The Epidemiology of Infectious Diseases

The Epidemiology of Infectious DiseasesInfectious diseases have evermore existed and have had a major impact on human development. It is widely believed that our immune systems and genetic organic law have evolved over many years under the selective pressure of potentially fatal diseases, such as malaria (Haldane 1948 Weatherall 1996).In addition, epizootics of infectious diseases have decimated entire communities, and have sometimes changed the course of history.ExamplesIn europium in the 14th Century, there were about 25 trillion oddments from bubonic plague out of a existence of approximately 100 million.In 1520 the Aztecs lost about half of their population of 3.5 million from smallpox, introduced by the more immune invading Spaniards. This has been proposed as an important feature in the defeat of the Aztecs by the Spanish invaders.In 1919, after the First adult male War, the global epidemics of influenza killed an estimated 20 million people during matchless year mo re than died as a entrust of the war.During the twentieth century, important advances in the measure and cook of many infectious diseases were achieved with the development of vaccines and antibiotic drugs. This has sometimes created the impression that infectious diseases ar no womb-to-tomb a major threat to humans wellness. However, this is far from being the case.The following is a quote from Dr Gro Harlem Brundtland, the Director-General of the World Health OrganizationIllness and death from infectious diseases dismiss be, in almost cases, avoided at an cheap cost. It is in everyones interest that these obstacles to development be removed. Because of drug resistance, increased travel and the emergence of modernistic diseases, we may only have a limited time in which to make rapid progress.In the following, you ordain see some of the reasons why infectious diseases are still an important challenge to public health at the beginning of the 21st century.MortalityInfectiou s diseases are a leading cause of global mortality, causing more than 13 million deaths a year.They are still the main cause of death among children under 5 and the main single cause of premature death in persons under the long time of 45.MorbidityInfectious diseases are also a major cause of global morbidity. They are responsible for(p) for a huge amount of disability and suffering in the world as measured in DALYs.DALYDisability Adjusted Life Years, a measure of disease burden.It includes years of life lost repayable to premature death, and years of healthy life lost due disability or nausea.Recurring episodes of illness and long-term disability have a major economic impact on the developing countries most affected by infectious diseases.Role in chronic diseaseInfectious diseases are more and more being implicated in the pathogenesis of many important diseases that were previously thought to have a non-infectious origin.cervical cancer is now know to be associated with human papillomavirus infection. Cervical cancer is the sixth most special K cancer worldwide and the most common cancer in women in many developing countries.In the past two decades, evidence has grown on the role of Helicobacter pylori infection in gastritis, duodenal ulcer, stomachic ulcer, gastric cancer and gastric-mucosa-associated lymphoid tissue (MALT) lymphoma.Chronic infection with hepatitis B or C can cause primary hepatocellular carcinoma (HCC). HCC is among the most common cancers in many parts of Africa and Asia.Potential for epidemic get aroundA specific feature of infectious diseases is their ability to be transmitted amidst individuals. This can result in the occurrence of large outbreaks.Between 1997-2000 there were more than 600 outbreaks of disease considered by the WHO to be of multinational importance.OutbreakThe term used to describe a localised epidemic, e.g. in a village, town or city.The term large outbreak is change magnitudely being used instead of epidemi c, as it is less emotive.With increase urbanisation and international travel, the world is becoming a smaller place, and the routes for transmission of infection are increasing. plane journeys enable individuals to travel in spite of appearance the incubation period of most infectious diseases.This allows infections to circulate to distant places in spite of appearance very short periods of time. An example of this is the annual global dispersal of meningococcal meningitis by pilgrims excreteing from the Haj Muslim religious festival (Saudi Arabia). lately emerging diseasesOver the past three decades, over 30 crude infectious diseases and pathogens have been identified for the first time in humans.These include diseases with a very exalted case-fatality appraise, such as new variant Creutzfeldt-Jacob disease (nvCJD) and Ebola