Infection Ecology & Epidemiology

In this infection ecology & epidemiology post we have briefly explained about infection, epidemiology of infection, transmission, infection etiology, diagnosis

Infection Ecology & Epidemiology


Infection is defined as the invasion and multiplication of pathogenic organisms in the host. An infection without symptoms is represented as subclinical; and with symptoms it is represented as clinically apparent. Illness caused through pathogenic organisms is termed as infectious disease or communicable disease or transmissible disease.

Infectious Disease Epidemiology

Epidemiology of infection is the branch of medical science that deals with the geographical distribution and timing of infectious disease occurrences. The study also includes the modes of transmission and maintenance in nature, with the goal of recognizing and controlling outbreaks.

The spectrum of occurrence or prevalence of disease in a defined population includes sporadic, endemic, epidemic and pandemic.


Sporadic refers to a disease that occurs infrequently and irregularly without a geographic focus. Examples of sporadic diseases include tetanus, rabies, and plague.


Endemic disease is an infectious disease which is restricted to a population in a given geographical region only and the constant rate of presence for years.


Epidemic refers to an increase in the number of cases of a disease in a particular geographical region within a short span of time when compared to the previous year infection rate. Influenza (common cold) is a good example of a common epidemic disease.


Pandemic refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people i.e. a wide geographical region. AIDS is an example for pandemic since it is present in many countries.

Transmission of Infection

Transmission of an agent causing an infectious disease can be direct or indirect. The transfer of an infectious agent directly into the body is known as direct transmission. There are four types of direct contact transmission.

1. Physical contact between hosts (Influenza, Skin infections).

2. Direct contact with body fluids or tissues of an infected individual (HIV, HPV).

3. Droplet contact in which large infectious particles sprayed into the air from the respiratory tract of an infected individual (pneumonia, mumps, measles).

4. Droplet nuclei contact in which small infective dried droplet particles that are suspended in the air are taken in by a host, and are capable of traveling to the lung (TB, chickenpox).

Indirect transmission is the transfer of a pathogen by a vector or vehicle. Malaria is an example of a vector borne disease. Examples of diseases spread through vehicle-borne transmission are food-borne diseases and waterborne diseases eg: Cholera. Zoonosis occurs when diseases are transferred from animals to people. Zoonotic diseases include anthrax from sheep and plague from rodents.

Infection Etiology

Etiology is the study of cause or origin of disease. The etiologic agent or causative agent is responsible for the cause of a disease. A pathogen or infectious agent is a biological agent that causes disease or illness to its host organism. Pathogenic organisms are of five major types; bacteria, virus, fungi, worms, and protozoa.

Infection Diagnosis

Laboratory tests may identify organisms directly (e.g., visually, using a microscope, growing the organism in culture) or indirectly (e.g., identifying antibodies to the organism).

They use a sample of blood, urine sputum, stool, throat swab or other fluid or tissue from the infected individual.

This sample may be stained and examined under a microscope, cultured, tested for antibodies, tested for a microorganism’s antigens or tested for genetic material (such as DNA or RNA) from the microorganism.


Infection Ecology & Epidemiology of Infection

Treatment and Prevention

Antibiotics, anti-virals, anti-fungals, and anti-parasitic agents along with quorum quenching methods are being used to treat infectious diseases depending upon the nature of infection. Many infectious diseases can be prevented by personal hygiene and vaccines.

Bacterial Infection

Bacterial infections include any type of illness caused by bacteria. Based on the structure and shape, there are three major groups of bacteria namely, Bacillus (cylindrical forms), Coccus (spherical forms) and Spiral.

Humans and animals have abundant normal flora (microbes) that usually do not produce disease under normal healthy condition. These bacteria are referred to as good bacteria or healthy bacteria or normal flora. Harmful bacteria that cause bacterial infections and disease are called pathogenic bacteria.

Bacterial diseases occur when pathogenic bacteria enter into the body and begin to reproduce and to grow in tissues that are normally sterile. Harmful bacteria may also emit toxins that can damage the body.

Viral Infections

Viruses are acellular obligate intracellular parasites. They contain only one type of nucleic acid, it may be either single or double stranded DNA or RNA.

Viral diseases range from minor ailments such as the common cold to severe diseases such as Rabies and Acquired Immune Deficiency Syndrome (AIDS).

They may be sporadic like Mumps, endemic like Infectious hepatitis, epidemic like Dengue fever or pandemic like Influenza.

Viral Infections

Fungal Infections

Fungi are eukaryotic protista, recognized as causative agents of human disease earlier than bacteria. Fungal infections (mycosis) are most common among those patients who use antibiotics for prolonged period of time.

These antibiotics not only kill pathogenic bacteria but also target the normal flora of human body (useful bacteria) and give rise to fungal growth.

Human fungal infections are usually of two types: superficial and deep infection. Fungi causing superficial mycoses are specialized saprophytes, with the capacity to digest keratin.

Superficial mycoses are of two types – surface infections (only on dead layers of skin) and cutaneous infections (cornified layer).

Further Readings


  1. of infection
  5. of infection