RESUMO
Many vertebrate species undergo population fluctuations that may be random or regularly cyclic in nature. Vertebrate population cycles in northern latitudes are driven by both endogenous and exogenous factors. Suggested causes of mysterious disappearances documented for populations of the Neotropical, herd-forming, white-lipped peccary (Tayassu pecari, henceforth "WLP") include large-scale movements, overhunting, extreme floods, or disease outbreaks. By analyzing 43 disappearance events across the Neotropics and 88 years of commercial and subsistence harvest data for the Amazon, we show that WLP disappearances are widespread and occur regularly and at large spatiotemporal scales throughout the species' range. We present evidence that the disappearances represent 7-12-year troughs in 20-30-year WLP population cycles occurring synchronously at regional and perhaps continent-wide spatial scales as large as 10,000-5 million km2. This may represent the first documented case of natural population cyclicity in a Neotropical mammal. Because WLP populations often increase dramatically prior to a disappearance, we posit that their population cycles result from over-compensatory, density-dependent mortality. Our data also suggest that the increase phase of a WLP cycle is partly dependent on recolonization from proximal, unfragmented and undisturbed forests. This highlights the importance of very large, continuous natural areas that enable source-sink population dynamics and ensure re-colonization and local population persistence in time and space.
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Artiodáctilos , Animais , Florestas , MamíferosRESUMO
Wheat blast, caused by Pyricularia oryzae Triticum lineage, is a major constraint to wheat production, mainly in the tropics of Brazil, where severe epidemics have been more frequent. We analyzed disease and wheat yield data from 42 uniform field trials conducted over 9 years (2012 to 2020) to assess whether the percent control and yield response were influenced by fungicide type, region (tropical or subtropical), and year. Six treatments were selected, all evaluated in at least 19 trials. Two fungicides were applied as solo active ingredients (MANCozeb, and TEBUconazole), and four were premixes (AZOXystrobin plus TEBU, TriFLoXystrobin plus PROThioconazole, TFLX plus TEBU, and PYRAclostrobin plus EPOXiconazole). Percent control, calculated from back-transforming estimates by a meta-analysis network model fitted to the log of the means, ranged from 43 to 58%, with all but PYRA plus EPOX showing efficacy >52% on average, not differing among them. The variation in both efficacy and yield response was explained by region, and all but TEBU performed better in the subtropics than in the tropics. Yield response from using three sequential sprays was approximately two times greater in the subtropics (319 to 532 kg/ha) than in the tropics (149 to 241.3 kg/ha). No significant decline in fungicide efficacy or yield response was observed in 9 years of study for any of the fungicides. These results reinforce the need to improve control by adopting an integrated management approach in the tropics given poorer performance and lower profitability, especially for the premixes, than in the subtropics.
Assuntos
Fungicidas Industriais , Brasil , Fungicidas Industriais/farmacologia , Doenças das Plantas/prevenção & controle , TriticumRESUMO
Mitigating the massive impacts of defaunation on natural ecosystems requires understanding and predicting hunting effort across the landscape. But such understanding has been hindered by the difficulty of assessing the movement patterns of hunters in thick forests and across complex terrain. We statistically tested hypotheses about the spatial distribution of hunting with circuit theory and structural equation models. We used a data set of >7000 known kill locations in Guyana and hunter movement models to test these methods. Comparing models with different resistance layers (i.e., different estimates of how terrain and land cover influence human movement speed) showed that rivers, on average, limited movement rather than serving as transport arteries. Moreover, far more kills occurred close to villages than in remote areas. This, combined with the lack of support for structural equation models that included latent terms for prey depletion driven by past overhunting, suggests that kill locations in this system tended to be driven by where hunters were currently foraging rather than by influences of historical harvest. These analyses are generalizable to a variety of ecosystems, species, and data types, providing a powerful way of enhancing maps and predictions of hunting effort across complex landscapes.
