Epidemic is an outbreak of a disease that spreads rapidly and affects a large number of humans within a certain region. Plague is an infectious disease from the group of zooanthroponoses, which has been responsible for epidemics and pandemics throughout human history. 

What is Epidemic?

Epidemic is an outbreak of a disease, that  spreads rapidly, with new cases significantly exceeding the usual and expected numbers.

The epidemic refers to a more or less local spread, if the rapid spread of disease goes beyond the borders of a continent, it is considered a pandemic.

The most common cause of the epidemic is an infectious agent, causing an infectious disease such as flu, coronavirus, plague, typhoid, cholera, diphtheria, etc.

The epidemic process is characterized by the continuous transmission of the pathogen between people. Three main factors are needed for its occurrence – a source of the infectious process, transmission mechanisms, and people susceptible to the disease.

Depending on the outbreak the epidemic can be: 

• Common source outbreak epidemic – the disease is transmitted from the same agent;
• Propagated outbreak epidemic – the disease is transmitted from one person to another;
• Mixed outbreak epidemic – secondary spread from one person to another after exposure to a common agent.

Infections whose source are only humans are called anthroponoses; when the source of infection in humans and animals, they are called zoonoses (anthropozoonoses or zooanthroponoses).

Depending on the nature of the disease, the main routes of infection are:

• Food or water – dysentery, typhus;
• Airborne – flu;
• Transmissible – malaria, typhus;
• Contact – AIDS, rabies.

In many cases, one disease can be transmitted via several routes. The course of the disease depends on the way of penetration.

The process of development of epidemics is influenced by the processes occurring in natural conditions (e.g. epizootics), and social factors (e.g. public utilities, living conditions, health status).

What is Plague?

Plague is a particularly dangerous infectious disease from the group of zooanthroponoses.

It is characterized by pronounced intoxication and has five main forms depending on the route of penetration of the infection:

• Bubonic form;
• Skin form;
• Pulmonary form;
• Intestinal form;
• Septic form.

The causative agent of the plague is the gram-negative bacterium Yersinia pestis. It is immobile, does not form spores, forms a capsule and releases endotoxins and exotoxins. A natural reservoir of Yersinia pestis are a number of rodents, and a specific vector are some species of fleas. Humans can be infected by inhalation, direct contact with infected materials or a bite of an infected flea. 

Plague has been responsible for widespread epidemics throughout history, but nowadays it is easily treated with antibiotics. If left untreated plague can be a very severe disease with a fatality ratio between 30% and 100%. 

Upon entering the human body, plague bacteria reach the regional lymph nodes, where they cause hemorrhagic inflammation with the formation of a bubo. From the primary bubo, the bacteria reach the other lymph nodes, blood, various organs and systems. An important feature is the involvement of the central nervous system in all clinical forms. Plague should be suspected in any febrile patient who has lived in an endemic area and has epidemic evidence of possible infection. The incubation period of the plague is from 1 to 8 days. 

Usually, the clinical picture begins suddenly and acutely with fever, chills, lethargy. Other symptoms include a characteristic face – facies pestica, perioral cyanosis, bleeding from the mouth, nose, rectum, or under the skin, gangrene in the extremities.

Thorough clinical and epidemiological data are required to diagnose the plague. It is necessary to isolate the plague bacteria from the bubo, sputum or blood. Differential diagnosis should be made with tularemia, tuberculosis, sepsis, anthrax, typhoid fever, and others.

Treatment is carried out with etiological and symptomatic means. Antibiotic groups of choice are aminoglycosides, fluoroquinolones, and tetracyclines.

Plague has been responsible for epidemics and pandemics throughout human history, with the best known being the Black Death which resulted 50 million dead in the 14th century. 

Difference Between Epidemic and Plague

Definition

Epidemic: Epidemic is an outbreak of a disease that spreads rapidly, with new cases significantly exceeding the usual and expected numbers.

Plague: Plague is a particularly dangerous infectious disease from the group of zooanthroponoses, responsible for epidemics and pandemics throughout human history.

Types 

Epidemic: Depending on the outbreak the epidemic can be a common source outbreak epidemic,  propagated outbreak epidemic, or mixed outbreak epidemic.

Plague: Depending on the route of penetration of the infection the plague can be bubonic form, skin form, pulmonary form, intestinal form, or septic form.

Routes of infection 

Epidemic: Depending on the nature of the disease, the main routes of infection are food, water, airborne, transmissible, contact. 

Plague: Humans can be infected by inhalation, direct contact with infected materials or a bite of an infected flea. 

Causative agent

Epidemic: The most common cause of the epidemic is an infectious agent (virus, bacteria, protozoan), causing an infectious disease such as flu, coronavirus, plague, typhoid, cholera, diphtheria, etc.

Plague: The causative agent of the plague is the gram-negative bacterium Yersinia pestis.

Severity

Epidemic: The severity of the epidemics depends on the particular disease, natural conditions, and social factors. 

Plague: If left untreated plague can be a very severe disease with a fatality ratio between 30% and 100%. 

Comparison Chart on Epidemic and Plague

Summary: 

• Epidemic is an outbreak of a disease that spreads rapidly, with new cases significantly exceeding the usual and expected numbers.
• Plague is a particularly dangerous infectious disease from the group of zooanthroponoses, responsible for epidemics and pandemics throughout human history.
• Depending on the outbreak the epidemic can be a common source outbreak epidemic,  propagated outbreak epidemic, or mixed outbreak epidemic. Depending on the route of penetration of the infection the plague can be bubonic form, skin form, pulmonary form, intestinal form, or septic form.
• Depending on the nature of the disease, the main routes of infection are food, water, airborne, transmissible, contact. Humans can be infected by inhalation, direct contact with infected materials or a bite of an infected flea. 
• The most common cause of the epidemic is an infectious agent (virus, bacteria, protozoan), causing an infectious disease such as flu, coronavirus, plague, typhoid, cholera, diphtheria, etc. The causative agent of the plague is the gram-negative bacterium Yersinia pestis.
• The severity of the epidemics depends on the particular disease, natural conditions, and social factors. If left untreated plague can be a very severe disease with a fatality ratio between 30% and 100%. 

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