Smallpox and Chickenpox and Measles

Difference Between Smallpox and Chickenpox and Measles

Introduction of Smallpox and Chickenpox and Measles

Smallpox: Smallpox is an extremely contagious and deadly illness caused by the Variola virus. It is characterized by a distinctive rash and flu-like symptoms. Thanks to a successful worldwide vaccination campaign, smallpox was declared eradicated in 1980, making it the first and only human disease to be wiped out through vaccination.

Chickenpox: Varicella-zoster virus (VZV) causes chickenpox or varicella. It typically presents with an itchy rash, fever, and general discomfort. Although usually less severe than smallpox, chickenpox can be particularly dangerous for certain vulnerable populations, like pregnant women and immunocompromised individuals.

Measles: Measles, caused by the Measles virus, is highly contagious and known for its characteristic red rash and fever. Measles can lead to severe complications, such as pneumonia and encephalitis, and remains a global concern due to sporadic outbreaks in unvaccinated populations, emphasizing the importance of vaccination campaigns and herd immunity.

What is Smallpox?

Smallpox, also known as variola, is a highly contagious and often deadly infectious disease caused by the Variola virus. It is characterized by the sudden onset of fever, severe malaise, and a distinctive rash consisting of raised, fluid-filled blisters. Smallpox was responsible for significant morbidity and mortality throughout human history until it was declared eradicated in 1980 through a successful global vaccination campaign.


The disease has two main forms: variola major, which is more severe and has a higher mortality rate, and variola minor, which is less severe. Smallpox vaccination played a pivotal role in eliminating this disease from the world, making it the first and only human infectious disease to be eradicated through vaccination efforts.

Smallpox Virus

Smallpox is caused by Variola virus, an orthopoxvirus family member. The virus exists in two main forms: Variola major and Variola minor. Variola major is the more severe form, associated with a higher mortality rate, while Variola minor typically leads to a milder illness.

Here are some key characteristics of the Smallpox virus:

  1. Structure: The Variola virus is a large, complex, double-stranded DNA virus. It is one of the largest viruses known to infect humans.
  2. Transmission: Smallpox is primarily transmitted through respiratory droplets when an infected person coughs, sneezes, or talks. It can also spread by direct contact with the virus from contaminated objects or skin lesions of an infected person.
  3. Incubation Period: After exposure to the virus, there is an incubation period of about 7 to 17 days before the first symptoms appear.
  4. Symptoms: Smallpox typically starts with a high fever, malaise, and severe fatigue. The characteristic symptom is a skin rash that progresses from macules (flat, red spots) to papules (raised, firm, red areas), and eventually to pustules (fluid-filled blisters). The rash covers the entire body and is often accompanied by intense itching.
  5. Complications: Smallpox can lead to severe complications, including pneumonia, encephalitis (inflammation of the brain), and even death. It is estimated that Variola major had a mortality rate of about 30%, making it a highly deadly disease.
  6. Vaccination: Smallpox vaccination, using a live attenuated virus called the vaccinia virus, was instrumental in eradicating the disease. The vaccine provides immunity against Variola virus. Routine smallpox vaccination is no longer necessary since the disease was declared eradicated in 1980. However, stockpiles of the vaccine still exist for emergency use.

It’s worth noting that smallpox is one of the most significant success stories in the history of medicine and public health, as it was the first human disease to be completely eradicated worldwide through vaccination campaigns. The last known natural case of smallpox occurred in 1977, and the World Health Organization declared the global eradication of smallpox in 1980.

