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38 Cards in this Set
- Front
- Back
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What are the 5 factors that Influence the virus-host Interactions?
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1. Entry into the Host
2. Spread in the Host 3. Host Immune Response 4. Shedding 5. Clearance |
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What are the 7 routes of infection into the host body?
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Skin: abrasion, arthropod vector
Urogenital tract Anus Eyes (conjunctiva) Mouth Respiratory tract Alimentary canal |
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How is the skin an effective barrier to viruses? How do viruses get in?
For which viruses is the skin is the principal portal of entry? |
Dead cells, cannot support virus replication.
Most viruses which infect via the skin require a breach in the physical integrity of this effective barrier, e.g. cuts or abrasions. Many viruses employ vectors, e.g. ticks, mosquitoes or vampire bats to breach the barrier. The skin is the principal portal of entry for some poxvirus, Herpesvirus, and Papillomaviruses |
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What is the mode of entry for papillomavirus? What is their pattern of gene expression?
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They have a selective tropism for the epidermis
They have unusual pattern of gene expression in its successive layers In basal cells, they express only the early gene (oncogenic protein) In the granular and keratinized layers, they express later viral genes and produce mature virions |
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What are the innate immune responses of the mouth and respiratory tract?
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The respiratory tract and all other mucosal surfaces possess sophisticated immune defense mechanisms, as well as non-specific inhibitory mechanisms:
-ciliated epithelium -mucus secretion -lower temperature |
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How might respiratory infection be initiated?
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either by virus contained in aerosols that are inhaled by the recipient host
or by virus that is contained in nasopharyngel fluids and is transmitted by hand to hand contact |
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How many viruses infect the host through oral and nasal tract?
How do they do it? |
A lot
They have ways to overcome the inhibitory measures that the respiratory tract employ. |
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What kind of viruses infect the oropharynx and GI tract?
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Most of these viruses are acid resistant.
Enteric viruses invade in a variety of site from oral cavity to the colon Most enteric viruses, such as rotaviruses, produce localized infections in the epithelium of small or large intestine Some enteroviruses, such as poliovirus, can also replicate in lymphoid tissue of the nasopharynx |
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What are the common features of enteroviruses?
What type of cells do they infect? |
They are resistant to acid pH, proteolytic attack, and bile!
Rhinoviruses, acid labile, can not infect by the intestinal route Hepatitis A is acid resistant, behaves epidemiologically as an enterovirus, whereas hepatitis B does not. Usually infect intestinal epithelium. |
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How are infections of the urogenital tract initiated?
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Infection is initiated either by penetration of the virus through breaks in the skin or by direct infection of the superficial epithelium of the mucous membrane.
Papillomaviruses HSV Hepatitis HIV |
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There are a few viruses that use conjunctiva as a primary portal of entry, what are they?
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- Adenovirus: “swimming pool conjunctivitis” and “shipyard eye”
- Enterovirus: coxsackievirus A24 and enterovirus type 70 - Vaccinia and HSV |
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What is Arbovirus?
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A large number of animal viruses, Arboviruses, are maintained in nature through a cycle that involves a vector (an insect) and a vertebrate host.
Bunyaviridae Flaviviridae Reoviridae Rhabdoviridae Togaviridae |
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What is the mechanical transmission by vectors?
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The vector act as “ flying Pin”
1) Myxoma virus of rabbits transmitted by mosquitoes or mites 2) Rabbit papillomatosis is also transmitted in a similar way. |
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What is the only virus that requires the bite of a host?
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Rabies is the only virus that infects host by the bite of a host!
It can enter the processes of peripheral nerves directly It can replicate in striated muscle, then cross the neuromuscular junction and spread along peripheral nerves to the central nervous system |
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How are viruses transmitted to the host by injection or transfusion?
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Virus may be accidentally transmitted by:
Repeated use of contaminated needles, Injection of a virus-contaminated therapeutic agent, Transfusion with virus-contaminated blood or blood products. Hepatitis B, C, and D Cytomegalovirus HIV |
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How might a local infection spread through the lymph?
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Following an initial infection at the site of entry, most viruses spread locally by cell-to-cell transmission of infection.
At the entry sites, viruses can be carried through afferent lymphatic drainage from the site of initial infection to the regional lymph nodes, either as free virions or in virus-infected phagocytic cell. Some viruses remain localized near their site of entry, whereas others spread widely. |
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What is a primary infection?
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Once the virus gets into a host, the virus must initiate an infection by entering a susceptible cell.
The primary infection is either localized at the site of entry or disseminated to other organs as systemic infection. |
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What factors influence local virus spread? How do the apical and basal surfaces play into this?
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Virus maturation inside cell influences the dissemination
Viruses that are released only at the apical surface tend to remain localized. Viruses that are released at the basal surface tend to disseminate systemically. |
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What are the routes of virus spreading within the host?
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1. through the lymphatic drainage system
2. through the blood stream 3. along the nervous system |
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At what point does the virus use lymphatics to move around?
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Following local virus replication, the free virions or virus-infected phagocytic cell can be carried through afferent lymphatic drainage from the site of initial infection to the regional lymph nodes, then to other organs.
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Which of the routes of spreading through the host is the most important to viruses?
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The most important mechanism for dissemination is the blood circulation, which can potentially carry the virus to any organ or tissue
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How do viruses get into the bloodstream to travel around the body?
