Acta Medica Okayama1383-57696042011Analysis of the effectiveness of control measures against Schistosoma mekongi using an intra- and inter-village model in Champasak Province, Lao PDR452459ENKazumaFukuharaSamlanePhompidaSithatInsisiengmayMasashiKirinokiYuichiChigusaSatoshiNakamuraHajimeMatsudaHirofumiIshikawaSchistosomiasis mekongi is prevalent in the Khong district of Lao PDR, made up of one big island. Khong, and numerous small islands in the Mekong River. Schistosoma mekongi is spread by Neotricula aperta as the intermediate host along the Mekong River. Therefore, even if an epidemic of S. mekongi were stamped out in a certain village, infection may recur if the source of infection is a village located in the upper reaches of the Mekong River. The purpose of this study was to construct a mathematical model for the transmission of S. mekongi among villages from the upper to lower Mekong River to estimate the effect of control measures against it. The chief characteristic of the present model is competence in dealing with the spread of infection among villages through the Mekong River in consideration of the reduction in longevity of cercariae and miracidia and their diffusion in the river. The model also takes into account seasonal fluctuation in the water level of the Mekong River, which affects human behavior in terms of water contact. The results of simulations indicated that the prevalence of schistosomiasis mekongi would be suppressed to a low level for a long time in a village further downstream when universal mass treatment is performed in villages further upstream simultaneously.No potential conflict of interest relevant to this article was reported.財団法人 学会誌刊行センターActa Medica Okayama0385-56005192007Mathematical Modeling of Severe Acute Respiratory Syndrome Nosocomial Transmission in Japan: The Dynamics of Incident Cases and Prevalent Cases823832ENAyakoFukutomeKoichiWatashiNoritoKawakamiHirofumiIshikawaAn outbreak of Severe Acute Respiratory Syndrome (SARS) occurred in Hong Kong in late February 2003, resulting in 8,096 cumulative cases with 774 deaths. The outbreak was amplified by nosocomial transmission in many hospitals. Using mathematical modeling, we simulated the number of new incident and prevalent cases of SARS after one infected person was admitted to a hospital (index case). The simulation was tested stochastically using the SEIR model based on previously reported Gamma distributions. We estimated the duration time until 10 beds in negative pressure rooms in Chiyoda-ku, one of the 23 wards in Tokyo, were fully occupied with SARS-infected patients. We determined the impact of an increasing number of days on the number of prevalent cases until the index case was isolated. The prevalent cases increase exponentially along with the increase of the non-isolation period of the index case, and all the beds were fully occupied if the index case was not isolated until more than 6 days. However even 2 days non-isolation period of the index case could fill up all the beds when 16% of secondary infections are transmitted outside the hospital. There is a possibility that an epidemic will occur with the isolation of the index case even at early days if the infection is transmitted outside the hospital. The simulation results revealed that it was important to recognize and isolate SARS patients as early as possible and also to prevent the transmission spreading outside the hospital to control an epidemic.No potential conflict of interest relevant to this article was reported.Acta Medica Okayama5512008Modelling the dynamics and control of Schistosoma japonicum transmission on Bohol island, the PhilippinesENHirofumiIshikawaHiroshiOhmaeRogelioPangilinanApolinarioRedullaHajimeMatsuda<p>We have investigated a mathematical model for the transmission of Schistosoma japonicum in the infested region of northeastern Bohol island in the Philippines. The development of transmission models is important for planning control strategies. Since S. japonicum has a complicated mode of transmission, the rates of transmission among its hosts cannot be measured directly by field observation. Instead, they have been estimated through model analysis. The model takes into account the seasonal variations and includes a function of control measures. In 1981, a project to eliminate schistosomiasis started on Bohol island. The prevalence decreased dramatically and has kept low level less than 1%. The simulations based on the model predicted that there is little probability of resurgence of an epidemic in the northeastem endemic villages of Bohol island due to the fact that the project has attained a high coverage of selective mass treatment based oil stool examination accompanied by a successful snail control operation. (c) 2005 Elsevier Ireland Ltd. All rights reserved.