1. Viro100: Virology 3 Credit hours NUST Centre of Virology & Immunology
LECTURE 8:
Virus transmission
Waqas Nasir Chaudhry
Viro100:
Virology
3 Credit hours
NUST Centre of Virology & Immunology

2. Transmission of plant viruses
The viruses have the "machinery" to enter the animal cells directly by fusing with the cell membrane
By contrast, plant cells have a robust cell wall and viruses cannot penetrate them unaided
Hence plant virus are transmitted by a vector organism that feeds on the plant
Aphid
Nematode
Parasitic Fungi
Around 80% plant virus are transmitted by vector

3. Nematode
The nematodes that transmit viruses are soil-dwelling animals that pierce root cells and then ingest their contents
An interesting aspect is vector specificity
Tobraviruses have rod shaped virions and are transmitted by nematodes in the family Trichodoridae
Nepoviruses have isometric virions and are transmitted by nematodes in the family Longidoridae

4. The basis of some cases of plant virus vector specificity lies in specific amino acid sequences in capsid proteins
In other cases important roles are played by virus coded non-structural proteins (helper factors) that are synthesized in the infected plant cell
GAG is capsid protein
VAP Virion associated protien
ATF Aphid transmission factor

5. Parasitic Fungi
Some plant parasitic fungi can also act as virus vectors, for example Spongospora subterranea, which infects potato causing powdery scab disease, is a vector of potato mop top virus
If a plant is infected with both a fungus and a virus, then virions may be taken into developing fungal spore

6. Plant viruses can be transmitted vertically
About 20 % of plant viruses can be transmitted vertically
Seed can be infected, leading to infection of the next generation
Most seed transmitted viruses are carried in the embryo, which may have acquired its infection from either an infected ovule or an infected pollen grain
Nepoviruses and the Tobraviruses

7. Non-vector transmission of vertebrate viruses
Many viruses of vertebrates (including humans) infect their hosts via the mucous membranes
An infected individual may shed virus-containing droplets into the air during sneezing, speaking and coughing
Virus present in genital secretions can be transmitted during sexual contact
viruses infecting the intestinal tract are shed in faeces

8. Non-vector transmission of vertebrate viruses

9. Transmission of invertebrate viruses
Many of these viruses have evolved occlusion bodies, which are large protein structures in which virions become embedded in the infected cell
Viruses that produce occlusion bodies include cypo-viruses and baculoviruses
Occlusion bodies may be expelled in the faeces of a virus infected insect or they may remain in the host until it is ingested by a predator or it dies as a result of the virus infection