Multiple Transmission Routes Research Articles

Transmission and prevention of SARS-CoV-2.

The coronavirus disease 2019 (COVID-19), caused by a novel virus of the β-coronavirus genus (SARS-CoV-2), has been spreading globally. As of July 2020, there have been more than 17 million cases worldwide. Determining multiple transmission routes of SARS-CoV-2 is critical to improving safety practices for the public and stemming the spread of SARS-CoV-2 effectively. This article mainly focuses on published studies on the transmission routes of SARS-CoV-2 including contact transmission, droplet transmission, aerosol transmission and fecal-oral transmission, as well as related research approaches, such as epidemiological investigations, environmental sampling in hospitals and laboratories and animal models. We also provide four specific recommendations for the prevention and control of SARS-CoV-2 that may help reduce the risk of SARS-CoV-2 infection under different environmental conditions. First, social distancing, rational use of face masks and respirators, eye protection, and hand disinfection for medical staff and the general public deserve further attention and promotion. Second, aerodynamic characteristics, such as size distribution, release regularity, aerosol diffusion, survival and decline, infectious dose and spread distance, still require further investigation in order to identify the transmissibility of COVID-19. Third, background monitoring of the distribution of pathogenic microorganisms and environmental disinfection in crowded public places, such as railway stations, schools, hospitals and other densely populated areas, can give early warning of outbreaks and curb the transmission routes of SARS-CoV-2 in those high-risk areas. Forth, establishing novel predictive models can help us to not only assess transmission and impacts in communities, but also better implement corresponding emergency response measures.

Dynamics of a seasonal brucellosis disease model with nonlocal transmission and spatial diffusion

Brucellosis has been increasingly concerned with the animal health and a huge loss of economics. Multiple transmission routes, seasonal pattern and spatial diffusion have been identified in brucellosis propagations. Meanwhile, infectious ability strongly depends on the distance of each adjacent infectious individual. Such property can be captured by a nonlocal infection with some integrable functions. In this paper, we first propose a seasonal brucellosis epidemic model with nonlocal transmissions and spatial diffusions. We calculate the next generation operator R(x) by a renewal process. The basic reproduction number R0 is defined as the spectral radius of R(x), which plays an equivalent role in a principal eigenvalue of a linear operator. It is shown that the proposed model exhibits the threshold dynamics in terms of R0, i.e, if R0<1, then the brucella-free steady state is globally asymptotically stable; otherwise, the model admits at least one positively periodic steady state. Numerical simulations elucidate that time heterogeneity enhances magnitudes of oscillations of animal population and brucella. Moreover, enlarging effective infection radii increases the risk of brucellosis propagations. As a result, we suggest that herdsmen should improve the sanitation of animals’ environment and isolate infected animals instantly to control brucellosis prevalence.

Research Note: Molecular relationship of the fowl adenovirus serotype 4 isolated from the contaminated live vaccine and wild strains isolated in China, 2013-2018

Since June 2013, hydropericardium-hepatitis syndrome caused by putative novel fowl adenovirus 4 (FAdV-4) infection has spread all over China, leading to great economic losses. Previous study found that the use of attenuated vaccines contaminated with FAdV-4 is likely to be an important cause of such large-scale transmission. Here, we sequenced the whole genome of this strain through the next-generation sequencing and carried out a retrospective analysis of the FAdV-4 strains that have been determined in China recently. Results show the vaccine strain was almost 100% identical with wild virus strains, especially with 4 strains considering the difference of the GA repeat region, further linking the relationship between vaccine contamination and FAdV-4 prevalence in China. Meanwhile, there is no time and regional preference for the emergence of FAdV-4 strains with different molecular characteristics in China, which indicates that there may be multiple routes of transmission of this virus, suggesting that we still need to pay more attention to and formulate correct prevention and control in the future.