</p>No potential conflict of interest relevant to this article was reported.Acta Medica Okayama5732008The evaluation of control measures against Schistosoma mekongi in Cambodia by a mathematical modelENNaotoHisakaneMasashiKirinokiYuichiChigusaMuthSinuonDuongSocheatHajimeMatsudaHirofumiIshikawa<p>We constructed a mathematical model for the transmission of Schistosoma mekongi in Cambodia. The simulation of the model will be instrumental in planning schistosomiasis control measures. The model includes two definitive hosts, humans and dogs, as animal reservoirs. Dogs are recognized to play an important role in schistosomiasis transmission in Cambodia. For the purpose of dealing with age-specific prevalence and intensity of infection, the human population was classified into eight age categories in the model. To describe the seasonal fluctuation of the intermediate host population of S. mekongi, the "Post-Spate Survival" hypothesis was adopted for the population dynamics of Neotricula aperta present in the Mekong River. We carried out simulations to evaluate the effect of universal treatment (UT) and targeted mass treatment (TT) with praziquantel on the reduction in prevalence of S. mekongi. The simulations indicated that biyearly UT for 8 years or yearly TT for 5 years after three courses of yearly UT could reduce the prevalence to below 5% when a UT or TT coverage of 85% of inhabitants was achieved. The simulation suggested that the suppression of S. mekongi in Cambodia would be possible by UT or TT with a high coverage rate.</p>No potential conflict of interest relevant to this article was reported.Acta Medica Okayama9162003A model for the transmission of Echinococcus multilocularis in Hokkaido, Japan444451ENHirofumiIshikawaYukioOhgaRikuoDoi<p>A mathematical model for Echinococcus multilocularis transmission would be
useful to estimate its prevalence and manage control strategies. We propose a
mathematical model which quantitatively describes the transmission of E. multilocularis
in Hokkaido, Japan. The model takes into account the influence of the dynamics of both
the definitive and the intermediate host populations, which show large scale seasonal
variations as they are wild animals. The simulations based on the model clarify the
mechanism for the seasonal transmission of E. multilocularis quantitatively,
notwithstanding a lack of seasonal prevalence data. At present, human alveolar
echinococcosis is prevalent throughout the mainland of Hokkaido. The risk of being
infected with alveolar echinococcosis in the human population has been investigated by
analyzing the seasonal fluctuation of parasite egg dispersal in the environment, which
should be necessary for planning more suitable preventive measures against E.
multilocularis.</p>No potential conflict of interest relevant to this article was reported.Acta Medica Okayama552008Mathematical modeling of Echinococcus multilocularis transmissionENHirofumiIshikawa<p>A mathematical model for the transmission cycle of Echinococcus multilocularis would be useful for estimating its prevalence, and the model simulation can be instrumental in designing various control strategies. This review focuses on the epidemiological factors in the E. multilocularis transmission cycle and the recent advances of mathematical models for E. multilocularis transmission.</p>No potential conflict of interest relevant to this article was reported.Acta Medica Okayama10232008A stochastic model of Echinococcus multilocularis transmission in Hokkaido, Japan, focusing on the infection process465479ENTomohikoNishinaHirofumiIshikawa<p>Echinococcus multilocularis causes human alveolar echinococcus. In Japan, high prevalence of E. multilocularis among the fox population has been reported throughout Hokkaido. Accordingly, control measures, such as fox hunting and the distribution of bait containing Praziquantel, have been conducted. This study developed a transmission model for individuals in the fox population and included a stochastic infection process to assess the prevalence of E. multilocularis. To make our model realistic, we used the worm burden for each individual in the fox population. We assumed that the worm burden depends on the number of protoscoleces in a predated vole and the number of infection experiences. We carried out stochastic simulations with 1,000 trials for the situations of Koshimizu and Sapporo, Hokkaido, Japan. The distribution of the worm burden among foxes obtained using the model agreed with dissection data. The simulation indicates that a careful choice of season is necessary for an effective distribution of Praziquantel-containing bait. A stochastic model for E. multilocularis, which can assess the range of the prevalence in the fox population, would be helpful in analyzing their complex life-cycle and also in designing control strategies.</p>
