Arquivo da tag: Epidemiologia

Theoretical tiger chases statistical sheep to probe immune system behavior (Science Daily)

Physicists update predator-prey model for more clues on how bacteria evade attack from killer cells

Date:
April 29, 2016
Source:
IOP Publishing
Summary:
Studying the way that solitary hunters such as tigers, bears or sea turtles chase down their prey turns out to be very useful in understanding the interaction between individual white blood cells and colonies of bacteria. Researchers have created a numerical model that explores this behavior in more detail.

Studying the way that solitary hunters such as tigers, bears or sea turtles chase down their prey turns out to be very useful in understanding the interaction between individual white blood cells and colonies of bacteria. Reporting their results in the Journal of Physics A: Mathematical and Theoretical, researchers in Europe have created a numerical model that explores this behaviour in more detail.

Using mathematical expressions, the group can examine the dynamics of a single predator hunting a herd of prey. The routine splits the hunter’s motion into a diffusive part and a ballistic part, which represent the search for prey and then the direct chase that follows.

“We would expect this to be a fairly good approximation for many animals,” explained Ralf Metzler, who led the work and is based at the University of Potsdam in Germany.

Obstructions included

To further improve its analysis, the group, which includes scientists from the National Institute of Chemistry in Slovenia, and Sorbonne University in France, has incorporated volume effects into the latest version of its model. The addition means that prey can now inadvertently get in each other’s way and endanger their survival by blocking potential escape routes.

Thanks to this update, the team can study not just animal behaviour, but also gain greater insight into the way that killer cells such as macrophages (large white blood cells patrolling the body) attack colonies of bacteria.

One of the key parameters determining the life expectancy of the prey is the so-called ‘sighting range’ — the distance at which the prey is able to spot the predator. Examining this in more detail, the researchers found that the hunter profits more from the poor eyesight of the prey than from the strength of its own vision.

Long tradition with a new dimension

The analysis of predator-prey systems has a long tradition in statistical physics and today offers many opportunities for cooperative research, particularly in fields such as biology, biochemistry and movement ecology.

“With the ever more detailed experimental study of systems ranging from molecular processes in living biological cells to the motion patterns of animal herds and humans, the need for cross-fertilisation between the life sciences and the quantitative mathematical approaches of the physical sciences has reached a new dimension,” Metzler comments.

To help support this cross-fertilisation, he heads up a new section of the Journal of Physics A: Mathematical and Theoretical that is dedicated to biological modelling and examines the use of numerical techniques to study problems in the interdisciplinary field connecting biology, biochemistry and physics.


Journal Reference:

  1. Maria Schwarzl, Aljaz Godec, Gleb Oshanin, Ralf Metzler. A single predator charging a herd of prey: effects of self volume and predator–prey decision-makingJournal of Physics A: Mathematical and Theoretical, 2016; 49 (22): 225601 DOI: 10.1088/1751-8113/49/22/225601

Researchers treat incarceration as a disease epidemic, discover small changes help (Science Daily)

Date: June 25, 2014

Source: Virginia Tech

Summary: By treating incarceration as an infectious disease, researchers show that small differences in prison sentences can lead to large differences in incarceration rates. The incarceration rate has nearly quadrupled since the U.S. declared a war on drugs, researchers say. Along with that, racial disparities abound. Incarceration rates for black Americans are more than six times higher than those for white Americans, according to the U.S. Bureau of Justice Statistics.

The incarceration rate has nearly quadrupled since the U.S. declared a war on drugs, researchers say. Along with that, racial disparities abound. Incarceration rates for black Americans are more than six times higher than those for white Americans, according to the U.S. Bureau of Justice Statistics.

To explain these growing racial disparities, researchers at Virginia Tech are using the same modeling techniques used for infectious disease outbreaks to take on the mass incarceration problem.

By treating incarceration as an infectious disease, the scientists demonstrated that small but significant differences in prison sentences can lead to large differences in incarceration rates. The research was published in June in the Journal of the Royal Society Interface.

Incarceration can be “transmitted” to others, the researchers say. For instance, incarceration can increase family members’ emotional and economic stress or expose family and friends to a network of criminals, and these factors can lead to criminal activity.

Alternatively, “official bias” leads police and the courts to pay more attention to the incarcerated person’s family and friends, thereby increasing the probability they will be caught, prosecuted and processed by the criminal justice system, researchers said.

“Regardless of the specific mechanisms involved,” said Kristian Lum, a former statistician at the Virginia Bioinformatics Institute now working for DataPad, “the incarceration of one family member increases the likelihood of other family members and friends being incarcerated.”

