Infected Immigrants Research Articles

Modeling the combined effects of careless susceptible and infective immigrants on the transmission dynamics of HIV/AIDS epidemics

In this paper, a non-linear mathematical model was proposed to study the combined effect of irresponsible infectives and irresponsible susceptible immigrants on the spread of human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) in a variable size population. The paper discussed biological feasibility of the model and also presents the basic reproductive number of the model. Also, the equilibrium points of the model are found and stability of the model around the equilibria was also studied. It is realized that at the disease free equilibrium, the model is stable when R0 < 0 and unstable otherwise. Also, the condition for asymptotical stability of the model near the endemic equilibrium is presented. The equilibra of model is given as. Numerical simulations reveal that the presence of infective immigrants significantly affects the spread of the disease and that behavioral change of all classes of individuals should be considered in efforts aimed at controlling the spread of the disease. Key words: Acquired immune deficiency syndrome (AIDS) epidemic, vertical transmission, stability, infective immigrants, simulation.

Self-sustained oscillations in epidemic models with infective immigrants

A relevant issue related to eco-epidemiological studies concerns the demographic mechanisms that can lead to self-sustained oscillations in the composition of a host population subject to infection. In particular, why does the prevalence of some contagious diseases oscillate over time? Here, we address this question by using susceptible-infective-recovered-empty models including migration of infective foreigners and variable population size. These models are described in terms of ordinary differential equations (ODE) and also in terms of probabilistic cellular automaton (PCA), in which each cell is connected to others either by a regular lattice or by a random graph favoring local contacts. Each cell in the PCA model can be either empty or occupied by a single individual. The amount of neighbors per cell affects the value of the basic reproduction number R0, which is, in fact, a bifurcation parameter. We show that, by varying the amount of neighbors per cell (and consequently R0), the number of infective individuals can start to exhibit periodic behavior, which corresponds to a Hopf bifurcation in the ODE model. This bifurcation gives rise to a self-sustained oscillation and it can only occur if the immigration rate of infective individuals is above a critical value. We also investigate how the sum of new infections, within the considered time window, depends on the number of neighbors per cell.

Disease Burden of Chronic Hepatitis B among Immigrants in Canada

The prevalence of chronic hepatitis B (CHB) infection among immigrants to North America ranges from 2% to 15%, 40% of whom develop advanced liver disease. Screening for hepatitis B surface antigen is not recommended for immigrants. To estimate the disease burden of CHB among immigrants in Canada using Markov cohort models comparing a cohort of immigrants with CHB versus a control cohort of immigrants without CHB. Markov cohort models were used to estimate life years, quality-adjusted life years and lifetime direct medical costs (adjusted to 2008 Canadian dollars) for a cohort of immigrants with CHB living in Canada in 2006, and an age-matched control cohort of immigrants without CHB living in Canada in 2006. Parameter values were derived from the published literature. At the baseline estimate, the model suggested that the cohort of immigrants with CHB lost an average of 4.6 life years (corresponding to 1.5 quality-adjusted life years), had an increased average of $24,249 for lifetime direct medical costs, and had a higher lifetime risk for decompensated cirrhosis (12%), hepatocellular carcinoma (16%) and need for liver transplant (5%) when compared with the control cohort. Results of the present study showed that the socio-economic burden of CHB among immigrants living in Canada is substantial. Governments and health systems need to develop policies that promote early recognition of CHB and raise public awareness regarding hepatitis B to extend the lives of infected immigrants.

Should We Look for Strongyloides Stercoralis in Foreign-Born HIV-Infected Persons?

The objective was to evaluate the implementation of a systematic Strongyloides stercoralis screening programme in HIV infected immigrants attending an HIV Unit in Spain. An enzyme-linked immunosorbent assay (ELISA) was performed to assess the presence of Strongyloides IgG. Patients with a positive serology were treated with ivermectin; serologic follow-up testing was performed. 237 patients were screened (65.4% men). Origin: 64.1% came from Latin America, 16.5% from Sub-Saharan Africa, 9.7% from the Caribbean, 9.7% from other areas. Strongyloides stercolaris IgG was positive in 13 cases (5.5%). In the multivariate analysis, factors associated with a positive Strongyloides serology were illiteracy (OR: 23.31; p=0.009) and eosinophilia (OR: 15.44; p<0.0001). Nine of the 13 patients positive for S. stercoralis IgG and treated with ivermectin had a follow up serologic test: 77.8% achieved a serologic response (55.5% seroreversion). Screening of HIV-positive immigrants may be desirable, at least in those with higher risk of hyperinfection syndrome. Serologic testing seems a useful tool in both diagnosis and follow-up of these patients.

