Viruses abound in the environment and are a big problem in the hospitals environment, both for staff and patients. This is especially true of respiratory viruses such as Respiratory syncitial virus on pediatric wards and gastroenteritis viruses. RSV has also been a problem for hospitalized adults and the elderly. While RSV usually causes the common cold in healthy adults, in hospitalized adults it can cause serious lifethreatening illness. Entry of virus into the cell.
Viruses are species specific with different tissue tropisms.
E.g. Human enteroviruses do not infect other species, while animal enteroviruses don't infect humans. However influenzae and rabies virus do cross species. Tissue tropism depends on viral attachment proteins and the cellular receptive molecule. Receptors may be carbohydrates, glycoproteins or proteins. Many receptors serve other cellular functions, and are also receptors for hormones and growth factors.