Building on this insight, incarceration is treated like a disease in the model and the incarcerated are infectious to their social contacts — their family members and friends most likely affected by their incarceration.

“Criminologists have long recognized that social networks play an important role in criminal behavior, the control of criminal behavior, and the re-entry of prisoners into society,” said James Hawdon, a professor of sociology in the College of Liberal Arts and Human Sciences. “We therefore thought we should test if networks also played a role in the incarceration epidemic. Our model suggests they do.”

Synthesizing publically available data from a variety of sources, the researchers generated a realistic, multi-generational synthetic population with contact networks, sentence lengths, and transmission probabilities.

The researchers’ model is comparable to real-world incarceration rates, reproducing many facets of incarceration in the United States.

Both the model and actual statistics show large discrepancies in incarceration rates between black and white Americans and, subsequently, the likelihood of becoming a repeat offender is high.

Comparisons such as these can be used to validate the assumption that incarceration is infectious.

“Research clearly shows that this epidemic has had devastating effects on individuals, families, and entire communities,” Lum said. “Since our model captures the emergent properties of the incarceration epidemic, we can use it to test policy options designed to reverse it.”

Harsher sentencing may actually result in higher levels of criminality. Examining the role of social influence is an important step in reducing the growing incarceration epidemic.

Journal Reference:

  1. K. Lum, S. Swarup, S. Eubank, J. Hawdon. The contagious nature of imprisonment: an agent-based model to explain racial disparities in incarceration ratesJournal of The Royal Society Interface, 2014; 11 (98): 20140409 DOI: 10.1098/rsif.2014.0409

Agora manteiga faz bem e carne faz mal? (Jornal da Ciência)

JC e-mail 4973, de 16 de junho de 2014

Artigo de Luís Maurício Trambaioli para o Jornal da Ciência

Está sendo amplamente divulgado na mídia um recente estudo em que os pesquisadores de Harvard, a partir de questionário de perguntas feito em 1991 a enfermeiras, inferiu que mulheres teriam 22 % de risco relativo aumentado de câncer de mama quando consumindo uma porção a mais de carne vermelha que mulheres que consomem menos.

Entretanto, risco relativo não é risco absoluto, o qual pode ser calculado pelos dados originais. A chance de desenvolver a doença seria vista em 1 em cada 100.000 mulheres, e não em 22 em cada 100 mulheres como tem sido noticiado pela falsa impressão que o ‘risco relativo’ nos dá. Mais, esta incidência é exatamente em grupos de mulheres que mais fumam.

É importante cuidado na forma que se divulga as notícias de estudos epidemiológicos e feitos por apenas um grupo. Melhor seria obter um parecer de especialistas na área e ainda preferencialmente resultados advindos de mais estudos obtidos por outros pesquisadores, evitando assim bias e viés na ciência. Sob risco de acontecer acusações levianas como ocorrido na década de 80 que levou a demonizar a gordura saturada há exatos 30 anos sem evidências científicas que suportassem tal idéia, o que direcionou a humanidade ao desespero de consumo de alimentos sem gordura e compensando com a ingestão de mais “carboidratos complexos” (amido) e baixos em micronutrientes. E o resultado foi a epidemia de diabetes e obesidade (chamado no exterior de diabesity), doenças cardiovasculares, câncer, dentre outras.

E agora, o que cortar do bacon: a gordura ou a carne ?

Luís Maurício Trambaioli é professor associado da Faculdade de Farmácia da UFRJ e pesquisador associado do INMETRO

Referências:

BMJ – “Dietary protein sources in early adulthood and breast cancer incidence: prospective cohort study” – http://dx.doi.org/10.1136/bmj.g3437

Resposta ao estudo: http://www.bmj.com/content/348/bmj.g3437?tab=responses

Time Magazine, 26/03/1984 – And Now the Bad News –
http://content.time.com/time/specials/2007/article/0,28804,1704183_1704257_1704499,00.html

Time Magazine, 23/06/2014 – Ending the War on Fat – http://time.com/2863227/ending-the-war-on-fat/
http://oglobo.globo.com/sociedade/saude/carne-vermelha-pode-aumentar-risco-de-cancer-de-mama-diz-estudo-de-harvard-12803653

One Percent of Population Responsible for 63% of Violent Crime, Swedish Study Reveals (Science Daily)

Dec. 6, 2013 — The majority of all violent crime in Sweden is committed by a small number of people. They are almost all male (92%) who early in life develops violent criminality, substance abuse problems, often diagnosed with personality disorders and commit large number non-violent crimes. These are the findings of researchers at Sahlgrenska Academy who have examined 2.5 million people in Swedish criminal and population registers.

In this study, the Gothenburg researchers matched all convictions for violent crime in Sweden between 1973 and 2004 with nation-wide population register for those born between 1958 to 1980 (2.5 million).

Of the 2.5 million individuals included in the study, 4 percent were convicted of at least one violent crime, 93,642 individuals in total. Of these convicted at least once, 26 percent were re-convicted three or more times, thus resulting in 1 percent of the population (23,342 individuals) accounting for 63 percent of all violent crime convictions during the study period.

“Our results show that 4 percent of those who have three or more violent crime convictions have psychotic disorders, such as schizophrenia and bipolar disorder. Psychotic disorders are twice as common among repeat offenders as in the general population, but despite this fact they constitute a very small proportion of the repeat offenders,” says Örjan Falk, researcher at Sahlgrenska Academy.

One finding the Gothenburg researchers present is that “acts of insanity” that receive a great deal of mass media coverage, committed by someone with a severe psychiatric disorder, are not responsible for the majority of violent crimes.

According to the researchers, the study’s results are important to crime prevention efforts.

“This helps us identify which individuals and groups in need of special attention and extra resources for intervention. A discussion on the efficacy of punishment (prison sentences) for this group is needed as well, and we would like to initiate a debate on what kind of criminological and medical action that could be meaningful to invest in,” says Örjan Falk.

Studies like this one are often used as arguments for more stringent sentences and US principles like “three strikes and you’re out.” What are your views on this?

“Just locking those who commit three or more violent crimes away for life is of course a compelling idea from a societal protective point of view, but could result in some undesirable consequences such as an escalation of serious violence in connection with police intervention and stronger motives for perpetrators of repeat violence to threaten and attack witnesses to avoid life sentences. It is also a fact that a large number of violent crimes are committed inside the penal system.”

“And from a moral standpoint it would mean that we give up on these, in many ways, broken individuals who most likely would be helped by intensive psychiatric treatments or other kind of interventions. There are also other plausible alternatives to prison for those who persistently relapse into violent crime, such as highly intensive monitoring, electronic monitoring and of course the continuing development of specially targeted treatment programs. This would initially entail a higher cost to society, but over a longer period of time would reduce the total number of violent crimes and thereby reduce a large part of the suffering and costs that result from violent crimes,” says Örjan Falk.

“I first and foremost advocate a greater focus on children and adolescents who exhibit signs of developing violent behavior and who are at the risk of later becoming repeat offenders of violent crime.”

Journal Reference:

  1. Örjan Falk, Märta Wallinius, Sebastian Lundström, Thomas Frisell, Henrik Anckarsäter, Nóra Kerekes. The 1 % of the population accountable for 63 % of all violent crime convictionsSocial Psychiatry and Psychiatric Epidemiology, 2013; DOI: 10.1007/s00127-013-0783-y

Mathematics Provides a Shortcut to Timely, Cost-Effective Interventions for HIV (Science Daily)

Apr. 15, 2013 — Mathematical estimates of treatment outcomes can cut costs and provide faster delivery of preventative measures.

South Africa is home to the largest HIV epidemic in the world with a total of 5.6 million people living with HIV. Large-scale clinical trials evaluating combination methods of prevention and treatment are often prohibitively expensive and take years to complete. In the absence of such trials, mathematical models can help assess the effectiveness of different HIV intervention combinations, as demonstrated in a new study by Elisa Long and Robert Stavert from Yale University in the US. Their findings appear in the Journal of General Internal Medicine, published by Springer.

Currently 60 percent of individuals in need of treatment for HIV in South Africa do not receive it. The allocation of scant resources to fight the HIV epidemic means each strategy must be measured in terms of cost versus benefit. A number of new clinical trials have presented evidence supporting a range of biomedical interventions that reduce transmission of HIV. These include voluntary male circumcision — now recommended by the World Health Organization and Joint United Nations Programme on HIV/AIDS as a preventive strategy — as well as vaginal microbicides and oral pre-exposure prophylaxis, all of which confer only partial protection against HIV. Long and Stavert show that a combination portfolio of multiple interventions could not only prevent up to two-thirds of future HIV infections, but is also cost-effective in a resource-limited setting such as South Africa.

The authors developed a mathematical model accounting for disease progression, mortality, morbidity and the heterosexual transmission of HIV to help forecast future trends in the disease. Using data specific for South Africa, the authors estimated the health benefits and cost-effectiveness of a “combination approach” using all three of the above methods in tandem with current levels of antiretroviral therapy, screening and counseling.