Comprensión de la Distribución de los Esfuerzos por Obtener Carne de Caza a lo largo de un Paisaje Mediante la Comprobación de Hipótesis sobre el Forrajeo Humano Resumen La mitigación de los impactos masivos de la defaunación sobre los ecosistemas naturales requiere de comprensión y predicción de los esfuerzos de caza a lo largo del paisaje. Dicha comprensión se ha visto obstaculizada por la dificultad que representa la evaluación de los patrones de movimiento de los cazadores en bosques densos y a través de un terreno complejo. Analizamos estadísticamente las hipótesis sobre la distribución espacial de la cacería mediante una teoría de circuito y modelos de ecuaciones estructurales. Usamos un conjunto de datos de más de 7000 localidades conocidas de sacrificios en Guayana y los modelos de movimiento de los cazadores para probar estos modelos. La comparación entre modelos con diferentes capas de resistencia (es decir, diferentes estimaciones de cómo el terreno y la cobertura de suelo influyen sobre la velocidad del movimiento humano) mostró que los ríos, en promedio, limitaron el movimiento en lugar de funcionar como arterias de transporte. Además, ocurrieron mucho más sacrificios cerca de las aldeas que en las áreas remotas. Lo anterior, combinado con la falta de apoyo para los modelos de ecuaciones estructurales que incluyeron los términos latentes para la reducción de presas causada por la sobrecaza pasada, sugiere que las localidades de sacrificios en este sistema tendieron a ser seleccionadas por la ubicación actual en la que los cazadores se encontraban forrajeando y no por la influencia de la cosecha histórica. Estos análisis son generalizables para una variedad de ecosistemas, especies y tipos de datos, lo que proporciona una manera poderosa de mejorar los mapas y las predicciones de los esfuerzos de cacería a través de paisajes complejos.
Assuntos
Conservação dos Recursos Naturais , Ecossistema , Florestas , Guiana , HumanosRESUMO
Biodiversity affects many ecosystem functions and services, including carbon cycling and retention. While it is known that the efficiency of carbon capture and biomass production by ecological communities increases with species diversity, the role of vertebrate animals in the carbon cycle remains undocumented. Here, we use an extensive dataset collected in a high-diversity Amazonian system to parse out the relationship between animal and plant species richness, feeding interactions, tree biomass and carbon concentrations in soil. Mammal and tree species richness is positively related to tree biomass and carbon concentration in soil-and the relationship is mediated by organic remains produced by vertebrate feeding events. Our research advances knowledge of the links between biodiversity and carbon cycling and storage, supporting the view that whole community complexity-including vertebrate richness and trophic interactions-drives ecosystem function in tropical systems. Securing animal and plant diversity while protecting landscape integrity will contribute to soil nutrient content and carbon retention in the biosphere.
Assuntos
Biodiversidade , Biomassa , Ciclo do Carbono , Mamíferos , Solo/química , Árvores/fisiologia , Animais , Florestas , GuianaRESUMO
The development of species distribution models (SDMs) can help conservation efforts by generating potential distributions and identifying areas of high environmental suitability for protection. Our study presents a distribution and habitat map for lowland tapir in South America. We also describe the potential habitat suitability of various geographical regions and habitat loss, inside and outside of protected areas network. Two different SDM approaches, MAXENT and ENFA, produced relative different Habitat Suitability Maps for the lowland tapir. While MAXENT was efficient at identifying areas as suitable or unsuitable, it was less efficient (when compared to the results by ENFA) at identifying the gradient of habitat suitability. MAXENT is a more multifaceted technique that establishes more complex relationships between dependent and independent variables. Our results demonstrate that for at least one species, the lowland tapir, the use of a simple consensual approach (average of ENFA and MAXENT models outputs) better reflected its current distribution patterns. The Brazilian ecoregions have the highest habitat loss for the tapir. Cerrado and Atlantic Forest account for nearly half (48.19%) of the total area lost. The Amazon region contains the largest area under protection, and the most extensive remaining habitat for the tapir, but also showed high levels of habitat loss outside protected areas, which increases the importance of support for proper management.
