| 1. |
- Labbé Sandelin, Lisa, 1977-
(författare)
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Neoehrlichia mikurensis in Sweden : An emerging tick-borne human pathogen
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Neoehrlichia mikurensis is an emerging tick-borne human pathogen, causing neoehrlichiosis in immunosuppressed and immunocompetent individuals. It targets the vascular endothelium, leading to thromboembolic and vascular events, but can also pass without symptoms. As symptoms easily are misinterpreted, immunosuppressive treatment or chemotherapy is often incorrectly initiated. Diagnostic delay can be considerable.The overall aim of this thesis was to gain a better understanding on N. mikurensis in Sweden, focusing on human infections and public health aspects. The prevalence of N. mikurensis in different populations was examined. The symptomatology of neoehrlichiosis and the risk of transfusion-mediated transmission was studied. N. mikurensis was observed in low prevalences in ticks collected from migratory birds, in tick-bitten individuals, in patients with persistent symptoms attributed to presumed tick-bite exposure, and in blood donors. Fourteen N. mikurensis-positive individuals were identified. The majority were immunocompetent and asymptomatic. Both spontaneous clearance and persistence was observed. Two of 102 tick-bitten individuals were N. mikurensis-positive. Both presented with erythema migrans, but borreliosis was a more probable cause in both. The findings do not support a change in practice regarding first-line treatment of erythema migrans, but further studies are warranted.Persistence of N. mikurensis in blood raises questions regarding the possibility of transmission by transfusion and the risk of activating the infection if immune status is altered. N. mikurensis was identified in seven out of 1 006 blood donors. Look-back and tracing identified 12 recipients who were transfused with blood components from N. mikurensis-positive donors. Several recipients had multiple risk factors for severe neoehrlichiosis, but transfusion-transmitted neoehrlichiosis was not detected. Nevertheless, the possibility that N. mikurensis can be transmitted by transfusion cannot be excluded.Isolates from birds and blood donors were identical to previously reported Swedish human isolates. Migrating birds can act as dispersal vectors of N. mikurensis, but their role as transmission hosts is still unclear.The disease burden and public health impact of neoehrlichiosis is probably small, but information is lacking in several areas. Suspicion of neoehrlichiosis is warranted in immunocompromised and/or splenectomised patients with persistent fever, with or without thromboembolic and vascular events. Furthermore, neoehrlichiosis should be included in the differential diagnosis of anaplasmosis. Besides raised awareness, a possible mandatory notification is proposed as well as a comprehensive surveillance system for transfusion-transmitted infections. One of the priority issues is the possible need for screening of patients living in N. mikurensis-endemic areas before and during immunosuppressive treatment.
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| 2. |
- Stark, Lisa
(författare)
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Staphylococcus aureus : aspects of pathogenesis and molecular epidemiology
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Staphylococcus aureus is a human commensal colonizing about 30 per cent of the population. Besides, it is a frequent cause of infections such as skin, wound and deep tissue infections and also more life-threatening conditions such as pneumonia, endocarditis and septicaemia. S. aureus may also cause different toxicoses. Moreover, this bacterium is one of the most common causes of nosocomial infections worldwide and an increase in antibiotic resistance, especially against methicillin, is seen. This underlines the importance to prevent and control outbreaks of S. aureus. The aims of this thesis were to increase the knowledge of S. aureus virulence and pathogenesis as well as to understand pattern of colonization and transmission.Various virulence factors operate together in the pathogenic process of S. aureus. The virulence of S. aureus was studied by the interaction with human umbilical vein endothelial cells (HUVEC) as a model. In paper I, we found that one bacterial isolate survived intracellularly and that 156 genes were differentially regulated in microarray analysis of HUVEC. The major part of these genes coded for proteins involved in innate immunity. In paper II, we wanted to explore possible differences in global gene expression patterns in HUVEC induced by invasive compared to colonizing isolates of S. aureus. We also used microarray to investigate possible differences in the presence of virulence genes between the two groups. The main finding was that virulent and commensal S. aureus