| 1. |
- Carlsson, Beatrice
(författare)
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Human Caliciviruses: a study of viral evolution, host genetics and disease susceptibility
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The viruses described in this thesis are the norovirus and sapoviruses, which belong to the family of human caliciviruses and are known to cause gastroenteritis in humans. Gastroenteritis has emerged as a global health problem and is based on the large number of infected considered as one of the most common diseases today. According to estimates of the World Health Organization (WHO), gastroenteritis causes over five times more pediatric deaths compared to pediatric deaths caused by HIV/AIDS worldwide. Norovirus, the cause of the famous “winter vomiting disease”, is alone responsible for more than 200 000 deaths each year in children less than 5 years of age.The mechanism for emergence and evolution of new human calicivirus strains, as well as protective immunity in the human population is poorly understood. The main focus for this thesis was to elucidate the possible correlation between human calicivirus evolution, host genetics and disease susceptibility. One of the main findings presented in this thesis is the documentation of in vivo capsid gene evolution and quasispecies dynamics during chronic NoV GI.3 infection (Paper 1). In paper II, we reported that the G428A nonsense mutation in the FUT2 gene provides strong but not absolute protection against symptomatic GII.4 NoV infection. In my last two papers (Paper III and IV), we were the first to investigate host genetic susceptibility factors during authentic SaV infection.To summarize, the results presented in this thesis show that the success of human calicivirus infection probably is determined by a delicate interplay between virus evolution and susceptibility of the host, both genetically and immunologically.
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| 2. |
- Hagbom, Marie, 1971-
(författare)
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Rotavirus Disease Mechanisms Diarrhea, Vomiting and Inflammation : How and Why
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rotavirus infections cause diarrhea and vomiting that can lead to severe dehydration. Despite extensive tissue damage and cell death, the inflammatory response is very limited. The focus of this thesis was to study pathophysiological mechanisms behind diarrhea and vomiting during rotavirus infection and also to investigate the mechanism behind the limited inflammatory response.An important discovery in this thesis was that rotavirus infection and the rotavirus toxin NSP4 stimulate release of the neurotransmitter serotonin from intestinal sensory enterochromaffin cells, in vitro and ex vivo. Interestingly, serotonin is known to be a mediator of both diarrhea and vomiting. Moreover, mice pups infected with rotavirus responded with central nervous system (CNS) activation in brain structures associated with vomiting, thus indicating a cross-talk between the gut and brain in rotavirus disease.Our finding that rotavirus infection activates the CNS led us to address the hypothesis that rotavirus infection not only activates the vagus nerve to stimulate vomiting, but also suppresses the inflammatory response via the cholinergic anti-inflammatory pathway, both of which are mediated by activated vagal afferent nerve signals into the brain stem. We found that mice lacking an intact vagus nerve, and mice lacking the α7 nicotine acetylcholine receptor (nAChR), being involved in cytokine suppression from macrophages, responded with a higher inflammatory response.Moreover, stimulated cytokine release from macrophages, by the rotavirus toxin NSP4, could be attenuated by nicotine, an agonist of the α7 nAChR. Thus, it seems most reasonable that the cholinergic anti-inflammatory pathway contributes to the limited inflammatory response during rotavirus infection. Moreover, rotavirus-infected mice displayed increased intestinal motility at the onset of diarrhea, which was not associated with increased intestinal permeability. The increased motility and diarrhea in infant mice could be attenuated by drugs acting on the enteric nervous system, indicating the importance and contribution of nerves in the rotavirus mediated disease.In conclusion, this thesis provides further insight into the pathophysiology of diarrhea and describe for the first time how rotavirus and host cross-talk to induce the vomiting reflex and limit inflammation. Results from these studies strongly support our hypothesis that serotonin and activation of the enteric nervous system and CNS contributes to diarrhea, vomiting and suppression of the inflammatory response in rotavirus disease.
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| 3. |
- Kindberg, Elin, 1981-
(författare)
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Host genetic risk factors to viral diseases - a double-edged sword : Studies of norovirus and tick-borne encephalitis virus
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is today well known that the outcome of a certain infection depends on factors of both the host and the pathogen. Studies of host genetic susceptibility to infectious diseases aim to increase the understanding of why some individuals are more susceptible than others, to a certain infection. Knowledge of genetic susceptibility to a viral disease may be used in development of new therapeutic means, and also to recognize individuals who are at increased risk of severe symptoms if infected with a pathogen. It seems however that a risk factor for one disease may play a protective role in another situation; like a double-edged sword.In this thesis I have studied genetic factors affecting susceptibility to norovirus (NoV) and factors affecting the risk of developing tick-borne encephalitis (TBE) after infection with TBE virus (TBEV). NoV is the cause of the “winter vomiting disease”, affecting millions of people every year, and causing up to 200,000 fatalities among children in developing countries, each year. It is today recognized that the secretor status of an individual, i.e. the ability to express ABO blood groups and related antigens, in secretions and on mucosa, affect the risk of being infected by NoV. By studying authentic NoV outbreaks in Denmark, Spain and Sweden and by comparing the secretor status of affected and unaffected individuals we were able to confirm that secretor status have indeed great impact on susceptibility to some NoV strains, but also that there are strains circulating, which infect individuals regardless of secretor status.TBEV is endemic in many parts of Europe and Asia but studies have shown that 70-95% of all infections are asymptomatic or sub-clinical. Some individuals do however develop TBE, a severe disease including meningitis or encephalitis with or without myelitis. Also, many patients suffer from long-time sequelae and TBEV infections may in worst case be fatal. The reason for difference in disease outcome is not known and we have chosen to study if genetic factors affecting the immune response may play a role in disease outcome. To do this we used a prospectively collected Lithuanian material with samples from patients with TBE, AME (aseptic meningoencephalitis) and matched healthy controls. So far we have found that a deletion in chemokine receptor 5 (CCR5), a gene encoding a receptor involved in cell migration, is a risk factor for developing disease. We have also data showing that toll-like receptor 3 (TLR3), a receptor recognizing double stranded RNA (dsRNA), which is a product of TBEV replication, may instead of being protective increase the risk of TBE.
