Difference Between Chickenpox and Smallpox

Chickenpox and smallpox are viral infections, which share some of the common characteristics and causes diagnostic confusion. But several features of the two diseases are significantly different. This article points out the differences between chickenpox and smallpox with regard to the organism responsible and its properties, clinical picture, complications, diagnosis, treatment and prevention. 


Varicella zoster, which belongs to the herpes virus family, is responsible for the disease. It is a DNA virus and has an ability to cause latent infections. The disease transmission is by respiratory droplets and direct contact with the lesions. It is highly infectious and more severe in adults, pregnant women and immune compromised people. Immunity following the disease is a lifelong.

Following an incubation period of 14-21 days vesicular eruption begins, often on the mucosal surfaces first and then rapid dissemination in a centripetal distribution mostly involving the trunk. The rash progresses from small pink macules to vesicles and pustules within 24 hours and then crust. The lesions appear to be in different stages of development. The pocks are more superficial, and the vesicles collapse on puncture.

The lesions are itchy, and scratching can lead to secondary bacterial infection, which is the most common complication. Rare complications involve self-limiting cerebella ataxia, varicella pneumonia, encephalitis and reye’s syndrome specially in children who are on aspirin.

Clinical diagnosis is made by the classic appearance of the rash. Aspiration of the vesicular fluid and PCR or tissue culture confirms the diagnosis.

Acyclovir is effective in the management of the disease specially if commence within 48 hours of the rash. Live attenuated VZV is given for highly susceptible contacts.


It is a severe deadly disease caused by a pox virus. It has a single stable serotype, which is the key to successful eradication. Human is the only reservoir. The disease transmission is by respiratory droplets or direct contact with virus either in the skin lesions or on fomites as bedding. Immunity following the disease is a lifelong.

Following an incubation period of 7-14 days, sudden onset of prodromal symptoms occur such as fever and malaise followed by rash. The lesions are typically deep seated centrifugal vesicular pustular rash worst on the face and the extremities with no cropping. The lesions appear to be in the same stage of development. Vesicles do not collapse on puncture.

The diagnosis is by growing the virus in cell culture or chick embryo or by detecting viral antigen in vesicular fluid.

There is no effective therapy currently. It has been eradicated with the use of live attenuated vaccina virus. Now there is a potential to use this virus as a bio terrorist weapon.


What is the difference between smallpox and chickenpox?

• Chickenpox is caused by a herpes virus while smallpox is caused by a pox virus.

• Smallpox is deadly severe comparing to chickenpox.

• Incubation period of chickenpox is 14-21 days, but in smallpox, it is 7-14 days.

• In smallpox, prodromal symptoms precede the rash by 2-3 days.

• In chickenpox, the lesions are superficial; appear in crops, Vesicles collapse on puncture, and belong to different ages. In smallpox, the lesions are more deep seated, do not appear in crops, not collapsing on puncture, and belong to the same age.

• Chickenpox is still prevailing, but smallpox has been eradicated on the face of the earth.

• There is a potential of using poxvirus as a bioterrorist weapon.