scholarly journals The Epidemic Risk of Dengue Fever in Japan: Climate Change and Seasonality

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Xia Wang ◽  
Hiroshi Nishiura
Keyword(s):  
Dengue Fever ◽  
Process Model ◽  
Reproduction Number ◽  
Volume Data ◽  
Temperature Dependent ◽  
Calendar Time ◽  
The Tropics ◽  
Epidemic Risk ◽  
Dengue Epidemic ◽  
Future Outbreak

Dengue fever is a leading cause of illness and death in the tropics and subtropics, and the disease has become a threat to many nonendemic countries where the competent vectors such as Aedes albopictus and Aedes aegypti are abundant. The dengue epidemic in Tokyo, 2014, poses the critical importance to accurately model and predict the outbreak risk of dengue fever in nonendemic regions. Using climatological datasets and traveler volumes in Japan, where dengue was not seen for 70 years by 2014, we investigated the outbreak risk of dengue in 47 prefectures, employing the temperature-dependent basic reproduction number and a branching process model. Our results show that the effective reproduction number varies largely by season and by prefecture, and, moreover, the probability of outbreak if an untraced case is imported varies greatly with the calendar time of importation and location of destination. Combining the seasonally varying outbreak risk with time-dependent traveler volume data, the unconditional outbreak risk was calculated, illustrating different outbreak risks between southern coastal areas and northern tourist cities. As the main finding, the large travel volume with nonnegligible risk of outbreak explains the reason why a summer outbreak in Tokyo, 2014, was observed. Prefectures at high risk of future outbreak would be Tokyo again, Kanagawa or Osaka, and highly populated prefectures with large number of travelers.

scholarly journals Epidemiological Analysis of the 2019 Dengue Epidemic in Bhutan

2021 ◽  
Vol 18 (1) ◽  
pp. 354
Author(s):  
Tsheten Tsheten ◽  
Angus Mclure ◽  
Archie C. A. Clements ◽  
Darren J. Gray ◽  
Tenzin Wangdi ◽  
...  
Keyword(s):  
Reproduction Number ◽  
Monsoon Season ◽  
Outbreak Response ◽  
Spatial And Temporal Patterns ◽  
Epidemiological Analysis ◽  
Preparedness Plan ◽  
Epidemic Period ◽  
Timely Response ◽  
National Preparedness ◽  
Dengue Epidemic

Bhutan experienced its largest and first nation-wide dengue epidemic in 2019. The cases in 2019 were greater than the total number of cases in all the previous years. This study aimed to characterize the spatiotemporal patterns and effective reproduction number of this explosive epidemic. Weekly notified dengue cases were extracted from the National Early Warning, Alert, Response and Surveillance (NEWARS) database to describe the spatial and temporal patterns of the epidemic. The time-varying, temperature-adjusted cohort effective reproduction number was estimated over the course of the epidemic. The dengue epidemic occurred between 29 April and 8 December 2019 over 32 weeks, and included 5935 cases. During the epidemic, dengue expanded from six to 44 subdistricts. The effective reproduction number was <3 for most of the epidemic period, except for a ≈1 month period of explosive growth, coinciding with the monsoon season and school vacations, when the effective reproduction number peaked >30 and after which the effective reproduction number declined steadily. Interventions were only initiated 6 weeks after the end of the period of explosive growth. This finding highlights the need to reinforce the national preparedness plan for outbreak response, and to enable the early detection of cases and timely response.

scholarly journals Assessing countermeasures during a hepatitis A virus outbreak among men who have sex with men

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Ryohei Saito ◽  
Akifumi Imamura ◽  
Hiroshi Nishiura
Keyword(s):  
Mathematical Model ◽  
Situation Awareness ◽  
Hepatitis A ◽  
Hepatitis A Virus ◽  
Reproduction Number ◽  
Risky Behaviors ◽  
Extrinsic Factors ◽  
Environmental Transmission ◽  
Sex With Men ◽  
Epidemic Risk

Abstract Background A hepatitis A epidemic occurred among men who have sex with men (MSM) in Japan in 2017–2018. In this study, we employ a parsimonious mathematical model to epidemiologically investigate the dynamics of infection, aiming to evaluate the effectiveness of campaign-based interventions among MSM to raise awareness of the situation. Methods A mathematical model describing a mixture of human-to-human transmission and environmental transmission was fitted to surveillance data. Taking seasonally varying environmental transmission into account, we estimated the reproduction number of hepatitis A virus during the course of epidemic, and, especially, the abrupt decline in this reproduction number following campaign-based interventions. Results The reproduction number prior to the countermeasures ranged from 2.6 to 3.1 and then began to decrease following campaign-based interventions. After the first countermeasure, the reproduction number decreased, but the epidemic remained supercritical (i.e., Rt > 1). The value of Rt dropped well below one following the second countermeasure, which used web articles to widely disseminate information about the epidemic risk. Conclusions Although the effective reproduction number, Rt, changes because of both intrinsic and extrinsic factors, the timing of the examined countermeasures against hepatitis A in the MSM population was consistent with the abrupt declines observed in Rt. Even without vaccination, the epidemic was brought under control, and risky behaviors may have been changed by the increase in situation awareness reached through web articles.

