Epidemiological chain

Epidemiological chain. It is the sequence of elements that intervene in the transmission of an agent from an infection source to a susceptible host, that is, the steps that a causal agent follows, from its natural habitat ( reservoir ) to the susceptible host.

Summary

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• 1 Development of the disease
• 2 Components
  • 1 Agent
    • 1.1 Agent characteristics
  • 2 Source of infection
  • 3 Exit door
  • 4 Transmission mechanisms
  • 5 Gateway
  • 6 Guest
• 3 Importance
• 4 Bibliography

Development of the disease

For a disease to occur there must be a series of events or facts that facilitate said disease, these facts constitute the so-called ecological triad composed of the causal agent – environment – host.

Components

The epidemiological chain has a series of other links that constitute the path followed by the causal agent of a certain disease until reaching the susceptible host.

Agent

It is that element that must be present in a disease for it to develop. It can be biological, physical or chemical.

• Biological agent: bacteriaor their toxins, viruses , spirochetes , rickettsiae , animal parasites (protozoa and metazoa) and vegetables ( fungi and yeasts ), among others.
• Physical agent: anyone who can produce a pathological state, such as a gunshot wound, trauma from accidents, burns caused by the sun, etc.

Chemical agents: they produce a pathological state when coming into contact with them either by direct or indirect exposure such as insecticides, pesticides, acids, radioactive substances etc.

Agent characteristics

1. Intrinsic: size, shape, chemical composition, etc.
2. Behavior in the host: contagiousness, pathogenicity, virulence, invasiveness, antigenicity.
3. Behavior towards the environment: resistance, aptitude that it presents for its vehiculization, temperature, humidity, etc.

Infection source

The source of infection can be:

1. Reservoir: It is the natural den where the agent grows, develops and multiplies and on which it depends for its survival. I could be:

• Human reservoir.
• Animal reservoir.

2. Environment: It constitutes a source but not a reservoir because the agents cannot multiply in it.

Exit door

It is the mechanism that the causal agent uses to get out of the source of infection.

These might be:

• Respiratory system
• Digestive system
• Skin
• Placenta
• Genitourinary tract

Transmission mechanisms

It is the route, form or means that the agent uses to get from the exit door of the reservoir to the entrance door of the guest and it can be in two ways:

• Direct Transmission.

The infectious agent passes immediately, from the infected reservoir to the entrance door of the susceptible host. This occurs through kissing, sexual contact, sprayed by micro drops due to sneezing and coughing. Direct transmission also includes exposure of tissues susceptible to fungal agents, spores of bacteria or other parasites located in the ground or in vegetation.

• Indirect Transmission:

The infectious agent uses an intermediary to reach the host, it can be a vehicle, a vector or by air. Transmission by vehicle occurs by indirect contact through inanimate objects (fomites), such as bedding, toys, or surgical instruments, as well as contaminated food, water, poorly sterilized needles.

The agent can multiply or develop within or on the vehicle, before being introduced into the host.

In vector transmission, it can be in two ways:

1. Mechanics: the infectious agent is transported by an arthropod or rodent to a susceptible host mechanically by dirtying its legs or its proboscis, in which case the multiplication of the agent in the vector does not occur.
2. Biological: The agent needs to make an asexual life cycle within the vector to be infectious, that is, it multiplies in the arthropod before being transmitted. Example: Plasmodium for the Anopheles albimanusmosquito to transmit yellow fever.

Indirect transmission can be through the air. Two types of particles are involved in this type of dissemination: dust and droplet nuclei.

Dusts: they are particles of different sizes that result from the new suspension of particles that have been deposited on floors or bedding, as well as particles raised from the ground by the wind.

Droplet nuclei: They are very small particles that represent the dried residue of droplets. They can be formed in different ways. One is by evaporation of droplets that have been released into the air by coughing or sneezing.

Front door

It is the place where the agent is going to penetrate the host. They may be:

• Conjunctivae
• Respiratory system
• Digestive system
• Genitourinary tract
• Wounds, bites, etc.

Guest

The susceptible host is the healthy individual in whom communicable disease can develop .

It has the following characteristics:

• Age
• Race
• Nutritional condition
• Living and working conditions
• Susceptibility, resistance, immunity.

Importance

The importance of the epidemiological chain lies in that identifying the possible links in each disease can interrupt the transmission chain and prevent the development and spread of these diseases.