Smallpox

Overview of smallpox

A few microbial diseases used to be a major threat in the past few decades, but have apparently disappeared in the recent years. But global health organizations are not yet sure whether those pathogens still exist in the environment in dormant form or not. In such cases, adequate measures need to be adopted before any unexpected epidemic outbreak occurs. A very common disease belonging to this category is “smallpox”. In the recent years, the occurrence of smallpox has not been observed. Still, proper knowledge of the disease is necessary in order to handle any unexpected occurrence at any point in time.

What is smallpox?

Smallpox is a form of a communicable viral disease which is mediated by the Variola virus which exists in close association with the human population.  

This virus is a part of the Orthopoxvirus genus, which belongs to the Poxviridiae family Smallpox is usually manifested as elevated bumps all over the skin, which leave permanent scars after complete healing.

Smallpox can lead to serious epidemic outbreaks that may result in millions of fatalities all over the world. Adequate immunizations are necessary to eradicate smallpox completely.

What causes smallpox?

Smallpox is primarily mediated through two viral species, all belonging to the Poxviridiae family. The causative agents of smallpox are listed below-

• Variola Major: It causes the more severe form of smallpox manifested through high fever and reddish, itchy skin rashes. Death cases due to Variola Major were reported as 20-40%. Variola Major has four distinct variants. These are-
• Ordinary Variola Major: It has a mortality rate of 90% or more.
• Mild Variola Major: It attacks previously vaccinated people as well. But the symptoms are mild and the mortality rates are not so high.
• Flat Variola Major: It usually causes a lethal form of smallpox.
• Haemorrhagic Variola Major: As the name implies, it causes internal bleeding and in many cases is fatal in nature.
• Variola Minor: It is a relatively benign form of the Variola species and accounts for 1% or fewer fatalities.

Transmission route of smallpox

Smallpox is extremely contagious in nature and can spread through direct or indirect contact with the infected person. Following are the main transmission mediums of smallpox-

• Direct contact with respiratory droplets of the infected person via coughing and sneezing
• Sharing common items of use such as utensils, bed-sheets, towels or cosmetics
• Direct contact with the smallpox blisters (and fluids discharged from the blisters) of the infected person while dressing them
• Touching objects used by the infected person and putting the hand on the face or inside the mouth without washing hands

Humans are the primary hosts of smallpox. It has to be noted in this context that smallpox infections spread from human to human directly without the mediation of animals or other insects. The patients may spread infection even after 7-10 days of separation of the smallpox scabs.

Pathophysiology or stages of smallpox

Smallpox progresses within the human body through few consecutive stages, which can be discussed according to the stage of infection. The pathological phases of smallpox infections are described below-

• The Variola virus is primarily acquired via inhalation. The incubation period of this virus ranges from 10-14 days. In the first stage, it invades the lungs. Gradually it invades the mucosal linings and progresses towards the lymph nodes, wherein it starts multiplying. After 2-3 days the virus enters the circulating blood and gets transferred to the spleen, bone marrow, and lymph nodes. The second phase of multiplication begins at this stage. At the end of this stage, the virus invades the leukocytes and later on spreads to the lungs, kidneys, and brain. Fever and toxemia are observed at this stage.
• The second stage is called the pre-eruptive stage. It lasts for 2-6 days and is characterized by high fever, severe headache, back pain and pain in the limbs. Nausea and vomiting may result, accompanied by intermittent chills.
• The third stage is called the eruptive stage, wherein macules (flattened red eruptions), vesicles (elevated lesions) and pustules (pus-filled blisters) appear on the skin (mainly on the face and trunk). This stage lasts for 4-6 days.
• In the next phase, which is called the discharge phase, the vesicles, papules, and pustules burst and release the virus-containing fluid. Most of the smallpox infections spread in this stage.
• In the final phase, the blisters become completely dried up and form crusty scales called scabs. These scabs finally peel off leaving deep scars on the skin.

Symptoms of smallpox

Smallpox is usually manifested through certain specific symptoms which are discussed according to the stages of infection-

• Pre-eruptive symptoms: The pre-eruptive symptoms include fever, general body ache, nausea, and vomiting.
• Early rashes: Small reddish spots appear on the tongue and inner linings of mouth. The rashes develop into contagious sores and fluid-filled blisters. The fluid is discharged at a later stage, releasing the virus into the body. Rashes also appear on the skin, which later on grows into fluid-filled blisters. Scabs are formed once these blisters get dried up.
• Resolving scabs: The pustules and papules stay for a few days and release a purulent discharge. Crusty scabs are formed after this, which fall off within a few days. Pigmented or non-pigmented scars are formed after complete healing.

Diagnosis

Diagnosis of smallpox is usually done after collecting the fluids from the pustules and vesicles. Examination of the smallpox virus is usually done under an electron microscope, wherein clustered virus particles called Guarnieri bodies are found.

Treatment & Prevention

At present, no treatment modality had been devised for smallpox. The treatment aims to provide symptomatic relief and prevention of dehydration. In case, the infected individual develops an infection on the skin or the lungs, an antibiotic course can be prescribed to manage the infection.

The disease can be prevented by means of a vaccine. The response of the individual to the vaccine may vary based on the time of administration of the vaccine.

The vaccine protects an individual from getting sick if administered before the contact with the virus. If given within 3 days of exposure to the virus, there are possibilities of not getting the disease. However, even if the individual gets sick, the severity of the disease is quite less. If the vaccine is given within 4 to 7 days of exposure to the virus, the severity of the disease is less as compared to an unvaccinated individual. The smallpox vaccine cannot render protection after the development of the smallpox rash.

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