Electromagnetic properties of Cr-substituted nickel ferrite nanoparticles and their microwave absorption performance

Chromium (Cr) substituted nickel ferrite nanoparticle was fabricated via a facile coprecipitation route and the microwave absorption performance was investigated within 8.2–18 GHz range. Several characterization approaches have been employed to investigate the morphology, phase composition, chemical composition, and structure of the Ni0·5Cr0·5Fe2O4 nanoparticles. We observed that the nanoparticles are spherical, having compact arrangement and traces of inter-particle porosity. This suggests that the morphology would favor multiple transmission routes for the absorption of EM wave. Analysis of the sample's microwave absorption performance reveals that 20 wt percent loading of Ni0·5Cr0·5Fe2O4 nanoparticles in paraffin can effectively attenuate a large portion of EM wave within 8.2–18 GHz frequency range. The sample achieved an optimum reflection loss value −47.3 dB at 16.0 GHz at 2.5 mm thickness. The EM wave absorption observed can be credited to impedance match, interfacial polarization, and good dielectric/magnetic loss coupling. The absorption bandwidth of the sample covers the X-band and P-band frequency via tuning of the absorber thickness between 2.5 and 4.5 mm. These results show that the Cr-substituted nickel ferrite has good EM properties and can be considered as a possible EM wave absorbing filler.

Fallacies and Facts Around COVID-19: The Multifaceted Infection.

It has been 5 months since the identification of first cases of coronavirus disease 2019 (COVID-19), however, unveiling clinical characteristics and modes of transmission of the disease is not complete yet. The initially identified clinical sign of COVID-19 was respiratory in nature in the form of pneumonia with possible fatal consequences due to severe acute lung fibrosis. Extrapulmonary symptoms of the disease are now well recognized with involvement of the liver, kidney, and even multisystem organ failure and acute cardiac arrest. Symptoms related to the gastrointestinal tract are particularly interesting and these could represent a mode of transmission requiring more attention from researchers and clinicians. Prevalence of diarrhea, nausea, vomiting, or abdominal discomfort is estimated to be approximately 5%.1 The possible multiple routes of transmission could be explained by the fact that angiotensin converting enzyme 2 protein presents in abundance on lung alveolar epithelial cells and enterocytes of small intestine remarkably.2 During the first days of the disease, a fallacy was distributed mainly through social media. Drinking hot drinks was promoted as a means to eradicate the virus before it goes beyond the pharynx; however, as more studies were conducted, it was revealed that SARS-CoV-2 can withstand temperatures up to 56°C.3 On the contrary to this fallacy, an important fact is related to the possibility of the fecal-oral route of transmission which has been identified in multiple case studies and clinical settings. The nucleic acid of the virus has been detected in the feces and anal swabs of some COVID-19 patients, and live virions were shown to exist in fecal specimens in patients with negative oropharyngeal specimen, which indicates that viral infection of the gastrointestinal tract and the potential fecal-oral transmission can outlast the viral clearance in the respiratory tract.4 An observation that needs further investigation was actually reported from clinicians caring for infected patients, whereby expulsion of excess colonic gas which has an unpleasant odor with or without diarrhea has been noticed (unpublished data). Although this observation is not yet documented, it should be further analyzed and investigated. Whether abdominal gases in COVID-19 patients with gastrointestinal manifestations can be a potential mode of transmission of the virus needs to be ascertained. Other fallacies that relate to the size of the virus claimed that airborne spread is not possible due to the large size of the virus which makes it drop onto surfaces after 3 hours. It was also claimed that COVID-19 primarily spreads through the respiratory tract, by droplets, respiratory secretions, and direct contact and is not transmitted by aerosol, therefore, only infection control precautions and social distancing for at least 1 m would suffice to prevent the spread of the infection. However, the most recent studies reported that it could be transmitted as an airborne infection for distances exceeding 4 m.5 Within this context, there has been some confusion about the types of masks that should be used among healthcare teams caring for COVID-19 patients. Several developing countries have adopted the use of regular surgical masks among healthcare workers caring for COVID-19 patients early in the course of the disease. Medical health workers who primarily use this type of masks are susceptible to infection. Although this is not documented yet, but many healthcare workers in developing countries like Egypt and other countries like Italy and Saudi Arabia have been infected and unfortunately were deceased due to COVID-19. These types of masks alone without complete face shield are not adequate for protection against COVID-19.6 Within the context of cross-infection control, we would like to stress that donning and doffing of personal protective equipment (PPE) should be conducted in a particular order to prevent infection. The recommended sequence involves removal of the high level maximum protective masks as the last step in doffing of PPE. Handling the contaminated mask itself may transmit the virus and hence cause infection.7 A suggestion to prevent transmission while doffing involves that PPE undergoes disinfection in a special room or to utilize a specific equipment for disposal of used PPE before doffing. In conclusion, more facts about COVID-19 transmission and effective preventive measures should be revealed and disseminated among the medical community to preserve the precious lives of healthcare team members. The aim of this correspondence is to draw attention of healthcare workers caring for COVID-19 patients especially those working in developing countries to the possibility of transmission of infection through the gastrointestinal route with particular reference to colonic gases. We further warn them against the use of conventional surgical masks because it is useless in the clinical setting, and also warn them against handling of the contaminated masks during doffing of PPE. Here we suggest the use of disinfection of PPE before removal and the proper way of disposal.