Globalization of Chagas Disease: A Growing Concern in Nonendemic Countries

Chagas disease, caused by the parasite Trypanosoma cruzi, is a major cause of morbidity and mortality in Central and South America. Initial infection and ensuing chronic infection often go undetected in the human host. High seroprevalence of T. cruzi infection is well documented in endemic areas. Designated as “a neglected tropical disease” by the World Health Organization, rural economically disadvantaged and marginalized populations in endemic countries traditionally have the highest rates of infection. As economic hardship, political instability, and the search for opportunity spur migration of infected humans from endemic to non-endemic areas of the world, blood bank data have documented rising seroprevalence of T. cruzi in traditionally nonendemic areas. In these areas, T. cruzi is transmitted through blood transfusion, organ transplantation, and maternal-fetal mechanisms. Increasing awareness of large numbers of infected immigrants in nonendemic countries, and the medical care they require, has focused attention on the need for strategic programs for screening affected populations, education of healthcare providers, and provision of necessary medical services for those infected. Physicians in nonendemic countries should be able to recognize signs and symptoms of acute and chronic Chagas disease as migration and globalization increase the burden of disease in non-endemic areas.

Global stability for a discrete SIS epidemic model with immigration of infectives

In this paper, we propose a discrete-time SIS epidemic model which is derived from continuous-time SIS epidemic models with immigration of infectives by the backward Euler method. For the discretized model, by applying new Lyapunov function techniques, we establish the global asymptotic stability of the disease-free equilibrium for and the endemic equilibrium for , where R 0 is the basic reproduction number of the continuous-time model. This is just a discrete analogue of a continuous SIS epidemic model with immigration of infectives.

Vaccination model for visceral leishmaniasis with infective immigrants

In this paper, we present and analyzed a mathematical model that describes the dynamics of visceral leishmaniasis in a population with immigration of infective humans under mass vaccination strategy. Our result shows that in order for the vaccine to play a role on disease control, it must be very effective. Results also show that vaccination coverage does not have any impact on disease control when the immigration rate is small, and it does not affect the long‐term behavior when the immigration rate is high. In the case of no immigration of infective, our system has disease‐free equilibrium, and it is globally asymptotically stable when , the basic reproduction number, is less than unity. Numerical simulation shows that in the case of no immigration of infective, our system undergoes forward bifurcation when passes throw unity. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Modelling the Effect of Treatment and Infected Immigrants on the Spread of Hepatitis C Virus Disease with Acute and Chronic Stages

This paper examines the effect of Treatment and Infected Immigrants on the spread of Hepatitis C Virus (HCV) disease with Acute and Chronic stages. A nonlinear mathematical model for the problem is proposed and analysed qualitatively using the stability theory of the differential equations. The results show that the disease free equilibrium is locally stable at threshold parameter less than unity and unstable at threshold parameter greater than unity. Globally, the disease free equilibrium is not stable due existence of forward bifurcation at threshold parameter equal to unity. However the disease becomes more endemic due to the presence of infected immigrants in the community. It is also shown that in the presence of treatment, the rate of infected immigrants (acute and chronic) decreases and consequently the treated infected individuals decreases continuously. Numerical simulation of the model is implemented to investigate the sensitivity of certain key parameters on the treatment and infected immigrants on the spread of the disease with acute and chronic stages.

Barriers to Testing and Treatment for Chagas Disease among Latino Immigrants in Georgia

Background. The lack of testing and treatment of Chagas disease (CD), caused by Trypanosoma cruzi, amongst infected immigrants in the USA increases the risk of serious health complications and transmission (congenital or via blood transfusions). Goal. Our goal was to identify the barriers to testing and treatment of CD and understand the process of seeking healthcare amongst Latino immigrants in Georgia. Methods. In this qualitative study, eleven focus group discussions were conducted with 82 Latino immigrants, including migrant farm workers. Grounded theory was used to collect and analyze the data to develop an inductive conceptual framework to explain the context and process of seeking healthcare for CD amongst this at-risk population. Results. Participants were not aware of CD. Three healthcare seeking behaviors were identified: delaying treatment, using traditional remedies, and using either mainstream or alternative health providers. Behaviors and motivations differed by gender, and the use of licensed medical providers was considered a last resort due to the cost of healthcare, loss of earnings while seeking care, and fear of diagnosis with fatal illness. Discussion. Providing free or low cost services, mobile clinics, and education regarding CD is critical to increase testing and treatment of CD in the US.

