Probability Of Virus Transmission Research Articles

Application of a time-delay SIR model with vaccination in COVID-19 prediction and its optimal control strategy.

In the classical infectious disease compartment model, the parameters are fixed. In reality, the probability of virus transmission in the process of disease transmission depends on the concentration of virus in the environment, and the concentration depends on the proportion of patients in the environment. Therefore, the probability of virus transmission changes with time. Then how to fit the parameters and get the trend of the parameters changing with time is the key to predict the disease course with the model. In this paper, based on the US COVID-19 epidemic statistics during calibration period, the parameters such as infection rate and recovery rate are fitted by using the linear regression algorithm of machine science, and the laws of these parameters changing with time are obtained. Then a SIR model with time delay and vaccination is proposed, and the optimal control strategy of epidemic situation is analyzed by using the optimal control theory and Pontryagin maximum principle, which proves the effectiveness of the control strategy in restraining the transmission of COVID-19. The numerical simulation results show that the time-varying law of the number of active cases obtained by our model basically conforms to the real changing law of the US COVID-19 epidemic statistics during calibration period. In addition, we have predicted the changes in the number of active cases in the COVID-19 epidemic in the USA over time in the future beyond the calibration cycle, and the predicted results are more in line with the actual epidemic data.

PRM24 - Fitting A Model of Dengue Transmission to Empirical Data: Example of Rayong Province in Thailand

A mathematical model of dengue transmission was developed to estimate the impact of dengue vaccination. It was first fitted to the empirical dengue seroprevalence data from Rayong province of Thailand in order to reproduce the epidemiology observed without vaccination. The deterministic age-structured compartmental model included explicit host and vector populations, seasonality, all four dengue serotypes and interactions between them. To fit the model to the empirical data, twenty-five calibration scenarios were determined. Each scenario was a combination of cross-protection duration and an increase in susceptibility following the primary infection. For each combination, the probability of virus transmission was estimated by fitting the model to the seroprevalence collected in children aged 6 to 18 in Rayong. Incidence curves predicted with each combination were visually assessed and compared to the reported incidence corrected for under-reporting. Scenarios with good fit to seroprevalence data and realistic incidence curves were characterised by high values of susceptibility enhancement (4- to 9-fold increases in susceptibility following primary infection) and cross-protection duration. A high susceptibility enhancement factor was required for the model to predict comparable prevalence of multiple dengue infections. The modelled prevalence was close to observed values for almost all age groups, although lower for children aged 6 to 7 by up to 10 percentage points. Scenarios with higher susceptibility enhancement and cross-protection predicted greater fluctuations in annual dengue incidence, in line with observed data (corrected for under-reporting). Several scenarios allowed fitting the model to the empirical data from Rayong province. The inclusion of susceptibility enhancement considerably improved the fit to seroprevalence data. Higher enhancement factors in combination with longer cross-protection duration also led to more realistic incidence patterns. The validated scenarios reproduced empirical dengue incidence in the Rayong province, which is a preliminary condition for analyses of vaccination impact scenarios.

Ecological drivers of Hepacivirus infection in a neotropical rodent inhabiting landscapes with various degrees of human environmental change.

Anthropogenic environmental change can impact community and population traits such as species diversity and population densities, which have been shown to influence the prevalence of viruses in wildlife reservoirs. In particular, host species resilient to changes in their natural habitat may increase in numbers, which in turn can affect the prevalence of directly transmitted viruses. We have carried out a survey of small mammal communities in three tropical landscapes differing in their degree of environmental change in Central Panama and investigated the effects of community changes on Hepacivirus prevalence. The modification of continuous habitat into partly connected or isolated habitat patches during the past century was linked to changes in species diversity and species assemblages, which was further associated with shifts in the abundance of generalist marsupial (Didelphis marsupialis, Philander opossum) and rodent (Proechimys semispinosus) species. The latter has become dominant in isolated habitat patches and was the only identified Hepacivirus host in our study system. Our analyses suggest that, in addition to the effects of host age and sex, host population density in interaction with sex ratio is a crucial predictor of infection probability. Although we found no significant relationships between species diversity per se and infection probability, the lowest prevalence detected in the landscape with the highest species diversity indicates that shifts in species assemblages (e.g. changes in the presence and abundance of marsupial predators) impact the host's intraspecific contact rates, the probability of virus transmission and, thus, the virus prevalence. Our study additionally provides important data on the influence of human-induced landscape changes on infection probability and, therefore, on virus prevalence in wildlife and emphasizes the importance of a landscape-scale approach with concomitant consideration of the complex interactions between ecological factors.

