1. 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.

2. 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

3. Table 19-1a
Table 1

4. Table 19-1b
Table 1

5. 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

6. 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

7. 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

8. 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

9. 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

10. (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

11. 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.

12. Fig
Figure Viral infection of plants

13. 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

14. Viroids in Plants

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

16. Scrapie in sheep