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| 4. |
- 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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| 5. |
- Reyes, Yaoska
(författare)
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Norovirus and rotavirus susceptibility : studies from a Nicaraguan birth cohort
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Norovirus and rotavirus are major causes of pediatric acute gastroenteritis (AGE). It is estimated that norovirus is responsible for ~20% of all diarrheal diseases in children worldwide and causes approximately 200,000 deaths each year, mostly in young children and the elderly. Despite this vast disease burden, there is no licensed vaccine available. The introduction of universal infant rotavirus vaccination has led to marked reductions in diarrhea incidence and diarrhea-associated mortality in children. However, rotavirus continues to cause a high disease burden, particularly in low- and middle-income countries (LMIC), associated with an estimated 128,500 deaths in young children. Susceptibility to both norovirus and rotavirus AGE is strongly associated with the secretor phenotype (expression of specific glycans in mucosa and secretions). This, along with the Lewis phenotype and ABO group form the differential expression of histo-blood group antigens (HBGAs) in the mucosa. These HBGAs can act as putative receptors or attachment factors facilitating infection of these viruses. The overall aim of this thesis was to address outstanding questions regarding susceptibility and immunity to norovirus and rotavirus infections in children. These questions are of relevance for understanding the effects of a future norovirus vaccine and factors influencing vaccine protection. Our questions were addressed by investigating norovirus and rotavirus disease burden, molecular epidemiology, and the role of HBGAs in susceptibility in children enrolled in a rotavirus-vaccinated birth cohort in Nicaragua. We further estimated the breadth and duration of immune response and protection after the first norovirus AGE episode. Our results showed that the incidence of rotavirus and norovirus was 9.3 and 21.9 per 100 child-years, respectively. Several different norovirus genotypes were observed (n=13), the most common being GII.4 (42%), GI.3 (18%), GII.12 (9%) and GII.17 (9%). Genotype GII.4 was not only the most common genotype but also infected children earlier in life and caused more severe AGE episodes compared to other genotypes. In contrast, the distribution of rotavirus genotypes was limited and dominated by animal-derived strains and the absence of the wild-type G1P[8] genotype, which is the component of the Rotarix vaccine used in Nicaragua. Secretor children had the highest risk of norovirus AGE, with the predominant and clinically more severe GII.4 genotype only observed in secretors. Secretor children also had the highest risk for rotavirus AGE after vaccination. This is of particular interest since previous studies have observed that non-secretors have a less immune response after vaccination of the live oral rotavirus vaccines. Hence, the mediation of protection against rotavirus AGE for these children is likely due to genetic resistance to wild-type infections and not by vaccine-induced immune protection. Using surrogate neutralization assays, we observed that the antibody-mediated immune response after the first AGE episode of norovirus GII.4 persisted for about 19 months, thus suggesting a relatively long-term protection. We further found that the immune response against GII.4 was genotype-specific in a significant proportion (60%) of children. The multitypic response exhibited in some children could be due to asymptomatic infections with two or more genotypes over the studied period. Using statistical models, we found that one episode of norovirus GI and norovirus GII conferred approximately 33% and 80% reduced hazard against future genogroup-specific episodes in the first 3 years of life, respectively. In summary, the results presented in this thesis suggest that a pediatric norovirus vaccine including norovirus GII.4, and given early in life, would significantly reduce the high burden of diarrheal disease in young children, particularly for secretors.
