Determining high-risk zones by using spatial point process methodology

Methods for constructing high-risk zones, which can be used in situations where a spatial point pattern has been observed incompletely, are introduced and evaluated with regard to unexploded bombs in federal properties in Germany. Unexploded bombs from the Second World War represent a serious problem in Germany. It is desirable to search high-risk zones for unexploded bombs, but this causes high costs, so the search is usually restricted to carefully selected areas. If suitable aerial pictures of the area in question exist, statistical methods can be used to determine such zones by considering patterns of exploded bombs as realisations of spatial point processes. The patterns analysed in this thesis were provided by Oberfinanzdirektion Niedersachsen, which supports the removal of unexploded ordnance in federal properties in Germany. They were derived from aerial pictures taken by the Allies during and after World War II. The main task consists of finding as small regions as possible containing as many unexploded bombs as possible. In this thesis, an approach based on the intensity function of the process is introduced: The high-risk zones consist of those parts of the observation window where the estimated intensity is largest, i.e. the estimated intensity function exceeds a cut-off value c. The cut-off value can be derived from the risk associated with the high-risk zone. This risk is defined as the probability that there are unexploded bombs outside the zone. A competing approach for determining high-risk zones consists in using the union of discs around all exploded bombs as high-risk zone. The radius is chosen as a high quantile of the nearest-neighbour distance of the point pattern. In an evaluation procedure, both methods yield comparably good results, but the theoretical properties of the intensity-based high-risk zones are considerably better. A further goal is to perform a risk assessment of the investigated area by estimating the probability that there are unexploded bombs outside the high-risk zone. This is especially important as the estimation of the intensity function is a crucial issue for the intensity-based method, so the risk cannot be determined exactly in advance. A procedure to calculate the risk is introduced. By using a bootstrap correction, it is possible to decide on acceptable risks and find the optimal, i.e. smallest, high-risk zone for a fixed probability that not all unexploded bombs are located inside the high-risk zone. The consequences of clustering are investigated in a sensitivity analysis by exploiting the procedure for calculating the risk. Furthermore, different types of models which account for clustering are fitted to the data, classical cluster models as well as a mixture of bivariate normal distributions.Methoden zur Konstruktion von Risikozonen, die verwendet werden können, wenn ein räumliches Punktmuster unvollständig beobachtet wurde, werden am Beispiel von Blindgängern auf Bundesliegenschaften in Deutschland eingeführt und evaluiert. Blindgänger aus dem Zweiten Weltkrieg stellen in Deutschland ein schwerwiegendes Problem dar. Es ist daher wünschenswert, Risikozonen nach Blindgängern abzusuchen. Da dies jedoch hohe Kosten verursacht, beschränkt sich die Suche normalerweise auf sorgfältig ausgewählte Gebiete. Falls für das fragliche Gebiet geeignete Luftbilder existieren, können zur Bestimmung solcher Zonen statistische Methoden angewandt werden, indem das Muster der detonierten Bomben als Realisation eines räumlichen Punktprozesses betrachtet wird. Die in dieser Arbeit analysierten Muster wurden von der Oberfinanzdirektion Niedersachsen zur Verfügung gestellt, die die Kampfmittelräumung auf deutschen Bundesliegenschaften unterstützt. Sie wurden aus Luftbildern gewonnen, die die Alliierten während und nach dem Zweiten Weltkrieg aufgenommen haben. Das primäre Ziel besteht darin, möglichst kleine Regionen zu finden, die möglichst viele Blindgänger enthalten. In dieser Arbeit wird ein Ansatz vorgestellt, der auf der Intensitätsfunktion des Prozesses basiert: Die Risikozonen bestehen aus denjenigen Teilen des Beobachtungsfensters, in denen die geschätzte Intensität am höchsten ist, d.h. in der die geschätzte Intensitätsfunktion einen Cutoff-Wert c überschreitet. Der Cutoff-Wert kann vom Restrisiko der entsprechenden Risikozone abgeleitet werden. Ein konkurrierender Ansatz zur Bestimmung von Risikozonen besteht darin, die Vereinigung aller Kreisscheiben um die detonierten Bomben herum als Risikozone zu definieren. Der Radius ergibt sich als hohes Quantil des Nächste-Nachbarn-Abstandes des Punktmusters. Bei der Evaluation liefern beide Methoden ähnlich gute Ergebnisse, jedoch sind die theoretischen Eigenschaften der intensitätsbasierten Risikozonen deutlich besser. Ein weiteres Ziel ist eine Risikoabschätzung für das untersuchte Gebiet, wofür die Wahrscheinlichkeit für Blindgänger außerhalb der Risikozone geschätzt wird. Dies ist insbesondere deswegen wichtig, weil sich die Schätzung der Intensität als kritischer Punkt der intensitätsbasierten Methode erwiesen hat und das Risiko im Voraus nicht exakt festgelegt werden kann. Es wird ein Verfahren zur Risikobestimmung vorgestellt. Mit Hilfe einer Bootstrap-Korrektur ist es möglich, das akzeptable Risiko festzulegen und die optimale (d.h. kleinste) Risikozone für eine vorgegebene Wahrscheinlichkeit, dass nicht alle Blindgänger in der Risikozone liegen, zu finden. Die Auswirkungen von Clustering werden in einer Sensitivitätsanalyse untersucht, wozu das Verfahren zur Risikobestimmung verwendet wird. Darüber hinaus werden verschiedene Arten von Clustermodellen an die Daten angepasst, sowohl klassische Clustermodelle als auch Mischungen von bivariaten Normalverteilungen