Modelling the effects of previous infection and re-infection on the costs of bovine viral diarrhoea outbreaks in beef herds

A previously published model was re-employed to examine the potential impact of different epidemiological circumstances on output losses due to bovine viral diarrhoea virus (BVDV) infection in typical British hill cow-calf enterprises. The average annuity equivalent of unchecked losses from 100 simulated 10-year disease scenarios ranged from almost pound0/cow to approximately pound40/cow. Significant differences were found under certain circumstances, depending on the initial disease status of the herd, the initial source of virus, the probability and source of further infection, the probability of virus transmission within the herd and herd size. For naïve herds, losses depended only on the risk of incursion. In most other circumstances, the losses could be mitigated if the annual risk of incursion was <0.3 and risk of within herd transmission was extremely low. Greater understanding of the interaction between these risk factors and management actions are required so that total costs of BVDV infection can be minimised under different circumstances.

Comparative whitefly transmission of Tomato chlorosis virus and Tomato infectious chlorosis virus from single or mixed infections

Tomato chlorosis virus (ToCV) and Tomato infectious chlorosis virus (TICV) are two criniviruses that are emerging worldwide, and induce similar yellowing diseases in tomato crops. While TICV is transmitted only by Trialeurodes vaporariorum, ToCV is transmitted by three whitefly species in two genera Trialeurodes vaporariorum, T. abutilonea and Bemisia tabaci. The efficiency of transmission by T. vaporariorum from plants infected by one virus or by both was compared, and the probability of virus transmission by a single whitefly was derived from group testing experiments. The estimated transmission probabilities ranged from 0·01 to 0·13, and were not significantly different between ToCV and TICV, or between single and mixed infections. Experiments using B. tabaci as a vector and source plants infected by TICV and ToCV did not reveal any functional trans‐complementation for transmission of TICV by ToCV, suggesting that if this phenomenon occurs in nature, it is at a very low frequency. Possible reasons why TICV did not establish in southern France while ToCV is now endemic are discussed.

Evaluation of Immunofluorescence and Cell Culture Techniques for Detecting La Crosse Virus Infection in Individual Aedes Triseriatus (Diptera: Culicidae)1

Two methods, (1) the indirect immunofluorescent antibody technique (IFAT) using head squashes, and (2) the method of tissue trituration and inoculation of supernatant into a susceptible assay system, were evaluated for detection of La Crosse (LAC) virus infection of individual Aedes triseriatus . Twenty-one days after fully engorging on an infectious blood meal containing LAC virus, 63% (119/189) of the control group females transmitted virus to suckling mice; virus infection persisted in 97% (184/189) of the control group females. The test group females were cut into 3 parts (head, anterior thorax, abdomen) to determine the extent of viral infection using IFAT on head squashes and the trituration method on thoracic and abdominal tissues. Head-squash I FAT indicated 71% (52/73) of the test group had disseminated infections; 21% (15/73) had nondisseminated infections. Exclusive use of head-squash IFAT would have indicated a 3 to 24% lower infection rate than the trituration method. However, judicious use of the IFAT will save time and reduce the cost of assay, since only mosquitoes with negative head squashes need be further assayed; in this study a 70% reduction in individual trituration assays would have been realized. A comparison of test and control groups indicated disseminated infections could not be directly equated with the probability of virus transmission.