A Dengue Vaccination Model for Immigrants in a Two-Age-Class Population

We develop a model of dengue transmission with some vaccination programs for immigrants. We classify the host population into child and adult classes, in regards to age structure, and into susceptible, infected and recovered compartments, in regards to disease status. Since migration plays important role in disease transmission, we include immigration and emigration factors into the model which are distributed in each compartment. Meanwhile, the vector population is divided into susceptible, exposed, and infectious compartments. In the case when there is no incoming infected immigrant, we obtain the basic reproduction ratio as a threshold parameter for existence and stability of disease-free and endemic equilibria. Meanwhile, in the case when there are some incoming infected immigrants, we obtain only endemic equilibrium. This indicates that screening for the immigrants is important to ensure the effectiveness of the disease control.

The increasing burden of imported chronic hepatitis B--United States, 1974-2008.

BackgroundWithout intervention, up to 25% of individuals chronically infected with hepatitis B virus (HBV) die of late complications, including cirrhosis and liver cancer. The United States, which in 1991 implemented a strategy to eliminate HBV transmission through universal immunization, is a country of low prevalence. Approximately 3,000–5,000 U.S.-acquired cases of chronic hepatitis B have occurred annually since 2001. Many more chronically infected persons migrate to the United States yearly from countries of higher prevalence. Although early identification of chronic HBV infection can reduce the likelihood of transmission and late complications, immigrants are not routinely screened for HBV infection during or after immigration.MethodsTo estimate the number of imported cases of chronic hepatitis B, we multiplied country-specific prevalence estimates by the yearly number of immigrants from each country during 1974–2008.ResultsDuring 1974–2008, 27.9 million immigrants entered the U.S. Sixty-three percent were born in countries of intermediate or high chronic hepatitis B prevalence (range 2%–31%). On average, an estimated 53,800 chronic hepatitis B cases were imported to the U.S. yearly from 2004 through 2008. The Philippines, China, and Vietnam contributed the most imported cases (13.4%, 12.5%, and 11.0%, respectively). Imported cases increased from an estimated low of 105,750 during the period 1974–1977 to a high of 268,800 in 2004–2008.ConclusionsImported chronic hepatitis B cases account for approximately 95% of new U.S. cases. Earlier case identification and management of infected immigrants would strengthen the U.S. strategy to eliminate HBV transmission, and could delay disease progression and prevent some deaths among new Americans.

A deterministic model of HIV/Aids with vertical transmission in the presence of infected immigrants

A non-linear mathematical model for HIV epidemic that spreads in a variable size population through both horizontal and vertical transmission in the presence of HIV infected immigrants is studied. The equilibrium points of the model are found and the stability is investigated. The model exhibits two equilibria, namely, the disease-free and the endemic equilibrium. It is shown that if the basic reproduction number, the disease-free equilibrium is always locally asymptotically stable and in such a case the endemic equilibrium does not exist. If , a unique endemic equilibrium exists, which is locally asymptotically stable and becomes globally asymptotically stable under certain conditions. This shows that the disease becomes endemic due to constant immigration of both HIV infected and non infected individuals into the community. Using stability theory and computer simulation, it is shown that by controlling the rate of vertical transmission, the spread of the disease can be reduced significantly and consequently the equilibrium values of infected population can be maintained at desired levels. A numerical study of the model is also used to investigate the influence of certain other key parameters on the spread of the disease and how to control their influence. Key words: AIDS epidemic, vertical transmission, immigration, stability, simulation.