RESUMO
PURPOSE: Tumor cells are known to secrete cytokines that modify their microenvironment in order to favor their survival and continuous proliferation. In this work, we evaluated if TGF-ß secreted in vitro by cervical cancer cells could interfere with the proliferation and survival of lymphocytes. METHODS: Lymphocytes were obtained from peripheral blood of healthy human volunteers, and isolated by density gradient centrifugation and cultured in 96-well plates. Lymphocyte proliferation was induced with phytohemaglutinin and co-cultured with conditioned media (CM) from cervical cancer cell lines, and the inhibition of proliferation was evaluated after 72 h by the incorporated radioactivity and a CFSE-labeling assay. TGF-ß quantification on these CM was evaluated by ELISA. Non-apoptotic cellular death was evaluated through disruption of cell membrane integrity by measuring the liberation of lactate dehydrogenase. The apoptosis process was evaluated by annexin-V and active caspase-3. The presence of CD4+ or CD8+ lymphocytes was evaluated by flow cytometry using specific antibodies. RESULTS: It was found that the conditioned media from these cells significantly inhibited the proliferation of lymphocytes and induced them to go into apoptosis. Antibodies against TGF-ß almost completely blocked this activity, suggesting that this cytokine is responsible for the inhibitory activity. When the induced apoptosis on subpopulations of lymphocytes was evaluated, it was detected that the CD4+ cells were specifically targeted. CONCLUSIONS: Cervical cancer cells secrete TGF-ß that inhibits lymphocyte proliferation and induces apoptosis in CD4+, but not in CD8+ lymphocytes.
Assuntos
Apoptose , Linfócitos T CD4-Positivos/fisiologia , Carcinoma/metabolismo , Fator de Crescimento Transformador beta/metabolismo , Neoplasias do Colo do Útero/metabolismo , Alphapapillomavirus/fisiologia , Carcinoma/imunologia , Carcinoma/virologia , Linhagem Celular Tumoral , Proliferação de Células , Meios de Cultivo Condicionados , Feminino , Humanos , Infecções por Papillomavirus/complicações , Neoplasias do Colo do Útero/imunologia , Neoplasias do Colo do Útero/virologiaRESUMO
Certain steroidal compounds have demonstrated an antiproliferative effect against several tumor cell lines; however, their complete role on cancer cells is not currently established. Herein, we report the synthesis and evaluation of two new 26-hydroxy-22-oxocholestanic steroids on cervical cancer CaSki cells. The title compounds were prepared from diosgenin and hecogenin in excellent yields. We determined their effect on cell proliferation, cell cycle, and cell death. The cytotoxic effect of the title compounds on CaSki and human lymphocytes was also evaluated, indicating that the main cell death process is not necrosis; the null effect on lymphocytes implies that they are not cytotoxic. The observation of apoptotic bodies as well as the increase in the expression of active caspase-3 along with the fragmentation of DNA confirmed that such new cholestanic frameworks induced apoptosis in tumor cells. Significantly, their antiproliferative activity on tumor cells did not affect the proliferative potential of normal fibroblasts from cervix and peripheral blood lymphocytes. The title compounds show selective antitumor activity and therefore serve as promising lead candidates for further optimization.
Assuntos
Antineoplásicos Fitogênicos/síntese química , Antineoplásicos Fitogênicos/farmacologia , Apoptose/efeitos dos fármacos , Colestanóis/química , Colestanóis/síntese química , Colestanóis/farmacologia , Diosgenina/química , Sapogeninas/química , Esteroides/química , Esteroides/síntese química , Esteroides/farmacologia , Sequência de Carboidratos , Caspase 3/metabolismo , Ciclo Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Fragmentação do DNA/efeitos dos fármacos , Feminino , Fibroblastos/efeitos dos fármacos , Corantes Fluorescentes , Humanos , Marcação In Situ das Extremidades Cortadas , Indóis , Linfócitos/efeitos dos fármacos , Espectroscopia de Ressonância Magnética , Dados de Sequência Molecular , Relação Estrutura-Atividade , Neoplasias do Colo do Útero/tratamento farmacológico , Neoplasias do Colo do Útero/patologiaRESUMO
Vaccination of pigs of mixed genetic make-up, raised as rustically as done in rural Mexico, resulted in effective protection to experimental challenge against Taenia solium cysticercosis. Maximum protection was achieved if pigs were immunized at 70 days of age. There was large variation of viable parasite load within vaccinated pigs and controls, which is suggestive of significant genetic factors influencing susceptibility, besides immunization. Our results strengthen the advisability of pig vaccination for control of T. solium cysticercosis, since it lowers the number of viable cysticerci capable of transforming into tapeworms.