did not differ in interaction with HUVEC and in the presence of virulence genes. All isolates survived intracellularly for days.Since no obvious differences in virulence between the two groups of isolates were found, we focused on epidemiology and transmission patterns. Colonization with S. aureus is an important risk factor for subsequent S. aureus infection. In paper III, we investigated S. aureus colonization and transmission among nursing home residents in three regions in the south of Sweden and used staphylococcal protein A (spa) typing as an epidemiological tool. A diverse distribution of different spa types was found and a majority of types were unique to one individual. Interestingly, we found a local accumulation of one spa type in one nursing home. Also common spa types were equally distributed in the different regions. We also noted that some individuals were colonized with two different spa types of S. aureus and in five of these cases there was one resistant and one non-resistant strain.The issue of multiclonal colonization and infection is highly important and clinical diagnostic laboratories do not routinely address this problem. Therefore, in paper IV a novel method to assess multiclonality of S. aureus was developed. It was based on denaturing gradient gel electrophoresis with the amplification of the spa gene. The method simultaneously separated eight different spa types. It also detected two spa types in an outbreak.In conclusion, we found no differences in virulence genes and in the interaction with HUVEC between commensal and invasive isolates. This indicates that any isolate of S. aureus might have a pathogenic potential. We also confirmed that some spa types are more successful colonizers with a potential to nosocomial spread. The method for detection of multiclonality of S. aureus is of importance in future epidemiological and clinical studies.
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| 3. |
- Fryland, Linda
(författare)
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Immune mechanisms in Borrelia burgdorferi sensu lato infection in relation to clinical outcome
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lyme borreliosis (LB) is the most common tick-borne disease in the northern hemisphere. The infection is caused by spirochaetes from the Borrelia (B.) burgdorferi sensu lato (s.l.) group. The clinical outcome after B. burgdorferi s.l. infection differs between individuals from asymptomatic infection without history of LB to individuals who experience persistent symptoms post-treatment for more than six months after treatment. The difference in clinical outcome is not thought to be associated with persistent infection, but could instead be affected by the host’s ability to mount an optimal immune response to the spirochaete.The hypothesis of this thesis was that a strong inflammatory Th1-like immune response is required in the early stage of infection in order to achieve both an optimal eradication of the B. burgdorferi s.l. bacteria and a good clinical outcome. The inflammatory response must be down-regulated by an anti-inflammatory response in order to avoid excessive immune responses that will end in tissue injury. The proper down-regulation will also protect against development of a chronic Th1-like inflammatory response, with activated cytotoxic cells, which may lead to LB with persistent symptoms post-treatment.The thesis aimed to investigate the immunological mechanisms behind the optimal resolution of human B. burgdorferi s.l. infection and to define the aberrant mechanisms leading to development of persisting symptoms.prospective study on newly tick-bitten individuals showed that although 25% of the collected ticks were infected with B. burgdorferi s.l. very few individuals bitten by infected ticks developed LB (3.7%). In addition, 4.9% of the individuals bitten by infected ticks developed asymptomatic infection, i.e. B. burgdorferi s.l.-specific antibody seroconversion without LB. Approximately one third of all tick-bitten study subjects reported self-experienced symptoms possibly associated with LB. Individuals bitten by infected ticks were more likely to report experience of symptoms than those bitten by uninfected ticks. Thus, only 8.6% of the individuals bitten by B. burgdorferi s.l.-infected ticks were infected, verified by seroconversion, and out of them 57% were asymptomatic.A prospective study on EM patients showed that a good clinical outcome was associated with a strong early Th1 immune response since EM patients with persistent symptoms six months after treatment had reduced expression of Th1 cytokines in their EM lesions compared with EM patients without symptoms.The investigation of blood samples from newly tick-bitten individuals, for detection of possible early immune biomarkers indicating good clinical outcome of LB, showed that none of the investigated markers clearly discriminated between the individuals who developed LB, asymptomatic individuals, or non-infected individuals. However, tick-bitten individuals who developed asymptomatic infection showed an increase of early Th1-associated biomarkers in blood compared to individuals who developed clinical LB.In an experimental study, Th2-immune-deviated mice had more pronounced clinical signs of infection and could not eradicate the spirochaete as efficiently as non-deviated B. burgdorferi sensu stricto (s.s.)