Many years ago, smallpox was sometimes mistaken with chickenpox—a fatal contagious disease that frequently occurs in children in the form of a low-grade fever and episodes of vesicles. Chickenpox and smallpox both differ in various interesting ways. Chickenpox wounds that occur due to disease or injury, in particular, appear in a subtle way at first.
The lesions appear mostly on the trunk, instead of the hands, arms, and face. Moreover, further series of lesions usually emerge in the same area. In turn, a patient experiences a combination of scabs, pustules (a small constrained rise of the skin with pus and an infused base), and vesicles (a small abnormal growth of the outer part of skin surrounding a water base).
Also worth knowing, a patient with chickenpox can inadvertently spread the virus to others before symptoms surface. This causes the symptoms to slowly take their toll and stay contagious until all scabs fade from the pustules.
Varicella zoster, a virus that's also part of the herpes virus family, is the chief cause of the disease. In essence, it's a DNA virus which has the potential of causing underlying infections. Chickenpox often spreads through respiratory droplets and direct contact with the wounds. It's very infectious and quite severe in pregnant women, adults, and immune compromised people. In fact, full immunity following the disease may take a long time to pull through.
After an incubation period of 14-21 days, vesicular eruption starts in the mucosal areas first, and rapid dissemination follows next. The rash spreads further from small pink macules pustules and vesicles within 24 hours. From there, it begins spreading toward the crust. At this time, the wounds occur in different stages, the blisters burst on puncture, and the pocks appear more shallow.
The lesions are also itchy, and severe scratching can cause a secondary bacterial infection. In fact, severe scratching is the most common issue that many patients experience. Most reported rare complications are varicella pneumonia, cerebellar ataxia, encephalitis, and Reye's syndrome, particularly in children on aspirin.
Smallpox is a much more severe disease than chickenpox and usually transmitted by a pox virus. It has a single versatile serotype—the core area for successful suppression and man is the only reservoir. The disease mainly spreads through respiratory droplets and close contact with virus from the skin lesions and materials such as beddings. Full recovery after treatment may take a long time, depending on a patient's immunity system.
Following an incubation period of about 7-14 days, abrupt emergence of prodromal symptoms arise as malaise and fever and subsequent rash. The wounds appear quite deep seated, although the rash may worsen if spread on the face. Moreover, the lesions undergo the same stage of formation and, unlike in chickenpox, cysts don't usually burst on puncture.
Official diagnosis is conducted in two ways: growing the virus in the chick embryo or cell culture and analyzing viral antigen levels in the vesicular fluid. Currently, no effective therapy exists as traces of live attenuated vaccine virus are found in patients even after treatment.
Smallpox is spread by a pox virus, while chickenpox is a herpes-transmitted virus. Smallpox is much more severe than chickenpox. The incubation period of smallpox is about 7-14 days, while that of chickenpox is about 14-21 days. In chickenpox, the wounds are suppressed and are conspicuous in crops. Its vesicles also rupture on puncture and belong to different ages. In smallpox, the lesions are more deep-seated, don't appear in crops, and don't break on puncture. They're also of the same age. And finally, chickenpox is still a global epidemic disease, but smallpox was long eradicated from the face of the earth.
Clinical diagnosis is frequently used to treat chickenpox, depending on the classic appearance of the rash. Acyclovir is effective in keeping the disease under control, especially if it's started within 2 days of the rash. And live attenuated VZC is provided for much more severe and highly vulnerable contacts.
In summary, smallpox and chickenpox are both viral infections, which often share the same characteristics—hence leading to diagnostic confusion. However, further classification of the two diseases tell otherwise and are interestingly different.