No potential conflict of interest relevant to this article was reported.Okayama University Medical SchoolActa Medica Okayama0386-300X5442000Estimation of the sporozoite rate of malaria vectors using the polymerase chain reaction and a mathematical model.165171ENMasakazuHaradaHirofumiIshikawaHiroyukiMatsuokaAkiraIshiiSetsuoSuguriArticle10.18926/AMO/32275<p>We developed a sensitive polymerase chain reaction (PCR) method for the detection of Plasmodium falciparum DNA from mosquitoes collected in the field. Plasmodium falciparum was detected from 15.2% of 1-parous mosquitoes, Anopheles farauti, in the Solomon Islands through use of the PCR method. A novel mathematical model was developed to estimate the sporozoite rate based on the malaria-positive rate of 1-parous mosquitoes. Using this model, the sporozoite rate of Anopheles farauti in the Solomon Islands was calculated to be 0.09%. This method enables estimation of the sporozoite rate based on a relatively small number (100-200) of mosquitoes compared with the number needed for the ELISA method.</p>
No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-90991412009Evaluation for interventions against influenza of H5N1 in Sapporo-city by using an Individual Based Model111ENTomokoMorimotoTomohiroZenihanaYusukeMaitaniHirofumiIshikawa10.18926/fest/15042The spread of the highly pathogenic avian influenza (H5N1) among domestic poultry and wild birds has caused global concern over the outbreak of an influenza pandemic of H5N1. The "Pandemic Influenza Preparedness Action Plan" determines the strategy against an influenza pandemic in Japan. Simulations were carried out using an individual based model (IBM). The IBM targeted a virtual area with a population of 100,000 using the demographic data of Sapporo-city, Hokkaido. The effectiveness of targeted antiviral prophylaxis (TAP), geographical targeted antiviral prophylaxis (GTAP), school closure, and pre-pandemic vaccination were explored. Moreover, this study focused on infections among children, who have a high attack rate, and analyzed the effectiveness of interventions for school-age targeted antiviral prophylaxis (STAP). Consequently, TAP, which is recommended by the "Pandemic Influenza Preparedness Action Plan", was found to have high effectiveness in the suppression of the outbreak. Moreover, this study showed the importance of intervention among children, such as STAP and school closure, to prevent the spread of H5N1 influenza.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-90991312008Analysis of the effectiveness of control strategies against bioterrorist smallpox attacks by using Individual Based Model2333ENTomohiroZenihanaNaotoHisakaneTomokoMorimotoHirofumiIshikawa10.18926/fest/12819We carried out simulations of various scenarios for bioterrorist attacks using smallpox occurring in a virtual area set up on the basis of the census of Okayama-city, Japan, which predict the effect of control strategies against bioterrorism and the loss scale. On simulating a smallpox epidemic, we followed the method of the Individual Based Model stochastically, which can treat the population in the virtual area as individuals. Individuals have personal information, behavior patterns, and interactions among social
groups. We took into consideration the influence of residual immunity due to past vaccination. We considered Traced Vaccination (TV) and Mass Vaccination (MV) strategies against bioterrorism. We investigated the effect of TV and MV strategies on the suppression of smallpox epidemics. Consequently, the TV strategy was found to have higher effectiveness than the MV strategy.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-90991312008石垣島におけるマラリア流行解析のための統計モデリング715ENMasaoUekiYuukiNakagawaKaoruFuedaHirofumiIshikawa10.18926/fest/12816It is necessary to consider a stochastic variability in modeling malaria epidemic behavior since the malaria infection cycle essentially depends on stochastic elements. For this requirement, we need to construct an appropriate statistical model from available data in advance. In this report, we provide some statistical models for the analysis of malaria epidemic behavior at Ishigaki Island. These models can be used for recurrence of past malaria epidemic and prediction of future malaria epidemic at Ishigaki Island.