In the initial growth phase, the virus seemed to move from cell to cell, but by around the 12th day, widespread lysis of infected cells occurred and the virus could be found in the bloodstream in large numbers, a condition known as viremia. This resulted in the second wave of multiplication in the spleen, bone marrow, and lymph nodes. Diagnosis
The clinical definition of ordinary smallpox is an illness with acute onset of fever equal to or greater than 38.3 °C (101 °F) followed by a rash characterized by firm, deep-seated vesicles or pustules in the same stage of development without other apparent cause. When a clinical case was observed, smallpox was confirmed using laboratory tests. Microscopically, poxviruses produce characteristic cytoplasmic inclusion bodies, the most important of which are known as Guarnieri bodies, and are the sites of viral replication. Guarnieri bodies are readily identified in skin biopsies stained with hematoxylin and eosin, and appear as pink blobs. They are found in virtually all poxvirus infections but the absence of Guarnieri bodies could not be used to rule out smallpox. The diagnosis of an orthopoxvirus infection can also be made rapidly by electron microscopic examination of pustular fluid or scabs. All orthopoxviruses exhibit identical brick-shaped virions by electron microscopy. If particles with the characteristic morphology of herpesviruses are seen this will eliminate smallpox and other orthopoxvirus infections. Definitive laboratory identification of Variola virus involved growing the virus on chorioallantoic membrane (part of a chicken embryo) and examining the resulting pock lesions under defined temperature conditions.
The latter view is frequently supported in the scientific community, particularly among veterans of the WHO Smallpox Eradication Program.On March 31, 2003, smallpox scabs were found inside an envelope in an 1888 book on Civil War medicine in Santa Fe, New Mexico. The envelope was labeled as containing scabs from a vaccination and gave scientists at the CDC an opportunity to study the history of smallpox vaccination in the United States. On July 1, 2014, six sealed glass vials of smallpox dated 1954, along with sample vials of other pathogens, were discovered in a cold storage room in an FDA laboratory at the National Institutes of Health location in Bethesda, Maryland. The smallpox vials were subsequently transferred to the custody of the CDC in Atlanta, where virus taken from at least two vials proved viable in culture. After studies were conducted, the CDC destroyed the virus under WHO observation on February 24, 2015.In 2017, Canadian scientists recreated an extinct horse pox virus to demonstrate that the smallpox virus can be recreated in a small lab at a cost of about $100,000, by a team of scientists without specialist knowledge. This makes the retention controversy irrelevant since the virus can be easily recreated even if all samples are destroyed.