9 research outputs found
An integrated approach to pathogen transmission via environmental reservoirs
To mitigate the effects of zoonotic diseases on human and animal populations,
it is critical to understand what factors alter transmission dynamics. Here we
assess the risk of exposure to lethal concentrations of the anthrax bacterium,
Bacillus anthracis, for grazing animals in a natural system over time through
different transmission mechanisms. We follow pathogen concentrations at
anthrax carcass sites and waterholes for five years and estimate infection
risk as a function of grass, soil or water intake, age of carcass sites, and
the exposure required for a lethal infection. Grazing, not drinking, seems the
dominant transmission route, and transmission is more probable from grazing at
carcass sites 1–2 years of age. Unlike most studies of virulent pathogens that
are conducted under controlled conditions for extrapolation to real
situations, we evaluate exposure risk under field conditions to estimate the
probability of a lethal dose, showing that not all reservoirs with detectable
pathogens are significant transmission pathways
Distribution and Molecular Evolution of Bacillus anthracis Genotypes in Namibia
The recent development of genetic markers for Bacillus anthracis has made it possible to monitor the spread and distribution of this pathogen during and between anthrax outbreaks. In Namibia, anthrax outbreaks occur annually in the Etosha National Park (ENP) and on private game and livestock farms. We genotyped 384 B. anthracis isolates collected between 1983–2010 to identify the possible epidemiological correlations of anthrax outbreaks within and outside the ENP and to analyze genetic relationships between isolates from domestic and wild animals. The isolates came from 20 animal species and from the environment and were genotyped using a 31-marker multi-locus-VNTR-analysis (MLVA) and, in part, by twelve single nucleotide polymorphism (SNP) markers and four single nucleotide repeat (SNR) markers. A total of 37 genotypes (GT) were identified by MLVA, belonging to four SNP-groups. All GTs belonged to the A-branch in the cluster- and SNP-analyses. Thirteen GTs were found only outside the ENP, 18 only within the ENP and 6 both inside and outside. Genetic distances between isolates increased with increasing time between isolations. However, genetic distance between isolates at the beginning and end of the study period was relatively small, indicating that while the majority of GTs were only found sporadically, three genetically close GTs, accounting for more than four fifths of all the ENP isolates, appeared dominant throughout the study period. Genetic distances among isolates were significantly greater for isolates from different host species, but this effect was small, suggesting that while species-specific ecological factors may affect exposure processes, transmission cycles in different host species are still highly interrelated. The MLVA data were further used to establish a model of the probable evolution of GTs within the endemic region of the ENP. SNR-analysis was helpful in correlating an isolate with its source but did not elucidate epidemiological relationships
GIS-based distribution analysis of Bacillus anthracis in Etosha National Park and farms with wildlife and livestock in Namibia using molecular- epidemiological methods
Milzbrand (Anthrax), als `Neglected Zoonotic Disease`, fĂĽhrt in
Entwicklungsländern immer noch zu hoher Mortalität bei Mensch und Tier. Das
Auftreten dieser Erkrankung bei Wild- und Nutztieren ist vor allem im
sĂĽdlichen Afrika endemisch und sorgt im Etosha Nationalpark (ENP) in Namibia
regelmäßig für vermehrte Fälle. In dieser Arbeit wurde das Auftreten von
Anthrax im ENP vor dem Hintergrund epidemiologischer Zusammenhänge untersucht
und mit vorliegenden Studien aus anderen Nationalparks verglichen. Mittels
molekularbiologischer Verfahren wurde die Diversität des Erregers be-stimmt,
um durch Clusteranalysen der Genotypen (GT) Aufschluss über ihre räumliche und
zeitliche Verteilung und das Ausbreitungsmuster im ENP zu erhalten. Es sollte
geprĂĽft wer-den, in wie weit diese Verfahren als unterstĂĽtzendes Mittel zur
Aufklärung epidemiologischer Zusammenhänge von gehäuften Anthraxfällen
sinnvoll eingesetzt werden können. Unter-sucht wurden Proben aus Kadavern
gefallener Tiere und Proben von Umwelthabitaten des ENP. B. anthracis-Isolate
wurden nach dem von Keim et al. (2004) vorgeschlagenem PHRANA-System
genotypisiert. Nach SNP-Analyse von 525 B. anthracis-Isolaten aus Gesamt-
Namibia ergaben sich vier phylogenetische Gruppen, die auf vier
unterschiedliche Einträge nach Namibia schließen lassen (Beyer et al., 2012).