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099111996Computational water analysis in an artificial lake: Kojima Lake case4753ENToruSasakiHirofumiIshikawaTsuyoshiKajiwaraMasajiWatanabe10.18926/fest/11610We treat the problem of water pollution by the method of a mathematical model. We illustrate the method of analysis with Kojima Lake. We analyze in-flow and out-flow of the lake, compute numerical solutions of the governing equations of the water flow and the pollutant. The simulation leads to the conclusion concerning the figure of Kojima Lake.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099111996The determination of small dimensions of the Hilbert Modular Type Cusp forms of Weight Two over Real Quadratic Fields2741ENHirofumiIshikawa10.18926/fest/11606The author has proved the dimension formula of the space of the Hilbert modular type cusp forms of weight two. We present further refinements of the dimension formula for a real quadratic number field Q(√D), and calculate it effectively. We tabulate the dimensions for square-free natural numbers D below 104 with the computer assistance. We also determine all the spaces of their dimension below 10.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099211997The Elliptic resolutions for Symmetric Hilbert modular surface and their applications917ENHirofumiIshikawa10.18926/fest/11595In this paper, we have calculated the elliptic singularities of the symmetric Hilbert modular group defined over a real quadratic number field. Applying those to the dimension formula, we tabulate the dimensions of the space of symmetric Hilbert modular forms of weight two satisfying certain cusp condition.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099311998Computational analysis of contamination in Kojima Lake using upwind-type finite element method3136ENToruSasakiTsuyoshiKajiwaraHirofumiIshikawa10.18926/fest/11560We have computed the phase of spreading contaminations in Kojima Lake by using the upwind-type finite element method. We have treated the two cases: the pollutant flows from the Sasagase river and from the Kurashiki River. We see that the upwind-type finite element method is effective in both cases, when the diffusion constant is quite small.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099311998The Fourier coefficients of certain Maass wave form for Γ0(2)59ENHirofumiIshikawa10.18926/fest/11554We investigate the Maass wave form for Γ(0)(2) whose eigenvalue of Laplacian Δ is 1/4-π(2)/log(2)(√2-1). In this note, we study the methods of calculation of its Fourier coefficients and carry out the numerical calculations.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099512000The prevalence of Plasmodium vivax in Vanuatu Islands: Computer simulation of malaria control trails16ENHirofumiIshikawaAkiraIshiiAkiraKaneko10.18926/fest/11548We have estimated the degree of transmission of Plasmodium vivax malaria in Vanuatu Islands, eastern Melanesia with the aid of the computer simulations, which has been carried out on the platform of a mathematical transmission model. The malaria caused by Plasmodium vivax has a relapse character, which arises from hypnozoites in the liver. This phenomen makes a malaria control strategy difficult. When the mass drug administration is executed, the prevalence of Plasmodium vivax decreases moderately as compared with that of Plasmodium falciparum, and it recovers before long being affected by the relapses. The simulations suggest that one cannot attain the eradication of Plasmodium vivax malaria without the concentrated execution of the mass drug administration and the vector control that fairly reduces the vactorial capacity.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099712002Mathematical Model for The Transmission of Lymphatic Filariasis and Its Applications716ENHiroyukiIshiiHirofumiIshikawaYukioOhga10.18926/fest/11512We have constructed a stochastic transmission model for lymphatic filariasis caused by Wuchereria bancrofti, and have analyzed its prevalence using computer simulations. In Pondicherry, India, where Wuchereria bancrofti has been spreading, the Vector Control Research Centre has carried out an integrated vector control strategy against malaria and filariasis for five years (1981~1985) with good results reported. Our study was aimed at evaluating the effect of vector control in the context of Pondicherry, and in particular the continuous effect for the post-control period. In this paper, we have used the LYMFASIM model proposed by Plaisier et al., the carrying capacity model by Rochet and the population dynamics model by us. In the LYMFASIM model and the