PC-FACS: COVID-19

PC-FACS (FastArticleCriticalSummaries forClinicians inPalliativeCare) provides hospice and palliative care clinicians with concise summaries of the most important findings from more than 100 medical and scientific journals. If you have colleagues who would benefit from receiving PCFACS, please encourage them to join the AAHPM at aahpm.org. Comments from readers are welcomed at pcfacs@aahpm.org.

Global Dynamics of a Vector-Borne Disease Model with Two Transmission Routes

In this paper, we study the dynamics of a vector-borne disease model with two transmission paths: direct transmission through contact and indirect transmission through vector. The direct transmission is considered to be a nonmonotone incidence function to describe the psychological effect of some severe diseases among the population when the number of infected hosts is large and/or the disease possesses high case fatality rate. The system has a disease-free equilibrium which is locally asymptotically stable when the basic reproduction number ([Formula: see text]) is less than unity and may have up to four endemic equilibria. Analytical expression representing the epidemic growth rate is obtained for the system. Sensitivity of the two transmission pathways were compared with respect to the epidemic growth rate. We numerically find that the direct transmission coefficient is more sensitive than the indirect transmission coefficient with respect to [Formula: see text] and the epidemic growth rate. Local stability of endemic equilibrium is studied. Further, the global asymptotic stability of the endemic equilibrium is proved using Li and Muldowney geometric approach. The explicit condition for which the system undergoes backward bifurcation is obtained. The basic model also exhibits the hysteresis phenomenon which implies diseases will persist even when [Formula: see text] although the system undergoes a forward bifurcation and this phenomenon is rarely observed in disease models. Consequently, our analysis suggests that the diseases with multiple transmission routes exhibit bistable dynamics. However, efficient application of temporary control in bistable regions will curb the disease to lower endemicity. Additionally, numerical simulations reveal that the equilibrium level of infected hosts decreases as psychological effect increases.

Venereal Transmission of Vesicular Stomatitis Virus by Culicoides sonorensis Midges.

Culicoides sonorensis biting midges are well-known agricultural pests and transmission vectors of arboviruses such as vesicular stomatitis virus (VSV). The epidemiology of VSV is complex and encompasses a broad range of vertebrate hosts, multiple routes of transmission, and diverse vector species. In temperate regions, viruses can overwinter in the absence of infected animals through unknown mechanisms, to reoccur the next year. Non-conventional routes for VSV vector transmission may help explain viral maintenance in midge populations during inter-epidemic periods and times of adverse conditions for bite transmission. In this study, we examined whether VSV could be transmitted venereally between male and female midges. Our results showed that VSV-infected females could venereally transmit virus to uninfected naïve males at a rate as high as 76.3% (RT-qPCR), 31.6% (virus isolation) during the third gonotrophic cycle. Additionally, VSV-infected males could venereally transmit virus to uninfected naïve females at a rate as high as 76.6% (RT-qPCR), 49.2% (virus isolation). Immunofluorescent staining of micro-dissected reproductive organs, immunochemical staining of midge histological sections, examination of internal reproductive organ morphology, and observations of mating behaviors were used to determine relevant anatomical sites for virus location and to hypothesize the potential mechanism for VSV transmission in C. sonorensis midges through copulation.

COVID 19: Are we fighting with the monster?