-infected mice. Non-deviated B. burgdorferi s.s.-infected mice showed a decrease of mRNA expression associated with Th2, anti-inflammatory and Treg/Th1 responses during the course of infection, which suggested a termination of the inflammatory response – something that was not seen in the immune-deviated mice. Trends for increased expression of pro-inflammatory GM-CSF and Treg marker Foxp3 in immune-deviated mice suggested on-going inflammation. Non-deviated B. burgdorferi s.s.-infected mice showed increased systemic expression of the Th1-associated CXCL9 and CXCL10 during the course of infection, while immune-deviated mice showed an initial decrease in both chemokines at day 15 p.i. compared with day 0 p.i.In conclusion, the risk of developing LB after a tick bite is low, and no infection or asymptomatic infection are the most common outcomes after a tick bite. The early immune response in humans and the immune response towards B. burgdorferi s.s. infection in mice support the hypothesis that a strong pro-inflammatory Th1 response is needed for an optimal clinical outcome and eradication of bacteria.
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| 4. |
- Lindblom, Pontus, 1982-
(författare)
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Epidemiological and Ecological Studies of Tick-borne Encephalitis Virus
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ticks are blood-sucking parasites that are an inconvenience for both humans and animals. The tick by itself is normally harmless unless they attack in excessive numbers. The harm from ticks stems from them being excellent vectors for other parasites, in the form of bacteria and virus that via the ticks are provided a bridge to move across the blood streams of different animals, including humans.One of the most pathogenic tick-borne disease for humans is caused by a flavivirus, the tick-borne encephalitis virus (TBEV). Each year approximately 10 000 individuals on the Eurasian continent develop neurological disease, in the form of meningitis, encephalitis, myelitis and radiculitis, following a bite by a TBEV infected tick.To evaluate the risk of TBEV infection after a tick-bite, we have developed a study to investigate ticks that have bitten humans and to follow up the tick-bitten humans to investigate if they get infected, and if they develop symptoms, and further trace the virus back to the tick that is infected with TBEV. Ticks, blood samples, and questionnaires were collected in collaboration with 34 primary health care centers in Sweden and on the Åland Islands during 2008 and 2009.Several demographical and biological factors were investigated regarding the interaction between ticks and humans. The main finding was that men removed the ticks later than women, and that both older men and older women removed the ticks later than younger individuals. This could in part explain why older individuals in general, and men in particular, are at greater risk of acquiring tick-borne encephalitis (TBE).Furthermore, the prevalence of TBEV in ticks that have bitten humans were investigated, in order to correlate the copy number of TBEV in the tick and the tick feeding-time to the risk of developing symptomatic and asymptomatic infection. This entailed the development of new methodology for tick analysis and TBEV real-time PCR. The result showed a very low risk of TBEV infection in the studied areas, only 5 of 2167 investigated ticks contained TBEV. Three of the individuals bitten by TBEV infected ticks were vaccinated and did not develop symptoms of TBEV infection. One unvaccinated individual got bitten by a tick containing 1800 virus copies, with a feeding-time of 12-24h, and interestingly showed no signs of infection. Another unvaccinated individual got bitten by a tick containing 7.7 million virus copies, with a feedingtime of >60h. This individual developed symptoms consistent with a 1st phase of TBE, including fever and headache, but did not develop the 2nd neurological phase of TBEV infection. Despite only finding 5 ticks infected with TBEV, a correlation between the virus load in the tick and the tick feeding-time was observed. In 2 other individuals, TBEV antibody seroconversion was detected during the 3 month study period, one without symptoms, while the other experienced symptoms consistent with the 1st phase of TBE. These observations support the hypothesis that a higher virus amount in the tick and a longer feeding time increases the risk of TBEV infection.To further examine TBEV in ticks that have bitten humans and find factors that may predict the risk of human infection and development of TBE, we characterized several TBEV strains genetically. Including TBEV strains isolated from ticks that have bitten human, from questing field-collected ticks, and TBEV strains isolated from patients with TBE. In one of the ticks detached from a human after >60h of feeding, there was a heterogeneous population of TBEV quasispecies with varying poly(A) length in the 3’ untranslated region of the genome was observed. These variations might have implications for differences in virulence between TBEV strains, and the heterogeneous quasispecies population observed could be the virus adapting from replication in tick cells to mammalian cells.We also investigated the response to TBEV vaccination in relation to 14 health-related factors in a population of older individuals on the Åland Islands. Blood samples, questionnaires, and vaccination records were collected from 533 individuals. Three different serological assays to characterize antibody response to TBEV vaccination were used. The main finding was that the number of vaccine doses in relation to age was the most important factor determining successful vaccination. The response to each vaccination dose declined linearly with age, and as much as 47% of individuals 50 years or older that had taken 3 vaccine doses were seronegative, compared to 23% that had taken 4 doses and 6% with 5 doses. Comparison between the serological assays revealed that the cutoffs determining the balance between sensitivity and specificity differed, but not the overall accuracy.Taken together, these results contribute to a better understanding of the TBEV epidemiology and can provide tools in the prevention of TBE.
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| 5. |
- Wilhelmsson, Peter
(författare)
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A STING from a Tick : Epidemiology, Ecology and Clinical Aspects of Lyme Borreliosis
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lyme borreliosis (LB) is the most common tick-borne disease in the Northern Hemisphere and the number of LB cases is increasing. The infection is caused by spirochetes belonging to the Borrelia burgdorferi sensu lato complex, and is, in Europe, transmitted to humans by Ixodes ricinus ticks.To gain a deeper knowledge of the interactions between ticks, humans and Borrelia bacteria, we investigated temporal differences in exposure to tick bites in different parts of Sweden and the Åland Islands, Finland during the years 2008 and 2009. We also investigated the site of tick attachment on the human body and the time it takes for a person to detected and remove such ticks. Furthermore, the distribution of Borrelia species and the number of Borrelia cells in the ticks were investigated. Sera taken from the tick-bitten persons at study inclusion were analyzed for the presence of Borrelia antibodies. Three months later, the clinical outcome and the serological response of the tick-bitten persons were investigated. A total of 2154 I. ricinus ticks and 1546 participants were included in the studies.Participants were exposed to tick bites between April and November, but temporal and spatial differences in exposure to ticks was found. The majority of the tick bites were caused by nymphs (70%) and most tick bites took place on the legs (50%). The site of tick attachment on the body as well as the age and gender of the participant influenced how soon a tick was detected. The majority of participants removed “their” ticks later than 24 hours of attachment. Of all ticks, 26% was Borrelia-infected, but the prevalence varied between the life stages of the tick and between the studied areas. Six species of the B. burgdorferi sensu lato complex and one Borrelia species that may cause tick-borne relapsing fever were detected. Adult ticks that had fed more than 36 hours contained a lower number of Borrelia cells than adult ticks that had fed less than 36 hours. The seroprevalence among the participants varied between genders as well as between the studied areas. Of all participants, 2% was diagnosed with LB and 2.5% seroconverted without an LB diagnose. A correlation between seroconversion and duration time of tick attachment was found, but the number of Borrelia cells in the tick, did not explain the risk of infection for the bitten person.A deeper knowledge and a better understanding of the interactions between ticks, humans and Borrelia bacteria may contribute reducing the risk for tick bites and the risk of developing LB after a tick bite.
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| 6. |
- Lager, Malin, 1975-
(författare)
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Molecular and serological tools for clinical diagnostics of Lyme borreliosis - can the laboratory analysis be improved?
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lyme borreliosis (LB) is caused by spirochetes within the Borrelia burgdorferi sensu lato complex and is the most common tick-transmitted disease in the northern hemisphere. The transmission of the spirochetes to humans in Europe is done by the Ixodes ricinus ticks, which can also transmit the relapsing fever species Borrelia miyamotoi. LB may cause clinical manifestations in the skin, in the central nervous system, in joints, and in the heart. Diagnosis of LB is mainly based on the patient´s medical history, self-described symptoms, and clinical signs in combination with the detection of Borrelia-specific antibodies (serological methods). In some cases/issues, detection of Borrelia-specific deoxyribonucleic acid (molecular methods) may be used as a complement to serology. All diagnosed LB infections are treated with antibiotics to prevent disease progression, and most patients fully recover without further sequelae. The overall aims of this thesis were to evaluate molecular and serological tools for laboratory diagnosis of LB, with a special focus on Lyme neuroborreliosis (LNB), and to identify potential improvements.The results presented in this thesis showed that the immunoglobulin (Ig) G assays, currently in use in northern Europe for detection of antibodies in serum, had high diagnostic sensitivity (88 %) together with comparable results both between and within assays. For the IgM assays, the diagnostic sensitivity was lower (59 %) with more heterogeneous results. Small variations in diagnostic performance for IgM and IgG were mainly presented for samples within the borderline zone. These results support the theory that separate testing of IgM antibodies in serum has low diagnostic value. However, simultaneous detection in serum and cerebrospinal fluid (CSF) for both IgM and IgG antibodies was essential for the diagnosis of LNB, at least for certain assays.So far (to our knowledge), no systematic evaluation and optimisation of the pre-analytical handling of CSF samples before molecular testing has been performed. By use of the precipitate concentrated by moderate centrifugation, extraction of total nucleic acid followed by reversetranscription to complementary deoxyribonucleic acid, in combination with the absence of polymerase chain reaction (PCR) inhibitors, detection of Borrelia garinii, Borrelia afzelii, Borrelia burgdorferi sensu stricto, and B. miyamotoi was possible. These four species are all known to be pathogenic to humans. The results revealed a high analytical sensitivity and specificity for the optimised pre-analytical conditions. The thesis also presents results showing that the real-time PCR protocols currently used in Scandinavia have high analytical sensitivity, specificity, and concordance. This indicates that the low diagnostic sensitivity for detection of Borrelia in CSF was not a result of poorly designed and evaluated PCR protocols, but was possibly due to the low number of spirochetes in the samples. However, to further evaluate the diagnostic performance for detection of Borrelia in CSF by PCR, clinical samples need to be evaluated based on our new recommendations for the pre-analytical handling of CSF samples.In conclusion, this thesis presents results revealing that both molecular and serological tools for detection of Borrelia have, in general high sensitivity and specificity with results comparable between different protocols and different laboratories. It also presents recommendations for pre-analytical handling of CSF samples before PCR-analysis, and shows the benefits in diagnostic performance by simultaneous detection of IgM and IgG antibodies in serum and CSF for accurate diagnosis of LNB. Even though the techniques mentioned above have high analytical performance, the ability to discriminate an active infection from a previous one is limited and further studies need to be carried out. These studies need to focus on finding diagnostic tools that can help physicians to determine ongoing infection to ensure adequate treatment. It is also desirable to improve the standardisation of the diagnostic tools and to find methods that can discriminate between different Borrelia species.