carrying capacity model, we have modified the quantities of parameters in order to fit the models to the parasitological, entomological and epidemiological data in Pondicherry. We have combined the improved LYMFASIM model with the other models. Through simulations of our combinated model, we have compared the prevalence rate in the human population as well as the mean number of L3-larvae in the mosquito population, with and without vector control. As a result, the simulations show that the prevalence rate would be restrained for a long time even if only a small continuous effect of the vector control remains in the post-control period. However, the mean number of L3-larvae would recovered within a short time comparatively. This is because of the differences in life spans between human and mosquito as well as the incubation periods between the adult worm in the human host and L3-larvae in the mosquito vector.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099712002Simulations on Prevalence of Echinococcus multilocularis in Hokkaido on the Basis of Vole Population Dynamics15ENYukioOhgaHirofumiIshikawaRikuoDoiHiroyukiIshii10.18926/fest/11510In our study, we have investigated the influence of the intermediate host population density on the prevalence of Echinococcus multilocularis in the definitive host using a mathematical model of transmission. For the vole population (intermediate host) in Hokkaido, a model of population dynamics has been constructed in this paper which follows the seasonal and annual fluctuations. In the northeastern area, the vole density appears to fluctuate periodically with a 4 year cycle. The prevalence of Echinococcus multilocularis in the fox population (definitive host) can be affected by the density of vole through the fox ingesting infectious voles. Therefore we have prepared a food habit function of foxes and the logistic distribution has been proposed. The simulations which have been carried out using the mathematical model for transmission of Echinococcus multilocularis together with the vole dynamics have indicated that the prevalence in foxes is correlated and synchronized with the population dynamics of vole. In addition they have also made us recognize that it is necessary to introduce a suitable food habit function into the transmission model.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099812003Studies on the transmission model of HIV/AIDS among commercial sex workers in Thailand17ENHirofumiIshikawa10.18926/fest/11487In 1990s, there were rapid increases in the number of HIV epidemics and AIDS cases in Thailand, Southeast Asia. In particular the risk of HIV infection was very high among female prostitutes who played a large part in the transmission of HIV infection. We formulated a mathematical model for the transmission of HIV in prostitutes. We carried out the model simulations to analyze the incipient spread of HIV infection and the effect of AIDS prevention methods in prostitutes. The simulation of our model indicates that even if the effect of AIDS prevention methods such as the recommendation of condom use for commercial sex workers would block the transmission at rate by 70%, the elimination of the HIV epidemic is still beyond attainment.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-90991012005Linear and Differential Cryptanalysis of SHA-25617ENHirofumiIshikawa10.18926/fest/11479The one-way hash function plays an important role in digital signatures and message authentication from the viewpoint of security. No effective attacking method has been discovered to the algorithm of hash function standard. In this study, we tried to attack SHA-256 in encryption mode using linear and differential cryptanalysis to solve a private key. We deduced that an estimate of the private key would require huge known and chosen plaintexts in both linear and differential cryptanalysis, and that it would be difficult to decipher SHA-256 in view of the required computation.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-9099912004A Study on the Linear Cryptanalysis of AES Cipher1926ENHirofumiIshikawa10.18926/fest/11449We have investigated the linear cryptanalysis of AES cipher in this article. As the previous encryption standard DES could be broken by the linear cryptanalysis, NIST decided a new encryption standard AES in 2000. We try to analyze one and two rounds AES cipher by the method of the linear cryptanalysis and learn the limits of this mehtod. AES cipher provides a conspicuous difficulty in breaking its keys because of small bias of its S-box. We report the experimental results of success rate and are led to conclusion that this method would not work well on more than 3 rounds to break keys.