Dr. Bob Morrison - Porcine Epidemic Diarrhea Virus (PEDv) Transmission
Virus transmission
description
Transcript of Virus transmission
Virus transmission
LECTURE 7:
Viro100: Virology3 Credit hoursNUST Centre of Virology & Immunology
Waqas Nasir Chaudhry
Virus infectionEpidermal
cells
Mesophyll cells
Bundle sheath cells
PhloemParenchyma
Companion cells
Phloem
Other host plants
Replication
Plant-to-plantmovement
Cell-to-cellmovement
Systemic
movement
Stages of viral infection cycle
• A minimum proportion of the virions produced in infected hosts must be transmitted to new hosts in which more virions can be manufactured.
• Viruses are dependent upon chance to encounters with susceptible cells, to which they may bind if receptors on the surface of those cells come into contact with virus attachment sites
• Viruses can’t move, hence they opt number of possibilities for transmission
• Some virus infections modify the behaviour of their hosts in order to increase the probability of transmission
• Some plant feeding insect larvae infected with baculoviruses become more mobile in the late stages of infection, thus aiding virus dispersal
• Mammals infected with rabies virus often become aggressive; this change in behaviour increases the likelihood of the host biting another individual and transmitting virus in the saliva
Transmission types
• Horizontal transmission• In Horizontal transmission virus travels from one host to
another between two individuals, generally in the same generation– Direct contact can occur due to touching, biting or licking or
sexual intercourse (HIV, HCV, Influenza)– Indirect contact can occur through vectors (Dengue Virus,
CLCV)
• Vertical transmission• Viruses that can be transmitted directly from a parent to
members of the next generation (HIV, Rubella Virus)
• Viruses may be moved over long distances in a variety of ways
• Rivers and winds• Bird migration (avian influenza viruses)• Human travel (SARS virus)• Animal export (monkey pox virus)• Once virions have entered a multicellular
organism they may have further to travel before suitable host cells are encountered
• Escape from host defense mechanisms• Minimum amount of virus required for infection
of a host is known as the minimum infective dose
Transmission via vectors; generalprinciples
• Many viruses of plants and animals are transmitted between hosts by organisms that feed on them; these organisms act as vectors
• Most vectors of viruses are arthropods, the arthropod transmitted viruses of vertebrates are sometimes referred to as arboviruses
• Many of the modern ‘plant viruses’ and ‘vertebrate viruses’ are descended from viruses of invertebrates that later extended their host ranges to plants or vertebrates
Vector feed on infected host Pick the virus Transfer to
uninfected host
If virus attach to Vector mouth
part
Transmission happens in
seconds and minutes
If virus cross the gut wall of vector
Virus enter into circulatory
system
Virus reach salivary
gland and secrete through
saliva
1
2 Circulative transmission
Non-Circulative transmission
• Some circulative viruses replicate in one or more tissues and organs of their vectors; thus there are viruses that can replicate in both invertebrates and plants
• If the reproductive organs of the vector are infected there may be possibilities for vector-to-vector transmission
• Some viruses are sexually transmitted (male to female and vice versa)
• Some are transmitted to the next generation within the egg; the latter is known as transovarial transmission
Cross-section of a mosquito . Some of the organs and tissues that may become infected by a virus acquired in a blood meal are indicated
Transmission of plant viruses• Plant viruses are classified
– as non-persistent – semi-persistent – and persistent
• In non-persistent transmission, viruses become attached to the distal tip of the stylet of the insect and on the next plant it feeds on, it inoculates it with the virus
• Semi-persistent viral transmission involves the virus entering the foregut of the insect
• Those viruses that manage to pass through the gut into the haemolymph and then to the salivary glands are known as persistent
Transmission of plant viruses
• Aphid• Nematode• Parasitic Fungi