Equine infectious anemia virus (EIAV) causes rapid development of acute disease followed by recurring episodes of fever, thrombocytopenia and viremia, termed chronic EIA. Most infected horses control the virus by immune mechanisms and become inapparent carriers. To further our understanding of the equine immune response to EIAV, a multi-probe ribonuclease protection assay (RPA) was developed to quantitate equine-specific cytokine mRNAs. Eleven template plasmids specific to ten equine cytokine genes and the ?-actin gene were generated, from which radiolabeled anti-sense RNA probes were produced. The RPA simultaneously quantitated mRNA levels of interleukin (IL)-1, IL-1, IL-6, IL-8, IL-10, IL-12 p35, IL-12 p40, interferon (IFN)-, transforming growth factor (TGF)-1 and tumor necrosis factor (TNF)- in equine peripheral blood mononuclear cells and equine monocyte-derived macrophages (EMDM). The assay detected as few as 5105 RNA molecules and displayed coefficients of variation of 0.03-0.08 when normalized to -actin expression. Using this RPA, cytokine expression in EMDM infected with 2 molecularly cloned viruses (EIAV17 and EIAV19) was determined. EIAV17 varies from EIAV19 only in env, rev and LTR and causes fatal disease in Shetland ponies. When added to EMDM cultures, virulent EIAV17 stimulated expression of IL-1, IL-1, IL-6, IL-10 and TNF-. These cytokine mRNAs were significantly elevated by 0.5 to 1 hr post infection (hpi) and returned to basal levels by 12 to 24 hpi, indicating modulation by early event(s), such as receptor binding. In contrast to EIAV17, EIAV19 is avirulent in vivo and failed to induce any of the tested cytokines in EMDM. These data show a direct correlation between the virulence of the EIAV clone and the induction of cytokines. The cytokines stimulated by EIAV17 may contribute to EIA-associated symptoms, enhance viral replication in the host, and regulate the host immune response. To determine whether cytokine induction requires EIAV17 replication, EMDM cultures were exposed to UV-inactivated EIAV17 and cytokine induction was monitored. UV-inactivation did not block cytokine induction by EIAV17, suggesting dispensability of viral replication. Given that EIAV17 induces cytokines in a rapid and replication-independent manner, the activation of cytokine expression is likely mediated by binding of EIAV17 to equine macrophage receptor(s).

An infectious cDNA clone of Vero cell adapted Beaudette strain of IBV was constructed using in vitro assembly of cDNA fragments. The entire genome of IBV was RT-PCR amplified into seven fragments, with each piece overlapping about 10 nucleotides. The fragments were ligated and transcribed to synthesize RNA, which was transfected into BHK-21 cells. These cells were then overlaid onto IBV susceptible Vero cells. After five days transfection, the virus was successfully rescued from the transfected cells. The cDNA clone from our laboratory strain has a five nucleotide insertion not present in the originally sequenced virus, resulting in total genome size of 27,613 nucleotides. The infectious cDNA clone was further manipulated to demonstrate its potential as a gene transfer vector, by replacing the ORF5a open reading frame with enhanced green fluorescent protein. The recombinant infectious cDNA clone was also successfully rescued after three days transfection of BHK-21 cells followed by co-culturing with Vero cells. This study showed that the 5a protein, whose function is not known, is not necessary for in vitro IBV replication. This study also showed that the 5a ORF is a good candidate for an insertion site of recombinant genes for the development of IBV infectious cDNA clone as a gene transfer vector.

