Understanding Infectious Diseases: Epidemiology and Drug Resistance
Understanding Infectious Diseases and Public Health
1. Differentiating Epidemic, Endemic, and Pandemic
An epidemic is an outbreak of an infectious disease that spreads quickly, infecting a large number of people within a specific region or population.
If the disease remains consistently present within a determined geographic area or population at predictable rates, it is called endemic.
If the disease infects many countries or continents at the same time, spreading globally, it is called a pandemic.
2. Factors Responsible for Increased Human Infectious Diseases
Several factors contribute to the increased incidence of human infectious diseases:
- Invasion and destruction of forests: If infectious agents reside in a specific habitat and that habitat is destroyed, they are forced to seek new hosts and environments, often bringing them into contact with humans.
- Large urban concentrations: The higher the population density in an area, the faster and wider a disease can spread among individuals.
- High geographical mobility of people: When an infected person travels to a new geographical area, they can introduce the pathogen, leading to local transmission and outbreaks.
- Mutations in some microorganisms: Mutations allow microorganisms to evolve, potentially making them more virulent or enabling them to become resistant to existing treatments, such as antibiotics.
- Construction of dams: This often leads to the destruction or alteration of habitats, which can change local ecosystems and increase human exposure to disease vectors or reservoirs.
- Lack of personal and food hygiene: Poor personal hygiene can attract germs, and consuming contaminated or spoiled food can introduce infectious agents into the body.
3. Characterizing Infectious Agents
Infectious agents are parasites that invade the body of a living being (host) and reproduce inside or on it, causing tissue damage. They include:
- Viruses: They are obligate intracellular parasites. They are the smallest infectious agents and are difficult to eliminate without destroying the cells in which they reside. An example of a disease caused by a virus is the flu (influenza).
- Bacteria: They are prokaryotic organisms and can often reproduce without invading other cells. An example of a disease caused by bacteria is tuberculosis.
- Protozoa and Fungi:
- Protozoa are unicellular and eukaryotic. Sleeping sickness is a disease caused by a protozoan.
- Fungi can be multicellular or unicellular. Athlete’s foot is caused by a fungus.
4. Robert Koch’s Ability to Prove Flu Causation
No, Robert Koch could not have proven that the flu is an infectious disease using the technology available during his time. The flu is caused by a virus, and viruses are too small to be seen with the optical microscopes available then. The electronic microscope, necessary to visualize viruses, did not exist during his lifetime.
5. Key Concepts Related to Infections
- Source of Infection
- A living being or object infected by a pathogenic germ from which the infection originates.
- Contagion
- The transmission of germs from a source of infection to a healthy organism, typically through direct or indirect contact.
- Vector
- An animal (often an arthropod like a mosquito or tick) that transports and transmits germs between hosts.
- Reservoir
- Animals or environments that harbor infectious agents and serve as a source of infection for human beings.
6. Understanding Immunity and How It Is Acquired
When a person is said to be immune to an infectious disease, it means their immune system has developed the capacity to recognize and defeat the disease-causing pathogen quickly and effectively, often preventing symptoms entirely.
A person can obtain this immunity in several ways, primarily by:
- Overcoming the disease naturally: After the initial infection, the immune system develops memory cells that “remember” how to eliminate the pathogen upon subsequent exposure.
- Vaccination: Introducing a weakened or inactive form of the pathogen (or parts of it) stimulates the immune system to build protective memory without causing the actual disease.
7. Distinguishing Vaccines, Antibiotics, and Antivirals
- Vaccines
- Biological preparations that introduce a whole pathogen (attenuated or inactivated) or parts of it into the body. They are not intended to cause infection but to stimulate the immune system’s reaction, providing long-term protection.
- Antibiotics
- Chemical substances used to kill bacteria or prevent their growth and reproduction. They are ineffective against viruses.
- Antivirals
- Drugs specifically designed to inhibit the replication of viruses. They work by preventing viruses from infecting cells or by preventing newly replicated viruses from being released to infect other cells.
8. Why Unnecessary Antibiotic Use Drives Resistance
Using antibiotics when they are not necessary (e.g., for viral infections) or failing to complete a prescribed course favors the emergence of resistance. When antibiotics are used, they kill susceptible bacteria. However, if a few bacteria possess natural resistance mechanisms, they survive the treatment. These resistant bacteria are the only ones left to reproduce, leading to a population where all bacteria will be immune to that specific antibiotic, making future treatments ineffective.
9. Flu Vaccine Necessity and Pandemic Risk
Why the Flu Vaccine Must Be Taken Annually
Influenza viruses are constantly mutating (antigenic drift). Because the surface proteins of the virus change every year, the immunity acquired from a previous infection or vaccination may not protect against the new circulating strains. Therefore, the vaccine must be reformulated and administered annually.
Why Flu Becomes a Pandemic with High Mortality
Flu sometimes becomes a pandemic with high mortality due to antigenic shift. This occurs when human flu viruses exchange genes with other animal flu viruses (like avian or swine strains). This genetic reassortment creates an entirely new subtype of the virus against which the human population has little or no pre-existing immunity, allowing it to spread rapidly and cause severe disease globally.
10. Original (Patent) Drugs Versus Generic Drugs
The primary difference between patent drugs (original drugs) and generic drugs is distribution rights and cost. Generic drugs are chemically identical to the original drug but are distributed by any pharmaceutical company after the patent expires, whereas patent drugs are exclusively distributed by the company that discovered and developed them.
Justification for Patents
Pharmaceutical companies justify the continuance of patents by arguing that they need to recoup the massive investment required for research, development, and clinical trials of the new drug. They seek exclusive earnings during the patent period to fund future innovation.
Beneficiaries of Generic Drugs
The production and importation of generic drugs primarily benefit developing or low-income countries and healthcare systems globally, as generic versions are significantly cheaper, making essential medicines more accessible to larger populations.