English

This paper examines the combined effects of screening and variable inflow of infective immigrants on the spread of HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome) in a population of varying size. A nonlinear deterministic mathematical model for the problem is proposed and analysed qualitatively using the stability theory of differential equations. The results show that the reproductive number R0&nbsp;&gt;1 as the rate of inflow of infective immigrants increases leading to persistence of the disease in the population. However, the presence of screening greatly reduces the spread of HIV/AIDS.Numerical simulation of the model is implemented&nbsp;to investigate the sensitivity of certain key parameters on the spread of the disease. &nbsp; Key words:&nbsp;Human immunodeficiency virus/acquired immune deficiency syndrome, screening, infective immigrants, reproductive number, stability analysis, numerical simulation.

Screening of immigrants in the UK for imported latent tuberculosis: a multicentre cohort study and cost-effectiveness analysis

SummaryBackgroundContinuing rises in tuberculosis notifications in the UK are attributable to cases in foreign-born immigrants. National guidance for immigrant screening is hampered by a lack of data about the prevalence of, and risk factors for, latent tuberculosis infection in immigrants. We aimed to determine the prevalence of latent infection in immigrants to the UK to define which groups should be screened and to quantify cost-effectiveness.MethodsIn our multicentre cohort study and cost-effectiveness analysis we analysed demographic and test results from three centres in the UK (from 2008 to 2010) that used interferon-γ release-assay (IGRA) to screen immigrants aged 35 years or younger for latent tuberculosis infection. We assessed factors associated with latent infection by use of logistic regression and calculated the yields and cost-effectiveness of screening at different levels of tuberculosis incidence in immigrants' countries of origin with a decision analysis model.FindingsResults for IGRA-based screening were positive in 245 of 1229 immigrants (20%), negative in 982 (80%), and indeterminate in two (0·2%). Positive results were independently associated with increases in tuberculosis incidence in immigrants' countries of origin (p=0·0006), male sex (p=0·046), and age (p<0·0001). National policy thus far would fail to detect 71% of individuals with latent infection. The two most cost-effective strategies were to screen individuals from countries with a tuberculosis incidence of more than 250 cases per 100 000 (incremental cost-effectiveness ratio [ICER] was £17 956 [£1=US$1·60] per prevented case of tuberculosis) and at more than 150 cases per 100 000 (including immigrants from the Indian subcontinent), which identified 92% of infected immigrants and prevented an additional 29 cases at an ICER of £20 819 per additional case averted.InterpretationScreening for latent infection can be implemented cost-effectively at a level of incidence that identifies most immigrants with latent tuberculosis, thereby preventing substantial numbers of future cases of active tuberculosis.FundingMedical Research Council and Wellcome Trust.

Impact of Chemo-therapy on Optimal Control of Malaria Disease with Infected Immigrants

We derived and analyzed rigorously a mathematical model that describes the dynamics of malaria infection with the recruitment of infected immigrants, treatment of infectives and spray of insecticides against mosquitoes in the population. Both qualitative and quantitative analysis of the deterministic model are performed with respect to stability of the disease free and endemic equilibria. It is found that in the absence of infected immigrants disease-free equilibrium is achievable and is locally asymptotically stable. Using Pontryagin's Maximum Principle, the optimal strategies for disease control are established. Finally, numerical simulations are performed to illustrate the analytical results.

Risk analysis of the re-emergence of Plasmodium vivax malaria in Japan using a stochastic transmission model

This study analyzed the risk of infection with Plasmodium vivax in local residents through a stochastic simulation in which an infected tourist, local resident, or immigrants from an endemic area would visit Himi-shi, Toyama prefecture, which is a formerly endemic area in Japan. In Toyama, the habitats of Anopheles sinensis, which can transmit P. vivax, have been examined previously. We constructed a stochastic model of P. vivax transmission that can handle small numbers of infected persons and infected mosquitoes. The seasonal fluctuation in the numbers of captured An. sinensis was taken into account in the model. Ten thousand trial simulations were carried out stochastically with a range of human blood indexes (HBI) of 1-10% for a range of months (June-September). The simulation results for a realistic assumption of a 1% HBI showed that the risk of infection for local residents was low (below 1%) except for the immigrants scenario. The risk of infection among local residents (second cycle) was estimated to be very low for all situations. Therefore, there is little possibility for P. vivax infection to become established in this area of Japan.

