Last Updated on April 10, 2020 by Sagar Aryal

The occurrence of COVID-19 has resurrected terminologies that are rarely used practically. The theoretical understanding of epidemiological terms i.e Epidemic, Endemic, and the pandemic have been in a class of Biology or Microbiology where you are taught what these terms represent when it comes to a disease spread. However, lately, the globe has been made to understand and differentiate what an epidemic and pandemic means, through COVID-19.

Definitions

An endemic references to disease occurrence within a population and it remains consistently within the population for a period of time without spreading to a large group of people. Its level is normally at zero, but at an observable level. It can remain constantly if there are no interventions made to curb it. For example, polio disease can remain redundant within a population for a long period of time if there are no vaccine interventions.

An epidemic defines the occurrences of a disease in a larger population as compared to an endemic, and these diseases have the ability to spread to a larger population if not contained. For example, Influenza Virus commonly occurs within the Asian continent, but in recent years it has spread to most parts of the world. If it spreads and affects other continents, hence becoming a global infection, then it is termed as a pandemic.

This note will give a detailed understanding of the epidemic and pandemic terminologies with cited examples from recent occurrences which a conclusion on their differences as well.

What is an epidemic?

This is the rapid spread of a disease in a large population of a community or a specific region, within a short period of time. It is normally restricted within a particular region (one location), whoever, when it spreads to other countries and continents, then it can be termed as a pandemic.

For example, COVID-19 started in Wuhan City, China and for a period of one month, the disease was restricted within China before it started to spread to other countries, within the Asian continent and then to the US. Then it was termed as an epidemic because it was localized within a specific region. But after the WHO observed the sporadic spread of the disease, from a global perspective, they classified it to be a pandemic type of disease.

Epidermic occurrences are caused by a number of factors, such as ecological changes within a population, genetic diversity of a causative agent within a community, emergence on a novel pathogen within a locality, community consumption of contaminated food materials such as water, foods, etc, seasonal infections like measles, whooping-cough, etc, natural disaster infections such as flood-related infections, among other causes.

Also, depending on the pattern of spread, epidemics can also be classified into:

Common-source – is one in which a group of persons are all exposed to an infectious agent or a toxin from the same source, for example, Point, Continuous, Intermittent. Propagate epidemics – A propagated epidemic is most often of infectious origin and results from person-to-person transmission of an infectious agent (e.g., epidemics of hepatitis A and polio). Mixed epidemics – these epidemics have features of both common-source epidemics and propagated epidemics.

Examples of Epidemic in the 20th and 21st Century

1. London flu (1972-1973)

This was influenza A viral flu infection that was first detected in Inia, in 1971 and later identified in Britain in early 1972. In December 1972, several cases were reported to have occurred in the US found in several states including Memphis, Kansas City, Baltimore, Anchorage, California, and Seattle, with the most hit state being California. It was later described to be a Variant of the Hong-Kong flu by the CDC, which had affected over 18 states within the US and had caused 1027 deaths as reported by the National Center for Disease control. Other outbreaks were reported by the World Health Organisation (WHO) to have occurred in the Soviet Union, Netherlands, Morocco, Switzerland, and Lebanon. The symptoms that were associated with the infection were flu-like symptoms with severe pneumonia in some patients. The laboratory identification of the viruses was done in the Rhesus Monkey Kidney cells. The infection affected all age groups, however the most affected were children aged 0-4 years, followed by 5-14 years and teenagers and adolescents as well. Generally, school-going children were most affected. A small number of adults and the elderly above 65 years were affected. The viral infection declined in early 1973, however cases of influenza B also started to arise with alternating occurrences for subsequent years for both viruses, majorly affecting 5-14-year-olds, especially during the winter seasons, December-April months.



2. 1998-1999 Malaysian Nipah Virus outbreak

This was a viral infection that was caused by a paramyxoviridiae (Henipavirus) known as the Nipah virus from September 1998 to May 1999 in the states of Perak, Negeri, Sembilan, and Selangor in Malaysia and in Singapore. The country’s public Health Authorities reported 265 cases of acute encephalitis and 105 deaths that were caused by the virus, throughout the outbreak. With its virulence similar to that of Ebola Viral Disease, this virus caused infection of the brain system and not the blood vessels. The virus is transmitted from pigs/swine and humans. It was listed as a new-emerging disease, causing several human and livestock deaths, including swine. The virus was also identified in India and Bangladesh. The virus name was drawn form Nipah River, where the virus was traced from. The infection was associated with febrile encephalitis and respiratory illness, which occurred in workers of swine farms and shades. Autopsies revealed disseminated cerebral microinfarctions resulting from vasculitis-induced thrombosis and direct neuronal involvement. It targeted the medium-sized and small blood vessels resulting in endothelial multinucleated syncytia and fibrinoid necrosis. There have been cases of febrile encephalitis reported in Malaysia but none in Singapore since the government banned swine farming. The was no human-to-human transmission reported or ever been reported.