For each intervention, they calculated the HIV incidence and prevalence over 10 years. At present rates of screening and treatment, the researchers predict that HIV prevalence will decline from 19 percent to 14 percent of the population in the next 10 years. However, they calculate that their combination approach including male circumcision, vaginal microbicides and oral pre-exposure prophylaxis could further reduce HIV prevalence to 10 percent over that time scale — preventing 1.5 million HIV infection over 10 years — even if screening and antiretroviral therapy are kept at current levels. Increasing antiretroviral therapy use and HIV screening frequency in addition could avert more than 2 million HIV infections over 10 years, or 60 percent of the projected total.

The researchers also determined a hierarchy of effectiveness versus cost for these intervention strategies. Where budgets are limited, they suggest money should be allocated first to increasing male circumcision, then to more frequent HIV screening, use of vaginal microbicides and increasing antiretroviral therapy. Additionally, they calculate that omitting pre-exposure prophylaxis from their combination strategy could offer 90 percent of the benefits of treatment for less than 25 percent of the costs.

The authors conclude: “In the absence of multi-intervention randomized clinical or observational trials, a mathematical HIV epidemic model provides useful insights about the aggregate benefit of implementing a portfolio of biomedical, diagnostic and treatment programs. Allocating limited available resources for HIV control in South Africa is a key priority, and our study indicates that a multi-intervention HIV portfolio could avert nearly two-thirds of projected new HIV infections, and is a cost-effective use of resources.”

Journal Reference:

  1. Long, E.F. and Stavert, R.R. Portfolios of biomedical HIV interventions in South Africa: a cost-effectiveness analysisJournal of General Internal Medicine, 2013 DOI:10.1007/s11606-013-2417-1

Rooting out Rumors, Epidemics, and Crime — With Math (Science Daily)

ScienceDaily (Aug. 10, 2012) — A team of EPFL scientists has developed an algorithm that can identify the source of an epidemic or information circulating within a network, a method that could also be used to help with criminal investigations.

Investigators are well aware of how difficult it is to trace an unlawful act to its source. The job was arguably easier with old, Mafia-style criminal organizations, as their hierarchical structures more or less resembled predictable family trees.

In the Internet age, however, the networks used by organized criminals have changed. Innumerable nodes and connections escalate the complexity of these networks, making it ever more difficult to root out the guilty party. EPFL researcher Pedro Pinto of the Audiovisual Communications Laboratory and his colleagues have developed an algorithm that could become a valuable ally for investigators, criminal or otherwise, as long as a network is involved. The team’s research was published August 10, 2012, in the journal Physical Review Letters.

Finding the source of a Facebook rumor

“Using our method, we can find the source of all kinds of things circulating in a network just by ‘listening’ to a limited number of members of that network,” explains Pinto. Suppose you come across a rumor about yourself that has spread on Facebook and been sent to 500 people — your friends, or even friends of your friends. How do you find the person who started the rumor? “By looking at the messages received by just 15-20 of your friends, and taking into account the time factor, our algorithm can trace the path of that information back and find the source,” Pinto adds. This method can also be used to identify the origin of a spam message or a computer virus using only a limited number of sensors within the network.

Trace the propagation of an epidemic

Out in the real world, the algorithm can be employed to find the primary source of an infectious disease, such as cholera. “We tested our method with data on an epidemic in South Africa provided by EPFL professor Andrea Rinaldo’s Ecohydrology Laboratory,” says Pinto. “By modeling water networks, river networks, and human transport networks, we were able to find the spot where the first cases of infection appeared by monitoring only a small fraction of the villages.”

The method would also be useful in responding to terrorist attacks, such as the 1995 sarin gas attack in the Tokyo subway, in which poisonous gas released in the city’s subterranean tunnels killed 13 people and injured nearly 1,000 more. “Using this algorithm, it wouldn’t be necessary to equip every station with detectors. A sample would be sufficient to rapidly identify the origin of the attack, and action could be taken before it spreads too far,” says Pinto.

Identifying the brains behind a terrorist attack

Computer simulations of the telephone conversations that could have occurred during the terrorist attacks on September 11, 2001, were used to test Pinto’s system. “By reconstructing the message exchange inside the 9/11 terrorist network extracted from publicly released news, our system spit out the names of three potential suspects — one of whom was found to be the mastermind of the attacks, according to the official enquiry.”

The validity of this method thus has been proven a posteriori. But according to Pinto, it could also be used preventatively — for example, to understand an outbreak before it gets out of control. “By carefully selecting points in the network to test, we could more rapidly detect the spread of an epidemic,” he points out. It could also be a valuable tool for advertisers who use viral marketing strategies by leveraging the Internet and social networks to reach customers. For example, this algorithm would allow them to identify the specific Internet blogs that are the most influential for their target audience and to understand how in these articles spread throughout the online community.