Determining high-risk zones by using spatial point process methodology

Methods for constructing high-risk zones, which can be used in situations where a spatial point pattern has been observed incompletely, are introduced and evaluated with regard to unexploded bombs in federal properties in Germany. Unexploded bombs from the Second World War represent a serious problem in Germany. It is desirable to search high-risk zones for unexploded bombs, but this causes high costs, so the search is usually restricted to carefully selected areas. If suitable aerial pictures of the area in question exist, statistical methods can be used to determine such zones by considering patterns of exploded bombs as realisations of spatial point processes. The patterns analysed in this thesis were provided by Oberfinanzdirektion Niedersachsen, which supports the removal of unexploded ordnance in federal properties in Germany. They were derived from aerial pictures taken by the Allies during and after World War II. The main task consists of finding as small regions as possible containing as many unexploded bombs as possible. In this thesis, an approach based on the intensity function of the process is introduced: The high-risk zones consist of those parts of the observation window where the estimated intensity is largest, i.e. the estimated intensity function exceeds a cut-off value c. The cut-off value can be derived from the risk associated with the high-risk zone. This risk is defined as the probability that there are unexploded bombs outside the zone. A competing approach for determining high-risk zones consists in using the union of discs around all exploded bombs as high-risk zone. The radius is chosen as a high quantile of the nearest-neighbour distance of the point pattern. In an evaluation procedure, both methods yield comparably good results, but the theoretical properties of the intensity-based high-risk zones are considerably better. A further goal is to perform a risk assessment of the investigated area by estimating the probability that there are unexploded bombs outside the high-risk zone. This is especially important as the estimation of the intensity function is a crucial issue for the intensity-based method, so the risk cannot be determined exactly in advance. A procedure to calculate the risk is introduced. By using a bootstrap correction, it is possible to decide on acceptable risks and find the optimal, i.e. smallest, high-risk zone for a fixed probability that not all unexploded bombs are located inside the high-risk zone. The consequences of clustering are investigated in a sensitivity analysis by exploiting the procedure for calculating the risk. Furthermore, different types of models which account for clustering are fitted to the data, classical cluster models as well as a mixture of bivariate normal distributions.Methoden zur Konstruktion von Risikozonen, die verwendet werden können, wenn ein räumliches Punktmuster unvollständig beobachtet wurde, werden am Beispiel von Blindgängern auf Bundesliegenschaften in Deutschland eingeführt und evaluiert. Blindgänger aus dem Zweiten Weltkrieg stellen in Deutschland ein schwerwiegendes Problem dar. Es ist daher wünschenswert, Risikozonen nach Blindgängern abzusuchen. Da dies jedoch hohe Kosten verursacht, beschränkt sich die Suche normalerweise auf sorgfältig ausgewählte Gebiete. Falls für das fragliche Gebiet geeignete Luftbilder existieren, können zur Bestimmung solcher Zonen statistische Methoden angewandt werden, indem das Muster der detonierten Bomben als Realisation eines räumlichen Punktprozesses betrachtet wird. Die in dieser Arbeit analysierten Muster wurden von der Oberfinanzdirektion Niedersachsen zur Verfügung gestellt, die die Kampfmittelräumung auf deutschen Bundesliegenschaften unterstützt. Sie wurden aus Luftbildern gewonnen, die die Alliierten während und nach dem Zweiten Weltkrieg aufgenommen haben. Das primäre Ziel besteht darin, möglichst kleine Regionen zu finden, die möglichst viele Blindgänger enthalten. In dieser Arbeit wird ein Ansatz vorgestellt, der auf der Intensitätsfunktion des Prozesses basiert: Die Risikozonen bestehen aus denjenigen Teilen des Beobachtungsfensters, in denen die geschätzte Intensität am höchsten ist, d.h. in der die geschätzte Intensitätsfunktion einen Cutoff-Wert c überschreitet. Der Cutoff-Wert kann vom Restrisiko der entsprechenden Risikozone abgeleitet werden. Ein konkurrierender Ansatz zur Bestimmung von Risikozonen besteht darin, die Vereinigung aller Kreisscheiben um die detonierten Bomben herum als Risikozone zu definieren. Der Radius ergibt sich als hohes Quantil des Nächste-Nachbarn-Abstandes des Punktmusters. Bei der Evaluation liefern beide Methoden ähnlich gute Ergebnisse, jedoch sind die theoretischen Eigenschaften der intensitätsbasierten Risikozonen deutlich besser. Ein weiteres Ziel ist eine Risikoabschätzung für das untersuchte Gebiet, wofür die Wahrscheinlichkeit für Blindgänger außerhalb der Risikozone geschätzt wird. Dies ist insbesondere deswegen wichtig, weil sich die Schätzung der Intensität als kritischer Punkt der intensitätsbasierten Methode erwiesen hat und das Risiko im Voraus nicht exakt festgelegt werden kann. Es wird ein Verfahren zur Risikobestimmung vorgestellt. Mit Hilfe einer Bootstrap-Korrektur ist es möglich, das akzeptable Risiko festzulegen und die optimale (d.h. kleinste) Risikozone für eine vorgegebene Wahrscheinlichkeit, dass nicht alle Blindgänger in der Risikozone liegen, zu finden. Die Auswirkungen von Clustering werden in einer Sensitivitätsanalyse untersucht, wozu das Verfahren zur Risikobestimmung verwendet wird. Darüber hinaus werden verschiedene Arten von Clustermodellen an die Daten angepasst, sowohl klassische Clustermodelle als auch Mischungen von bivariaten Normalverteilungen