Symptoms and Transmission

Here are the symptoms and transmission methods for smallpox:

Symptoms of Smallpox:

  1. Incubation Period: Smallpox has an incubation period of about 7 to 17 days, during which the virus replicates in the body without causing symptoms.
  2. Initial Symptoms: The disease typically starts with flu-like symptoms, which can include:
    • High fever
    • Malaise (a general feeling of discomfort)
    • Severe fatigue
  3. Skin Rash: After a few days, a distinctive skin rash develops. This rash goes through several stages:
    • Macules: Flat, red spots on the skin.
    • Papules: Raised, firm, red areas that are more pronounced than macules.
    • Vesicles: Fluid-filled blisters.
    • Pustules: Blisters become filled with pus.
    • Scabs: Pustules eventually form a scab, which falls off over time.
  4. Distribution: The rash spreads and covers the entire body, including the face, arms, legs, and trunk.
  5. Complications: Smallpox can lead to severe complications, including pneumonia, encephalitis (inflammation of the brain), and hemorrhagic (bleeding) smallpox. Variola major, the more severe form, has a higher mortality rate, estimated at about 30%.

Transmission of Smallpox:

  1. Respiratory Transmission: The primary mode of transmission is through respiratory droplets released when an infected person coughs, sneezes, talks, or even breathes. These droplets contain the virus and can infect individuals who inhale them.
  2. Direct Contact: Smallpox can also spread through direct contact with an infected person’s:
    • Skin lesions
    • Bodily fluids (e.g., saliva, respiratory secretions)
    • Contaminated objects (fomites) like bedding or clothing
  3. Airborne Transmission: In enclosed settings, the virus can become aerosolized, meaning it can remain suspended in the air for extended periods, increasing the risk of transmission.

Due to its high level of contagiousness, smallpox posed a significant public health threat before it was successfully eradicated through vaccination efforts. Routine smallpox vaccination is no longer required because the disease has been eradicated, but stockpiles of the vaccine exist for emergency use in case of a bioterrorism threat or accidental release of the virus.

What is Chickenpox?

Chickenpox, medically known as Varicella, is a highly contagious viral infection primarily caused by the Varicella-zoster virus. It is characterized by an itchy skin rash that starts as small, red, itchy spots and progresses into fluid-filled blisters that eventually crust over. Alongside the rash, individuals with chickenpox may experience fever, fatigue, and general discomfort.


Chickenpox is most common in children, but it can affect people of all ages. While it is usually a self-limiting and relatively mild disease in healthy individuals, it can be more severe and pose complications, especially in adults, infants, and those with weakened immune systems. Vaccination against chickenpox has become widespread, reducing the incidence and severity of the disease.

Varicella-Zoster Virus

The Varicella-Zoster Virus (VZV) is a human herpesvirus that causes two distinct diseases:

  1. Chickenpox (Varicella): VZV is responsible for the common childhood illness known as chickenpox. When a person is first infected with the virus, it causes chickenpox. The virus is highly contagious and is typically transmitted through respiratory droplets from an infected person’s cough or sneeze. Chickenpox is characterized by an itchy skin rash that starts as red spots, progresses to fluid-filled blisters, and eventually crusts over. Erythroderma can often result in general discomfort and fever. Most cases of chickenpox are mild, but it can lead to complications, especially in adults and those with weakened immune systems.
  2. Shingles (Herpes Zoster): After a person recovers from chickenpox, the Varicella-Zoster Virus remains dormant in nerve cells near the spinal cord and can reactivate later in life. When it reactivates, it causes a painful condition known as shingles or herpes zoster. Shingles typically presents as a painful rash with blisters, often localized to one side of the body or face, following the distribution of a specific nerve. Elderly individuals and those with weak immune systems are at higher risk for disease.

Key points about Varicella-Zoster Virus (VZV):

  • It is a member of the herpesvirus family and is closely related to other herpesviruses, such as herpes simplex virus (HSV).
  • Once a person has had chickenpox, they carry the VZV in a dormant state in nerve cells. Reactivation of the virus causes shingles.
  • Vaccination against chickenpox (Varicella vaccine) has been highly effective in preventing the disease and reducing its prevalence.
  • A separate vaccine, called the herpes zoster vaccine, is available to reduce the risk of shingles in older adults.
  • VZV is highly contagious, especially during the chickenpox phase, and it can spread through direct contact and respiratory droplets.
  • While chickenpox is primarily a childhood illness, shingles tends to occur later in life, often when a person’s immune system is weaker due to aging or other factors.
  • Prompt treatment with antiviral medications can help alleviate symptoms and reduce complications in cases of shingles.

