Pandemic Of Infectious Words From A To Z: From Ancestral Strain To Zoonosis

From 'ancestral strain' to 'zoonosis,' the coronavirus has added new words to our personal lexicons. While we don't qualify to become epidemiologists, we know more technical knowledge of epidemics and pandemics this year than ever before. Since the coronavirus has reached pandemic proportions, scientific terms and the understanding of viruses have tripped from our lips lightly. Here's a glossary for those who are still 'sheltered in place' and a healthy congratulations for those who no longer have to.

Ancestral Strain

Scientists have uncovered what appear to be two very slightly different strains of the coronavirus, one dubbed “L” and the other dubbed “S”. The “S” strain has been described as ancestral – this means it is the older of the two – with the “L” strain emerging from this through genetic changes.

The “L” strain appears to be more prevalent – something that may suggest it is better able to pass from person to person – although it is not yet clear if this is the case, or whether the two strains cause different severity of COVID-19.


Bats are thought to be the Coronavirus source, and some research teams think they know why?

A bats' immune system may protect viruses that cause diseases in humans. If true, it would be the latest disease-causing virus in China to transfer from bats to people. "We don't know the source yet, but there's pretty strong evidence that this is a bat origin coronavirus," said Dr. Peter Daszak. President of Eco-Health Alliance.

In addition to bats, the coronaviruses are known to infect mammals and birds, dogs, chickens, cattle, pigs, cats, and pangolins. Bats are able to transfer the coronavirus to pangolins which can then transfer it to humans. Please see "Bats Can Transmit Covid-19 To Humans Via The Intermediate Host Pangolin."


CDC is the Centers for Disease Control and Prevention. As the nation's health protection agency, CDC saves lives and protects people from health, safety, and security threats.


So far the U.S. has been in the “containment” phase. Containment means that cases of COVID-19 are identified and isolated as they emerge, and then quarantining individuals who are believed to have the virus symptoms... The aim is to prevent the virus from freely circulating in the population. The slowdown in coronavirus cases in China offers hope that this global pandemic can be contained globally.


Coronaviruses are a family of viruses that can cause deadly diseases – and may jump from animals to humans [see Bats above). The current crisis in the U.S. pertains to a new coronavirus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, it is not the only coronavirus that infects humans. The World Health Organization (WHO) notes, Middle East Respiratory Syndrome (Mers) and Severe Acute Respiratory Syndrome (Sars ) are also coronaviruses – as are some of the viruses that cause the common cold.


Technically, COVID-19 is the name of the disease caused by infection with the new coronavirus, Sars-CoV-2. COVID-19 is an acronym where 'CO' stands for coronavirus disease of 2019... It started in Wuhan, China in late 2019 and has since spread worldwide. Diseases are officially named by WHO in the International Classification of Diseases (ICD).


Some countries are currently poised to move from a “containment” to a “delay” phase in managing the coronavirus outbreak. The delay means the disease is slowing down – it is about buying time, both to ease pressure on health services, and to test possible drugs. Measures to delay the spread of disease may include canceling public gatherings, restricting travel and other measures – as has been done in China and Italy, and other European nations successfully.

Droplet transmission

People emit respiratory droplets from their noses and mouths through talking, coughing, sneezing, yelling, or even singing. Droplet transmission occurs when a respiratory droplet carrying an organism – like the coronavirus – reaches and lands on another person's mouth, nose, or eyes and infects them. Droplet transmission may also occur when someone touches an inanimate object (or fomite) that's recently been contaminated with infected droplets and then touches his or her own face.


As the US Centers for Disease Control and Prevention points out, an epidemic is, essentially, an outbreak over a larger geographical area. According to WHO, an epidemic is “the occurrence in a community or region of cases of an illness, specific health-related behavior, or other health-related events clearly in excess of normal expectancy”, adding that the timing and area affected can be pinpointed. The number of cases needed to meet this definition can differ by a range of factors including the disease itself and whether a population has previously been exposed to it.


An epidemiologist's responsibilities fall into three significant categories: research, analysis, and communication. The role of this researcher is to determine the cause of a disease or a public health concern. Researchers may work in the field or a lab to find data and clarify details. Analysts in epidemiology use the research to analyze data and put together a hypothesis or theory. Once determined, epidemiologists seek solutions to prove those theories.

The epidemiologist Larry Brilliant once said, “outbreaks are inevitable, but pandemics are optional.” But pandemics only remain optional if we have the will to disrupt our politics as readily as we disrupt nature and wildlife. In the end, there is no real mystery about the animal source of pandemics. It’s not some spiky scaled pangolin or furry flying bat. It’s populations of warm-blooded primates: The true animal source is us."

