Читать книгу Principles of Virology, Volume 2 - Jane Flint, S. Jane Flint - Страница 62

Infection by viruses is often described in terms associated with warfare. There are opposing forces, each equipped with weapons to defeat the other. Once the battle ensues, each side fights with maxi mum force until a victor emerges. A more fitting metaphor to define the events pursuant to a viral infection would be a game of chess played by two masters. For each action, there follows a counter action. Powerful tactics, such as induction of the adaptive immune response, may take many “moves” to be put into action . As one thinks about infection and immunity, it is imperative to bear in mind that we have coevolved with many of the viruses that infect us today. Such coevolution implies that, at a population level, both host and virus will survive. On an individual level, however, the consequence of infection is dictated by the host species and immune fitness, the dose and strain of virus, and numerous environmental parameters (Chapter 1).

The pathogenesis of ectromelia virus, the agent of mousepox, highlights how the outcome of infection is affected by some of these variables (Fig. 2.1). Ectromelia virus is shed in the feces of its natural mouse host and gains access to naïve mice via small abrasions in the footpad. Therefore, the first hurdle to be overcome is penetration of dead skin, which serves as an inhospitable barrier against infection. There is no guarantee that a mouse in a cage with infected feces will become infected. Virus particles must come in physical contact with permissive and susceptible cells for infection to occur, necessitating some disruption of the skin to allow access of the virus to live cells. Once the virus has gained entry, local reproduction in the epidermis and dermis of the footpad takes place. Within a day after exposure, the virus moves to draining lymph nodes, enters the bloodstream, and can be found in the spleen and liver by 3 days after infection. Thereafter, the virus continues to spread throughout the host, causing massive inflammation and severe skin lesions by 10 to 11 days after exposure.