Signs and Spread

Let’s discuss the signs and spread of chickenpox and shingles, which are both caused by the Varicella-Zoster Virus (VZV).

Chickenpox (Varicella):

Signs and Symptoms:

  • Fever
  • General malaise and fatigue
  • An itchy rash that begins as red spots and progresses to fluid-filled blisters before crusting over
  • Rash usually begins on the chest, face or back and spreads quickly to other parts of the body.
  • Blisters can appear in different stages, so you may have a mixture of red spots, blisters, and crusts at the same time

Spread of Chickenpox:

  • Chickenpox is highly contagious.
  • Spread through respiratory droplets when an infected person coughs, sneezes or speaks.
  • Direct contact with the rash or fluid from the blisters can also transmit the virus.
  • People infected with chickenpox may be exposed one or two days prior to its rash appearing until the blisters have crusted over and have all closed over.

Shingles (Herpes Zoster):

Signs and Symptoms:

  • Pain, burning, tingling, or itching in a specific area of the skin
  • Development of a painful rash with red patches and fluid-filled blisters, typically localized to one side of the body or face along a nerve pathway
  • Often accompanied by flu-like symptoms
  • The rash and pain can last for several weeks.

Spread of Shingles:

  • Shingles is less contagious than chickenpox, and it does not spread through the respiratory route.
  • The virus spreads through direct contact with the open blisters or fluid from the blisters.
  • However, coming into contact with the rash or fluid from shingles blisters can transmit VZV and cause chickenpox in individuals who have never had chickenpox or been vaccinated.
  • People with shingles are typically contagious until the rash crusts over.

Vaccination is the most effective way to prevent chickenpox and, indirectly, shingles. The Varicella vaccine is given to children to protect them from chickenpox, and the herpes zoster vaccine is available for older adults to reduce the risk of shingles. If you suspect you have chickenpox or shingles, it’s advisable to seek medical advice for proper diagnosis and management, and to take precautions to prevent the spread of the virus to others.

What is Measles?

Measles (also referred to as rubeola) is an infectious viral condition caused by Measles virus and can spread easily between people. It is characterized by a distinctive red or reddish-brown rash that typically starts on the face and then spreads to cover the entire body. Measles is accompanied by symptoms such as high fever, cough, runny nose, and red, watery eyes. The disease can lead to severe complications, including pneumonia, encephalitis (inflammation of the brain), and in severe cases, it can be fatal.


Measles spreads easily through respiratory droplets when an infected person coughs or sneezes, making it one of the most contagious diseases known to humans. Vaccination with the measles, mumps, and rubella (MMR) vaccine has been highly effective in preventing measles and reducing its prevalence worldwide.

Measles Virus

The Measles virus, also known as rubeola, is a highly contagious virus that belongs to the Paramyxovirus family. Measles is responsible for causing measles, a contagious and potentially serious respiratory illness.

Key features of the Measles virus include:

  1. Structure: The Measles virus has a spherical shape and is enveloped by a lipid membrane. It contains a single strand of RNA as its genetic material.
  2. Transmission: Measles is primarily transmitted through respiratory droplets when an infected person coughs, sneezes, or talks. These droplets can remain suspended in the air for extended periods, making measles one of the most contagious diseases known.
  3. Incubation Period: After exposure to the virus, there is an incubation period of about 7 to 14 days before the onset of symptoms.
  4. Symptoms: Measles typically starts with flu-like symptoms, followed by a characteristic rash. Common symptoms include:
    • High fever
    • Cough
    • Runny nose
    • Red, watery eyes (conjunctivitis)
    • Koplik spots (small white spots with blue-tinged centers) on the inside of your mouth may indicate Koplik syndrome.
  5. Skin Rash: The distinctive measles rash typically appears 3 to 5 days after the onset of symptoms. It consists of red or reddish-brown, flat or raised spots that often join together as the rash spreads. It usually starts on the face and then moves downward to cover the entire body.
  6. Complications: Measles can lead to severe complications, especially in young children, pregnant women, and individuals with weakened immune systems. Complications may include pneumonia, encephalitis (inflammation of the brain), and in severe cases, death.
  7. Vaccination: Vaccination with the measles, mumps, and rubella (MMR) vaccine is highly effective in preventing measles. The vaccine has contributed to a significant reduction in measles cases and related deaths worldwide.
  8. Eradication Status: Measles has not been globally eradicated like smallpox but remains a significant public health concern, especially in areas with low vaccination rates. Outbreaks can occur when vaccination coverage is insufficient to maintain herd immunity.
  9. Global Impact: Measles continues to be a global health challenge, with periodic outbreaks and ongoing efforts to improve vaccination rates and surveillance.