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| 7. |
- Pettersson, John H.-O. 1981-
(författare)
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The Origin of the Genus Flavivirus and the Ecology of Tick-Borne Pathogens
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis examines questions related to the temporal origin of the Flavivirus genus and the ecology of tick-borne pathogens. In the first study, we date the origin and divergence time of the Flavivirus genus. It has been argued that the first flaviviruses originated after the last glacial maximum. This has been contradicted by recent analyses estimating that the tick-borne flaviviruses emerged at least before 16,000 years ago. It has also been argued that the Powassan virus was introduced into North America at the time between the opening and splitting of the Beringian land bridge. Supported by tip date and biogeographical calibration, our results suggest that this genus originated circa 120,000 (156,100–322,700) years ago if the Tamana bat virus is included in the genus, or circa 85,000 (63,700–109,600) years ago excluding the Tamana bat virus. In the second study we estimate the prevalence of tick-borne encephalitis virus (TBEV) in host-seeking Ixodes ricinus from 29 localities in Sweden and compare our data with those of neighbouring countries. Nymphs and adult ticks were screened for TBEV using a real-time PCR assay. The mean TBEV prevalence for all tick stages combined was 0.26% for Sweden and 0.28% for all Scandinavian countries, excluding Iceland. The low prevalence of TBEV in nature may partly be explained by the fact that TBEV occurs in spatially small foci and that the inclusion of ticks from non-infected foci will reduce the prevalence estimate. In the third and fourth study, we conducted the first large-scale investigations to estimate the prevalence and geographical distribution of Anaplasma spp. and Rickettsia spp. in host-seeking larvae, nymphs and adults of I. ricinus ticks in Sweden. Ticks were collected from several localities in central and southern Sweden and were subsequently screened for the presence of Anaplasma spp. and Rickettsia spp. using a real-time PCR assay. For all active tick stages combined, the mean prevalence of Anaplasma spp. and Rickettsia spp. in I. ricinus in Sweden was estimated to 1.1% and 4.8%, respectively. It was also shown that A. phagocytophilum and R. helvetica are the main Anaplasma and Rickettsia species occurring in Sweden.
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| 8. |
- Berglund, Björn, 1983-
(författare)
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Deliberations on the impact of antibiotic contamination on dissemination of antibiotic resistance genes in aquatic environments
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The great success of antibiotics in treating bacterial infectious diseases has been hampered by the increasing prevalence of antibiotic resistant bacteria. Not only does antibiotic resistance threaten to increase the difficulty in treating bacterial infectious diseases, but it could also make medical procedures such as routine surgery and organ transplantations very dangerous to perform. Traditionally, antibiotic resistance has been regarded as a strictly clinical problem and studies of the problem have mostly been restricted to a clinical milieu. Recently, non-clinical environments, and in particular aquatic environments, have been recognised as important factors in development and dissemination of antibiotic resistance. Elevated concentrations of antibiotics in an environment are likely to drive a selection pressure which favours resistant bacteria, and are also believed to promote horizontal gene transfer among the indigenous bacteria. Antibiotic resistance genes are often located on mobile genetic elements such as plasmids and integrons, which have the ability to disseminate among taxonomically unrelated species. The environmental bacteria can thus serve as both reservoirs for resistance and hot spots for the development of new antibiotic resistance determinants.There is still a lack of data pertaining to how high antibiotic concentrations are necessary to drive a selection pressure in aquatic environments. The aim of this thesis is to determine the effect of high and low concentrations of antibiotics on environmental bacterial communities from different aquatic environments. In the studies performed, antibiotics were measured using liquid chromatography-mass spectrometry. Bacterial diversity and evenness were assessed using molecular fingerprints obtained with 16S rRNA gene-based denaturing gradient gel electrophoresis, and antibiotic resistance genes and class 1 integrons were quantified using real-time PCR.Water and sediment samples were collected from different rivers and canals in Pakistan. The environments differed in anthropogenic exposure from undisturbed to heavily contaminated. A general trend could be observed of high concentrations of antibiotics correlating to elevated concentrations of antibiotic resistance genes and integrons. Extremely high concentrations of antibiotic resistance genes and integrons were found in the sediments downstream of an industrial drug formulation site, which likely correlated to the high load of antibiotics found in the water. Antibiotic and antibiotic resistance gene concentrations were also shown to increase downstream of Ravi river, which flows through