As per a recently published article, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA has been detected in faecal samples up to 47 days after the appearance of the first symptom (mean 27.9 ± 10.7 days), and it was ≅ 1.7 times more in duration compared to respiratory samples in 55% of the patients.[1] Reporting of SARS-CoV-2 from enteral system indicates initial zoonotic origin, may be from bat or pangolin. SARS-CoV-2 hence poses a significant threat of being transmitted faecal-orally, and the presence of angiotensin-converting enzyme 2 (ACE2) in intestinal epithelium supports the hypothesis.[1] In general, most of viruses causing human illnesses don't transmit by enteral and parenteral routes simultaneously because of their structural and functional limitations. The presence of viral RNA in faecal samples breaks this usual rule of nature, giving the virus unique capability to cause disease. Currently, the respiratory transmission is considered as the only by different routes of acquiring the infection. The findings of the study may be significant in the future as we exactly don't know much about the SARS-CoV-2, especially in densely populated areas and the countries with reduced sanitation levels. This may be analogous to the Hepatitis E virus, which epidemiologically shows variable transmission of different genotype, as faecal-oral in the developing world and zoonotic in the developed world.[2] With time, it can be clarified whether it can have significant enteral though only alimentary canal is involved in HEV transmission. The faecal-oral transmission may be significant in the Indian subcontinent. In one of the studies, the median half-lives of SARS-CoV-2 under different circumstances was compared with previous SARS-CoV-1. The study clearly showed the comparable half-lives of both virus under different experimental settings i.e. aerosol, and copper except cardboard where SARS-CoV-2 had longer half-life.[3] Despite the similarities, it has been much more disastrous than the previous one, owing to its very high infectivity and high viral load in pharynx and nasal cavity (upper respiratory tract) and shedding of virus irrespective of the presence of symptoms.[3] It is the actual and practical problem of testing, especially in the underdeveloped resource-limited countries, where prudent utilization of resources is a prerequisite. Presently, there are no data available regarding the temperature and humidity survival of SARS-CoV-2. A recently published study analyzed the characteristics of areas with community spread. It was more common in areas of temperature range 5-11°C with low absolute humidity (4-7 g/m3).[4] Previous SARS-CoV-1 was sensitive to a relatively higher temperature and at >29°C was not able to survive; however, there is a mixed opinion regarding the temperature sensitivity and exposure-duration in light about SARS-CoV-2, as this is the new virus which is highly unpredictable. Considering the study,[4] countries with day temperature >35°C and longer duration of day-light, the airborne spread may reduce significantly. We only can hope like its previous counterpart it may not survive at higher temperatures, which may be beneficial to the Indian subcontinent. Multiple possible transmission routes, high viral load even in asymptomatic patients, and unpredictable effects of temperature made it a pandemic. Fortunately, the majority of patients have a mild illness (80%-85%), and mortality rate of 2%-4%. Considering the huge number of infected people, even with this mortality rate, the number of deceased is going to be very high. Regarding long-term outcomes, we will have to wait regarding chronic complications. After looking into the characteristics, admittedly, we are struggling against the monster. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Genomic analyses of Pseudomonas syringae pv. actinidiae isolated in Korea suggest the transfer of the bacterial pathogen via kiwifruit pollen.

Introduction. The bacterial pathogen, Pseudomonas syringae pv. actinidiae (Psa), has emerged as a major threat to kiwifruit cultivation throughout the world. One pandemic strain (from the Psa3 group) has occurred in various geographical regions. It is important to understand how this pathogen is being transmitted.Aim. Although Psa has been found in Korea since 1992, the isolates were until recently of a distinct type (Psa2). Recently, the more virulent Psa3 type has been detected. The purpose of this study was to describe the variety of Psa3 now found in Korea.Methodology. Strains were isolated from kiwifruit plants in Korea and from pollen imported into Korea from New Zealand. The genomes of 10 isolates were sequenced using the Illumina platform and compared to the completely assembled genomes of pandemic Psa3 strains from New Zealand and China. Comparisons were also made with pandemic strains from Chile and non-pandemic Psa3 isolates from China.Results. Six of the 10 Psa3 isolates from Korea show a clear relationship with New Zealand isolates. Two isolates show a distinct relationship to isolates from Chile; one further isolate has a sequence that is highly similar to that of M228, a strain previously isolated in China; and the last isolate belongs to the Psa3 group, but is not a member of the pandemic lineage.Conclusion. This analysis establishes that there have been multiple routes of transmission of the Psa3 pandemic strain into Korea. One route has involved the importation of pollen from New Zealand. A second route probably involves importation from Chile.