scholarly journals Global dynamics of a Huanglongbing model with a periodic latent period

2021 ◽  
Vol 0 (0) ◽  
pp. 0
Author(s):  
Yan Hong ◽  
Xiuxiang Liu ◽  
Xiao Yu
Keyword(s):  
Reproduction Number ◽  
Threshold Value ◽  
Transmission Model ◽  
Threshold Dynamics ◽  
Global Dynamics ◽  
Temperature Dependent ◽  
Candidatus Liberibacter ◽  
Effects Of Temperature ◽  
Disease Free ◽  
The Basic Reproduction Number

<p style='text-indent:20px;'>Huanglongbing (HLB) is a disease of citrus that caused by phloem-restricted bacteria of the Candidatus Liberibacter group. In this paper, we present a HLB transmission model to investigate the effects of temperature-dependent latent periods and seasonality on the spread of HLB. We first establish disease free dynamics in terms of a threshold value <inline-formula><tex-math id="M1">\begin{document}$ R^p_0 $\end{document}</tex-math></inline-formula>, and then introduce the basic reproduction number <inline-formula><tex-math id="M2">\begin{document}$ \mathcal{R}_0 $\end{document}</tex-math></inline-formula> and show the threshold dynamics of HLB with respect to <inline-formula><tex-math id="M3">\begin{document}$ R^p $\end{document}</tex-math></inline-formula> and <inline-formula><tex-math id="M4">\begin{document}$ \mathcal{R}_0 $\end{document}</tex-math></inline-formula>. Numerical simulations are further provided to illustrate our analytic results.</p>

scholarly journals Smallpox and Season: Reanalysis of Historical Data

2009 ◽  
Vol 2009 ◽  
pp. 1-10 ◽  
Author(s):  
Hiroshi Nishiura ◽  
Tomoko Kashiwagi
Keyword(s):  
Time Series ◽  
Historical Data ◽  
Reproduction Number ◽  
Negative Association ◽  
Short Term ◽  
Calendar Time ◽  
Annual Cycles ◽  
Annual Peak ◽  
Time Series Analyses ◽  
Reported Data

Seasonal variation in smallpox transmission is one of the most pressing ecological questions and is relevant to bioterrorism preparedness. The present study reanalyzed 7 historical datasets which recorded monthly cases or deaths. In addition to time series analyses of reported data, an estimation and spectral analysis of the effective reproduction number at calendar time , , were made. Meteorological variables were extracted from a report in India from 1890–1921 and compared with smallpox mortality as well as . Annual cycles of smallpox transmission were clearly shown not only in monthly reports but also in the estimates of . Even short-term epidemic data clearly exhibited an annual peak every January. Both mortality and revealed significant negative association () and correlation (), respectively, with humidity. These findings suggest that smallpox transmission greatly varies with season and is most likely enhanced by dry weather.

scholarly journals Temperature Dependent Viral Tropism (TDVT): Understanding Viral Seasonality and Pathogenicity as Applied to the Avoidance and Treatment of Endemic Viral Respiratory Illnesses

2021 ◽  
Author(s):  
Patrick D. Shaw Stewart ◽  
Julia Bach
Keyword(s):  
Thermal Sensitivity ◽  
Respiratory Illness ◽  
Respiratory Viruses ◽  
Upper Respiratory Tract ◽  
Temperature Dependent ◽  
Viral Tropism ◽  
Local Climate ◽  
Respiratory Illnesses ◽  
The Tropics ◽  
Viral Respiratory