Candidatus Neoehrlichia mikurensis in rodents in an area with sympatric existence of the hard ticks Ixodes ricinus and Dermacentor reticulatus, Germany

Background: Candidatus Neoehrlichia mikurensis (CNM) has been described in the hard tick Ixodes ricinus and rodents as well as in some severe cases of human disease. The aims of this study were to identify DNA of CNM in small mammals, the ticks parasitizing them and questing ticks in areas with sympatric existence of Ixodes ricinus and Dermacentor reticulatus in Germany. Methods: Blood, transudate and organ samples (spleen, kidney, liver, skin) of 91 small mammals and host-attached ticks from altogether 50 small mammals as well as questing I. ricinus ticks (n=782) were screened with a real-time PCR for DNA of CNM. Results: 52.7% of the small mammals were positive for CNM- DNA. The majority of the infected animals were yellow-necked mice (Apodemus flavicollis) and bank voles (Myodes glareolus). Small mammals with tick infestation were more often infected with CNM than small mammals without ticks. Compared with the prevalence of similar to 25% in the questing I. ricinus ticks, twice the prevalence in the rodents provides evidence for their role as reservoir hosts for CNM. Conclusion: The high prevalence of this pathogen in the investigated areas in both rodents and ticks points towards the need for more specific investigation on its role as a human pathogen

Babesia spp. and Anaplasma phagocytophilum in questing ticks, ticks parasitizing rodents and the parasitized rodents - Analyzing the host-pathogen-vector interface in a metropolitan area

Background: The aims of this study were to evaluate the host-tick-pathogen interface of Babesia spp. and Anaplasma phagocytophilum in restored areas in both questing and host-attached Ixodes ricinus and Dermacentor reticulatus and their small mammalian hosts. Methods: Questing ticks were collected from 5 sites within the city of Leipzig, Germany, in 2009. Small mammals were trapped at 3 of the 5 sites during 2010 and 2011. DNA extracts of questing and host-attached I. ricinus and D. reticulatus and of several tissue types of small mammals (the majority bank voles and yellow-necked mice), were investigated by PCR followed by sequencing for the occurrence of DNA of Babesia spp. and by real-time PCR for A. phagocytophilum. A selected number of samples positive for A. phagocytophilum were further investigated for variants of the partial 16S rRNA gene. Co-infection with Rickettsia spp. in the questing ticks was additionally investigated. Results: 4.1% of questing I. ricinus ticks, but no D. reticulatus, were positive for Babesia sp. and 8.7% of I. ricinus for A. phagocytophilum. Sequencing revealed B. microti, B. capreoli and Babesia spp. EU1 in Leipzig and sequence analysis of the partial 16S RNA gene of A. phagocytophilum revealed variants either rarely reported in human cases or associated with cervid hosts. The statistical analysis revealed significantly less ticks infected with A. phagocytophilum in a city park in Leipzig as compared to the other sampling sites. A. phagocytophilum-DNA was detected in 2 bank voles, DNA of B. microti in 1 striped field-mouse and of Babesia sp. EU1 in the skin tissue of a mole. Co-infections were detected. Conclusion: Our results show the involvement of small mammals in the natural endemic cycles of tick-borne pathogens. A more thorough understanding of the interactions of ticks, pathogens and hosts is the essential basis for effective preventive control measures