Multiple transmission routes sustain high prevalence of a virulent parasite in a butterfly host.

Understanding factors that allow highly virulent parasites to reach high infection prevalence in host populations is important for managing infection risks to human and wildlife health. Multiple transmission routes have been proposed as one mechanism by which virulent pathogens can achieve high prevalence, underscoring the need to investigate this hypothesis through an integrated modelling-empirical framework. Here, we examine a harmful specialist protozoan infecting monarch butterflies that commonly reaches high prevalence (50–100%) in resident populations. We integrate field and modelling work to show that a combination of three empirically-supported transmission routes (vertical, adult transfer and environmental transmission) can produce and sustain high infection prevalence in this system. Although horizontal transmission is necessary for parasite invasion, most new infections post-establishment arise from vertical transmission. Our study predicts that multiple transmission routes, coupled with high parasite virulence, can reduce resident host abundance by up to 50%, suggesting that the protozoan could contribute to declines of North American monarchs.

Transmission routes of rare seasonal diseases: the case of norovirus infections.

Norovirus (NoV) is the most commonly recognized cause of acute gastroenteritis, with over a million cases globally per year. While usually self-limiting, NoV poses a substantial economic burden because it is highly contagious and there are multiple transmission routes. Infection occurs through inhalation of vomitus; faecal-oral spread; and food, water and environmental contamination. While the incidence of the disease is predictably seasonal, much less is known about the relative contribution of the various exposure pathways in causing disease. Additionally, asymptomatic excretion and viral shedding make forecasting disease burden difficult. We develop a novel stochastic dynamic network model to investigate the contributions of different transmission pathways in multiple coupled social networks representing schools, hospitals, care-homes and family households in a community setting. We analyse how the networks impact on transmission. We used ward-level demographic data from Northumberland, UK to create a simulation cohort. We compared the results with extant data on NoV cases from the IID2 study. Connectivity across the simulated cohort was high. Cases of NoV showed marked seasonality, peaking in early winter and declining through the summer. For the first time, we show that fomites and food appear to be the most important exposure routes in determining the population burden of disease. This article is part of the theme issue 'Modelling infectious disease outbreaks in humans, animals and plants: epidemic forecasting and control'. This theme issue is linked with the earlier issue 'Modelling infectious disease outbreaks in humans, animals and plants: approaches and important themes'.

Modelling the transmission dynamics of Campylobacter in Ontario, Canada, assuming house flies, Musca domestica , are a mechanical vector of disease transmission

Campylobacter's complicated dynamics and multiple transmission routes have made it difficult to describe using a mathematical framework. Vector-borne disease transmission has been proposed as a potential transmission route of Campylobacter with house flies acting as a mechanical vector. This study aimed to (i) determine if a basic SIR compartment model that included flies as a mechanical vector and incorporated a seasonally forced environment compartment could be used to capture the observed disease dynamics in Ontario, Canada, and (ii) use this model to determine potential changes to campylobacteriosis incidence using predicted changes to fly population size and fly activity under multiple climate change scenarios. The model was fit to 1 year of data and validated against 8 and 12 years of data. It accurately captured the observed incidence. We then explored changes in human disease incidence under multiple climate change scenarios. When fly activity levels were at a 25% increase, our model predicted a 28.15% increase in incidence by 2050 using the medium–low emissions scenario and 30.20% increase using the high emissions scenario. This model demonstrates that the dynamics of Campylobacter transmission can be captured by a model that assumes that the primary transmission of the pathogen occurs via insect vectors.

Vesicular Stomatitis Virus Transmission: A Comparison of Incriminated Vectors.