Preventing measles through vaccination is crucial not only to protect individuals but also to maintain herd immunity and prevent the virus from spreading in communities. It is recommended that individuals receive two doses of the MMR vaccine for lifelong protection against measles.

Symptoms and Transmission

Let’s discuss the symptoms and transmission of measles:

Symptoms of Measles:

  1. Incubation Period: Measles has an incubation period of about 7 to 14 days after exposure to the virus before symptoms appear.
  2. Initial Symptoms:
    • High fever
    • Cough
    • Runny nose (coryza)
    • Red, watery eyes (conjunctivitis)
    • Koplik spots: Small white spots with blue centers that appear inside the mouth, usually on the inner cheeks. These are a characteristic early sign of measles.
  3. Measles Rash: After a few days of the initial symptoms, a distinctive rash develops. Key features of the rash include:
    • Red or reddish-brown in color
    • Flat or slightly raised
    • Spots that often join together as the rash spreads
    • Typically starts on the face and then moves downward, covering the entire body
    • Itchy skin
  4. Other Symptoms:
    • Malaise (a general feeling of discomfort)
    • Fatigue
    • Loss of appetite

Transmission of Measles:

  1. Highly Contagious: Measles is one of the most contagious diseases known, primarily due to the ease with which the virus spreads.
  2. Respiratory Transmission: The virus spreads through respiratory droplets when an infected person coughs, sneezes, or talks. These droplets can remain suspended in the air for extended periods and can infect individuals who breathe them in.
  3. Contaminated Surfaces: Measles virus can also spread by touching surfaces or objects contaminated with respiratory secretions from an infected person and then touching the mouth, nose, or eyes.
  4. Infectious Period: Infected individuals are contagious from about 4 days before the rash appears until 4 days after the rash develops.
  5. Vulnerable Populations: Measles can infect people of all ages, but it is particularly dangerous for young children, pregnant women, and individuals with weakened immune systems.
  6. Herd Immunity: Achieving and maintaining high vaccination coverage in a population is crucial for herd immunity, which helps protect those who cannot be vaccinated or have weakened immune systems.
  7. Global Impact: Measles remains a significant global health concern. Periodic outbreaks occur, especially in areas with low vaccination rates, and the virus can be imported to other regions through international travel.

Given the highly contagious nature of measles and the potential for severe complications, vaccination with the measles, mumps, and rubella (MMR) vaccine is strongly recommended as a preventive measure. Timely vaccination helps protect individuals and contributes to the control of measles on a broader scale.

Comparison Table of Smallpox and Chickenpox and Measles

Here is a comparison table of Smallpox, Chickenpox, and Measles:

Characteristic Smallpox Chickenpox Measles
Causative Agent Variola virus Varicella-zoster virus Measles virus
Transmission Respiratory droplets Respiratory droplets Respiratory droplets
Incubation Period 7-17 days 10-21 days 7-14 days
Initial Symptoms Fever, malaise, fatigue Fever, malaise Fever, cough, runny nose, red eyes
Skin Rash Pustular, raised, fluid-filled blisters Itchy red spots progressing to blisters and crusts Red or reddish-brown rash
Rash Distribution All over the body All over the body Starts on the face and spreads
Complications High risk of severe complications, including death Can cause pneumonia, especially in adults; rare severe complications Pneumonia, encephalitis, and other severe complications
Mortality Rate About 30% for variola major, lower for variola minor Very low, primarily in vulnerable populations About 0.1% globally, higher in developing regions
Vaccination Available Eradicated in 1980, no longer required Available and recommended for children Available as part of the MMR vaccine
Eradication Status Eradicated globally Not eradicated Not eradicated
Public Health Concerns No longer a concern due to eradication Concerns about outbreaks in unvaccinated populations Ongoing concern, especially in areas with low vaccination rates