Objective: Globally, about 50 to 100 million patients are infected with dengue fever per year and the average mortality rate is about 3.5 to 5% in Asia. Because of appropriate geographic location and cultural factors, dengue fever has been the important subject of infectious disease that Taiwan faces. In order to control and prevent the spread of dengue fever effectively, how to diagnose the suspected case correctly by the clinical symptoms and to improve the early reporting rates become critical research questions. The purpose of this study is to explore the correlation between clinical symptoms and diagnosis of dengue fever, and the factors associated with being reported at the first outpatient visit among confirmed case by using Dengue Fever Survey Form, which including demographics, clinical symptoms, level of the first outpatient visit and whether the patient is reported at the first outpatient visit. Design: 593 virologically confirmed cases during 2006 Dengue endemics in Kaohsiung city were studied. The data were from Dengue Fever Survey Form, which were collected from January 1 to December 31,2006. Result: The mean age of cases was 46.45¡Ó19.06 years (range 2 years to 89 years). The most common symptoms were fever (97.3%), pain (75.2%), GI symptoms (74.7%), skin rash (49.2%), and thirsty/dry mouth (49.1%). Chi-square tests showed gender, age in group, viral type, whether dengue hemorrhagic fever or not, level of the first outpatient visit, pain and gastrointestinal symptoms were significantly associated with being reported at the first outpatient visit. The result of the analysis of logistic regression indicated that the significant predictors of being reported at the first outpatient visit were gender, age in group, viral type, level of the first outpatient visit, gastrointestinal symptoms and fatigue. Conclusion: Reporting of infectious disease is essential to detection of outbreaks, planning of control program and provision of appropriate treatment. Clinical symptoms of dengue fever and the level of the first outpatient visit will influence rates of being reported at the first outpatient visit. All medical providers involved in diagnosis and treatment of dengue fever should strengthen their knowledge by continuing learning in order to improve early identification rates. In addition, health department could try to improve the detection and reporting systems to make the reporting steps more convenient and advance early reporting rates.

This work comprises three projects that extend previous models to include features of practical significance for the statistical analysis of infectious disease data. In the first, we find from a simulation study how the degree of heterogeneity in the number contacts that individuals have affects the relationship between estimates of a pathogen's effective population size based on coalescent theory and the true prevalence and incidence of that pathogen. In the second, we find that aggregating data from many small outbreaks allows the parameters of stochastic epidemic models to be consistently estimated with a generalized linear model. Application of this method to a set of 77 small norovirus outbreaks reveals interesting differences in the transmission parameters between hospital and nursing-home outbreaks. In the third project, we gain insight into HIV contact networks in the United States by fitting data from a number of surveys to a simple stochastic model of a dynamic network. / text

The modern multimodal transportation system provides an extensive network for human mobility and commodity exchange around the globe. As a consequence these interactions are often accompanied by disease and other biological infectious agents. This dissertation highlights the versatility of network models in quantifying the combined impact transportation systems, ecological systems and social networks have on the epidemiological process. A set of predictive models intended to compliment the current mathematical and simulation based modeling tools are introduced. The main contribution is the incorporation of dynamic infection data, which is becoming increasingly available, but is not accounted for in previous epidemiological models. Three main problems are identified. The objective of the first problem is to identify the path of infection (for a specific disease scenario) through a social contact network by invoking the use of network based optimization algorithms and individual infection reports. This problem parallels a novel and related problem in phylodynamics, which uses genetic sequencing data to reconstruct the most likely spatiotemporal path of infection. The second problem is a macroscopic application of the methodology introduced in the first problem. The new objective is to identify links in a transportation network responsible for spreading infection into new regions (spanning from a single source) using regional level infection data (e.g. when the disease arrived at a new location). The new network structure is defined by nodes which represent regions (cites, states, countries) and links representing travel routes. The third research problem is applicable to vector-borne diseases; those diseases which are transmitted to humans through the bite of an infected vector (i.e. mosquito), including dengue and malaria. The role of the vector in the infection process inherently alters the spreading process (compared to human contact diseases), which must be addressed in prediction models. The proposed objective is to quantify the risk posed by air travel in the global spread of these types of diseases. / text

Viruses cause 60% of human infections and are probably the most common cause of infectious disease acquired indoors. Rapid spread of viral illness in indoor establishments facilitates disease morbidity and mortality. The goal of this dissertation is to clarify the role of fomites in the viral infection cycle. Research methods include investigation of published literature, and the use of polymerase chain reaction (PCR) for viral detection. The Appendix A study reviewed published literature to assess the significance of fomites in the transmission of ten common respiratory and enteric viruses (rhinovirus, respiratory syncytial virus (RSV), influenza A, parainfluenza 1 (HPIV1), coronavirus, rotavirus, calicivirus, hepatitis A virus (HAV), astrovirus and adenovirus). Results suggest that fomites play an important role in the transmission of common viral pathogens, and the use of disinfectants may limit the spread of viral disease. The Appendix B study examined PCR primer detection limits by determining the time length viruses can be isolated on fomites. Results indicated that poliovirus 1 and hepatitis A virus could be detected for up to 60 days. Parainfluenza 1 virus isolation yielded detection at 30 days and 50 days. Norovirus isolation yielded detection at 20 days and 30 days. Influenza virus isolation results were inconsistent, yielding no initial detection and detection up to 20 days. Appendix C assessed the occurrence of human parainfluenza 1 virus (HPIV1) on surfaces in office settings. HPIV1 was detected on 37% of fomites. HPIV1 was detected most on desktops (47%), and least on light switches (19%). Study results indicated a statistically significant difference between positive fomites in different buildings (Chi-square p < 0.011), and between building cubicles and conference room fomites (Chi-square p < 0.011). Appendix D evaluated the prevalence of influenza A virus on surfaces in day care and home settings. Influenza A was isolated on 23% of fall day care fomites and 53% of spring day care fomites. Influenza was isolated on 59% of home fomites sampled during March, and no influenza was detected on home fomites sampled during the summer. Overall, Influenza A virus was isolated on over 50% of fomites in homes and day care centers.