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-90991212007クロロキシン薬剤耐性に関する熱帯熱マラリア数理モデル解析 ―ソロモン諸島を対象としたシミュレーション1927ENTiantianChenTomohikoNishinaNaotoHisakaneHirofumiIshikawa10.18926/fest/11425The Solomon Islands are known as a high endemic region of malaria. The resistance of Plasmodium falciparum to chloroquine has been confirmed since 1980 in the Solomon Islands, and the spread of chloroquine resistance is a big hurdle to malaria control. We have constructured the model for P. falciparum making allowance of chloroquine resistance. We distinguish the infection of resistance strains from that of sensitive strains in both the human and the vector populations. Since the overall parasite rate and the parasite rate of gametocytes for P. falciparum are strongly dependent on age, the human population is divided into 7 age groups in the model. The epidemiological parameters are determined by malariological survey in northeastern Guadalcanal (Ishii et al.) and the sporozoite rate in vector population is assumed as 0.1% based on the entomological study (Harada et al.) Our study aims at estimating the effect of mass drug administration under the presence of drug-resistance and also analyzing the escalation of drug-resistance through the transmission model for P. falciparum which can deal with chloroquine resistance.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-90991112006A stochastic model of Echinococcus multilocularis focusing on protoscoleces914ENHirofumiIshikawa10.18926/fest/11424The red fox (Vulpes vulepes) and the vole (
Clethrionomys refocanus) are principal hosts of Echinococcus multilocularis in Hokkaido, Japan. How protoscoleces increases in voles and the level of immunity in foxes remain unknown because of the lack of survey data, so that it is important to clarify these mecahnisms in order to develop control strategies against E. multilocularis. In this study, the growth of protoscoleces in the infected voles was approximated as the logistic curve, the level of immunity in the fox was assumed to depend on the experience of the infection with E. multilocularis, and the worm burden in the fox was assumed to be governed by the amount of protoscoleces in the vole. Our model showed that the population densities of the hosts and the level of immunity influenced the prevalence of the E. multilocularis.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-90991212007The order elliptic curves over finite fields of characteristic two using the Schoof algorithm718ENHirofumiIshikawa10.18926/fest/11423The elliptic curve cryptosystem is a popular cryptosystem. Its safety depends on the difficulty of the elliptic curve discrete logarithm problem (ECDLP). From the viewpoint of ECDLP, it is very interesting to determine the order of elliptic curves. We tabulate the order of elliptic curves on the finite field of characteristic two using the Schoof algorithm, which is an efficient algorithm to decide orders. The Schoof algorithm is carried out by O(log(8)q). Because the calculation of y(q2) occupies most of the time used to execute the Schoof algorithm, it is necessary to reduce the amount of y(q2) calculations.No potential conflict of interest relevant to this article was reported.岡山大学環境理工学部Acta Medica Okayama1341-90991112006Modeling of re-emerging Plasmodium vivax in the Northern Area of the Republic of Korea Based on a Mathematical Model17ENHirofumiIshikawa10.18926/fest/11422Plasmodium vivax re-emerged in 1993 near the demilitarized zone (DMZ) in South Korea, although P. vivax malaria disappeared in South Korea in 1979. The re-emergence of malaria in South Korea is believed to have originated from infection by mosquitoes from North Korea across the DMZ. The principal vector of P. vivax in the Korean Peninsula is Anopheles sinensis. The density of An. sinensis has a peak during the second week of July. The North Korean strain of P. vivax has 2 characteristics: a wide distribution of the terms of relapse and a high rate of relapse. Therefore, we may well wonder why the incidence of malaria is concentrated in summer, especially in August. Mathematical models in North Korea and South Korea were constructed in which the South Korean model was affected unidirectionally by the North Korean model. We carried out simulations of the model for the Paju-shi and Yonchon-gun situations near the DMZ region. The simulation results followed the time-course of the re-emergence of P. vivax there, and revealed the mechanism of the elevation of the incidence of P. vivax in summer.No potential conflict of interest relevant to this article was reported.