Smallpox flat-type

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). 

CDC Case Definition An illness with acute onset of fever >101°F followed by a rash characterized by firm, deep seated vesicles or pustules in the same stage of development without other apparent cause. Clinically consistent cases are those presentations of smallpox that do not meet this classical clinical case definition (1) hemorrhagic type, (2) flat type, and (3) variola sine eruptione. Laboratory criteria for diagnosis is (1) polymerase chain reaction (PCR) identification of variola DNA in a clinical specimen, or (2) isolation of smallpox (variola) virus from a clinical specimen (Level D laboratory only confirmed by variola PCR). 

Three quarters of endemic cases of variola major fell into the classic, or ordinary, variety (see Figure 27-1). The fatality rate was 3% in vaccinated patients and 30% in unvaccinated. Other clinical forms of smallpox were associated with variola major, and it is likely that differences in both strain virulence and host response were responsible for these variations in clinical manifestations.68 Flat-type smallpox, noted in 2% to 5% of patients, was typified by (a) severe systemic toxicity and (b) the slow evolution of flat, soft, focal skin lesions (Figure 27-3). This syndrome caused 66% mortality in vaccinated patients and 95% mortality in unvaccinated. Hemorrhagic-type smallpox, seen in fewer than 3% of patients, was heralded by the appearance of extensive pete-chiae (Figure 27-4), mucosal hemorrhage, and intense toxemia death usually intervened before the development of typical pox lesions.69... 

Bacterial superinfection of pox lesions was relatively uncommon except in the absence of proper hygiene and medical care. Arthritis and osteomyelitis developed late in the course of disease in about 1% to 2% of patients, more frequently occurred in children, and was often manifested as bilateral joint involvement, particularly of the elbows.70 Viral inclusion bodies could be demonstrated in the joint effusion and bone marrow of the involved extremity. This complication reflected infection and inflammation of a joint followed by spread to contiguous bone metaphyses, and sometimes resulted in permanent joint deformity.71 Cough and bronchitis were occasionally reported as prominent manifestations of smallpox, with attendant implications for spread of contagion however, pneumonia was unusual.72 Pulmonary edema occurred frequently in hemorrhagic- and flat-type smallpox. Orchitis was noted in approximately 0.1% of patients. Encepha-... 

Fig. 27-3. Flat-type smallpox in an unvaccinated woman on the sixth day of rash. Extensive flat lesions (a and b) and systemic toxicity with fatal outcome were typical. Reprinted with permission from Fenner F, Henderson DA, Arita I, Jezek Z, Ladnyi ID. Smallpox and Its Eradication. Geneva, Switzerland World Health Organization 1988 33. Photographs by F. Dekking.

The Variola major rash presents in four distinct ways, ordinary, modified, flat, and hemorrhagic. The type of rash presentation is probably associated with the strength of the immune response. Ordinary smallpox is most frequent, whereas the mild modified form, seen primarily in previously vaccinated patients, is uncommon. The most severe presentations, flat and hemorrhagic, are usually fatal but are fortunately rare. Smallpox infection can also occur without a rash. A mild but uncommon variation of variola infection, variola sine eruptione (meaning smallpox without a rash) occurs generally in previously vaccinated people and involves a febrile illness alone. Asymptomatic infections are also possible, yet rare. 

There are two clinical forms of smallpox. Variola major is the severe and most common form of smallpox, with a more extensive rash and higher fever. There are four types of variola major smallpox ordinary (the most frequent type, accounting for 90% or more of cases) modified (mild and occurring in previously vaccinated persons) flat and hemorrhagic (both rare and very severe). Historically, variola major has an overall fatality rate of about 30% however, flat and hemorrhagic smallpox usually are fatal. Variola minor is a less common presentation of smallpox, and a much less severe disease, with death rates historically of 1 % or le.ss. 

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