Die MLVA 31 Marker ergab 44 GT, 24 GT davon wurden ausschlieĂźlich im ENP
nachgewiesen. Die von fĂĽnf GT bisher durchgefĂĽhrten SNR-Analysen von 268
Isolaten ergaben 53 SNR-Typen. Die Ergebnisse der MLVA 31 Marker zeigten, dass
das Auftreten von Anthrax durch unterschiedliche GT verursacht wurde, die bei
einzelnen Spezies (Zebra und Springbock) signifikant häufiger als bei anderen
Wildtierspezies nachgewiesen wurden. Ebenso wurden Regionen im Park
identifiziert, in denen signifikant gehäuft bestimmte GT isoliert wurden.
Räumliche und spezies-spezifische Nachweise von GT wurde auf Standorte der
jeweiligen Wildspezies zurĂĽckgefĂĽhrt und durch Ergebnisse der Korrelation
zwischen GT und Bodentypen bzw. Vegetationszonen bestätigt. Der Vergleich der
Cluster positiver Nachweise mit GT-Clustern im Park zeigte, entgegen der
Erwartung, ein deutlich kleineres Cluster für den am häufigsten nachgewiesenen
GT (53% der ENP-Isolate) im Vergleich zum zweit häufigsten GT (22% der ENP-
Isolate). Die GT-Cluster deckten sich mit dem Cluster positiver Anthrax-
Nachweise und lieferten keine weiteren Aussagen zum möglichen Anthrax-
Ausbreitungsmuster. Signifikant vermehrt positive Nachweise bei Tierproben
fanden sich für die Periode 1983-2011 zwar in der Regenzeit. Bei gleichmäßiger
Surveillance während der Regen- und Trockenzeit (2009/2010) zeigte sich
allerdings kein signifikanter Zusammenhang zwischen dem Ereignis Regen und
vermehrt positiven Nachweisen. Lindeques (1991) Ergebnisse zum saisonalen
Auftreten vermehrt positiver Nachweise bei einzelnen Spezies konnten nur
teilweise bestätigt werden. Die Langzeitstudie der Umweltproben bestätigte für
die untersuchten Einteilungskategorien, mit einer Ausnahme, die
„Inkubator“-Theorie für „Risiko-Habitate“. Zur Untermauerung der sich
abzeichnenden Tendenz wären jedoch weitere, einen noch längeren Zeitraum
abdeckende Untersuchungen erforderlich. Da zwar signifikant vermehrt positive
Ergebnisse von B. anthracis in Umweltproben in der Trockenzeit mit im
Vergleich zur Regenzeit jedoch geringeren Konzentrationen vorlagen, könnte ein
jahreszeitenabhängiges Infektionsrisiko mit erhöhtem Risiko während der
Regenzeit abgeleitet werden. Doppelinfektionen traten nach Feststellung von
sich räumlich überlappenden Clustern involvierter GT nicht unerwartet auf.
Nach Detektion mehrerer GT aus teilweise derselben Wasserstelle und dem
Vergleich der GT aus Tier- und Umweltproben können Wasserstellen als
potentielle Infektionsquellen nicht ausgeschlossen werden.Anthrax, one of the Neglected Zoonotic Diseases, still remains a major cause
of high mortalities in humans and animals in developing countries. The disease
is endemic in southern Africa in domestic animals and wildlife and occurs
regularly in the Etosha National Park (ENP) in Namibia. This dissertation
presents results of a molecular-epidemiological study using genotyping methods
such as SNP-Analysis, MLVA 31 Marker and SNR-Analysis to determine the
diversity of B. anthracis strains present in Namibia. Based on a total of 44
Namibian genotypes (GTs) ArcGIS was used for the cartography of isolates and
the spatial, temporal and spatio-temporal cluster analysis for the GTs found
in ENP. A statistical approach was used to compare results with previous
studies carried out in other National Parks. The goal of this dissertation was
to show the advantages of molecular fingerprinting methods over routine
bacteriology of B. anthracis as well as their use in establishing disease
patterns. Sample material included historic and recent carcass swabs of wild
and domestic animals originating from Namibia as well as soil samples obtained
from different habitats within ENP. SNP-analysis revealed four distinct
phylogenetic groups that imply four different entries of B. anthracis strains
into Namibia (Beyer et al., 2012). Analysis of 525 isolates using MLVA 31
Marker determined that 44 distinct GTs are found in Namibia, of which 24 have
been shown to be exclusively present in ENP. Moreover, 268 isolates of five
selected GTs for SNR analysis represent a total of 53 SNR-types. It is further
eminent that certain B. anthracis GTs predominantly did affect selected
species such as zebra and springbok and specific regions within the Park.