This review seeks to explain four features of viral respiratory illnesses that have perplexed generations of virologists: (1) the seasonal timing of respiratory illness; (2) the common viruses causing respiratory illness worldwide, including year-round disease in the Tropics; (3) the rapid response of outbreaks to weather, specifically temperature; (4) the rapid arrival and termination of epidemics caused by influenza and other viruses. The inadequacy of the popular explanations of seasonality is discussed, and a simple hypothesis is proposed, called Temperature Dependent Viral Tropism (TDVT), that is compatible with the above features of respiratory illness. TDVT notes that viruses can transmit themselves more effectively if they moderate their pathogenicity (thereby maintaining host mobility) and suggests that endemic respiratory viruses accomplish this by developing thermal sensitivity within a range that supports organ-specific viral tropism within the human body, whereby they replicate most rapidly at temperatures below body temperature. This allows them to confine themselves to the upper respiratory tract and to avoid infecting the lungs, heart, gut etc. Biochemical and tissue-culture studies show that &ldquo;wild&rdquo; respiratory viruses show such natural thermal sensitivity. The typical early autumn surge of colds and the existence of respiratory illness in the Tropics year-round at intermediate levels are explained by the tendency for strains to adapt their thermal sensitivity to their local climate and season. The TDVT hypothesis has important practical implications for preventing and treating respiratory illness including Covid-19. TVDT is testable with many options for experiments to increase our understanding of viral seasonality and pathogenicity.

scholarly journals The effectiveness of social bubbles as part of a Covid-19 lockdown exit strategy, a modelling study

2020 ◽  
Author(s):  
Trystan Leng ◽  
Connor White ◽  
Joe Hilton ◽  
Adam Kucharski ◽  
Lorenzo Pellis ◽  
...  
Keyword(s):  
Reproduction Number ◽  
Base Case ◽  
Exit Strategy ◽  
Epidemic Threshold ◽  
Case Scenario ◽  
Base Case Scenario ◽  
The Social ◽  
The Uk ◽  
The Impact ◽  
Epidemic Risk

AbstractBackgroundDuring the Covid-19 lockdown, contact clustering in social bubbles may allow extending contacts beyond the household at minimal additional risk and hence has been considered as part of modified lockdown policy or a gradual lockdown exit strategy. We estimated the impact of such strategies on epidemic and mortality risk using the UK as a case study.MethodsWe used an individual based model for a synthetic population similar to the UK, that is stratified into transmission risks from the community, within the household and from other households in the same social bubble. The base case considers a situation where non-essential shops and schools are closed, the secondary household attack rate is 20% and the initial reproduction number is 0.8. We simulate a number of strategies including variations of social bubbles, i.e. the forming of exclusive pairs of households, for particular subsets of households (households including children and single occupancy households), as well as for all households. We test the sensitivity of the results to a range of alternative model assumptions and parameters.ResultsClustering contacts outside the household into exclusive social bubbles is an effective strategy of increasing contacts while limiting some of the associated increase in epidemic risk. In the base case scenario social bubbles reduced cases and fatalities by 17% compared to an unclustered increase of contacts. We find that if all households were to form social bubbles the reproduction number would likely increase to 1.1 and therefore beyond the epidemic threshold of one. However, strategies that allow households with young children or single occupancy households to form social bubbles only increased the reproduction number by less than 10%. The corresponding increase in morbidity and mortality is proportional to the increase in the epidemic risk but is largely focussed in older adults independently of whether these are included in the social bubbles.ConclusionsSocial bubbles can be an effective way of extending contacts beyond the household limiting the increase in epidemic risk, if managed appropriately.

scholarly journals Mathematical Modeling of the Coinfection Dynamics of Malaria-Toxoplasmosis in the Tropics

2019 ◽  
Vol 56 (2) ◽  
pp. 139-163
Author(s):  
Oluwatayo M. Ogunmiloro
Keyword(s):  
Reproduction Number ◽  
Model System ◽  
Host Population ◽  
Globally Asymptotically Stable ◽  
Susceptible Host ◽  
Tropical Regions ◽  
First Order ◽  
Mathematical Techniques ◽  
The Tropics ◽  
The Impact

SummaryCoinfection by Plasmodium species and Toxoplasma gondii in humans is widespread, with its endemic impact mostly felt in the tropics. A mathematical model is formulated as a first-order nonlinear system of ordinary differential equations to describe the coinfection dynamics of malaria-toxoplasmosis in the mainly human and feline susceptible host population in tropical regions. Comprehensive mathematical techniques are applied to show that the model system is bounded, positive and realistic in an epidemiological sense. Also, the basic reproduction number (Romt) of the coinfection model is obtained. It is shown that if Romt < 1, the model system at its malaria-toxoplasmosis absent equilibrium is both locally and globally asymptotically stable. The impact of toxoplasmosis and its treatment on malaria, and vice versa, is studied and analyzed. Sensitivity analysis was performed to investigate the impact of the model system parameters on the reproduction number of the transmission of malaria-toxoplasmosis coinfection. Simulations and graphical illustrations were made to validate the results obtained from the theoretical model.

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