3. Mweka Ebola epidemic (2007)

This was an outbreak of Ebola Viral Disease or Ebola Hemorrhagic Fever, in Mweka Territories (Kananga, Kasai Occidental)in the Democratic Republic of Congo, (DRC), on September 11th, 2007. The outbreak response was slow, because of the poor infrastructures and roads in the country. The testing of patient samples was done in Gabon and Center for Disease Atlanta. About 160 deaths had been confirmed by the time these tests were being done. The fatality rate of the Mweka Ebola epidemic was averaging at 71% according to the WHO. The Ebola virus is a highly contagious virus that is known to cause very high fatality rates, ranging from 50% to 90%. Initial symptoms include fever, headache, joint and muscle aches, sore throat, and weakness, followed by diarrhea, vomiting, and stomach pain, according to the US Centers for Disease Control and Prevention (CDC). Hallmarks of Ebola infection include internal and external bleeding, and there is no vaccine or specific treatment for the disease. The virus was found to have reached the Western part of Uganda in late 2007, and named the subtype as Bundibugyo with a lower fatality rate of 36% as compared to that of DRC. Since this epidemic, several isolation facilities have been built and training for medical providers and health workers offered on responses to the emergence of new outbreaks. However, the virus has occurred in the DRC and spread to other countries, like in the case of Dec 2013- Jan 2016 where the virus was identified in several countries including Italy, UK, Spain, West African countries like Senegal, Mali, Nigeria, Guinea, Liberia. To date, there is no vaccine or treatment for the virus.



What is a pandemic?

This is when an epidemic turn pandemic, to mean, the disease or infection spreads to a larger population, affecting a whole continent, or several continents or even the globe, for example, the on-going COVID-19 disease. Normally, the disease of this kind must be infectious and associated with human-human transmission, but diseases like cancer, which have a global effect are not considered pandemics because they are not infectious and have a rare human-human type of transmission.

Pandemics have very high mortality rates, a negative impact on the global socio-economic factors and global hardships.

Pandemics are rare but they are not uncommon. They occur due to the emergence of novel pathogens that have high infectivity rates, highly infectious and associated with strong virulence factors. The adverse effects of pandemics and their causes are well described here. Preventive and control measures are the major ways of curbing these kinds of infections.

Examples of Pandemic in the 20th and 21st Century

1. HIV/AIDS Global pandemic

This an ongoing global pandemic. The virus is known as the Human Immuno-Deficiency Virus (HIV), causing Acute Immunodeficiency Syndrome (AIDS). Currently, there are 37.2 million people living with the HIV virus (36.2 million were adults and 1.7 million were children (<15 years old)) of 2018, and it is the worst global Public Health problem. The virus had approximately 1.6 million cases per year as of 2018, and caused over 700,ooo million deaths a year. HIV is transmitted sexually with an infected person, mother-child transmission from an infected mother, blood transfusion of infected blood. Approximately 79% of people with HIV globally knew their HIV status in 2018. The remaining 21% (about 8.1 million people) still need access to HIV testing services. HIV testing is an essential gateway to HIV prevention, treatment, care, and support services. In 2018, 23.3 million people with HIV (62%) were accessing antiretroviral therapy (ART) globally, an increase of 1.6 million since 2017 and up from 8 million in 2010. HIV treatment access is key to the global effort to end AIDS as a public health threat. People with HIV who are aware of their status, take ART daily as prescribed, and get and keep an undetectable viral load can live long, healthy lives and have effectively no risk of sexually transmitting HIV to their HIV-negative partners.



