Smallpox characteristics

One of the most distinguishing features between smallpox and chickenpox is the presence of a prodrome, including a fever, before rash onset. Patients with smallpox characteristically have a severe febrile prodrome beginning 1 days before rash onset. The fever tends to be high, at least 101°F. but most frequently is between 102 and 104°F. hi comparison, children with chickenpox have either no prodrome or a short, mild prodrome, and have little fever before rash onset. Chickenpox in adults may be more severe, and adults are more likely to have some fever before rash onset. However, in either adults or children, if there is no history of a febrile prodrome, smallpox is very unlikely. 

DNA viruses Poxviruses Variola Vaccinia Large particles 200 x 250nm complex symmetry Variola is the smallpox virus. It produces a systemic infection with a characteristic vesicular rash affecting the face, arms and legs, and has a high mortality rate. Vaccinia has been derived from the cowpox virus and is used to immunize against smallpox... 

Variola virus causes smallpox. The incubation period is about 12 days with a range of 7 to 17 days following exposure. Initial symptoms include high fever, fatigue, and head and back aches. A characteristic rash, most prominent on the face, arms, and legs, follows in 2-3 days. The rash starts with flat red lesions that evolve at the same rate. Lesions become pus-filled and begin to crust early in the second week. Scabs develop and then separate and fall off after about 3-4 weeks. Most patients with smallpox recover, but death occurs in up to 30% of cases. 

Within the first 2 to 3 days of exposure a person will experience symptoms such as malaise, fever, headache, chills, and backache. The fever can last 1 to 5 days. Usually after the fever is gone, a skin eruption or rash appears. It begins as a pimple lesion for 1 to 4 days, becomes blister-like for 1 to 4 days, and then fills with pus for 2 to 6 days. It then forms a crust that falls off 2 to 4 weeks after the first skin lesion appears, leaving pink scars. An important characteristic is that all smallpox lesions in any affected area are generally found in the same state. In contrast, chickenpox lesions are not synchronous they form in crops. Smallpox lesions are also said to be more numerous on the face and extremities rather than the trunk, unlike chickenpox. The case fatality rate in unvaccinated patients is 15 to 40%. In vaccinated people, the fatality rate is <1%. Patients with smallpox are infectious as soon as a rash is evident and remain infectious until their scabs fall off— a duration of about 3 weeks.3... 

A very important characteristic of the body s immune system is a capacity to distinguish between self and non-self, In terms of the immune system, the ability to make such distinctions proceeds at the biochemical level without conscious awareness of the individual. Less than a century ago, the ability of the body to distinguish self from non-self (foreign), at the biochemical level, was considered impossible. Over the yeais, however, much descriptive information accumulated which, without ample explanation, proved that the body does remember at the biochemical level. Seldom, for example, have medical records shown a second infection with mumps, measles, or smallpox, once an individual survived the first attack. The question, how does the body remember remained a mystery for many decades until the concept of the immune system was first outlined in a very general way. 

Rash. Whereas fever is characteristic in many different infectious and noninfectious processes, the concomitant occurrence of a rash should provoke further clinical evaluation. In particular, clinicians should he familiar with the characteristic rash produced hy smallpox and the features that distinguish it from the rash produced by varicella (Henderson et al., 1999). The initial vesicular lesions of smallpox progress to large, firm pustules. The lesions are synchronous, that is, at the same stage of development, and centrifugal, that is, more numerous on the face and extremities than on the trunk. This pattern of lesions is a key feature for clinical recognition of smallpox (Henderson et al., 1999). 

The characteristic rash of smallpox is described as synchronous and centrifugal. What does that mean with regard to the pattern of lesions on an affected individual ... 

The skin rash usually begins with a few macules, herald spots, on the face, particularly the forehead. Next, lesions appear on the proximal extremities, later spreading to the distal extremities and the trunk. Within 24 h, the rash is visible on the entire body. Within 2-3 days, the macules become raised papules, and by the third or fourth day, the papular lesions become vesicular. Huid within the vesicles at first is opalescent, but within 24-48 h, it becomes opaque and turbid. A characteristic faint erythematous halo surrounds the skin lesions. Another distinctive feature of the distended smallpox lesions, their central depression or dimple, umbilication, is less common in other vesicular or pustular rashes such as varicella. 

Flat-type refers to the characteristic lesions, which are flush with the skin rather than raised vesicles. In outbreaks in India, flat-type smallpox was responsible for between 5 and 10% of cases, with most of the flat-type cases (72%) occurring in children (25). Constitutional symptoms associated with the 3 day prodrome are more severe than in ordinary smallpox and continue after the rash develops. Patients have a high fever and appear toxic throughout the course of the illness. Oral lesions tend to be extensive, and the skin lesions evolve slowly. By the 7 or 8 day, the flat skin lesions appear buried in the skin. In comparison to ordinary smallpox, the vesicles contain little fluid and do not develop the characteristic umbilication. Unlike ordinary smallpox, flat-type smallpox lesions are soft and velvety in texture. The lesions may contain hemorrhages. Respiratory complications are common, and the prognosis for flat-type smallpox is grave. Most cases are fatal (25). 

A. Characteristics. The smallpox virus is an orthopoxvirus with a narrow host range confined to humans. Eradication of the natural disease was completed in 1977. Appearance of human cases would signal use of the virus as a biological weapon. Under natural conditions, the virus is transmitted by direct contact with an infected case, by fomites, and occasionally by aerosols. Smallpox virus is highly stable and retains infectivity for long periods outside of the host. A related virus, monkeypox, clinically resembles smallpox and causes sporadic human disease in West and Central Africa. The incubation period is typically 12 days (range, 10-17 days). 

Over the years, researchers have unraveled some of the mysteries of the immune system and have used its properties as a therapeutic aid. The first vaccine, that against smallpox, was developed about 200 years ago. Since that time it has been used so effectively as a preventive measure that smallpox has been eradicated. The action of vaccines of this sort depends on exposure to the infectious agent in a weakened form. The immune system mounts an attack, and the immune system retains memory of the exposure. In subsequent encounters with the same pathogen, the immune system can mount a quick and effective defense. This ability to retain memory is another major characteristic of the immune system. It is hoped that current research can be carried to the point of developing vaccines that can treat AIDS in people who are already infected. Other strategies are directed at finding treatments for autoimmune diseases. StiU others are attempting to use the immune system to attack and destroy cancer cells. 

The smallpox virus preferentially attacks skin cells, and by days 14-15, smallpox infection becomes obvious. The attack on skin cells causes the characteristic pimples associated with the disease. The pimples tend to erupt first in the mouth, then the arms and the hands, and later the rest of the body. At that point, the... 

By the fourth day, the bumps fill with a thick, opaque fluid and often have a depression in the center that looks like a bellybutton. (This is a major distinguishing characteristic of smallpox.)... 

D. Smallpox Infection causes generalized malaise and fever due to viremia, followed by a characteristic diffuse pustular rash with most of the lesions in the same stage of development. 

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