Introduction to Smallpox:
The variola virus, which belongs to the orthopoxvirus family, is the cause of smallpox, an acute contagious illness. It was among the deadliest illnesses that people had ever encountered. The World Health Assembly approved a plan to eradicate smallpox worldwide in 1959. After a worldwide vaccination campaign, it was deemed extinct in 1980.
Etiology and Viral Structure:
Smallpox, a grave and highly transmissible disease, stems from the variola virus—a double-stranded DNA virus classified under the Poxviridae family and the Orthopoxvirus genus. Structurally, the virus presents as an enveloped entity with a brick-like to variable shape and possesses a non-segmented, linear genome that is covalently closed.
Types of Variola Virus:
Two distinct variants of the virus exist: variola major and variola minor. Of these, variola major is the predominant and more lethal form, often triggering intense symptoms and leading to death in roughly 20% to 30% of cases, typically within the first week of illness.
Smallpox is not only highly infectious but can also be fatal. The variola major type manifests in four clinical forms:
Ordinary – the most prevalent and classic presentation;
Modified – a milder version, generally affecting individuals with prior vaccination;
Flat – an uncommon but extremely severe form;
Hemorrhagic – rare, aggressive, and frequently fatal.
Modes of Transmission:
Smallpox is typically transmitted from person to person by direct and reasonably extended face-to-face contact. Direct contact with bodily fluids that are infected or contaminated items like clothing or bedding can also spread smallpox. Rarely, the virus that causes smallpox can travel in enclosed spaces like buses, trains, and buildings. Variola only naturally occurs in humans, and neither insects nor animals are known to spread smallpox.
A person with smallpox can occasionally spread the disease when they have a fever (prodromal phase), but they are most contagious when they start to rash. Until the final smallpox scab falls off, the sick person remains contagious.
Incubation Period and Infectious Timeline:
There is a time after being exposed to the smallpox virus during which there are no symptoms, known as the incubation phase. Although it typically lasts 12 days, it can last as little as 7 days or as long as 17 days. The symptoms of the sickness include lethargy, head and body aches, and occasionally vomiting. It starts with a temperature (101 to 104 0F). After two to four days, a rash develops, which goes through the typical phases of papules, vesicles, pustules, and scabs. By the end of the third or fourth week, the scabs come off.
Clinical presentation:
- Papules: a small pimple or swelling on the skin, often forming part of rash
- Vesicles: a small fluid-filled bladder, sac, cyst, or vacuole within the body
- Pustules: a small blister or pimple on the skin containing pus.
- Scabs: a dry, rough protective crust that forms over a cut or wound during healing.
Disease Progression Timeline:
- Two to four days after the patient’s initial feverish illness, the rash emerges. A few elevated patches known as papules show up on the first day of the rash. Usually, the face is where they are initially noticed, followed by the body and limbs.
- More papules show up on the second day of the rash. They all look fairly similar, despite their slight size differences. The rash has grown more noticeable and elevated above the skin’s surface by day three. Vesicles are being formed by the accumulation of fluid in the papules.
- The vesicles become more pronounced on day four. To the touch, they feel extremely hard even though they contain fluid. Because the fluid is trapped in numerous tiny compartments, they do not collapse when broken.
- By day 5, the fluid in the vesicles has become cloudy and looks like pus. At this stage, the pocks are called pustules. At this time, the fever usually rises. On day 7, the rash is definitely pustular. Pocks, although varying somewhat in size, all resemble each other in appearance. The rash is now so characteristic and used as diagnosis of smallpox
- The pustules get a little bigger on days eight and nine. They are completely ingrained in the skin and feel firm to the touch. Dark scabs develop as the pustules gradually dry up. Ten to fourteen days after the rash initially appears, the scabs start to show. The smallpox virus is alive in the scabs. The patient is contagious until all of the scabs have disappeared.
- By day 20, the scabs have fallen off, revealing areas that are light-colored or depigmented. Over several weeks, the skin progressively regains its natural appearance. However, the face may still have permanent scars. These scars are a sign of a prior smallpox illness.
Flat-type Smallpox:
The course of lesions in flat-type smallpox is as follows: delayed macule appearance. Lesions typically have a soft, flat look and progress slowly. Sections of skin may peel off. When significant toxemia is present, the majority of cases are deadly. Patients who have a weak cellular immune response to the virus are more likely to have this type of smallpox.
Hemorrhage-causing smallpox:
- The course of lesions in hemorrhagic-type smallpox is as follows:
- A tiny red or purple mark on the skin’s surface is called a skin petechiae.
- Conjunctival and mucous membrane bleeding
- When there is subcutaneous bleeding, the skin and conjunctivae appear deeply red.
Early multi-organ failure mortality, typically prior to maculae development. This uncommon type of smallpox is common in patients with a highly weakened immune system, when the spleen and bone marrow are experiencing strong viral replication. It is also associated with intense toxemia.
Fig: Progression of Small pox infection