2. 2009 Swine flu pandemic

This was an influenza pandemic that lasted from January 2009- August 2010, the second largest after the 1918-1920 Spanish flu pandemic. It was caused by the H1N1 influenza virus, a new strain that was officially designated as A(H1N1)pdm09 strain or novel influenza A (H1N1) or 2009 H1N1 virus . It resulted from an assorted bird species, swine, and human flu viruses which combined into a Eurasian pig flu virus causing the swine flu. The name was acquired from the fact that it infected pigs and transmitted to humans. An estimated 11-21% of the global population contracted the disease. This was about 700 million01.4 billion people, a number larger than that of the Spanish flu. The flu affected majorly children below the age of 16 years (35%) and elderly above 65 years (5%), however, the numbers of the elderly who were affected were much smaller than those of children and even in comparison to the Spanish flu. This was quite unique for this form of infection. The transmission was from person to person contact and inhalation of infected droplets from infected persons, through sneezing and coughing. The risk factors of this virus were that it affected individuals that had underlying diseases such as asthma, and those who Obstructive Congestive Pulmonary disorders (OCPD), young children, the elderly, and pregnant women. The symptoms of the virus included fever, typical dry cough, headaches, muscle, and joint pain, sore throat, fatigue, chills, running nose. Some cases of diarrhea, vomiting, and neurological problems were also reported. Some Patients with acute illnesses developed flu symptoms progressed to pneumonia (viral pneumonia or secondary bacteria pneumonia) or acute respiratory distress syndrome with difficulty in breathing. This occurred at least 6 days after the onset of flu symptoms. The diagnosis was by collecting nasopharyngeal or nasal or oropharyngeal swabs and testing by Real-Time RT-PCR which had the ability to differentiate H1N1 from seasonal flu. Direct and Indirect Immunofluorescence Assays were also done including viral isolation. A rapid Infuelnza Diagnostic Test was developed but it was found to produce false-negative results. A specific Real-Time RT-PCR test was developed for H1N1/09 and named, CDC Influenza 2009A (H1N1) pdm Real-Time RT-PCR Panel (IVD) The patients were given pain medication to relieve pain such as ibuprofen and acetaminophen, and for critical cases with severe infection, administration of antiviral drugs i.e oseltamivir and zanamivir was recommended. However, a large percentage of patients developed resistance to Oseltamivir leaving zanamivir as the drug of choice. The public was advised to do personal or self-assessment and follow isolation and quarantine restrictions if you had developed flu symptoms. Travel restrictions were also put in place especially travels to China and areas that were most at risk. Institutions such as schools and universities were closed since the virus seemed to affect persons from 6 months to those aged 24 years. The use of masks was also advised for only the persons who had flu symptoms and those who were caregiving the infected patients, along with health care providers and medical practitioners. Some countries banned animal husbandry and importation of pigs such as Indonesia and Azerbajaijan and slaughtering of pigs at the time, like Egypt and Indonesia. A decline in the number of cases was steeping off by May 2010, with its occurrences having moved to the post-pandemic phase, according to the WHO. The pandemic came to an end on August 0f 2010 and reported by the then Director of the WHO, Margaret Chan on the 10th August 2010.



Comparison between Epidemic and Pandemic

Characteristic Epidemic Pandemic CAUSES Ecological changes within a population such as an increase in vector-transmission density.

Genetic changes in pathogen reservoirs

The emergence of novel pathogens within a population.

Reduced host immunity within a population causing a high transmission threshold.

Infected food supplies within a community or region, for example, expired foodstuffs in local shops.

Consumption of contaminated supplied consumptives such as drinking water, soft drinks, snacks, etc.

Migration of disease-transmitting vectors.

Seasonal epidemics such as common colds, flu, and sore throats are associated with the winter season.

Infections that are transmissible from human-to-human contacts such as flu and animal (pets)-to-human contact.

Exposure to chemicals or radioactive agents within a region/locality such as exposure to mercury causes Minamata.

Diseases associated with epidemics such as drought lead to migration and accumulation of tsetse flies which cause Trypanosomiasis. The emergence of new pathogen strains or subtypes that are highly transmissible from human-to-human.

The emergence of Antimicrobial-resistant pathogens especially bacteria, that are highly transmissible through human-to-human contact.

Some pandemics have the ability to spread rapidly, for example, the black death.

Mutated pathogens especially viruses that spread rapidly and widely within a population and across borders.

Airborne associated pathogenic outbreaks.

Human-human transmissible pathogenic outbreaks. TRANSMISSION Human-human transmission

Vector-borne transmission

Airborne transmission

Fecal-route transmission

Foodborne transmission

Developmental Transmission

Propagated Transmission

Vertical Transmission Human-human transmission

Vector-borne transmission

Airborne transmission TYPES Common-source epidemics

Propagated epidemics

Mixed source epidemics Pandemics are epidemics that have spread rapidly to other areas in large areas such as countries and continents. EFFECT Some are severe and fatal causing massive deaths. Most cases are severe and fatal, causing massive deaths. MANAGEMENT AND CONTROL They are easier to contain, manage and control as compared to pandemics, because it involves a smaller population. They are difficult to contain, manage and control because it intensely affects a large population within a short period of time, considering the mode of transmission.

References and Sources