730 HUMAN GENETIC VARIANTS LINKED TO CHRONIC HEPATITIS B ARE ASSOCIATED WITH EXPRESSION OF HLA-DPA1 AND HLA-DPB1

prevalence and the patterns of HBV infection in a large cohort of immigrants in Rome. Methods: Between August 2008 and July 2009, 1203 consecutive patients were visited at our Department (68.2% female, 32.8% male, mean age 30 years). 58.78% were from Africa, 22.04% from Asia, 13.06% from Eastern-Europe and 6.12% from South-America. A screening form with demographic, clinical and laboratory data was collected for each HBsAg-positive patient, in order to identify the patterns of HBV infection, to optimize their management and treatment and to observe their evolution over time. Results: The prevalence of HBsAg-positive patients was 16.5% (199/1203). 71.44% of these subjects were from Africa, 16.66% from Eastern-Europe, 9.52% from Asia and 2.38% from South-America. Mean age was 27 years (61.9% male, 38.1% female). HBeAg was positive in 373 patients (30.9%). Respectively 8.7% and 15% of HBV infected immigrants were co-infected with HCV and HDV. The diagnostic categories assigned were: inactive carrier state 58.7%, chronic hepatitis B (CHB) 31.6% and HBV-related cirrhosis 9.7%. Conclusions: Chronic infection with HBV is an important health issue in immigrated patients, partly as a result of absence of vaccine prophylaxis in many countries. Although universal vaccination has dramatically reduced the incidence of HBV in Italy, there is a risk of a rise in HBV infections in our country, as result of the increase of imported cases through immigration from highly endemic countries. Another alarming finding of this study is the high prevalence of anti-HDV antibodies in immigrants. This is a particularly serious issue because co-infection with HDV has been shown to accelerate the progression to cirrhosis, and rates of response to anti-viral treatment are lower than in mono-infected patients.

Effects of infected immigrants and seasonality in malaria transmission

A simple mathematical model for malaria transmission with the inflow of infected immigrants is presented and analysed. The model is extended to incorporate and analyse the effects of seasonality in the transmission rates. The results obtained show that the model does not have a disease free equilibrium but has multiple endemic equilibria depending on the value of the fraction of infected immigrants. We also deduce that the seasonal strength influences the endemic levels in a population. Finally numerical analysis is carried out to determine the behaviour of the models under different scenarios

OPTIMAL CONTROL MEASURES FOR TUBERCULOSIS MATHEMATICAL MODELS INCLUDING IMMIGRATION AND ISOLATION OF INFECTIVE

Optimal control theory is applied to a system of ordinary differential equations modeling the population dynamics of tuberculosis with isolation and immigration of infective. Seeking to minimize the number of infectious individuals and reduce the transmission of the disease, we use controls to represent the screening/medical testing of infected immigrants into the population as well as isolation of infective in the population. The optimal controls are characterized in terms of the optimality system, which is solved numerically for several scenarios using an iterative method with Runge-Kutta fourth order scheme. Parameter values used are those reported for Nigeria.

Mosquito distribution and Japanese encephalitis virus infection in the immigration bird (Asian open-billed stork) nested area in Pathum Thani province, central Thailand

Japanese encephalitis virus infection is a mosquito-borne emerging or re-emerging infectious disease in several countries. The ecology of this virus in nature includes amplifying avian or mammal hosts and mosquito vectors. Infected immigration birds from epidemic areas may play important roles in the outbreak of the disease. The prevalence is high during the raining season in Thailand and human cases have been reported from several provinces including Bangkok suburbs. This study was conducted to investigate the mosquito distribution and Japanese encephalitis virus infection in the immigration bird (Asian open-billed stork) nested area, Pathum Thani province, central Thailand. Mosquitoes were collected by using CO(2)-baited Centers for disease control and prevention (CDC) light traps, and dry ice was used as a source of CO(2) to attract mosquitoes from March 2008 to January 2009. Eight traps were operated from 4 p.m. until 7 a.m. on each study day. There were seven genera collected: Aedes, Anopheles, Armigeres, Coquillettidia, Culex, Mansonia, and Uranotaenia. Culex tritaeniorhynchus was the most collected species in each month, except November, in which Culex gelidus was the most collected species. Sixty pools of C. gelidus and of C. tritaeniorhynchus, each of which had 50 mosquitoes, were tested for Japanese encephalitis virus infection by using reverse transcription polymerase chain reactions; however, none of them was infected with the virus.