Flattened Curve

In epidemiology, the idea of slowing a virus' spread so that fewer people need to seek treatment at any given time is known as "flattening the curve."

If the spread of a disease can be reduced – for example through increased handwashing and other social distancing – it means cases will be more spread out over time and fewer people will be seeking healthcare at the peak of the outbreak. This will cause a “flattened curve” when cases are plotted on a graph against time.


Protection from an infectious disease. If you are immune to a disease, you can be exposed to it without becoming infected.


Immunization refers to the process of both getting a vaccine and becoming immune to the disease following vaccination. This term is often used interchangeably with vaccination or inoculation.


An outbreak is a sudden uptick in cases of a disease within an area, or as the WHO puts it, “the occurrence of disease cases in excess of normal expectancy.”

Mortality rate

As the Centers for Disease Control and Prevention (see above for CDC) notes, “the mortality rate is a measure of the frequency of occurrence of death in a defined population during a specified interval”. In the case of coronavirus, the rate that is often discussed is the crude mortality ratio or the number of reported deaths divided by the reported cases – which is currently estimated in the U.S. at 3.4%.

Mortality rates can differ by age, sex and other factors. At present, men appear to have a higher rate than women, and older people are at a far higher risk than younger people.


A pandemic is often described as a global epidemic: in other words a sudden increase in cases of a disease, above what may be expected, in multiple countries or regions affecting, as the CDC notes, a large number of people. The WHO declared the coronavirus a pandemic on March 11, 2020.


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It's a fancy word for the main ingredients of any chemical-based test, which in this pandemic includes inorganic solutions as well as enzymes, probes, and primers created to match the coronavirus's genome. They are a necessity for coronavirus test kits to detect those with telltale antibodies that signal possible immunity.


The basic reproduction number: R0, (pronounced R-naught) is the average number of people who will catch the disease from a single infected person, in a population that’s never seen the disease before. If R0 is 3, then on average every case will create three new cases.

Shelter in place

To 'shelter in place' is a serious cautionary warning. It requires all residents to remain at their place of residence, except to conduct essential activities, essential businesses, and essential government functions.

Social distancing

Social distancing is the physical measure of feet apart from other people. This action is to reduce person-to-person contact in a given community, with the goal to stop or slow down the spread of a contagious disease. Currently, that measure in the U.S. is to stand 6 feet apart from anyone else.


Super-spreaders are those infected who are able to infect an unusually high number of other people under normal conditions. However, the term is controversial, with some pointing out that, depending on circumstances – such as how crowded an environment is, how good the ventilation is, or how much someone has to travel at a given time – anyone could end up infecting a greater number of others than usual.


A ventilator is a machine that supplies oxygen to the lungs of a patient with severe respiratory problems. This is when the oxygen levels in the patient's bloodstream drop below a certain point. So that the ventilator can deliver oxygen to the patient, its tube is placed down the patient's throat to open up the patient's airways. Many hospitals in the U.S. face possible ventilator shortages as the number of COVID-19 cases continues to spike.


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A substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from the causative agent of a disease, its products, or a synthetic substitute, treated to act as an antigen without inducing the disease.


Vaccination is the term used for getting a vaccine – that is, actually getting the injection or taking an oral vaccine dose. Immunization refers to the process of both getting the vaccine and becoming immune to the disease following vaccination.

Wet Market

Wet markets are collections of stalls that sell fresh produce, from fruit to meat, as opposed to dry or tinned goods or packaged chilled meat. The term wet market is often used to signify a live animal market in which vendors slaughter animals at the time of a customer's purchase. Not all wet markets carry living animals or wildlife products, but those that do have been linked to outbreaks of zoonotic diseases (see below) including the coronavirus disease 2019.

Zoonosis, or Zoonotic Disease

A zoonosis, or zoonotic disease, is a disease that can be passed between animals and humans. This is not unusual – rabies and malaria are among existing zoonotic diseases, as is Mers which jumped from camels to humans. The new coronavirus is also a zoonotic disease. While it is not clear from which animal COVID-19 jumped to humans, the event has been linked to a wet market in Wuhan. Others say that bats carry the new coronavirus that is transmitted to humans (see bats above).


As the coronavirus continues to spread globally, we learn more and more about the scientific underpinnings of the virus and its disease. I hope this glossary and their definitions will help in keeping you abreast of the global pandemic we are experiencing, and that whether the source of the coronavirus is a bat or something else, here's wishing that each and every one of you and your loved ones remain safe in the trying months ahead.

Primary Source: The Guardian

[Note: In researching these definitions, I have used The Guardian's glossary in most cases, but have also linked other sources when necessary.]