that the buffalo
found in the Potgietersrus region were moved there from the
northern part of the KNP, either directly or indirectly. Similar
molecular epidemiological studies have been used successfully
The gel patterns of M. bovis isolates from buffalo in the KNP and
HUP differ significantly (Fig. 3). Therefore, by establishing the
RFLP pattern of BTB isolates obtained from buffalo whose
origin is suspect, it would be possible to establish whether the
animals originated from the KNP or HUP. Due to the restricted
occurrence of FMD in South Africa, FMD-free buffalo would
not be expected to originate from the KNP, but may have been
obtained from HUP or various infection-free regions in South
Africa. Should FMD virus be detected in buffalo in South
Africa, the region in the KNP (or other location outside the
country) from which the buffalo originate could be determined
by comparing the FMD virus isolated with known
representatives of topotypes identified in southern Africa. If
infected with M. bovis, it is possible to determine whether the
buffalo originated from the HUP or KNP.
Conclusions
The wider use of genetic characterisation of animal pathogens
and the information available in genome databases has led to
the identification of other applications for this information. The
use of genetic information to trace the possible origin of African
buffalo in southern Africa is a positive spin-off from the
databases that have greatly assisted the understanding of the
epidemiology of FMD and BTB in southern Africa. However,
this novel application cannot be used in isolation, and further
epidemiological information should be considered before
reaching conclusions on the possible origins of animals.
Nevertheless, the technique offers the exciting possibility of
tracing the origin of buffalo, thereby playing a role in the
prevention of the spread of animal pathogens in South Africa.
Acknowledgement
The authors would like to thank Ms E. Kirkbride for the
graphics in Figure 1.
636
Rev. sci. tech. Off. int. Epiz., 20 (2)
Le traçage des déplacements de buffles en Afrique australe
W. Vosloo, A.D.S. Bastos, A. Michel & G.R. Thomson
Résumé
Le typage génétique de deux agents pathogènes, à savoir le virus de la fièvre
aphteuse et Mycobacterium bovis, isolés chez le buffle d’Afrique (Syncerus caffer)
en Afrique australe, a été utilisé pour déterminer l’origine de buffles dans des
situations où il était difficile de déterminer la source de l’infection. En établissant
la relation phylogénétique de divers isolats du virus de la fièvre aphteuse à l’aide
du séquençage partiel du principal déterminant antigénique, VP1, on a pu tracer
l’origine de buffles introduits illégalement dans la région non enzootique de
l’Afrique du Sud, et remonter ainsi jusqu’au Parc national Kruger où la fièvre
aphteuse sévit à l’état enzootique parmi la population de buffles. L’analyse
comparée des « empreintes génétiques » d’isolats de l’agent de la tuberculose
bovine provenant de buffles et de bovins a permis de tracer la source de l’infection
dont sont atteints les buffles du Parc national Kruger. De plus, ces analyses ont
contribué à tracer l’origine d’animaux infectés qui ont été déplacés vers d’autres
régions d’Afrique du Sud.
Mots-clés
Afrique australe – Buffle d’Afrique – Traçabilité – Tuberculose bovine – Virus de la fièvre
aphteuse.
■
Rastreo del movimiento de búfalos en África austral
W. Vosloo, A.D.S. Bastos, A. Michel & G.R. Thomson
Resumen
La caracterización genética de dos patógenos (el virus de la fiebre aftosa y
Mycobacterium bovis) aislados en búfalos africanos (Syncerus caffer) en África
austral sirvió para dilucidar el origen de búfalos en situaciones en que la fuente de
infección resultaba difícil de determinar. Gracias a la secuenciación parcial del
principal determinante antigénico (VP1) de varias cepas del virus de la fiebre
aftosa, pudo determinarse el grado de parentesco filogenético entre esas cepas,
lo que a su vez sirvió para rastrear el origen de búfalos transportados ilegalmente
a la zona no endémica de Sudáfrica. Esos animales resultaron provenir del Parque
Nacional Kruger, donde la fiebre aftosa es endémica entre la población de búfalos.
Por otro lado, el análisis comparativo de la “huella genética” de diversas muestras
del bacilo de la tuberculosis bovina obtenidas en búfalos y ganado vacuno ayudó
a localizar la fuente original de infección de las poblaciones de búfalos del Parque
Kruger. Esos análisis resultaron de ayuda también para determinar el origen de
animales infectados que han sido transportados a otras partes de Sudáfrica.
Palabras clave
África austral – Búfalo africano – Rastreabilidad – Tuberculosis bovina – Virus de la fiebre
aftosa.
■
Rev. sci. tech. Off. int. Epiz., 20 (2)
637
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