Читать книгу Principles of Virology, Volume 2 - Jane Flint, S. Jane Flint - Страница 93

In a number of systemic viral infections, rashes are produced when virus particles leave blood vessels and enter the cells that comprise the skin. Viruses that cause rashes include measles virus, rubella virus (German measles), varicella-zoster virus (chicken pox and shingles), some parvoviruses (fifth disease), poxviruses (smallpox), and Coxsackieviruses (hand, foot, and mouth disease). Skin lesions resulting from these infections are notably distinct, distinguished by size, color, frequency, and elevation (an indication of inflammation). Rashes may appear coincident with or subsequent to an infection, although most all appear toward the end of the acute infection. Destruction of cells by virus reproduction and the host immune system are the primary causes of most skin lesions.

Rashes are not restricted to the skin. Lesions may also occur in mucosal tissues, such as those in the mouth and throat. Because these surfaces are wet, vesicles break down more rapidly than on the skin. During measles infection, ulcerating vesicles in the mouth, called Koplik spots, appear 2 to 4 days before the characteristic skin lesions. Identifying a viral infection early has obvious containment benefits: by the time that the infection is recognized from the skin rash, viral transmission to other individuals may already have occurred.

Figure 2.21 How viruses gain access to the central nervous system. (Left) A summary of the mechanisms by which viruses can enter the brain is shown. CSF, cerebrospinal fluid. (Right) Schematic of the composition of the blood-brain barrier.