Effectiveness assessment of countermeasures against bioterrorist smallpox attacks in Japan using an individual-based model

<p><b>OBJECTIVES</b>This study is aimed at the evaluation of countermeasures in terms of the total number of patients and deaths, the number of vaccine doses used, and the time for eradication as examined through simulations of the outbreak of smallpox following a bioterrorist attack in the center of Okayama City. Three countermeasures were considered: traced vaccination (TV), mass vaccination (MV), and school closure.</p><p><b>METHODS</b>An individual-based model was adopted, in which every individual is assigned their own personal information, behavioral pattern, and interactions among social settings to simulate the situation on a realistic basis. The influence of residual immunity obtained by past vaccination reflected age-dependent immunity to smallpox in Japan.</p><p><b>RESULTS</b>MV performed within a 2-day period at the same time in 10 school districts had the highest effectiveness in reducing the total number of patients and deaths among all simulations. Performing both TV and MV simultaneously was much more effective than performing TV or MV individually. The decrease in the number of patients with TV or MV in combination with school closure was faster than that by TV or MV without school closure.</p><p><b>CONCLUSIONS</b>According to the simulations results, it was advisable to carry out MV, or both TV and MV, simultaneously with school closure as countermeasures against a smallpox epidemic initiated by a bioterrorist attack.</p>

Modeling the Dynamics and Control of Transmission of Schistosoma japonicum and S. mekongi in Southeast Asia

A mathematical model for transmission of schistosomes is useful to predict effects of various control measures on suppression of these parasites. This review focuses on epidemiological and environmental factors in Schistosoma japonicum and Schistosoma mekongi infections and recent advances in mathematical models of Schistosoma transmission.

Risk assessment of re-emerging Plasmodium falciparum on Ishigaki Island using a stochastic transmission model

On Ishigaki Island, <I>Plasmodium falciparum</I> and <I>Plasmodium vivax</I> epidemics occurred in 1945-1946 and were successfully suppressed. The epidemic re-emerged in 1949 because many settlers immigrated to the former endemic areas, but it terminated in 1961. The present study aimed at predicting an outbreak of a new epidemic based on the situation in which <I>P. falciparum</I> malaria patients stay on Ishigaki Island and also examined the re-emergence of the <I>P. falciparum</I> epidemic in 1951-1960 to determine the reliability of the model.<br>A stochastic transmission model of <I>P. falciparum</I> was constructed to detect a small number of infected persons. The seasonal fluctuation of the <I>Anopheles minimus</I> population obtained by observational data and meteorological data through statistical processing was introduced into the model.<br>Simulations were carried out to predict the risk of a new epidemic with scenarios in which the attribute of index patient, visiting season, and reduced inoculation rates of <I>An. minimus</I> were assumed. When an infected person visited the island in summer, a small number of patients with primary infections derived from the index patient appeared for all 1,000-iterations. On the other hand, when an infected person visited the island in winter, few or no patients with primary infections appeared for any of the 1,000-iterations because of the low mosquito density. In realistic conditions, the simulation results showed that there was little possibility of the occurrence of <I>P. falciparum</I> infection.