ABSTRACT
A huge number of viruses are now known to science, and their structure and behavior are amazingly diverse, although we shall ignore the viruses of insects, plants, and bacteria and consider only those of warm-blooded vertebrates (Table 1). Fortunately, although we need to think of some of the viruses that affect farm animals, those involved in asthma all belong to the group commonly called respiratory viruses of humans. To molecular biologists this is an unsatisfactory classification, for it brings together viruses with profound differences in their genome. Some encode genes in DNA, but many more use RNA, and in many the particle contains a positive sense strand while in some it is negative stranded; profound differences in the strategy of virus replication result from this. Proteins, some of which are enzymes, are encoded by the genes and synthesized with the ribosomes of the host cell. In some cases they condense around nucleic acid and
Table 1 Classification and Basic Structure of Viruses Causing Human Respiratory Infections
Size Lipid Family Name Genome (nm) envelope Serotypes Picornaviridae Rhinovirus RNA ss+ 20-30 0 100+ Picornaviridae Coxsackie RNA ss+ 20-30 0 70+
(enterovirus) viruses A & B Echovirus
Orthomyxoviridae Influenza RNA ss-80-120 + Types A, virus B, and C
Many strain differences
Pararnyxoviridae Human RNA ss-150-300 + 4 (pararnyxovirus) parainfluenza
virus Pararnyxoviridae Respiratory RNA ss-150-300 + 2
(pneumovirus) syncytial virus Pararnyxoviridae Measles virus RNA ss-150-300 +
(morbillivirus) Coronaviridae Human RNA ss+ 80-160 + 2
corona virus Adenoviridae Human DNA ds± 70-90 0 35+
(mastadenovirus) adenovirus ss = single stranded; ds = double stranded; + and - indicate polarity of nucleic acid in panicle.