Assuntos
Anticorpos Anti-Helmínticos/biossíntese , Cisticercose/veterinária , Doenças dos Suínos/prevenção & controle , Taenia/imunologia , Vacinação/veterinária , Fatores Etários , Animais , Cisticercose/prevenção & controle , Predisposição Genética para Doença , México , Suínos , Doenças dos Suínos/genética , Doenças dos Suínos/imunologiaRESUMO
The aim of the present study was to evaluate diagnostic procedures for porcine cysticercosis. Sera were obtained from 32 pigs reared in commercial farms, 47 pigs before and after experimental infection, 42 carefully necropsied rural pigs and 191 slaughtered pigs from rural communities in which the presence of the Taenia solium metacestode was assessed by tongue dissection. Sera were analyzed by ELISA to detect antibodies against T. solium antigens and to detect parasite antigens. Most sera from the necropsied rural pigs were also evaluated by the Western blot method. Antigen and antibody ELISA detection assays showed high sensitivity and specificity when applied to sera from pigs reared in commercial farms. In contrast, all methods (Ag-ELISA, Ab-ELISA assays, EITB and tongue inspection) showed lower sensitivity and specificity when applied to the generally lightly infected rurally reared pigs. The probability distribution of cysts in carcasses were also determined. These results emphasize the difficulties in detecting cysticercosis in rural pigs with low levels of cyst burdens.
Assuntos
Cisticercose/veterinária , Cysticercus , Doenças dos Suínos/diagnóstico , Animais , Animais Domésticos , Anticorpos Anti-Helmínticos/sangue , Cisticercose/sangue , Cisticercose/diagnóstico , Ensaio de Imunoadsorção Enzimática , México , Valor Preditivo dos Testes , Saúde da População Rural , Sensibilidade e Especificidade , Suínos , Doenças dos Suínos/sangue , Doenças dos Suínos/parasitologia , TaeniaRESUMO
Theoretical predictions of disease prevalence due to helminth infections based upon a simple probabilistic model which considers the infection prevalence, the mean worm burden and the degree of worm aggregation are presented. A numerical reappraisal of the likely estimates of the degree of aggregation based upon maximum likelihood estimates of the negative binomial distribution is presented. The prevalence of disease shows a positive relationship with the mean worm burden. This association is hyperbolic when helminth parasites are severely aggregated but is s-shaped when helminth parasites tend to be overdispersed. The prevalence of disease decreases with the degree of worm aggregation when the values of the mean intensity are low; as the mean intensity increases this association becomes positive. The relationship between prevalence of disease and prevalence of infection is hyperbolic for severe degrees of parasite aggregation and is s-shaped for intermediate degrees of aggregation. However, if the mean intensity is low and the degree of aggregation is high there could be a negative relationship between the prevalence of disease and the prevalence of infection. The presence of disease due to helminth parasites is feasible for determined ranges of values of the infection prevalence, mean intensity and the degree of worm clumping.
Assuntos
Helmintíase/epidemiologia , Helmintos/isolamento & purificação , Enteropatias Parasitárias/epidemiologia , Animais , Helmintíase/parasitologia , Helmintíase/transmissão , Humanos , Enteropatias Parasitárias/parasitologia , Enteropatias Parasitárias/transmissão , Funções Verossimilhança , México/epidemiologia , Modelos Teóricos , PrevalênciaRESUMO
OBJECTIVE: The degree of aggregation is determined for the whole population and for different age-specific strata and is used for assessing the reinfection rate after a mass antihelminthic chemotherapeutic intervention. MATERIAL AND METHODS: The degree of aggregation of Ascaris lumbricoides is derived from prevalence and intensity of infection date obtained from an epidemiological study of ascariasis carried out in Coatzacoalcos, Veracruz, México by means of maximum likelihood estimation of the negative binomial distribution. RESULTS: The results show that the distribution of the parasite for the whole population differs from the distribution of the parasite within each age-specific stratum; the reinfection rate is not uniform, the dynamics of the host-parasite association exhibits a clear destabilization of its endemic equilibrium after a first round of mass treatment. CONCLUSIONS: It is suggested that the aggregation among the different age-groups is highly variable and hence the infection and reinfection rates are heterogeneous with regard to age; these states of the host-parasite system are transient. Given the heterogeneity of the infection, the selective treatment seems to be the most adequate strategy to diminish helminth infection rates.