Infectious disease outbreaks can have a significant impact on healthcare resources and are disruptive to routine healthcare programs and services. There is very little literature on the economic burden of infectious disease outbreaks; thus, this research attempts to provide insight into the healthcare resources used to contain a mumps outbreak. The Nova Scotia 2007 mumps outbreak provides an opportunity to produce a costing framework to capture the economic burden an outbreak has on the Nova Scotia healthcare system. The costing framework for this study used an accounting model to costing; in particular, it used an activity-based costing approach. The total mumps outbreak cost is estimated at $2,478,500 or $3,511 per mumps case. Given the significant impact an infectious disease outbreak has on healthcare resources, more economic evaluations should be done to help guide policies around infectious disease prevention strategies, and to maximize the allocation of healthcare resources.

Host-pathogen investigations have conceptually evolved during the last two decades, from a basic and descriptive approach to a current hypothesis-driven and a more theoretical discipline shaped by evolutionary biology. Our deeper understanding of the elements influencing the mutual selective pressures that the host and the pathogens exert on each other, together with recent conceptual advances, currently position this field of research at the frontier between ecology and evolution. Recent theoretical considerations define hostpathogens systems as an evo-eco mosaic comprised of evolutionary and ecological attributes in turn underlying the context-dependent nature of the system dynamic. Therefore, investigations of host-pathogen interactions should integrate the diversity of the systems drivers by using an integrative approach in order to elucidate both coevolutionary trajectory and epidemiological dynamic of the system. In this thesis, such a framework is used to investigate Amphibian/ranavirus interactions. Ranaviruses are emerging pathogens known to have caused amphibian die-offs on five continents with the greatest number of reported mortality events documented in North America and Europe. Despite an increasing understanding of ranaviral disease properties, ranavirus disease dynamics in the environment remain poorly understood. For instance, the influence of potential abiotic and biotic mechanisms including temperature, local landscape features, larval developmental stages, host density and genetic variability as well as genotypic interactions between the host and the pathogen has on the prevalence and virulence of the virus remains to be elucidated. In order to improve our knowledge regarding these specific determinants of ranaviral disease, I designed a combination of manipulative laboratory experiments and a field mensurative survey using the ranid amphibian Lithobates (Rana) pipiens as the host model for this system. I observed that populations of amphibian hosts inhabiting urbanized landscapes suffered from significant decline in genetic diversity in turn promoting the accrued infection by the ranavirus (manuscript 1). Complementary analysis using two amphibian host species, L.pipiens and L.sylvaticus, and three ranavirus strains revealed significant variation among hosts for their susceptibility to ranavirus, and significant variation among ranavirus strains for infectivity. I also showed that specific amphibian/ranavirus interactions might have a tighter coevolutionary history than other combinations, resulting in sharper mutual coadaptations and the potential for frequency-dependent selection to operate in this system. However, the coevolutionary trajectories in this host-pathogen system are dependent on the temperature conditions in which the interaction takes place. Amphibian/ranavirus interactions outcomes iv are therefore temperature, host, and pathogen genotype-dependent suggesting that the range of infection outcomes in this system is potentially large (manuscript 2). Further, I observed that increasing animal holding density is detrimental for host fitness as mortality rate is higher, day of death earlier, development longer, and growth rate significantly lower when tadpoles are experimentally exposed to ranavirus in high holding density situations. These results paralleled a linear increase of detrimental effects when ranavirus doses increased in low density conditions, with control tadpoles having a significantly higher overall relative fitness. However, this pattern was not observed in high density conditions, where the effects of increasing ranavirus dose were limited, revealing non-trivial density-dependence of virulence expression (manuscript 3). Finally, ranavirus infection rate varied with the host developmental stage as the host immune system clears the infection over the course of individual host development. However the intensity of the clearing depends on both the timing and number of ranavirus exposures (manuscript 4). Overall the results described in my thesis suggest that ranavirus virulence depends on a diversity of ecological, epidemiological, and evolutionary determinants. The underlying complexity of ranavirus