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| 6. |
- Vildevall, Malin, 1980-
(författare)
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The Norovirus Puzzle : Characterization of human and bovine norovirus susceptibility patterns
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Winter vomiting disease is caused by norovirus (NoV) and affects millions of people every year resulting in 200.000 deaths among children in developing countries. It was observed early that not all individuals exposed to the norovirus became ill. The reason for this is now recognized to be dependent upon the secretor status of an individual. The secretor status determines the ability of an individual to express histo-blood group antigens (HBGA) on mucosa and in saliva. A non-secretor is unable to express HBGAs due to a mutation in a gene called FUT2. In this thesis, I have investigated the antibody prevalence and titer in humans in Sweden and Nicaragua to the most common GII NoV and the correlation to secretor status, Lewis status and ABO. I found that secretors had significantly higher antibody prevalence and titer to GII NoV than non-secretors suggesting that non-secretors are less prone to be infected by the GII NoV. In Nicaragua, I also found several different NoV strains circulating at the same time. The NoVs have been circulating and evolving in the human population for some time and the same individuals seems to be infected over and over again with the same virus. This suggests that there is no long-term immunity present but possibly short-term immunity, which would make it very difficult to produce a vaccine against NoV. However, recent studies have shown the possibility of using virus like particles as a vaccine candidate and have demonstrated long-term immunity.The bovine NoV (boNoV) cause gastroenteritis in cattle and are closely related to the human NoV. The possibility of zoonotic transfer to humans is currently being investigated. I found that 26% of Swedish blood donors have antibodies to the boNoV suggesting that they have been exposed to the virus. The human NoV has been observed to be able to infect and cause disease in cattle, could the boNoV do the same in humans? To date, no boNoV strain has been found in humans. The proposed receptor structure for boNoV is the αGal epitope, which is present in many mammals like cow, pig, horse, sheep and rabbit but not in humans. This indicates that humans are not at risk for boNoV infection because we lack the proper receptor structure. However, recombinations between different NoV strains have been demonstrated and the possibility of more than one receptor being present has been suggested. I found that aa position 365-379 on the boNoV capsid seems to be important for binding to erythrocytes. In this thesis, I hope to add some new pieces to the Norovirus Puzzle.
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| 7. |
- Wallensten, Anders, 1974-
(författare)
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Influenza A virus in wild birds
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Influenza virus is a RNA virus that exists as different types and subtypes. Influenza A virus strains are known to cause disease in several bird and mammalian species. Wild birds are believed to constitute the natural reservoir for influenza A virus.In humans, influenza A virus causes yearly seasonal influenza epidemics of respiratory disease resulting in high morbidity and severe economic consequences. Due to the virus’ ability to change its antigenic properties by mutation, yearly vaccination is required for protection from the disease.There are many different subtypes of influenza virus which are characterized according to two surface structures - the hemagglutinin and neuraminidase proteins - , for example; H5N1. These subtypes have the ability to recombine, and thereby creating new variant combinations. If a subtype that the living population of humans has not encountered before starts to spread among humans, it can result in a pandemic. Pandemic outbreaks have occurred at irregular intervals throughout history and have had a devastating impact on mankind. For example the Spanish influenza pandemic of 1918 is thought to have killed more than 50 million people.Influenza A virus is also an important cause of disease in poultry where virus strains of some subtypes may change into forms that are highly pathogenic. These virus strains may transmit directly to man and multiple other species. This has been the case in the ongoing outbreak that started in South East Asia in 2003. All known subtypes of influenza A virus have been isolated from wild birds living in aquatic environments, mainly dabbling ducks. These species are considered to be the reservoir for influenza A virus. The virus causes sub clinical gastrointestinal infection in ducks. High amounts of virus are excreted in the feces and spread via the fecal-oral route through water where it can persist for a prolonged time.There are still many unknowns about the ecology of influenza virus in the wild bird reservoir. This thesis includes five articles where data are presented that add new knowledge on this subject. We add proof that wild ducks are indeed the host for most influenza A virus subtypes by presenting data from a meta-analysis on all published screening data from wild birds and by presenting data from a four year screening of migratory ducks that were caught and sampled at Ottenby Bird Observatory. Our investigations have shown that the prevalence of influenza virus in the wild duck population of western Eurasia shows temporal differences in comparison to the results found in studies in North America. The prevalence in western Eurasian ducks is high during the period August to December and also rises in the spring. These findings are of importance for the understanding of how influenza virus is perpetuated in nature. During the course of the study only low pathogenic subtypes were isolated. Of concern is the high frequency of isolation of virus strains of the H5 and H7 subtypes that are prone to change into highly pathogenic variants in poultry. Many of the strains isolated in our study are similar to the ones that have caused influenza outbreaks in poultry in Europe during the last seven years. This indicates that wild bird surveillance for influenza A virus can be of major value as a sentinel system to prevent outbreaks in domestic poultry.Studies on Black-headed Gulls (Larus ridibundus) revealed a previously unknown subtype, H16. This finding widened the spectra of known influenza A virus subtypes in nature.Influenza A virus was also isolated in samples from Guillemots (Uria aalge) in the Baltic Sea. This was the first time influenza A virus was isolated from this species in Europe. The isolated virus strains contained a mix of genes, some of which must have been derived from influenza A virus strains present in the North American bird population. This finding proves that limited exchanges between the virus strains present on the American and the Eurasian continents exist, which is of concern for evaluating the risk of spread of highly pathogenic virus strains by wild birds to the Americas.
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