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

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

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

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

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

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

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

Non-vector transmission of vertebrate viruses

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