vorgelegt von

high-risk zones by using spatial point process methodolog

<it>Candidatus</it> Neoehrlichia mikurensis in rodents in an area with sympatric existence of the hard ticks <it>Ixodes ricinus</it> and <it>Dermacentor reticulatus</it>, Germany

Abstract Background Candidatus Neoehrlichia mikurensis (CNM) has been described in the hard tick Ixodes ricinus and rodents as well as in some severe cases of human disease. The aims of this study were to identify DNA of CNM in small mammals, the ticks parasitizing them and questing ticks in areas with sympatric existence of Ixodes ricinus and Dermacentor reticulatus in Germany. Methods Blood, transudate and organ samples (spleen, kidney, liver, skin) of 91 small mammals and host-attached ticks from altogether 50 small mammals as well as questing I. ricinus ticks (n=782) were screened with a real-time PCR for DNA of CNM. Results 52.7% of the small mammals were positive for CNM-DNA. The majority of the infected animals were yellow-necked mice (Apodemus flavicollis) and bank voles (Myodes glareolus). Small mammals with tick infestation were more often infected with CNM than small mammals without ticks. Compared with the prevalence of ~25% in the questing I. ricinus ticks, twice the prevalence in the rodents provides evidence for their role as reservoir hosts for CNM. Conclusion The high prevalence of this pathogen in the investigated areas in both rodents and ticks points towards the need for more specific investigation on its role as a human pathogen.</p

Occurrence of <it>Babesia </it>spp., <it>Rickettsia </it>spp. and <it>Bartonella </it>spp. in <it>Ixodes ricinus </it>in Bavarian public parks, Germany

<p>Abstract</p> <p>Background</p> <p>Only limited information is available about the occurrence of ticks and tick-borne pathogens in public parks, which are areas strongly influenced by human beings. For this reason, <it>Ixodes ricinus </it>were collected in public parks of different Bavarian cities in a 2-year survey (2009 and 2010) and screened for DNA of <it>Babesia </it>spp., <it>Rickettsia </it>spp. and <it>Bartonella </it>spp. by PCR. Species identification was performed by sequence analysis and alignment with existing sequences in GenBank. Additionally, coinfections with <it>Anaplasma phagocytophilum </it>were investigated.</p> <p>Results</p> <p>The following prevalences were detected: <it>Babesia </it>spp.: 0.4% (n = 17, including one pool of two larvae) in 2009 and 0.5 to 0.7% (n = 11, including one pool of five larvae) in 2010; <it>Rickettsia </it>spp.: 6.4 to 7.7% (n = 285, including 16 pools of 76 larvae) in 2009. DNA of <it>Bartonella </it>spp. in <it>I. ricinus </it>in Bavarian public parks could not be identified. Sequence analysis revealed the following species: <it>Babesia </it>sp. EU1 (n = 25), <it>B. divergens </it>(n = 1), <it>B. divergens/capreoli </it>(n = 1), <it>B. gibsoni</it>-like (n = 1), <it>R. helvetica </it>(n = 272), <it>R. monacensis </it>IrR/Munich (n = 12) and unspecified <it>R. monacensis </it>(n = 1). The majority of coinfections were <it>R. helvetica </it>with <it>A. phagocytophilum </it>(n = 27), but coinfections between <it>Babesia </it>spp. and <it>A. phagocytophilum</it>, or <it>Babesia </it>spp. and <it>R. helvetica </it>were also detected.</p> <p>Conclusions</p> <p><it>I. ricinus </it>ticks in urban areas of Germany harbor several tick-borne pathogens and coinfections were also observed. Public parks are of particularly great interest regarding the epidemiology of tick-borne pathogens, because of differences in both the prevalence of pathogens in ticks as well as a varying species arrangement when compared to woodland areas. The record of DNA of a <it>Babesia gibsoni</it>-like pathogen detected in <it>I. ricinus </it>suggests that <it>I. ricinus </it>may harbor and transmit more <it>Babesia </it>spp. than previously known. Because of their high recreational value for human beings, urban green areas are likely to remain in the research focus on public health issues.</p