Communicable Disease

Epidemic, endemic, and pandemic diseases

Endemic

Endemic: The amount of a particular disease that is usually present in a community. 

Endemic diseases include malaria, bilharzia, measles, gonorrhea, and syphilis. 

Malaria is an endemic disease prevalent in Africa, Asia, Latin America, and the Middle East. It is transmitted by a parasite. They destroy the red blood cells in the spleen and liver. This causes anemia in the patients and can prove fatal if left untreated. According to recent research, 200 to 500 million people suffer from malaria every year out of which 1.5 to 2.7 million do not survive.

Measels is a very infectious viral disease that is often caught by young children. It is transmitted through the air in tiny droplets after an infected person sneezes. It causes a fever and skin rash. Many children are given vaccines against measles. Infection can cause more serious effects like infertility in adults who did not catch the disease as children.

An outbreak of measles can form an epidemic. 

Syphilis is a sexually transmitted disease. Sores develop on genitals of men and women.  Syphilis spreads through contact with these sores. After the initial infection, the bacteria can remain inactive in the body for decades before becoming active again.

Gonorrhea is a sexually transmitted disease. Signs and symptoms in men include painful urination, pus-like discharge from the penis, and pain or swelling in one testicle. The signs and symptoms in women include increased vaginal discharge, painful urination, vaginal bleeding after intercourse, and abdominal or pelvic pain. 

The spread of both diseases is easily preventable by following safe sex measures including wearing a condom.

Epidemics

Epidemic: An increase — often sudden — in the number of cases of a disease above what is normally expected in that population in a specific area.

TB infection occurs more often in people with HIV/AIDS and in those who smoke. TB is one of the top causes of death in people who have HIV. Furthermore, people who have HIV are 18 times more likely to develop active TB.

In 2018, tuberculosis was the leading cause of death worldwide from a single infectious agent.

Plague There are three types of plague. Bubonic plague is the most common and is caused by being bitten by a flea. The disease starts with fever, chills, head, and body aches as well as weakness, vomiting, and nausea.  Without treatment, plague results in the death of 30% to 90% of those infected. 

There have been three pandemics caused by the plague claiming the lives of millions of people.

In the 1347, Europe experienced the deadliest disease outbreak in history when the second pandemic of bubonic plague killed one-third of the European human population.

Cholera is an extremely virulent disease that can cause severe acute watery diarrhoea. It takes between 12 hours and 5 days for a person to show symptoms after ingesting contaminated food or water. Cholera affects both children and adults and can kill within hours if untreated.

During the 19th century, cholera spread across the world from the Ganges delta in India.  It then became a pandemic as it spread to all other continents killing millions of people. Cholera is now endemic in many countries.

Pandemics

Pandemic: An epidemic that has spread over several countries or continents and affects many people.

Influenza Commonly known as "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin from one to four days after exposure to the virus. 

The 1918 flu pandemic was a deadly global influenza pandemic caused by the H1N1 influenza A virus. The earliest documented case was March 1918 in Kansas, United States. By 1920, an estimated 500 million people across the globe had been infected in four waves. Estimates of deaths range from 17 million to 50 million, making it one of the deadliest pandemics in history.

Covid-19 The COVID-19 pandemic, also known as the coronavirus pandemic, was a global pandemic of coronavirus disease 2019 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus was first identified in an outbreak in the Chinese city of Wuhan in December 2019. Attempts to contain it there failed, allowing the virus to spread to other areas of Asia and later worldwide. 

COVID-19 symptoms range from undetectable to deadly, but most commonly include fever, dry cough, and fatigue. Severe illness is more likely in elderly patients and those with certain underlying medical conditions. COVID-19 transmits when people breathe in air contaminated by droplets and small airborne particles containing the virus. The risk of breathing these in is highest when people are in close proximity, but they can be inhaled over longer distances, particularly indoors. Transmission can also occur if contaminated fluids reach the eyes, nose, or mouth, or, more rarely, through contaminated surfaces. 

Infected individuals are typically contagious for 10 days and can spread the virus even if they do not develop symptoms. 

Mutations have produced many strains (variants) with varying degrees of infectivity and virulence.

The World Health Organization (WHO) began referring to it as a pandemic on 11 March 2020. As of 7 May 2023, the pandemic had caused 765,222,168 cases and over seven million confirmed deaths, making it one of the deadliest in history.

Confirmed deaths per 100,000 population as of 18 January 2023 are shown on the map below:

Image: Dan Polansky. CC By SA 4.0

The WHO declared the pandemic over on the 6th of May 2023 declaring that Covid-19 no longer represents a "global health emergency".  Officials said the virus's death rate had dropped from a peak of more than 100,000 people per week in January 2021 to just over 3,500 on 24 April 2023.

Scientists believe that Covid-19 will eventually become endemic. 

Credit: Scientificus. History of Coronavirus in 90 Seconds | First 500 million Case

Other pandemics are listed in the table below: