What is Epidemiology

Epidemiology is the science that studies the causes and effects of health and disease in a population used in public health to identify risks factors for diseases, and in preventive care to monitor exposure and symptoms and to control the diffusion.

Measures of control based on knowledge of how the virus is transmitted are utilized to limit the spread of the infection. It is important to find the source, or sources of the outbreak and to identify the virus to produce the right weapons to fight and control the transmission and diffusion.

The most used system is the vaccination, and the production of vaccines takes an exceptionally long time to go through the variety of steps of preparation and tests of safety, reliability, and validation; when vaccines are not available, sanitation and disinfection and other measures of control are necessary, in addition to antiviral therapies and immune support.

Infected people are isolated from the rest of the community, and those that have been exposed to the virus are placed in quarantine. Most viral infections of humans and other animals have incubation periods during which the infection causes no signs or symptoms. Incubation periods for viral diseases range from a few days to weeks, during these periods an infected individual or animal is contagious and can infect another person or animal. This too is known for many viral infections, and knowledge of the length of both periods is important in the control of outbreaks. When outbreaks cause an unusually high proportion of cases in a population, community, or region, they are called epidemics. If outbreaks spread worldwide, they are called pandemics.

Viral epidemiology is the branch of medical science that investigates the transmission and control of virus infections in humans. Transmission of viruses can be vertical, as from mother to child, or horizontal, as from person to person. Examples of vertical transmission include hepatitis B virus and HIV, where the baby is born already infected with the virus.

Horizontal transmission is the most common mechanism of spread of viruses in populations and can occur when body fluids are exchanged by saliva, or other secrets, or when contaminated food or water is ingested. It can also occur when aerosols containing viruses are inhaled or by insect vectors, such as when infected mosquitoes penetrate the skin of a host. Most types of viruses are restricted to just one or two of these mechanisms and they are referred to as “respiratory viruses” or “enteric viruses”. The rate or speed of transmission of viral infections depends on factors like the population density, the number of susceptible individuals, as immune-deficient or with chronic disease or any other risk factors, lifestyle, health management, environment, weather and more.

Epidemiologists collect and analyze statistical data to interpret for clinical research purposes and for the monitoring of diseases. The area of study includes the etiology of diseases which is the cause, the origin, the study among people, the transmission, outbreak investigation, surveillance, and more.

Epidemic and Endemic

Epidemic and endemic both analyze mainly the virulence, the modality of transmission and the probability of contaminations.

Endemics are diseases that manifest within a population and which are recurrent, like for example, the malaria in Africa due to the environmental conditions, the vector’s multiplication, the mosquitoes genus Anopheles, and physical condition of population, or HIV among a specific population like heterosexuals and toxic dependents and which originated from a virus present in chimpanzee’.

Epidemics are those that arise periodically and with catastrophic consequences, like influenzas, for example, or infectious diseases like those from staphylococcus, or metabolic diseases like obesity, for example.

Hippocrates, the father of the Medicine was the first scientist to see the relation between diseases and environmental influence, what today is the subject of investigation of the epigenetics, the study of the external causes on genes modification, lifestyle and factors that can influence and modify a genetic pattern and causing mutations of genes that can be turned on and off based on these factors.

The evolution of a species is the result of constant struggle between inherited traits and environmental challenge, and mutations are the adaptation of a trait to survive to the natural selection. Without genetic variation there is not evolution, and some mutations confer advantages to a population to survive adverse conditions while others instead can make more susceptible to a disease. (Peter D’Adamo, Blood Type Diet Encyclopedia)

A way to express the famous laws of Charles Darwin on natural selection, adaptation to the environment and evolution, the foundational principles of Biology.

Epidemiology, as the study of the disease among population along the centuries takes consideration of these important phenomena and reasons why some of these diseases have developed by time based on mutations of species derived from drastic changes of the environment.


The chronology of epidemiology begins with the discover of the microbiology.

Around the 16th century scientists started to realize that diseases were caused from alive agents, and that the diffusion and contagious could happen throughout the air, but they still did not know about bacteria and viruses.

A new science developed based on these new founding, the hygiene, as the study of methods and ways to prevent diseases, like disinfectant agents and sterilization techniques, and simple precautions to avoid contagious.

They finally started to figure out that the cause of infections were agents that could be transferred from an individual to another, or a population to another and thanks to the development of the first microscope by Anton Van Leeuwenhoek in 1675 the Germ Theory of disease was born.

