Viruses stored in various solutions for extended periods are not viable for culture detection and may be unsuitable for molecular testing. Much work was done trying to identify the severe acute respiratory syndrome (SARS) agent before it was classified by EM as a coronavirus ( 20, 50), and the monkeypox outbreaks in the United States in 2003 ( 6, 31, 75) were discovered by EM to be caused by a poxvirus. Further, the Henipavirus ( Hendra and Nipah) outbreaks in Australia and Asia were first described by use of EM ( 15, 42, 44), and in 2003, EM recognized lymphocytic choriomeningitis virus as the cause of fatalities of recipients of organs transplanted from a single donor ( 23).
#THREE DISADVANTAGES OF ELECTRON MICROSCOPE SKIN#
In 1999, the causative agent of a strange skin infection in an immunosuppressed patient, coined trichodysplasia spinulosa, was identified by EM as a polyomavirus ( 36) since then, eight additional cases have been described and confirmed by EM of thin sections of skin biopsy specimens. EM was instrumental in elucidating the viral agent of the first outbreak of Ebola virus in Zaire in 1976 ( 8, 45, 71) and in identifying the Ebola Reston infection of a monkey colony in Reston, VA, in 1989 as being caused by a filovirus ( 28). For example, norovirus (Norwalk agent) was discovered by EM ( 46), and EM continues to serve to confirm infection in quality control of molecular techniques ( 87). Finally, in cases of dual infections, molecular or antigen-based testing would likely miss the second agent.Įven today, in the age of molecular diagnostics, EM is a mainstay in detecting new and unusual outbreaks. Another fact to keep in mind is that reagents do not exist for all viruses when they grow poorly or not at all in in vitro systems, obtaining enough material to produce commercial test kits is difficult. EM, though it may not be able to identify a virus beyond the family level, at least points the way for more specific identification by other methods such as biochemical assays for specific pathogens. On the other hand, EM allows an “open view” (a term coined by Hans Gelderblom) of whatever might be present, while molecular tests require knowledge about the potential agent(s) to determine the correct test(s).
In the event of a disease caused by an unknown pathogen, it is hard to know which reagent to pick. Other tests involving molecular and serological methods require that a specific probe be available for virus identification. One of the main advantages of using EM for viral diagnosis is that it does not require organism-specific reagents for recognizing the pathogenic agent. Even today, taxonomy books include electron micrographs of viruses in their descriptions ( 22). That virus was later determined to be the cause of transient aplastic crisis in patients with sickle cell disease and of “fifth disease,” a childhood exanthem. Cossart et al., in noticing an anomalous reaction while testing normal blood for hepatitis B virus, excised a precipitation band from a gel and, using EM, demonstrated that it contained a very small virus (parvovirus B19) ( 16). Early virus classification depended heavily on morphology as shown by EM ( 2, 4, 60), and many of the intestinal viruses were discovered by EM examination of feces after negative staining ( 32, 46, 54, 96).
The first image of poliovirus was taken in 1952 ( 74), and virus-host relationships began to be studied in the mid-1950s ( 24, 25).
In 1948, differences between the virus that causes smallpox and the virus that causes chicken pox were demonstrated by EM ( 62, 92). Other historical electron microscopic observations have led to the discovery of new viruses. Eight years later, Ruska and colleagues Kausche and Pfankuch were the first to visualize viruses (tobacco mosaic virus) with the EM ( 47), and in 1986, Ruska shared the Nobel Prize with Binnig and Rohr, developers of the scanning tunneling electron microscope. Ernst Ruska, with his mentor Max Knoll, built the first electron microscope in 1931 as the project for his Ph.D.
Organisms smaller than bacteria have been known to exist since the late 19th century ( 11), but the first EM visualization of a virus came only after the electron microscope was developed. Electron microscopy (EM) has long been used in the discovery and description of viruses.