Biomedical subjects

J X Velasco-Hernandez

Publications and source records attributed to J X Velasco-Hernandez.

6 recordsLinked to original sources

PubMed2004

Detachment and diffusive-convective transport in an evolving heterogeneous two-dimensional biofilm hybrid model.

Under the hypothesis of correlation between biofilm survival and nutrient availability, by considering fluid drag forces and mortality due to nutrient depletion, a biofilm detachment/breaking condition is derived. The mechanisms leading to biofilm detachment/breaking are discussed. We construct and describe a hybrid model for a heterogeneous biofilm attached to walls in a channel where liquid is flowing. The model is called hybrid because it couples conservation equations with a cellular automaton. The biofilm layer is viewed as a porous medium with variable porosity, tortuosity, and permeability. The model is solved using asymptotic and finite differences methods. Results for porosity, nutrient distribution, and average surface location are presented. The model is capable of reproducing biofilm heterogeneity as well as the typical surface fingering (mushroomlike structure).

Bacterial Adhesion↗

PubMed2002

Could widespread use of combination antiretroviral therapy eradicate HIV epidemics?

Current combination antiretroviral therapies (ARV) are widely used to treat HIV. However drug-resistant strains of HIV have quickly evolved, and the level of risky behaviour has increased in certain communities. Hence, currently the overall impact that ARV will have on HIV epidemics remains unclear. We have used a mathematical model to predict whether the current therapies: are reducing the severity of HIV epidemics, and could even lead to eradication of a high-prevalence (30%) epidemic. We quantified the epidemic-level impact of ARV on reducing epidemic severity by deriving the basic reproduction number (R(0)(ARV)). R(0)(ARV) specifies the average number of new infections that one HIV case generates during his lifetime when ARV is available and ARV-resistant strains can evolve and be transmitted; if R(0)(ARV) is less than one epidemic eradication is possible. We estimated for the HIV epidemic in the San Francisco gay community (using uncertainty analysis), the present day value of R(0)(ARV), and the probability of epidemic eradication. We assumed a high usage of ARV and three behavioural assumptions: that risky sex would (1) decrease, (2) remain stable, or (3) increase. Our estimated values of R(0)(ARV) (median and interquartile range [IQR]) were: 0.90 (0.85-0.96) if risky sex decreases, 1.0 (0.94-1.05) if risky sex remains stable, and 1.16 (1.05-1.28) if risky sex increases. R(0)(ARV) decreased as the fraction of cases receiving treatment increased. The probability of epidemic eradication is high (p=0.85) if risky sex decreases, moderate (p=0.5) if levels of risky sex remain stable, and low (p=0.13) if risky sex increases. We conclude that ARV can function as an effective HIV-prevention tool, even with high levels of drug resistance and risky sex. Furthermore, even a high-prevalence HIV epidemic could be eradicated using current ARV.

Anti-HIV Agents↗

PubMed1999

Density-dependent dynamics and superinfection in an epidemic model.

A mathematical model of the interaction between two pathogen strains and a single host population is studied. Variable population size, density-dependent mortality, disease-related deaths (virulence), and superinfection are incorporated into the model. Results indicate that coexistence of the two strains is possible depending on the magnitude of superinfection. Global asymptotic stability of the steady-state that gives coexistence for both strains under suitable and biologically feasible constraints is proved.

Communicable Diseases↗

PubMed1995

Community treatment of HIV-1: initial stage and asymptotic dynamics.

Treatment with antiviral drugs (zidovudine and ddI) has been reported to delay progression to AIDS, and may even possibly lower the infectiousness of the infectives. However, its effect on the community level is still uncertain. The latter is important since a successful community treatment program must meet both public health and individual health goals. Our study will focus on the effect of a community-wide treatment program initiated at the early stages of the disease as well as the long-term effect of the program. Using a simple mathematical model, we demonstrate that a community-wide treatment program could be instrumental in decreasing HIV incidence rate and eradicating the disease in the future if certain conditions on the parameters are met. On the other hand, when the above mentioned conditions on the parameters are not satisfied, we show that even if the treatment does improve survival in AIDS patients and decrease the rate at which HIV infection spreads in the community, it is still possible for the treatment program to have an adverse effect on the spread of AIDS in the population in the long run. Hence, a public health policy maker must exercise caution in order to design an effective treatment program for HIV/AIDS.

Community Health Services↗

PubMed1994

Modelling the effect of treatment and behavioral change in HIV transmission dynamics.

In this paper we analyze a model for the HIV-infection transmission in a male homosexual population. In the model we consider two types of infected individuals. Those that are infected but do not know their serological status and/or are not under any sort of clinical/therapeutical treatment, and those who are. The two groups of infectives differ in their incubation time, contact rate with susceptible individuals, and probability of disease transmission. The aim of this article is to study the roles played by detection and changes in sexual behavior in the incidence and prevalence of HIV. The analytical results show that there exists a unique endemic equilibrium which is globally asymptotically stable under a range of parameter values whenever a detection/treatment rate and an indirect measure of the level of infection risk are sufficiently large. However, any level of detection/treatment rate coupled with a decrease of the transmission probability lowers the incidence rate and prevalence level in the population. In general, only significant reductions in the transmission probability (achieved through, for example, the adoption of safe sexual practices) can contain effectively the spread of the disease.

HIV Infections↗

PubMed1994

Habitat suitability and herbivore dynamics.

We derive a dynamic model for a plant herbivore system describing the interaction of a gall-forming aphid and a single plant. We compare the behavior of our model with experimental observations obtained from an aphid plant system studied by Whitham (Whitham, T.G. 1978, Habitat selection of Pemphigus aphids in response to resource limitation and competition. Ecology 59, 1164-1176). A simple parameter estimation shows a close correlation between the predicted and observed results.

Animals↗