Vesicular stomatitis (VS) is a viral disease of veterinary importance, enzootic in tropical and subtropical regions of the Americas. In the U.S., VS produces devastating economic losses, particularly in the southwestern states where the outbreaks display an occurrence pattern of 10-year intervals. To date, the mechanisms of the geographic spread and maintenance cycles during epizootics remain unclear. This is due, in part, to the fact that VS epidemiology has a complex of variables to consider, including a broad range of vertebrate hosts, multiple routes of transmission, and an extensive diversity of suspected vector species acting as both mechanical and biological vectors. Infection and viral progression within vector species are highly influenced by virus serotype, as well as environmental factors, including temperature and seasonality; however, the mechanisms of viral transmission, including non-conventional pathways, are yet to be fully studied. Here, we review VS epidemiology and transmission mechanisms, with comparisons of transmission evidence for the four most incriminated hematophagous dipteran taxa: Aedes mosquitoes, Lutzomyia sand flies, Simulium black flies, and Culicoides biting midges.

A Systematic Review and Meta-Analysis of the Association between Water, Sanitation, and Hygiene Exposures and Cholera in Case-Control Studies.

.Case–control studies are conducted to identify cholera transmission routes. Water, sanitation, and hygiene (WASH) exposures can facilitate cholera transmission (risk factors) or interrupt transmission (protective factors). To our knowledge, the association between WASH exposures and cholera from case–control studies has not been systematically analyzed. A systematic review was completed to close this gap, including describing the theory of risk and protection, developing inclusion criteria, searching and selecting studies, assessing quality of evidence, and summarizing associations between cholera and seven predicted WASH protective factors and eight predicted WASH risk factors using meta-analysis and sensitivity analysis. Overall, 47 articles describing 51 individual studies from 30 countries met the inclusion criteria. All eight predicted risk factors were associated with higher odds of cholera (odds ratio [OR] = 1.9–5.6), with heterogeneity (I2) of 0–92%. Of the predicted protective factors, five of seven were associated with lower odds of cholera (OR = 0.35–1.4), with heterogeneity of 57–91%; exceptions were insignificant associations for improved water source (OR = 1.1, heterogeneity 91%) and improved sanitation (OR = 1.4, heterogeneity 68%). Results were robust; 3/70 (5%) associations changed directionality or significance in sensitivity analysis. Meta-analysis results highlight that predicted risk factors are associated with cholera; however, predicted protective factors are not as consistently protective. This variable protection is attributed to 1) cholera transmission via multiple routes and 2) WASH intervention implementation quality variation. Water, sanitation, and hygiene interventions should address multiple transmission routes and be well implemented, according to international guidance, to ensure that field effectiveness matches theoretical efficacy. In addition, future case–control studies should detail WASH characteristics to contextualize results.

Modes of Transmission of Zika Virus.

For >60 years, Zika virus (ZIKV) has been recognized as an arthropod-borne virus with Aedes species mosquitoes as the primary vector. However in the past 10 years, multiple alternative routes of ZIKV transmission have been identified. We review the available data on vector and non-vector-borne modes of transmission and interventions undertaken, to date, to reduce the risk of human infection through these routes. Although much has been learned during the outbreak in the Americas on the underlying mechanisms and pathogenesis of non-vector-borne ZIKV infections, significant gaps remain in our understanding of the relative incidence of, and risk from, these modes compared to mosquito transmission. Additional research is urgently needed on the risk, pathogenesis, and effectiveness of measures to mitigate non-vector-borne ZIKV transmission.

Evidence of multiple intraspecific transmission routes for Leptospira acquisition in Norway rats (Rattus norvegicus).

Infectious diseases frequently have multiple potential routes of intraspecific transmission of pathogens within wildlife and other populations. For pathogens causing zoonotic diseases, knowing whether these transmission routes occur in the wild and their relative importance, is critical for understanding maintenance, improving control measures and ultimately preventing human disease. The Norway rat (Rattus norvegicus) is the primary reservoir of leptospirosis in the urban slums of Salvador, Brazil. There is biological evidence for potentially three different transmission routes of leptospire infection occurring in the rodent population. Using newly obtained prevalence data from rodents trapped at an urban slum field site, we present changes in cumulative risk of infection in relation to age-dependent transmission routes to infer which intra-specific transmission routes occur in the wild. We found that a significant proportion of animals leave the nest with infection and that the risk of infection increases throughout the lifetime of Norway rats. We did not observe a significant effect of sexual maturity on the risk of infection. In conclusion, our results suggest that vertical and environmental transmission of leptospirosis both occur in wild populations of Norway rats.