Lahore, a city of more than 10 million inhabitants. Rivers not impacted by anthropogenic contamination were found to contain antibiotics and resistance gene concentrations of similar levels as in Europe and the U.S. Similar measurements were performed in the Swedish river Stångån. The concentrations of antibiotic resistance genes and class 1 integrons were shown to increase in the river after it had passed, and received urban wastewater effluent from the city of Linköping.A series of constructed wetlands were exposed to a mixture of different antibiotics at environmentally relevant concentrations over a few weeks. The antibiotic exposure did not observably affect the bacterial diversity or integron concentrations. Antibiotic resistance genes were found at low background concentrations, but the antibiotic exposure did not observably affect the concentrations. The constructed wetlands were also found to reduce most antibiotics at levels comparable to conventional wastewater treatment schemes, suggesting that constructed wetlands may be useful supplementary alternatives to conventional wastewater treatment.To investigate the effect of antibiotics on an uncontaminated aquatic environment in a more controlled setting, microcosms were constructed from lake water and sediments and subsequently exposed to varying concentrations of antibiotics (ranging from wastewater-like concentrations to 1,000 times higher). The water and sediments were gathered from the lake Nydalasjön, near Umeå, which is not exposed to urban waste. While antibiotic resistance genes and class 1 integrons were found in the lake sediments, no increase in the concentrations of these genes could be observed due to the antibiotic additions.In conclusion, although antibiotic resistance genes and integrons are part of the environmental gene pool, low concentrations of antibiotics do not seem to immediately impact their prevalence. However, aquatic environments exposed to anthropogenic waste do exhibit elevated levels of antibiotic resistance genes and integrons. Aquatic environments heavily polluted with antibiotics also clearly display correspondingly high concentrations of antibiotic resistance genes and integrons. These results clearly indicate the necessity to keep down pollution levels as well as the need to establish the range of antibiotic concentrations which do promote resistance. This must be done in order to enable risk assessments and to establish acceptable levels of antibiotic pollution. It should also be stressed that more research is required to elucidate what effect low levels of antibiotic exposure has on environmental bacterial communities.
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| 9. |
- Nordgren, Johan, 1980-
(författare)
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Norovirus Epidemiology : Prevalence, transmission, and determinants of disease susceptibility
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Norovirus (NoV) is today recognized as the most important agent of acute human gastroenteritis, causing a high number of diarrheal episodes in both adults and children. Outbreaks in hospitals, nursing homes, day-care centers, and from consumption of contaminated food and drinking water are common. Wastewater can be a source of NoV dissemination, e.g. when used for irrigation of crops, or due to shellfish cultivation near the outlet of wastewater treatment plants. Today, at least 25 different genotypes of NoV belonging to two major genogroups (GG) have been observed in humans. These genotypes are associated with different transmission patterns and disease severity in humans. Also host genetic factors, such as presence of ABO antigens and mutations in the FUT2 gene affect susceptibility, and can even render complete resistance to symptomatic infections, but only the most common NoV genotypes have been studied regarding this.In this thesis, we wanted to find prevention strategies for NoV disease through four studies of NoV epidemiology: Development of a sensitive real-time PCR assay for detection and quantification of human NoVs, characterization of NoV in children with diarrhea in Nicaragua, investigation of the prevalence and parameters influencing NoV concentration in a wastewater treatment plant in Gothenburg, Sweden, and studying host susceptibility factors in a foodborne NoV outbreak in Jönköping, Sweden.First we developed a real-time PCR assay which can detect and quantify NoV in various settings, both in stool samples of patients, and in wastewater samples from which virus was first concentrated using ultracentrifugation. This assay was found to be more sensitive than commercial immunological assays and conventional PCR methods. The assay is furthermore able to differentiate between the two major human genogroups of NoV using melting curve analysis, which provides valuable information about the circulating NoV strains.The survey of NoV in pediatric diarrhea in Nicaragua revealed a large impact of NoV, both in community and hospital based settings, with 15% of the severe diarrhea cases attributed to NoV. Peaks of clinically diagnosed NoV gastroenteritis were associated with emerging variants of genotype GGII.4, largely replacing the many different NoV genotypes circulating before the peak of diarrheal cases. Children infected with the GGII.4 genotype were found to shed more virus compared to children infected with other genotypes, which could partly