Assuntos
Ascaríase/epidemiologia , Ascaris lumbricoides , Distribuição por Idade , Animais , Ascaríase/terapia , Criança , Pré-Escolar , Humanos , Lactente , México/epidemiologia , Modelos Biológicos , Prevalência , RecidivaRESUMO
The pattern of seropositivity of rubella obtained through the National Seroepidemiological Survey (NSS) of 1987-1988 is compared with the observed annual patterns of morbidity and with theoretical serological profiles based upon the age-distribution of cases. In spite of a lack of direct correspondence among the NSS results and the ones obtained from morbidity data, a relationship among the patterns and trends is observed. The theoretical methods used for inferring the proportion of seropositives as a function of age provide an inexpensive and fast alternative in order to monitor the current policy of no vaccination against rubella in Mexico.
Assuntos
Rubéola (Sarampo Alemão)/epidemiologia , Adolescente , Adulto , Fatores Etários , Criança , Pré-Escolar , Humanos , México/epidemiologia , Rubéola (Sarampo Alemão)/diagnóstico , Rubéola (Sarampo Alemão)/prevenção & controle , Testes SorológicosRESUMO
An analysis of the transmission dynamics of rubella in Mexico based upon notified cases during 1983-1990 is presented. It is observed, for the first time, that the force of infection in the age-group of 15-44 years old and the average age of the infection at the national level show a slight increase simultaneously. The theoretical estimates of the interepidemic period coincide with the observed ones. The annual proportion of susceptible individuals is practically constant during 1983-1990. The intrinsic reproductive rate of rubella at national level and for the different age-groups is assessed. The annual estimates of Ro are small and they are practically unchanged for all age-groups, excepting the group of 15-44 years. The herd immunity of rubella for the different age-groups is evaluated and it is concluded that the best strategy for preventing congenital rubella in Mexico is to continue with the no vaccination policy against rubella. Nonetheless, the continuous monitoring of this policy is necessary.
Assuntos
Rubéola (Sarampo Alemão)/epidemiologia , Adolescente , Adulto , Fatores Etários , Métodos Epidemiológicos , Feminino , Humanos , Recém-Nascido , Masculino , México/epidemiologia , Gravidez , Complicações Infecciosas na Gravidez/prevenção & controle , Rubéola (Sarampo Alemão)/congênito , Rubéola (Sarampo Alemão)/prevenção & controleRESUMO
In order to carry out this work, the following questions were made: how has the development of the coverage of Primary Health Care (PHC) for each entity of the Mexican Republic been? has it been homogeneous? If heterogeneous, which states show similar development? and, which are the indicators of PHC that account for these differences? A statistical multimodal analysis known as Cluster analysis, based upon the PHC indicators recommended by the World Health Organization (WHO) in 1985, was carried out in order to answer the questions above made. One of the main results of this work was to identify clearly that there are important inequities among the different federal agencies regarding coverage. These differences indicate that the coverage of PHC in México has been polarized.
Assuntos
Atenção à Saúde/organização & administração , Atenção Primária à Saúde/organização & administração , Regionalização da Saúde/organização & administração , Humanos , México , Organização Mundial da SaúdeRESUMO
In 1978 the World Health Organization proposed as a goal the following slogan: "Health for everyone in the 2000 year". Though, to obtain the covering first assistance indicators is crucial for the evaluation work and for the analysis of the health strategies. In 1981 the World Health Organization proposed 13 indicators, based on them, this work builds up three new indicators. These indicators allow to have a simple and reliable description of the covering that each one of the federal entities of the Mexican Republic keep. The 1985 WHO indicator, PROM, and our mixed indicator, Institutional Medical Assistance Request, are highly correlated. The Mixed indicators of Health Covering allow the making of global covering evaluations. Also allows the studding of all the covering relations and correlations reached with other indicators or variables.