Edge-based epidemic dynamics with multiple routes of transmission on random networks

This paper concerns the SIR dynamics with two types of spreading mechanism, i.e., local spreading through network contacts and global spreading through casual contacts. A low-dimensional edge-based model of ordinary differential equations incorporating arbitrary heterogeneous number of individual contacts is formulated. The basic reproduction number $$R_{0}$$ is obtained, and on networks of Poisson type, it is the sum of the basic reproduction numbers for global and local spreading pathways; however, on networks of other type, it is a nonlinear function of the basic reproduction numbers for global and local spreading pathways. To measure the control efforts imposed on one specific transmission pathway, type reproduction numbers for global and local transmission pathways are calculated, respectively. Equations of the final epidemic size are analytically derived. Finally, the numerical solutions to our model are compared with the ensemble averages of the stochastic simulations. Simulations have shown that casual contacts in the population may trigger large stochastic fluctuations, which may cause huge variances around their mean; thus, in this scenario the ensemble mean is not a good representation of the behavior of the stochastic epidemic process. However, increasing the local infection rate or the connectedness of networks yields better predictions. The results presented provide insights in setting a framework for the analysis and containment of multiple routes of epidemic transmission in reality.

The risk of sustained sexual transmission of Zika is underestimated.

Pathogens often follow more than one transmission route during outbreaks—from needle sharing plus sexual transmission of HIV to small droplet aerosol plus fomite transmission of influenza. Thus, controlling an infectious disease outbreak often requires characterizing the risk associated with multiple mechanisms of transmission. For example, during the Ebola virus outbreak in West Africa, weighing the relative importance of funeral versus health care worker transmission was essential to stopping disease spread. As a result, strategic policy decisions regarding interventions must rely on accurately characterizing risks associated with multiple transmission routes. The ongoing Zika virus (ZIKV) outbreak challenges our conventional methodologies for translating case-counts into route-specific transmission risk. Critically, most approaches will fail to accurately estimate the risk of sustained sexual transmission of a pathogen that is primarily vectored by a mosquito—such as the risk of sustained sexual transmission of ZIKV. By computationally investigating a novel mathematical approach for multi-route pathogens, our results suggest that previous epidemic threshold estimates could under-estimate the risk of sustained sexual transmission by at least an order of magnitude. This result, coupled with emerging clinical, epidemiological, and experimental evidence for an increased risk of sexual transmission, would strongly support recent calls to classify ZIKV as a sexually transmitted infection.

Transmission routes maintaining a viral pathogen of steelhead trout within a complex multi-host assemblage.

This is the first comprehensive region wide, spatially explicit epidemiologic analysis of surveillance data of the aquatic viral pathogen infectious hematopoietic necrosis virus (IHNV) infecting native salmonid fish. The pathogen has been documented in the freshwater ecosystem of the Pacific Northwest of North America since the 1950s, and the current report describes the disease ecology of IHNV during 2000–2012. Prevalence of IHNV infection in monitored salmonid host cohorts ranged from 8% to 30%, with the highest levels observed in juvenile steelhead trout. The spatial distribution of all IHNV‐infected cohorts was concentrated in two sub‐regions of the study area, where historic burden of the viral disease has been high. During the study period, prevalence levels fluctuated with a temporal peak in 2002. Virologic and genetic surveillance data were analyzed for evidence of three separate but not mutually exclusive transmission routes hypothesized to be maintaining IHNV in the freshwater ecosystem. Transmission between year classes of juvenile fish at individual sites (route 1) was supported at varying levels of certainty in 10%–55% of candidate cases, transmission between neighboring juvenile cohorts (route 2) was supported in 31%–78% of candidate cases, and transmission from adult fish returning to the same site as an infected juvenile cohort was supported in 26%–74% of candidate cases. The results of this study indicate that multiple specific transmission routes are acting to maintain IHNV in juvenile fish, providing concrete evidence that can be used to improve resource management. Furthermore, these results demonstrate that more sophisticated analysis of available spatio‐temporal and genetic data is likely to yield greater insight in future studies.