Isoenzyme characterisation of Entamoeba histolytica into pathogenic and non-pathogenic zymodemes substantiated previously held views that this parasite con5titutes two distinct strains or even sub-species that are morphologically identical but vary in their pathogenicity. A reappraisal of the epidemiology of amoebiasis and investigation of the patho-physiological relationships between these pathogenic and non-pathogenic zymodemes and their host was therefore indicated. Only pathogenic zymodemes were isolated from hospitalised patients with amoebic liver abscess (ALA) and amoebic dysentery (AD). In the amoebiasis endemic peri-urban population of Durban, I. histolytica occurred at an overall prevalence of 10%. Carriers of non-pathogenic zymodemes constituted 9% of the population. A key observation was that asymptomatic infections with pathogenic zymodemes occurred at a prevalence of 1%. Higher prevalence of E. histolytica occurred in association with poor sanitary conditions. Furthermore., both pathogenic and non-pathogenic zymodemes tended to cluster into family units suggesting person-to-person transmission of the parasite by the faecal-oral route. Although invasive amoebiasis occurs far more frequently in males than females (8:1) both pathogenic and non-pathogenic zymodemes are equally distributed in male and female E. histolytica cyst passers. Ninety percent of carriers of pathogenic zymodemes spontaneously cleared their infections and remained asymptomatic throughout the study period of 2 years while 10% developed AD which required treatment with metronidazole. No spontaneous changes in zymodemes from the non-pathogenicto the pathogenic type was observed in a longitudinal study. The serological response of asymptomatic carriers of pathogenic zymodemes (100% seropositive) was identical to that of patients with ALA or AD with a high proportion (94-100%) of them being strongly seropositive. The prevalence of seropositivity amongst subjects who were not infected by E. histolytica (13% seropositive) was not statistically different (p>0,5) from that of the random population of this endemic area (19% seropositive) and carriers of non-pathogenic zymodemes (21% positive); the prevalence of strongly seropositive reactions among this group was only between 2-4%. It is concluded that a positive serological response is directly due to past or present contact with pathogenic zymodemes. This is further substantiated by the observation that the proportion of seropositive subjects was found to increase dramatically in a population near Cape Town where an outbreak of invasive amoebiasis (ALA and AD) occurred indicating a high prevalence of pathogenic zymodemes in this community. Another community in northern Transvaal (Gazankulu) where ALA and AD does not occur was, as expected, uniformly seronegative. Axenic growth of pathogenic zymodemes was possible but could not be accomplished with the non-pathogenic zymodemes. Even though monaxenic growth together with Trypanosoma cruzi was possible with both strains, the pathogenic zymodemes tended to grow more prolificly. No zymodeme changes from non-pathogenic to pathogenic and vice versa were observed with such changes in culture conditions. Cyst production by the pathogenic zymodemes in vivo was confirmed experimentally, thereby demonstrating the ability of pathogenic E. histolytica to independently complete their life-cycle thus giving it the ability to propagate itself successfully as a species. / Thesis (M.D.)-University of Natal, Durban, 1989.

The purpose of this research was to understand how the risks associated with West Nile virus (WNV) were presented by the Winnipeg Free Press. A detailed content analysis was completed on all Winnipeg Free Press articles and Manitoba Health news releases, between 1999 and 2008, containing information related to West Nile. Additional data included interviews with government and media representatives. Several recurring frames, including blame, controversy, rights and fairness, risk, and uncertainty were found in the newspaper data. Over time there was a decrease in both the coverage and prominence of WNV-related issues by the Winnipeg Free Press. In terms of the use of sources by media, the provincial government was found to be the most commonly used source in this context. Reporting of WNV-related issues by the Winnipeg Free Press has been relatively clear and balanced despite some initial alarmist coverage surrounding the uncertainty of the arrival of WNV.