What is Smallpox?
Smallpox is known as the first infectious disease spread between humans that was completely wiped out all over the world. This achievement was officially recognized by the World Health Assembly in 1980. Despite its eradication, smallpox still holds significance in medicine today because of fears about it potentially being released or used as a weapon.
What Causes Smallpox?
Smallpox is a type of virus that falls under the family of poxviruses. It specifically belongs to the orthopoxvirus category and is known by the scientific name variola virus. When we think of viruses, we usually think of tiny organisms. However, poxviruses are the largest viruses known to infect humans. If you were to spot them under a powerful microscope, they would look somewhat like bricks.
The variola virus, which is what causes smallpox, is roughly 300 to 350 nanometers long. Just to give you a sense of scale, a nanometer is a billionth of a meter, so we’re definitely talking microscopically tiny here.
One interesting thing about poxviruses is that they contain a special type of genetic material made of double-stranded DNA. What makes them unique is that their genes encode all the proteins they need to copy themselves. This means they can reproduce themselves independently in the fluid-filled space, or cytoplasm, inside our cells. That’s quite different from many other kinds of viruses, which need to tap into our cells’ own machinery to make copies of themselves.
Risk Factors and Frequency for Smallpox
Smallpox is a disease that only affects humans, and this made it easier for us to completely get rid of it. Edward Jenner played an important role in this, back in the late 1700s. He found out that people could be protected against smallpox by using the cowpox virus. Later, a virus called vaccinia replaced cowpox in the vaccine. This virus is different from cowpox and nobody knows exactly where it came from. Before smallpox was eradicated, it killed over 300 million people globally in the 20th century. About 30% of people who got the disease would die from it, and a lot of those who survived would be left with significant health problems, like blindness and skin scarring. The last known case of smallpox was in Somalia in 1977.
Smallpox spreads through tiny drops of fluid from someone’s respiratory system (like when they sneeze or cough), or by touching wounds from the disease or items that have been contaminated by it. The virus can get released into the air when wounds in the mouth and throat shed and the particles become airborne. Someone with the disease can spread it from when the first wounds show up, until the last crusts of wounds fall off. It’s also known to have spread in hospitals and labs, and when dealing with smallpox, it’s really important to have good ways to prevent infection and isolate the disease.
Signs and Symptoms of Smallpox
Smallpox is a disease which starts with fever-like symptoms such as high fever, chills, stomach pain, vomiting, headache, and backache. These symptoms, known as febrile prodrome, typically occur 1 to 3 days before the appearance of skin lesions or rashes. The rashes initially show up on the forearms or face and then gradually spread all over the body, often affecting the palms of the hands and the soles of the feet.
The lesions or rashes are generally more numerous on the face and limbs compared to the torso. All the lesions on a specific part of the body will be at the same stage of development at any given time throughout the illness. The rashes go through several stages, changing from flat spots (macules) to small raised bumps (papules), to fluid-filled blisters (vesicles), to pus-filled blisters (pustules), and finally to crusts. Each stage occurs approximately every 48 hours.
The entire process, from the initial appearance of the rashes to the final crusting, typically takes 2 to 3 weeks. Each spot or lesion looks deep-seated, round, firm, clearly defined, and is about 7mm to 10mm in diameter.
major and minor
Testing for Smallpox
The Centers for Disease Control and Prevention (CDC) has created a guide for doctors examining patients who might have smallpox. This guide uses major and minor criteria to help determine how likely it is that the patient has smallpox.
Major criteria include the following signs: fever before the rash appears, typical smallpox blister look, and all blisters in the same stage of development. Minor criteria are rash spread more on the distant parts of the body and face, the first blister showings on the mouth lining or roof, face or forearms, rash appearing on the palms and soles of the feet, slow rash development (taking 1 to 2 days to move onto the next stage) and patient looking very ill.
Patients are then categorized into low, moderate, or high risk for having smallpox. This classification helps doctors to decide whether they should carry out diagnostic tests to confirm if the patient has smallpox.
For patients who are likely to have smallpox (classified as low or moderate risk) and there’s no known smallpox outbreak, lab testing is usually not recommended. However, for cases where testing is needed, a technique called PCR can be used on a sample of blood or tissue. This should only be done after consulting with public health authorities.
Treatment Options for Smallpox
Before eradication, treatment options for smallpox were mostly limited to supportive care, such as rest and hydration. But even after its eradication, researchers have continued to work on developing medicines to treat the virus. In 2018, the United States approved the first antiviral therapy for smallpox, called tecovirimat. This antiviral treatment had not been fully tested on human patients yet, it has been safely used on human volunteers and used in emergencies for patients with post-vaccination complications.
Vaccination, a process where a person is given a weaker or inactive version of a disease to help their immune system recognize and fight it, was instrumental in eradicating smallpox worldwide. Originally, people were infected with a small amount of infectious smallpox to help them develop immunity, a practice known as ‘variolation’. However, this method was risky and could cause severe illness or even death. The practice changed in 1798 when Edward Jenner found that cowpox could be used instead of smallpox to induce immunity, making vaccination safer. By the 20th century, the vaccinia virus, closely related to horsepox, replaced cowpox in vaccines and was used in large-scale global vaccination programs.
However, vaccines using live viruses always come with some risks. In the case of the smallpox vaccine, side effects could range from skin rashes, eczema, disease progression to brain inflammation. These side effects could sometimes affect others through contact with the vaccinated person, or from a vaccinated mother to her unborn child.
On the other hand, advancements in technology have led to safer vaccines. Researchers have developed vaccines made in tissue cultures, weakened or “attenuated” viruses, and portions of the virus (subunits). Currently, smallpox vaccines are only recommended for certain people who are more likely to be exposed to the virus, such as researchers, certain healthcare workers, and select US military personnel.
What else can Smallpox be?
When trying to identify smallpox, doctors need to be able to distinguish it from other conditions that could cause similar skin rashes. These conditions might include:
- Chickenpox
- Disseminated Herpes Simplex Virus (HSV) or Eczema Herpeticum
- Disseminated Varicella-Zoster Virus (VZV)
- Hand-Foot-Mouth Disease caused by Enterovirus
- Skin reactions to medication, such as Stevens-Johnson Syndrome or Toxic Epidermal Necrolysis
- Generalized Vaccinia
- Monkeypox
