Animal Viruses Because viruses are lifeless partials, their spread depends on other agents. A ( ) is an intermediate host that transfers a pathogen or parasite to another organism Classified as ( ) or ( ) viruses, ( ) or ( )-stranded Many have envelopes with glycoproteins that are specific for receptors. The glycoproteins are made by the ER and added to the host cell’s membrane which envelopes the emerging viruses.

Capsid and viral genome enter the cell Capsid Fig. 19-7 Capsid and viral genome enter the cell Capsid RNA HOST CELL Envelope (with glycoproteins) Viral genome (RNA) Template mRNA Capsid proteins ER Copy of genome (RNA) Glyco- proteins Figure 19.7 The reproductive cycle of an enveloped RNA virus New virus

Table 19-1a Table 1

Table 19-1b Table 1

RNA Viruses The broadest variety of RNA genomes is found in viruses that infect animals ( ) use ( ) to copy their RNA genome into DNA (HIV is ex.) The viral DNA that is integrated into the host genome is called a ( ) Unlike a prophage, a provirus remains a permanent resident of the host cell

Viral envelope Glycoprotein Capsid RNA (two identical strands) Reverse Fig. 19-8a Glycoprotein Viral envelope Capsid RNA (two identical strands) Reverse transcriptase HOST CELL HIV Reverse transcriptase Viral RNA RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation Figure 19.8 The reproductive cycle of HIV, the retrovirus that causes AIDS mRNA New virus

Membrane of white blood cell HIV HIV entering a cell Fig. 19-8b Membrane of white blood cell HIV Figure 19.8 The reproductive cycle of HIV, the retrovirus that causes AIDS 0.25 µm HIV entering a cell New HIV leaving a cell

Viral diseases in animals Symptoms caused by - toxins - body’s defense mechanisms ( ) – weakened or derivatives of viral particles capable of causing an immune response ( ) not effective Some antiviral medications interfere with viral ( ) synthesis

Where do new viruses come from? ( ) of existing viruses The dissemination of an existing virus to a more widespread population Or spread between species ( ) – general outbreak of a disease ( ) – global epidemic

(a) The 1918 flu pandemic (b) Influenza A H5N1 virus Fig. 19-9 (a) The 1918 flu pandemic 0.5 µm Figure 19.9 Influenza in humans and other animals For the Discovery Video Emerging Diseases, go to Animation and Video Files. (b) Influenza A H5N1 virus (c) Vaccinating ducks

Plant viruses More than 2,000 types of viral diseases of plants are known and cause spots on leaves and fruits, stunted growth, and damaged flowers or roots Most plant viruses have an RNA genome Plant viral disease can spread by vertical transmission from parent plant or by horizontal transmission from an external source.

Fig. 19-10 Figure 19.10 Viral infection of plants

Viroids and Prions: The Simplest Infectious Agents ( ) are circular RNA molecules that infect plants and disrupt their growth ( ) are slow-acting, virtually indestructible infectious misfolded proteins that cause brain diseases in mammals Prions propagate by converting normal proteins into the prion version Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans are all caused by prions

Viroids in Plants

Misfolding of proteins to form prions Fig. 19-11 Misfolding of proteins to form prions Original prion Prion Aggregates of prions New prion Normal protein Figure 19.11 Model for how prions propagate

Scrapie in sheep