This table is based on the status of these diseases as of my last knowledge update in September 2021, and there may have been developments or changes since then.

The Importance of Vaccination for Smallpox and Chickenpox and Measles

Vaccination, also known as immunization, is a critically important tool in public health for several reasons:

  1. Disease Prevention: Vaccines are designed to prevent or mitigate the effects of serious and potentially deadly diseases. They stimulate the immune system to recognize and fight specific pathogens (bacteria or viruses), reducing the risk of infection.
  2. Individual Protection: Vaccination provides individual protection against diseases. It helps people stay healthy, avoid illness, and in some cases, it can prevent complications or death from infections.
  3. Herd Immunity: High vaccination rates in a community lead to herd immunity or community immunity. When a significant portion of the population is vaccinated, the spread of a disease is slowed or stopped, protecting vulnerable individuals who cannot be vaccinated, such as infants, elderly people, and those with certain medical conditions.
  4. Preventing Outbreaks: Vaccination helps prevent outbreaks of vaccine-preventable diseases. Diseases like measles and whooping cough can spread rapidly if vaccination rates drop, leading to outbreaks that can strain healthcare systems and result in severe illness or death.
  5. Reducing Healthcare Costs: Vaccination reduces the burden of vaccine-preventable diseases on healthcare systems. By preventing illness, it lowers the costs associated with treating diseases, including hospitalization and long-term care.
  6. Global Health: Vaccination is a critical tool in global health efforts. It has played a central role in the eradication of smallpox and the near-eradication of polio. Vaccination campaigns have saved millions of lives worldwide.
  7. Public Health Preparedness: Vaccination programs are essential components of public health preparedness. They provide a rapid and effective response to emerging infectious disease threats, bioterrorism, and pandemics.
  8. Quality of Life: Vaccination improves the overall quality of life by reducing the incidence of debilitating diseases and their associated complications. It allows people to live healthier and more productive lives.
  9. Safe and Effective: Vaccines are rigorously tested for safety and efficacy before being approved for use. Continuous monitoring ensures their safety once they are in use. Adverse events following vaccination are rare.
  10. Social Responsibility: Getting vaccinated is not only an individual choice but also a social responsibility. It protects vulnerable members of the community and contributes to the common good.
  11. Research and Innovation: Vaccine development drives scientific research and innovation. Advances in immunology and vaccine technology have broader applications in medicine and disease prevention.

Vaccination is a cornerstone of public health, preventing disease, saving lives, and contributing to the well-being of communities and society as a whole. It is a collective effort to protect individuals and maintain the health and resilience of our societies.

Global Eradication Efforts

Global eradication efforts refer to organized and coordinated initiatives aimed at completely eliminating a specific infectious disease from all regions of the world. These efforts are typically led by international organizations, governments, and public health agencies, and they involve vaccination campaigns, surveillance, research, and community engagement.

Here are notable examples of global eradication efforts:

