Bovine
tuberculosis has emerged as a serious threat to conservation wildlife. In
Africa the disease has been reported in several wildlife species. It is endemic
in African buffaloes (Syncerus caffer) in the Kruger and Ruwenzori National
Parks and in Kafue lechwe antelopes (Kobus leche kafuensis) of the Kafue basin.
As pointed out by Bengis and others, the African buffalo and the Kafue lechwe
antelopes have become true sylvatic wildlife maintenance hosts with sporadic
spill over to other species. The earliest reports of bovine tuberculosis in the
Kafue lechwe date back to the 1940s. Circumstantial evidence indicates that the
disease could have been introduced from cattle to lechwe through the practice
of transhumance grazing in the Kafue basin.
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| Kafue lechwe |
Apart
from the Kafue lechwe, Zambia is endowed with the Red lechwe (Kobus leche
Leche) which is also found in Botswana and predominantly in the Liuwa plains of
Western Province and the Black lechwe (Kobus leche smithemani) inhabiting the
Bangweulu plains of northern Zambia. All Kobus leche subspecies are
semi-aquatic medium sized antelopes that live in wetlands areas. They live in
herds that increase in size during the rainy season when flood waters
accumulate and during lekking in the breeding season when territorial males
occupy small discrete areas clustered by groups of females that go for mating.
These characteristics are common for all Kobus leche antelopes indicating that
these animals have similar population structures besides inhabiting similar
ecosystems comprising of wetlands and marsh areas. As pointed out elsewhere,
gregarious species that cluster in large numbers have the potential to maintain
bovine tuberculosis within herds for a long time with occasional spillover to
other species. In some areas, the wetlands inhabited by the Kobus leche
antelopes are also used by livestock as grazing pastures leading to
interspecies transmission of animal diseases between wildlife and livestock as
commonly observed in the Kafue basin. It has been assumed that the persistence
of bovine tuberculosis could have contributed to the decrease in Kafue lechwe
population of the Kafue basin leading to their subsequent inclusion on the
International Union of Conservation (IUCN) red list of endangered species.
However, the decrease in population is across all lechwe species.
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| Black lechwe |
The
absence of a livestock/wildlife interface area in the presence of one of the
three lechwe species in the Bangweulu swamps provided a unique and important
epidemiological determinant in assessing the maintenance of tuberculosis in
wildlife and cattle in Zambia given that the Kafue lechwe of the Kafue basin
have been shown to be a reservoir host of tuberculosis.
The
key explanatory difference between the Kafue basin and the Bangweulu swamps is
the absence of a livestock/wildlife interface area in the latter. As for the
Black lechwe, there is marked paucity of information with regards to
tuberculosis. Information obtained on the ground during the sampling period
from Zambia Wildlife Authority (ZAWA) and seasonal Safari hunters indicated
that they have never come across any suspected case of tuberculosis in the
Black lechwe antelopes of the Bangweulu swamps. However, ZAWA officials, cattle
owners and Safari hunters in the Kafue basin are very much aware of the
presence of tuberculosis in the Kafue lechwe antelopes. Further, in the Kafue
basin, tuberculosis prevalence is estimated at 27.7% in Kafue lechwe antelopes.
In cattle, tuberculosis prevalence is estimated at 9.6% in the blue lagoon area
whilst in Lochinvar it's estimated at 5.2%. Epidemiological models and baseline
studies conducted on the prevalence of bovine tuberculosis within Zambia
indicate foci of infection and a relatively high prevalence level in the Kafue
basin. This focus of tuberculosis is probably due to active and continuous
disease transmission between and within species. The grazing range of Kafue
lechwe and cattle extensively overlap and during the dry season the frequency
of interaction increases especially at watering points and in areas with green
pastures. This scenario increases the opportunity for interspecies transmission
of tuberculosis. The pathology and epidemiology of the disease in cattle and
lechwe is similar and respiratory in nature. However, to date, no structured
studies or documentation of tuberculosis are available on Black lechwe
antelopes from the Bangweulu plains.
ZAWA,
an organization mandated by government to restore natural environments and
ecological communities that inhabit them have for a long time recorded and
reported a continuous decline in the Kobus leche populations in Zambia. The
Black lechwe population on the Bangweulu plains declined from approximately
150,000 animals in 1930s to about 30,000 in the 1980s while the Kafue lechwe
has decreased by 85% in the last 75 years from 250,000 animals in 1931 to
38,000 in 2005 leading to their subsequent inclusion on the IUCN red list of
endangered species. However, current population censuses of the Black lechwe
indicate slight recovery in numbers as a result of a deliberate policy by ZAWA
utilizing light off-take rates able to sustain a positive population recovery.
Although
studies have shown that animal diseases inclusive of bovine tuberculosis have
significantly contributed to the reduction of the Kafue lechwe population on
the Kafue basin, factors leading to the reduction of the Black lechwe population
on the Bangweulu plains are yet to be elucidated. Hence, ZAWA through its
research unit has embarked on carrying out investigations aimed at determining
causal factors that have the potential to cause extinction of the Kobus leche
populations in Zambia. These investigations are expected to determine, among
other things, ecological factors that allow for the introduction of exotic
diseases into both sympatric and allopatric wildlife populations, assessing the
impact of these diseases on conservation and identifying mitigation measures
aimed at preventing and or reducing the occurrence of animal diseases in
wildlife populations. In this present study, the objective was to determine if
the Black lechwe found in the Bangweulu swamps an area predominantly occupied
by wildlife without the presence of livestock are infected with tuberculosis.
Thus
livestock/wildlife interaction in disease transmission was assessed using a
similar wildlife population that has no contact with wildlife to elucidate the
effect of this interaction. The study showed that out of 30 black lechwe which
were sampled from bangweulu swamps, no black lechwe was found with bacteria
that lead to tuberculosis. Out of the 14 Kafue lechwe sampled from Kafue basin,
11 were found with microscopic bacteria’s leading tuberculosis. This work was
funded by the Norwegian Programed for Development, Research and Education
(NUFU). The Zambia Wildlife Authority
(ZAWA) played role in the provision of the study animals and their continued
support in this research work. The
University of Zambia, through the School of Veterinary Medicine helped for
offering an enabling environment to conduct research.
This
was the first epidemiological study in Black lechwe of the Bangweulu swamps
demonstrating the absence of tuberculosis.
The sample size of antelopes from the Kafue basin was not the case. The
Limitations in sample size in wildlife studies are not uncommon especially with
rare wildlife species threatened with extinction; nonetheless, the results were
a valid assessment and representation of the epidemiological situation with
regards to tuberculosis in both the Kafue basin and the Bangweulu swamps.
Specifically, this being the first study to systematically analyze results
suggesting the absence of tuberculosis in the Black lechwe of the Bangweulu
swamps were cattle are absent, intimating on cattle to be a vital deterministic
factor in tuberculosis transmission with wildlife.
Due the meat inspection on animals obtained
from safari hunting and epidemiological surveys carried out in the Kafue basin
indicate the presence of the disease. With the Kafue lechwe being the most
sought after wildlife species utilized for game meat consumption these findings
pose a significant public health threat to the general public. The observations
further indicate that the close interaction between cattle and the Kafue lechwe
is likely to enhance sharing of diseases between the two animal species and
this is in concordance with earlier findings. Hence, inter-species transmission
of bovine tuberculosis and other diseases between cattle and Kafue lechwe could
be an ongoing process although it is not yet clear which of the two animal
species maintains the infection in the ecosystem
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