explain the high transmission of GGII.4.At the wastewater treatment plant in Gothenburg, both NoV GGI and GGII were detected during a whole year, not only during the winter season when clinical cases are common. This indicates that NoV infections are frequently occurring at clinical and/or sub-clinical levels in the community. During winter, GGII was present in high concentrations, whereas GGI concentration increased to higher levels than GGII in summer, possibly due to the emergence of new genotypes following the winter outbreaks. The levels of NoV GGI were stable during the year, and hence incoming concentrations were affected by dilution factors such as rain. Primary treatment and treatment in a conventional, non-nitrifying activated sludge system reduced the NoV concentration by a factor of about 30. The detection of NoV in outgoing water, together with the low reduction and lack of correlation to indicator bacteria, suggest that better monitoring tools for virus in wastewater are warranted to reduce environmental contamination.A foodborne NoV outbreak in Jönköping in October 2007, by a NoV GGI.3 strain, revealed a surprising pattern of host susceptibility. In contrast to previous findings, this strain infected individuals irrespective of secretor status and Lewis (Le) phenotype, with non-secretors and Lea+bindividuals having a higher risk of disease. Individuals with blood group B had a partial protection to symptomatic infection, but none of the host factors investigated mediated complete resistance. Furthermore, we observed differences in susceptibility regarding homozygosity and heterozygosity in the FUT2 gene, with heterozygous secretor-positive individuals being more susceptible to symptomatic NoV infection than homozygous secretors.In summary, the developed LUX real-time PCR assay was successfully used in all studies in this thesis, which yielded important information about the prevalence and transmission of NoV. We observed the emergence of GGII.4 variants, causing the majority of diarrheal cases in children, largely replacing the other circulating genotypes, possibly due to better replication leading to a higher viral shedding. After the peak of NoV-induced diarrheal episodes, the incidence of GGII.4 decrease and other strains emerge which can infect people not previously exposed. This was observed in the foodborne outbreak in Jönköping, where individuals expected to be resistant to NoV were infected, and indeed had a higher risk of developing disease. A similar seasonal pattern was also indirectly observed in wastewater, with high levels of GGII in winter, which subsequently declined, followed by an increase of GGI in summer. Taken together, these results provide a better insight into the epidemiology of the virus, which hopefully can lead to better preventive measures for NoV gastroenteritis.
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| 10. |
- Olofsson, Magnus, 1971-
(författare)
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Microbiological Surveillance in Primary Health Care : New Aspects of Antimicrobial Resistance and Molecular Epidemiology in an Ageing Population
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BackgroundThe inexorable rise in antimicrobial resistance (AMR) interferes with the goals of health care services around the world, given how critical the antibacterials are in making infections treatable and surgical procedures doable. Nursing homes residents have been identified as a reservoir for AMR, possibly due to the combination of being physically and mentally frail, frequently treated with antibacterials, and frequently moved between nursing home and hospital. Microbiological surveillance is a key countermeasure against further AMR development. Yet, surveillance data is easily biased due to precision problems regarding how the data is collected and evaluated.MethodsBeginning in 2008, we launched two programmes (“SHADES” and “MIDIO”) aimed to gathering AMR data in a systematic fashion from elderly nursing home residents and elderly people living in their own place of residence. In doing so, we focused on colonizing strains of the two most important nosocomial infectious agents, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The bacteria were collected from multiple body sites and analysed with respect to antimicrobial susceptibility and genetic diversity.ResultsActive surveillance of AMR showed that (i) a S. aureus isolate could be retrieved from 1 in every 2 individuals given a single round of sampling, but aggregating several rounds of sampling, this figure might reach 7 in every 10 individuals, (ii) an E. coli isolate could be retrieved from 4 in every 5 individuals, (iii) the overall prevalence of AMR was favourable when compared to the situation in many other countries, (iv) the genetic diversity of S. aureus was generally high and provided only limited evidence of clonal expansion or contraction, and (v) diabetes mellitus was one of very few patient-level factors to show an association with the degree of genetic diversity in S. aureus.ConclusionsThe prevalence of colonization with S. aureus and E. coli was somewhat higher than expected, but the degree of AMR was very low. The genetic diversity of S. aureus was generally high. Diabetes mellitus emerged as the only patient-level factor associated with a higher degree of genetic diversity in S. aureus.
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