  1. Smallpox Eradication: Smallpox was the first and so far the only human infectious disease to be globally eradicated. The World Health Organization (WHO) led the effort, which involved mass vaccination campaigns, strict surveillance, and isolation of cases. Smallpox was officially declared eradicated in 1980, following a successful vaccination program that spanned several decades.
  2. Polio Eradication: The Global Polio Eradication Initiative, spearheaded by WHO, Rotary International, the Centers for Disease Control and Prevention (CDC), UNICEF, and the Bill & Melinda Gates Foundation, aims to eradicate polio from the planet. Significant progress has been made, with wild poliovirus transmission restricted to a few countries as of my last knowledge update in September 2021.
  3. Guinea Worm Disease Eradication: Guinea worm disease (dracunculiasis) is close to eradication. The Carter Center, led by former U.S. President Jimmy Carter, has been instrumental in efforts to eliminate this parasitic disease. In 2020, only a few cases were reported in isolated regions.
  4. Measles and Rubella Elimination: Various regions and countries have set goals to eliminate measles and rubella (German measles). The Measles & Rubella Initiative, composed of partners like WHO, CDC, UNICEF, and others, is working to reduce measles and rubella deaths globally through vaccination campaigns.
  5. Malaria Elimination: While not yet global eradication, there are ongoing efforts to eliminate malaria in various regions. The Roll Back Malaria Partnership, WHO, and other organizations are working to reduce the global burden of malaria through vector control, treatment, and improved diagnostics.
  6. Tuberculosis (TB) Elimination: Although global eradication of TB remains challenging due to latent infections, there are efforts to eliminate TB as a public health threat in specific regions. Targeted interventions include improved diagnostics, treatment, and vaccination.
  7. Eradication of Emerging Diseases: In response to emerging diseases like Ebola and Zika, international organizations and governments have launched efforts to control and potentially eradicate these diseases through public health measures, research, and vaccine development.

These global eradication efforts demonstrate the commitment of the international community to combat infectious diseases and improve public health worldwide. They require sustained funding, research, and collaboration among nations to achieve their goals. While complete eradication is challenging, these initiatives have often led to significant reductions in disease burden and improved health outcomes for populations.

Similarities between Smallpox and Chickenpox and Measles

While Smallpox, Chickenpox, and Measles are distinct diseases with unique characteristics, there are some similarities between them:

  1. Viral Infections: All three diseases are caused by viruses. Smallpox is caused by the Variola virus, Chickenpox by the Varicella-zoster virus, and Measles by the Measles virus.
  2. Respiratory Transmission: They are all transmitted through respiratory droplets when an infected person coughs or sneezes. This makes them highly contagious, especially in crowded or unvaccinated populations.
  3. Fever and General Malaise: In the initial stages of infection, individuals with all three diseases typically experience fever, malaise, and general discomfort.
  4. Skin Rash: Each disease presents with a characteristic skin rash. While the rashes look different, they all involve skin eruptions. Smallpox has pustular, raised blisters, Chickenpox has itchy red spots progressing to blisters and crusts, and Measles has a red or reddish-brown rash.
  5. Incubation Period: They all have an incubation period during which the virus replicates in the body before symptoms appear. Smallpox has an incubation period of 7-17 days, Chickenpox has an incubation period of 10-21 days, and Measles has an incubation period of 7-14 days.
  6. Complications: While the severity of complications varies, all three diseases can lead to serious health issues. Smallpox is notorious for its high risk of severe complications, Chickenpox can cause pneumonia in adults and severe complications in certain populations, and Measles can lead to pneumonia, encephalitis, and other severe complications.
  7. Vaccination: Vaccines are available for all three diseases, and vaccination has played a crucial role in reducing their prevalence and severity. Smallpox has been eradicated globally due to vaccination, Chickenpox vaccination is recommended for children, and Measles vaccination is part of the MMR (Measles, Mumps, Rubella) vaccine.

Despite these similarities, these diseases have distinct characteristics, complications, and public health implications, and they are managed differently in clinical and public health settings.


Smallpox, Chickenpox, and Measles are distinct infectious diseases with varying degrees of severity and historical impact. Smallpox, once a global scourge, was successfully eradicated through vaccination, marking a historic achievement in public health.

Chickenpox, characterized by an itchy rash, is usually a milder childhood illness, while measles, known for its red rash and severe complications, continues to pose global health challenges, emphasizing the ongoing importance of vaccination and public health measures. These diseases serve as reminders of the critical role vaccines play in preventing and controlling infectious diseases, protecting individuals, and maintaining community well-being.

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