hemorrhagic fever. Some of these new infections are passing prevalent, for example Hepatitis C and rotavirus. Other infections, such as human immunodef iciency virus, have rapidly spread around the world.New variant Creutzfeldt-Jacob disease (nvCJD)A new variant of Creutzfeldt-Jakob disease was described in the United acres in 1996. The agent is considered to be the same as that causing bovine spongiform encephalopathy, a disease that emerged in the 1980s and affected thousands of cattle in the United Kingdom and other, mainly European countries.EbolaThe first outbreaks of Ebola haemorrhagic fever occurred in 1976 and the discovery of the virus was reported in 1977. Cases reported to WHO up to June 1997 indicated a case-fatality rate of over 70%. A major outbreak in Uganda in 2000 was thought to be associated with spread of the virus by soldiers moving across the country.Hepatitis CThis virus was identified in 1989, and is now known to be the most common cause of post-transfusion hepatitis worldwide. So far, up to 3% of the world population are estimated to be infected, among whom 170 million are chronic carriers at risk of develo ping liver cirrhosis and/or liver cancer.RotavirusFirst recognised in 1973, rotavirus is the most common cause of childhood looseness of the bowels worldwide. 20% of all diarrhoeal deaths and 5% of all deaths in under-5 year olds are due to rotavirus.HIVAlthough the Acquired Immune Deficiency Syndrome (AIDS) was recognised in 1981, the causal virus, HIV, was first isolated in 1983. It is estimated that, since the start of the epidemic, 30.6 million people worldwide have become HIV-infected and nearly 12 million have died from AIDS or AIDS-related diseases.Re-emerging diseasesIn addition to the emergence of new infectious diseases, many old diseases that had previously been under tell are starting to appear in increased numbers or in previously unimpressed populations.Resurgence of infectious diseases can occur because of any of the following reasonschanges in social or environmental conditions,failure to maintain immunisation programmes,increased drug resistanceDrug resistance is currently an increasing problem for a number of diseases worldwide, and we are often in a race to develop new treatments faster than the pathogens can develop resistance.ExampleSince the mid-1980s there has been a major resurgence of diphtheria in several(prenominal) countries of Eastern Europe, which had previously been progressing towards elimination of the disease. In 1993, 15,211 diphtheria cases were reported in Russia and 2,987 cases in Ukraine. The main reason for the return of diphtheria in these countries was a decreased immunisation coverage due to an irregular supply of vaccines and large-scale population movements(Galazka et al 1995).ExampleMortality and morbidity rates from tuberculosis (TB) in industrialised countries dipd during most of the 20th century. However, from the mid-1980s onwards, many of these countries have seen an important increase in the incidence of TB. This is mainly due to a decline in TB control programmes, the increased incidence of multi-drug re sistance TB and the effect of the HIV epidemic (Grange 1998).Potential for prevention and controlThe mechanisms involved in many infectious diseases are well understood, from the molecular aspects of the infectious agent to the demographic characteristics of host populations. This level of understanding has enabled potentially very effective prevention and control measures to be developed for some infectious diseases.With efficient intervention strategies and the advent of national public health agencies, elimination of specific infectious diseases has become feasible. In some cases, there has even been the fortuity (or reality) of global eradication.Following the successful WHO programme for the global eradication of smallpox through vaccination, the last by nature acquired case of this disease occurred in October 1977 in Somalia.The countries of the Western Hemisphere have set a derriere for the elimination of measles by the end of the year 2005.Polio and guineaworm are now al so on the verge of eradication, after intensive, globally co-ordinated programmes. Strategies to immunise millions of children on the same day have resulted in few countries now reporting cases due to wild poliovirus.Infectious disease epidemiologyIn epidemiology, we are interested in describing and explaining the distribution of diseases in populations. The distribution of an infectious disease depends on the transmission of the infectious agent within the host population.This is a dynamic process, which is influenced by characteristics of the specific infectious agent, characteristics of the host population and characteristics of the relationship between the infectious agent and the host.