Spatial and species-specific distribution of GTs was attributed to certain
migration patterns of wildlife species such as zebra and elephants in the ENP
and showed correlation with specific soil types and vegetation zones.
Comparisons of the cluster of diagnostic findings of B. anthracis with GTs
did, contrary to expectation, show a much smaller cluster for the most
dominant GT (53% of ENP isolates) than the second most dominant (22% of ENP-
isolates). GT clustering failed to reveal disease pattern not already apparent
from clustering of findings of conventional diagnostics. Beyer et al. (2012)
postulated Anthrax outbreaks in ENP as recurrent or ongoing events lasting for
different time periods. While the predominant number of historic cases in
wildlife species in ENP was reported for the rainy season, continuous
surveillance during rainy and dry season in ENP did not show significant
seasonal variation in disease cases. Results previously obtained by Lindeque
(1991) regarding the seasonal increase of Anthrax cases could only be
confirmed partially. Studies of the fate of B. anthracis in different habitats
within ENP seem to support the “incubator” theory, except for one of the
analyzed categories. Further data are necessary to confirm this trend. The
herein presented data seem to be reflective of a seasonal dependent infection
risk. Although a higher proportion of samples tested positive in the dry
season compared to the rainy season, the B. anthracis concentration of
positive cases from the latter season were higher, indicative for a higher
risk for lethal infections. The observed overlapping pattern of GT clusters
coincided with the occurrence of multiple strain infections. Often different
GTs were found in the same habitat and were isolated both from wildlife
species and water holes, indicating these water places to be potential sources
of infections
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Lethal exposure: An integrated approach to pathogen transmission via environmental reservoirs.
To mitigate the effects of zoonotic diseases on human and animal populations, it is critical to understand what factors alter transmission dynamics. Here we assess the risk of exposure to lethal concentrations of the anthrax bacterium, Bacillus anthracis, for grazing animals in a natural system over time through different transmission mechanisms. We follow pathogen concentrations at anthrax carcass sites and waterholes for five years and estimate infection risk as a function of grass, soil or water intake, age of carcass sites, and the exposure required for a lethal infection. Grazing, not drinking, seems the dominant transmission route, and transmission is more probable from grazing at carcass sites 1-2 years of age. Unlike most studies of virulent pathogens that are conducted under controlled conditions for extrapolation to real situations, we evaluate exposure risk under field conditions to estimate the probability of a lethal dose, showing that not all reservoirs with detectable pathogens are significant transmission pathways
Percentage of isolates of the most prevalent GTs in the ENP per year.
<p>Numbers are given for years 2005–2010 when most of the samples were collected. Years 1983, 1987 and 1988–2002, including sampling gaps in 1990, 1993, 1996–99, and 2001, are pooled into the first data point. Total sample sizes are shown below x-axis.</p
Genetic distance as a function of temporal distance and host species similarity.
<p>Isolates of <i>Bacillus anthracis</i> collected from the ENP during the period 1983–2010 are included.</p
Median probabilities and 95% credible intervals for genotypes sampled from the Etosha National Park.
<p>GTs occurring ≤5 times are pooled into the “Other” category.</p
Distribution of genotypes isolated by year.
<p>The total number of isolates per year and per GT. GTs 2, 3, 6, 9, 18, and 22 (highlighted in grey) were found both within and outside the ENP.</p
Confirmed cases of anthrax in the four most commonly affected species in the ENP.
<p>The period between 1988–2010 is shown. Isolates prior to 1988 have been excluded from this figure, having been collected during only short field studies in the Park. The insert indicates the mean monthly rain fall (in l/m<sup>2</sup>) in the Okaukuejo region, in 1983–2010.</p