In this lesson, you’ll learn out about the famous and deadly smallpox virus.
In addition, you’ll get an extra treat by learning about cowpox, monkeypox, and Edward Jenner.
The Poxviridae Virus Family
Monkeys, humans and cattle. Scientific research and big bombs. What could they all possibly have in common? A lot of history, a lot of deaths and a lot of viruses in the Poxviridae virus family. In this lesson, we’ll take a look at some of the most famous viruses and diseases associated with this family and how they have shaped the history of everything from medicine to warfare.
Structure and Transmission
The viruses of the Poxviridae family are very large in size. In general, the larger the size of the virus, the larger the genome it can accommodate inside of it.
In this case, the genome is made of linear, double-stranded DNA. Since the genome is quite large and it can code for more nasty things with a larger genome, it is therefore more likely to cause a more complex disease than a small virus that has a smaller genome. It’s like a computer in a sense, the larger the genome, or processing power, the more it can do.The flip side is, because it has a larger genome, there is a higher likelihood that we have more targets for therapeutic intervention. Kind of like hackers, who have more ways by which to exploit a computer that has a lot more information. This means that compared to a small virus, we may have more than one way of trying to knock this virus out of the water because its genome is so big.
The viruses in this family can be enveloped or non-enveloped, and they can be ovoid in shape or brick-shaped, which is the more common shape of viruses in the Poxviridae family.Viruses in this family can be transmitted in a number of ways. If you breathe it in via the respiratory route, you will get what’s known as a systemic infection, meaning it will affect your entire body. On the flip side, if you only touch an area infected with a poxvirus, you may get a localized infection instead.
Regardless, you may be able to get this virus from the air, a contaminated surface, a human or even an animal!
Cowpox, Smallpox and Edward Jenner
One of the animals humans can get a poxvirus from is cattle. Cowpox is a zoonotic poxvirus that causes a localized skin disease in humans. When cattle are infected with this virus, they exhibit red blisters on their udders. When a person milks the cow with their hands, they also get blisters on any area of skin that comes into contact with the viruses secreted by the blisters on the cow. That is why this is called a zoonotic disease.
It’s because a zoonotic disease can spread from an animal to a human or vice versa.Now, one really brilliant man named Edward Jenner did something extraordinary with cowpox. Edward Jenner was an English physician, known as the father of immunology, credited with creating the first vaccine, a vaccine for smallpox. Jenner noted that, for some reason, people who milked cattle were immune to a terrible and deadly disease called smallpox.
This is a virus, also known as Variola, that causes a contagious rash, scarring and death. In fact, it is smallpox that is credited with wiping out more than half of the indigenous people of the New World when Europeans and African slaves carrying this disease arrived on the two continents.When a person is infected with smallpox, a rash full of open sores occurs. It spreads from the mouth to the entire body within 24 hours. The rash turns into vesicles and pustules, basically bumps on the skin.
Eventually, these bumps scab over and leave permanent scars on the skin. However, in some people, the rash that forms doesn’t just end with scars; it ends in death. Sometimes, the virus will turn into two fatal forms, called malignant or hemorrhagic smallpox, and if these two forms occur, the chances of death are near 100%.So, in 1796, along came Edward Jenner, who decided to save the world from the deadly smallpox disease. He noticed that milkmaids were immune to smallpox. He, therefore, correctly assumed that the cowpox affecting cattle was similar enough to the smallpox affecting humans.
However, the cowpox that infected humans was relatively harmless compared to smallpox.Hence, he came up with the smallpox vaccine by way of giving contaminated cowpox material to people, who then developed immunity to smallpox. Since the cowpox was similar to smallpox, the body’s immune system created defense systems against cowpox that could also be used against smallpox.Since there is no real treatment for smallpox itself, vaccination is utterly critical to preventing the disease. Thankfully, through massive international effort, smallpox has been virtually wiped out not only as a disease, but also a virus. However, the United States and Russia are the only two countries left in the world that still harbor this deadly virus under the pretense of scientific study.
However, many suspect both nations retain this virus for the purposes of potentially utilizing it as a form of biological weapon of mass destruction if the need should arise.
Monkeypox and Other Viruses
In any case, there are plenty more poxviruses that can cause disease in all sorts of animals, ranging from cattle and humans to sheep and monkeys. One is a rare zoonotic virus typically localized to Africa that is carried by rodents, called monkeypox. I know that made absolutely no sense! Why in the world are rodents carrying a disease named after monkeys? It’s because this virus was first identified in laboratory primates as opposed to rodents.In the wild, it’s rodents who carry the virus more so than primates. If a person comes into contact with an animal infected with this virus, they can become infected.
The symptoms are similar to smallpox, but death is less likely to occur, especially if the person has been vaccinated for smallpox.As I mentioned, there are many other forms of poxviruses that affect goats, sheep, chickens and so on. While many of them may not infect a human, they are still utterly important, as they can cause serious economic loss to food, wool and leather producers.
Even though smallpox is of little concern to most people these days, hopefully this lesson was of interest given its important historical context. Let’s take a look back at the important points in this lesson.In 1796, Edward Jenner did something extraordinary with cowpox. He was an English physician, known as the father of immunology, credited with creating the first vaccine, a vaccine for smallpox. The cowpox he used for his vaccine is a zoonotic poxvirus that causes a localized skin disease in humans. The vaccine he made was for smallpox. This is a virus, also known as Variola, that causes a contagious rash, scarring and death.
There are many other types of poxviruses besides smallpox and cowpox. For example, one is a rare zoonotic virus typically localized to Africa that is carried by rodents, called monkeypox. Regardless of anything else, the most common shape of viruses in the Poxviridae family is something that appears brick-shaped when looked at under the microscope.
Upon completing this lesson, you will be able to:
- Describe the structure of the Poxviridae virus family and how it is transmitted
- Explain how and why Edward Jenner used cowpox to create a vaccine for smallpox
- Summarize the historical background of smallpox
- Identify the symptoms of smallpox and its mortality rate
- List another poxvirus and describe its symptoms and transmission