Epidemies at those times were frequent and destructive, of course, the knowledge and the tools were still not those we have at present, not vaccines, not antibiotics, or antiviral, or even more norms of modern hygiene and habits of civic populations. The Smallpox, the Black Plague, the Cholera, the Tetanus, and so on, are all diseases almost disappeared thanks to vaccinations.

Louis Pasteur, scientist of the 1800 century, French, chemist, and microbiologist was the founder of the principle of vaccination, the microbial fermentation, and the pasteurization.

His discover was of vital importance at that time and did reduce the mortality of diseases quite common in those periods like, the anthrax, the rabies and puerperal fever. Pasteur is also famous for the discover of the “spontaneous generation” where he was demonstrating with a famous experiment with putrefied meat that nothing can come from nothing, and so that microorganisms could not develop without contamination.

With the new century and advancement of biomedical science, genetic and molecular biology, statistics and epigenetics, new tools of research and analysis and collection of data have changed the spectrum of the study of the epidemiology so as the introduction of variety of conventional and alternatives therapies in addition to the restrictive roles and tools of hygiene have decreased the necessity for vaccinations in many cases.

Epidemiology today is not simply the study of the spreading of diseases mainly as infections through populations in the course of the centuries but has been extended to the analysis of the present diseases, of the diseases of the modern society:  cancer, diabetes, obesity, cardiovascular, neurodegenerative, and genetic.

The factors analyzed in relation to race, gender, and age, are usually fundamental metabolic parameters, and habits, like smoking, alcohol or drugs use, environmental exposure, stressors, chemicals, toxins, etc.

Based on these statistics the most evident correlations are always mainly between lung cancer and smoking, high blood pressure and heart disease, or blood sugar and diabetes, but thanks mainly to the integrative medicine more associations are being evaluated and considered, and for the most connected to the health of the gut microbiome and individual immune resistance.

Epidemics and Pandemics

pandemic is a worldwide epidemic. The 1918 flu pandemic, which lasted until 1919, was a category 5 influenza pandemic caused by an unusually severe and deadly influenza A virus. The victims were often healthy young adults, in contrast to most influenza outbreaks, which predominantly affect, elderly, or otherwise weakened and already debilitated patients. Older estimates were showing that it killed 40–50 million people, while more recent research suggests that it may have killed as many as 100 million people, or 5% of the world’s population in 1918.

Although viral pandemics are rare events, during the 20th century there were four pandemics caused by influenza virus and those that occurred in 1918, 1957 and 1968 were severe.

Several highly lethal viral pathogens are members of the Filoviridae. Filoviruses are filament-like viruses that cause viral hemorrhagic fever and include Ebola virus. Ebola virus disease has also caused intermittent outbreaks with high mortality rates since 1976 when it was first identified. The worst and most recent one is the 2013–2016 West Africa Epidemic.

With the exception of smallpox, most pandemics are caused by newly evolved viruses, these emergent viruses are usually mutants of less harmful viruses that have circulated previously either in humans or other animals.

Severe acute respiratory syndrome, SARS, and Middle East Respiratory Syndrome, MERS, have been caused by new types of coronaviruses. Other coronaviruses are known to cause mild infections in humans, so the virulence and rapid spread of SARS infections—that by July 2003 had caused around 8,000 cases and 800 deaths—was unexpected and most countries were not prepared.

The present coronavirus, SARS Cov-2, originated in bats and responsible of the Covid-19 pandemic emerged in Wuhan, China in November 2019 and has spread rapidly around the world. Unprecedented restrictions in peacetime have been placed on international travel and imposed in several major cities worldwide with lockdown and isolation, public sanitation and regulations, and all reality has change for everyone in this world since then.

Because viruses use vital metabolic pathways within host cells to replicate, they are difficult to eliminate without using drugs that cause toxic effects to host cells in general. The most effective medical approaches to viral diseases are vaccinations to provide immunity to infection, and drugs that selectively interfere with viral replication, but today there are additional variety of alternative therapy suggested mainly to support the immune system, which is the most important tool to fight diseases, and natural compounds capable to contrast the virus multiplication or even the entrance in the host’s cells.

Thanks For Reading.

Mariarosaria M.


Epidemiology, Wikipedia

Picture by: Georgia Coastal Health District

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