PIP: This work describes and illustrates the use of 3 new indicators of primary health care coverage based on the 13 indicators proposed by the World Health Organization in 1981. The new compound indicators permit a simple and reliable description of the health coverage of each of Mexico's states and federal entities. The data correspond to the year 1985 and the compound indicators are those that depend lineally on 1 or more of the simple indicators proposed by Kumate and Barnard in their 1988 study of the 13 WHO indicators in Mexico. Principal components analysis was used to transform the original indicators that are correlated among themselves into a group of new indicators that are not correlated. 3 of the compound indicators that together explained 82.2% of the variation in the original 13 simple indicators were retained. The 1st compound indicator included prenatal care, attention at delivery, postpartum care of the infant, growth monitoring, medical consultations, and hospitalizations. It was termed the indicator of demand for institutional medical attention and explained 59.4% of the variation. The 2nd compound indicator, termed access to facilities for diagnosis and treatment of endemic diseases, included the 2 WHO indicators diagnosis and treatment of endemic diseases and facilities (a measure of the population with reasonable access to health facilities). This indicator explained 13.04% of the variation in the original indicators. The 3rd compound indicator included vaccinations with BCG and DPT, and medical care in terminal illness, potable water, and health facilities. It was termed the indicator of comparison between prevention by immunization and access to health and hygienic resources and explained 9.82% of the original variation. The indicator termed demand for institutional medical attention was very highly correlated with a compound indicator proposed by the WHO in 1985 that consisted of the arithmetic average of its 13 simple indicators. The high correlation demonstrates that primary health care coverage is adequately represented by either the WHO 1985 indicators or the indicator of demand for institutional medical attention. The simple indicators most important in describing health coverage are those included in the demand for institutional medical attention. The 3 compound indicators can be used to represent the different characteristics of the states graphically in 2 or 3 dimensions for purposes of comparison. They can also be used for overall comparisons of coverage between states.
Assuntos
Indicadores Básicos de Saúde , Atenção Primária à Saúde/estatística & dados numéricos , México , Análise Multivariada , Organização Mundial da SaúdeRESUMO
A review of the general aspects of the transmission dynamics of measles is presented. Similarities and differences in the patterns of transmission of measles in developed and developing countries are pointed out. Epidemiological, demographic and nutritional variables relevant to the design of an immunization program are briefly discussed. Since there is no cohort in developing countries in which most individuals are susceptible, it is concluded that there is no single optimum age at which to vaccinate against measles. Finally, a simple method based upon case notification records, for calculating the force and average age of infection as well as the optimum age for vaccination against measles is illustrated.
Assuntos
Países em Desenvolvimento , Vacina contra Sarampo/administração & dosagem , Sarampo/epidemiologia , Adolescente , Adulto , Fatores Etários , Anticorpos Antivirais/análise , Criança , Pré-Escolar , Feminino , Humanos , Lactente , Recém-Nascido , Masculino , Sarampo/imunologia , Vírus do Sarampo/imunologia , México , Estatística como AssuntoRESUMO
In this paper the inherent characteristics of the demographic and epidemiological transitions are described. The main differences of the transitions between Western Europe of the 18th and 19th centuries and of the Latin American countries of the 20th century are pointed out. The demographic transition in Mexico is briefly described and the attributes that make it sui generis are indicated. It is emphasized that there has been a slowing of the rate of decline in fertility in Mexico since 1980 and some factors likely associated with this phenomenon are propounded. The different schools of thought regarding the changes of infant mortality during the transition are succinctly reviewed. The hypothesis that reductions of the birth rates induce reductions of infant mortality rates is supported by general theoretical results of the population dynamics of infectious diseases and some empirical evidences.
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Epidemiologia/tendências , Crescimento Demográfico , Economia , Humanos , Lactente , Mortalidade Infantil/tendências , MéxicoRESUMO
A Primary Health Care (PHC) score is obtained by averaging thirteen indicators of PHC of each state of Mexico with data of 1985. Some correlations between the PHC score with other indicators of development, such as education and urbanism, are analyzed. The socioeconomic and educational status of women impinge directly in the processes of PHC. Based upon results of basic research some features of coverage and selectivity of PHC strategies are analyzed.
Assuntos
Países em Desenvolvimento , Atenção Primária à Saúde/tendências , Humanos , Imunização , México , Saúde Pública , Mulheres TrabalhadorasRESUMO
The history of human disease has to be based almost entirely on what we know about the changes in mortality and life expectancy; illness and suffering do not lend themselves to hard statistics, whereas births and deaths can be counted. To learn about the way diseases have been conquered in the past we have, therefore, to look at mortality. From this study we see that the major lethal diseases were conquered not so much by discovering how to treat them as by prevention. The decline on mortality began at the start of the past century, at a time of revolution and reform, and was greatly accelerated when the causes of many diseases were discovered at the end of the nineteenth century. Even in the twentieth century, the greatest improvements are still being achieved by preventive measurements.