History of Infectious Disease, Microbiology, and Pathogen Identification
Historical Context and Characteristics of the Human Influenza Pandemic
The 1918 outbreak is historically known as the Spanish flu, although the virus did not originate in Spain. The naming convention was based on where early cases were reported.
Current evidence suggests the first cases of this influenza actually occurred in Kansas, United States.
The death toll for this pandemic is enormous, with estimates ranging from to deaths globally, and some sources suggesting as many as .
In the United States alone, approximately deaths occurred within a single winter season.
For comparison, the peak of the COVID pandemic saw approximately deaths in a year, which does not approach the scale of the 1918 pandemic relative to the time frame and population.
The 1918 influenza was an H1 strain, specifically identified later as H1N1.
H1N1 reappeared recently, approximately years ago (around to ). Initially, public health officials feared a repeat of the 1918 mortality rates, but the virus had evolved to be less dangerous, resulting in about deaths.
During the major 1918 pandemic, about people, or of the world population, were infected.
The mortality rate of the 1918 pandemic was at least . In contrast, the fatality rate for COVID during its worst periods was in the to range.
Influenza Pandemic Cycles and Perspectives
Other major influenza pandemics occurred in the and . These were different strains, specifically H2 and H3, often named the Asian and Hong Kong flus.
These later pandemics caused between and deaths each per season.
To provide perspective, at the peak of the HIV crisis, the world lost approximately people annually.
There is a theoretical cycle for influenza outbreaks of approximately years. Adding years to the H2 outbreak points to the year . Scientists monitor these approximate windows for potential major pandemics.
The biological reasoning for the -year cycle is tied to population immunity. When a mass exposure occurs, survivors develop immunity but do not pass it to their children. After approximately years, the majority of the population with natural immunity has passed away, leaving the current population vulnerable.
Avian Influenza (H5N1) and Global Monitoring
Avian influenza, often identified by the strain H5N1, is extremely deadly in humans, with a mortality rate of approximately .
Despite its lethality, the number of confirmed human cases remains low, totaling approximately cases (under ) globally.
There has been no detected human-to-human transmission. Infections occur from birds to humans, typically in settings where humans handle ducks, chickens, or geese, such as farms, slaughterhouses, or markets in Asia.
The World Health Organization (WHO) has not significantly updated their tracking of this in the last years as the threat of a human pandemic has not yet materialised.
The CDC monitors Highly Pathogenic Avian Influenza (HPAI) in domesticated birds and industrial feedlots.
While hundreds of millions of cases occur in birds, human infections remain rare because the virus does not easily adapt to the human body.
The Bubonic Plague: Etiology and History
Bubonic plague is a bacterial infection caused by the species Yersinia pestis.
It is a zoonotic infection, meaning it is transmitted from non-human animals to humans. Specifically, it often moves from rodents to humans via flea bites.
In its later stages, the bacteria can enter the respiratory system, allowing for human-to-human transmission via droplets or airborne particles.
Characteristic symptoms include buboes, which are enormous swellings of the lymph nodes, particularly in the groin area.
If the disease is transmitted through the respiratory system, it is referred to as Pneumonic plague.
Small modern outbreaks have occurred in China, such as an -case outbreak in and a -case outbreak in , both of which were met with strict government quarantines.
Plague is treated effectively with antibiotics if diagnosed early, though there is currently no vaccine.
The disease is ancient, with medical records from Greece dating back years (named over years ago) and archaeological evidence in remains that are years old.
The Peloponnesian War in ancient Greece around BC saw an outbreak that killed of the population, roughly people.
Major Plague Pandemics in History
War conditions—stress, crowding in refugee camps, and lack of medical care—often enhance the impact of infectious disease outbreaks.
The Black Death in the was a bubonic plague pandemic that killed approximately of the European population and approximately of the Asian population.
In the , London experienced a plague outbreak that killed many over an -month period.
In the , an outbreak in China and India caused approximately deaths.
The bacterium Yersinia pestis was isolated and identified as the etiological agent (the root cause) in the late .
Historical records are sometimes scrutinized because plague symptoms overlap with typhoid fever, which is spread through contaminated water and food (e.g., the case of the asymptomatic cook known as Typhoid Mary).
Smallpox: Impact, Evolution, and Eradication
Smallpox is caused by the variola (also pronounced variola) virus.
Transmission is through respiratory droplets. Although skin pockmarks and scabs are defining features, they appear in later stages and are not highly infectious themselves.
Smallpox has been historically very deadly, with mortality rates exceeding .
The disease is over years old, originating in Africa. It reached Europe in the century (). Over a thousand years of exposure, natural selection led to some resistance building within the European population.
In , contact between Europeans and Native Americans introduced smallpox to the Americas. Native populations had no prior exposure or immunity, leading to a massive mortality rate that caused the vast majority of Native American deaths.
Smallpox was used as a biological weapon by European colonists, who gave blankets contaminated with the virus to Native Americans as "gifts."
In , the WHO declared smallpox the only human infectious disease to be successfully eradicated through global vaccination programs.
Smallpox samples are still stored in high-security labs in the US and Russia for research, primarily to guard against potential bioterrorism or future outbreaks of related viruses like Mpox (formerly monkeypox).
The History and Development of Vaccination
While Edward Jenner is credited in Western textbooks for inventing vaccination in the , the practice existed for centuries prior in China, Africa, and India.
In China, almost years ago, physicians ground smallpox scabs into powder and blew them up the noses of uninfected people to induce mild illness and subsequent immunity.
In Western Africa, practitioners used a method similar to injection or scarring on the arm, a practice brought to the Americas by enslaved people.
Jenner observed that milkmaids immune to cowpox were also immune to smallpox.
In his experiments, Jenner inoculated an -year-old boy with cowpox and later intentionally exposed him to smallpox to test immunity. This was done without what modern medicine calls informed consent.
Microscopy and the Principles of Cell Theory
Microorganisms were first seen in the century () following the invention of the microscope.
Robert Hooke, a British scientist, observed thin slices of cork. He described the rectangle-shaped structures as "cells," reminiscent of monastery or prison cells.
Hooke's Cell Theory states that all living things are composed of one or more cells.
Antonie van Leeuwenhoek, a Dutch craftsman and lens maker, created handheld microscopes capable of magnification up to . He was the first to observe pond water, human blood, and sperm samples.
The Theories of Biogenesis and Spontaneous Generation
Spontaneous Generation: The hypothesis that life can arise from nonliving matter (e.g., nutrients and oxygen).
Biogenesis: The theory that all life arises from preexisting life.
Louis Pasteur settled this debate in with his goose-neck flask experiment.
Pasteur boiled nutrient broth to sterilize it. The bent neck of the flask allowed air (nonliving gases) to enter but trapped dust and bacteria (living cells) in the curve.
The broth remained sterile indefinitely until the flask was tipped to allow the broth to touch the trapped microbes, at which point it spoiled.
The Germ Theory of Disease and Medical Sanitation
The Germ Theory posits that microorganisms cause disease.
In the , Joseph Lister in Europe and Civil War surgeons in the United States began using chemical disinfectants to treat wounds and surgical tools. Lister used phenol, while others used bromine. This significantly reduced post-surgical fevers and deaths.
Public sanitation efforts, such as wastewater treatment and indoor plumbing, reduced common waterborne diseases like cholera and dysentery by limiting human contact with microbes.
Ignaz Semmelweis, a Hungarian physician, promoted hand washing after noticing that doctors who performed cadaver dissections before delivering babies frequently passed "childbirth fever" to mothers. Despite his evidence, he was largely ridiculed by his contemporaries.
Robert Koch and the Methodology of Pathogen Identification
Robert Koch developed a specific set of criteria (Koch's Postulates) in the late to identify the etiological agent of a particular disease.
The steps involved in Koch’s Postulates are:
The specific microorganism is isolated from a diseased or dead host.
The microorganism is grown in a pure culture to identify types of colonies.
The microorganism from the pure culture is introduced (via injection, aerosol/droplet, or ingestion) into a healthy, susceptible lab animal (host).
The disease is reproduced in the lab animal.
The same microorganism is isolated from the newly diseased animal and identified as being identical to the original.
Koch won the Nobel Prize for his work identifying Mycobacterium tuberculosis. He also identified the causes of anthrax, cholera, and staph infections.
Limitations: Treponema pallidum (the bacterium causing syphilis) cannot be grown in a lab on petri dishes, making it impossible to fulfill the naming postulates strictly, though identification is made via clinical observation of the bacteria in sores.
Viral diseases like SARS require a modified version of Koch’s postulates because viruses cannot be grown on standard agar like bacteria.
Modern Scientific Nomenclature
Practicing the names of pathogenic species is essential for historical and scientific accuracy. Species mentioned include:
Bacillus anthracis (Anthrax)
Mycobacterium tuberculosis (Tuberculosis)
Vibrio cholerae (Cholera)
Staphylococcus aureus (Staph infections)
Treponema pallidum (Syphilis)
Vocations and Professional Discussion
A specialized CNA training program in North Bay is discussed as a faster alternative to other junior college (JC) routes. The program takes weeks full-time in the summer and costs approximately .
Students discuss the window for taking the TEAS test, typically between November and January. The JC often only accepts the score from the first attempt, though retakes are allowed every months.
Questions & Discussion
Question on Cycle Predictability: Why are influenza pandemics predicted to follow an approximately -year cycle?
Myra's Input: Mentioned it is likely related to the resistance and evolvement of the market over years.
Luis's Input: Suggested that if a person gets it at the start of the cycle, the flu evolves with subsequent generations and gets stronger.
Sheila's Input: Correctly identified that years is close to the average lifespan. People exposed during the first outbreak who survived have immunity, but they do not pass it to their offspring. Once those individuals die out after a full life, there is very little immunity left in the population.
Question on Jenner's Subjects: Why did Jenner use children for his experiments?
Response: Historically, children under age have less developed immune systems. Jenner likely used children because older individuals in England were more likely to have already been exposed to smallpox, making children a "naive immunologic population" necessary for the experiment.
Question on Disease Origins: What was the origin of smallpox?
Response: Viruses like smallpox, COVID, and HIV have ancestors that infect other mammals or primates. These viruses evolve the ability to "jump" to humans. The exact first human case of smallpox is currently unknown and an area of active study.
Layla's Query: Asked for clarification regarding the difference in transmission methods and the modified postulates used for viruses versus bacteria.**