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Virus may get into the bloodstream by direct inoculation - e.g. Arthropod vectors, blood transfusion or I.V. drug abuse
The virus may travel free in the plasma (Togaviruses, Enteroviruses) The virus may travel in association with red cells, platelets (HSV), lymphocytes (CMV) or monocytes |
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How do viruses spread through the nervous system?
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Virus spreading occurs directly by contacting with nerve ending at the primary site of infection.
Once in peripheral nerves, the virus can spread to the CNS by axonal transport along axons (classic - HSV). Viruses can cross synaptic junctions since these frequently contain virus receptors, allowing the virus to jump from one cell to another. |
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What is the life cycle of HSV-1 in vivo?
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One of the unique features about the a herpes virus is that following the initial infection at peripherial site of entry, the virus travels to CNS via retrograde axonal transport and become latent in the trigeminal ganglion. The latent infection can often be reactivation, virus then travel to the periphery site through anterograde axonal transport and produce recurrent disease.
1 Virus replicate at peripheral entry site in epithelial cells 2 Virions from epithelial cell can spread to the peripheral nerve ending, and travel to PNS via retrograde axonal transport 3 Latency established in sensory nerve ganglion, remain latent for life 4 Virus Sporadic reactivation 5 Virions travel back to the periphery site by anterograde axonal transport 6 Recurrent epithelial infection at or near site of primary infection |
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What are some viruses that spread by the neural route?
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Piconaviridae polio
Flaviviridae Yellow fever Alphaviridae Venezuelan equine encephalitis Coronaviridae mouse hepatitis Rhabdoviridae Rabies Reoviridae Reovirus Herpesviridae Bovine herpesvirus type 1&2 Pseudorabies |
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Define viremia.
Define active viremia. Primary viremia Secondary viremia |
Viremia: viruses circulate either freely in the plasma phase of the blood or associated with formed elements in the blood system.
Active viremia: means there is active replication of virus in the host and virus is circulating in the blood stream. Primary viremia: virus spreads from a local site of entry to other organs. Secondary viremia: it is generated after secondary infection after spreading to target organs. |
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Define secondary replication.
What happens if you prevent the virus from reaching the target tissues? |
It occurs in systemic infections when a virus reaches target tissues where it is capable of replication, e.g.:
Poliovirus (gut epithelium, neurons in brain & spinal cord) Lentiviruses (macrophages, CNS, many other tissues). If a virus can be prevented from reaching target tissues where secondary replication can occur, generally no disease occurs. |
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Define plasma viremia and passive viremia.
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Plasma Viremia: virus is not associated with any of the formed elements of blood.
Passive viremia: virus in the circulation is injected by intravenous, intraperitoneal, intracerebral, intradermal, intramuscular, or subcutaneous routes without any intervening stage of replication. |
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What is cell-associated viremia?
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Virus in the circulation is inside blood cells.
Virus can replicate inside those blood cells: Monocytes B or T lymphocytes rarely, erythrocytes |
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What are the sources of viremia?
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Virus can enter the circulation from a number of different sites, including:
The efferent lymphatics Vascular endothelium Peripheral blood monocytic cells (such as monocytes and lymphocytes) |
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What is the difference between acute and persistent viremia?
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Acute – you can find the virus in the blood system for two weeks
Persistent – you can find the virus in the blood for a month or more. |
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What is the difference between acute and persistent viral shedding? Where is it shed?
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Acute viral infections are characterized by brief periods of intensive virus shedding.
Virus may be shed into respiratory aerosols, feces, urine, or other body secretion or fluids. A given virus may be excreted from several portals, only a few of which are relevant for transmission. Persistent viruses may be shed at relatively low levels, but these low levels is adequate for transmission over period of infection. |
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How are viruses shed from the respiratory tract?
What are some viruses shed nasally and orally? |
Viral shedding from the respiratory track:
Shedding in mucus or saliva Coughing Sneezing Eating and drinking Virus shed in nasal and oral secretion: BHV-1, paramyxo-, corona-, and bovine respiratory syncytial virus |
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What viruses are shed from the skin?
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Viral shedding from the skin via direct contact or small abrasion:
-Cowpox, vaccinia, orf, pseudocowpox, molluscum contagiosum viruse, papillomaviruses, herpesvirus -Feather follicles: Marek’s disease virus |
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Which viruses shed from the urinary tract? Genital tract?
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Viral shedding from the Urinary tract:
Rinderpest virus, Flu viruses, Picornaviruses, hepatitis virus, FMDV, arenaviruses, Virus shedding from the genital tract: Equine arteritis Herpesvirus Papillomavirus |
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Which viruses shed from the milk? Blood and tissues?
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Viral shedding in milk:
Caprine arthritis-encephalitis virus Mouse mammary tumor virus Tick-borne flaviviruses Viral shedding via blood and tissue Equine infectious anemia virus Bovine leukemia virus |
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Why are viruses so infectious?
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They shed into the environment. Millions of particles are sneezed out and are light enough to blow off into the wind.
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What cells are involved in virus clearance?
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Circulating virus is removed by the reticuloendothelial system
-Primarily by the Kupffer cells of the liver, and to a lesser extent in the lung , spleen, and lymph nodes. The virus may be degraded inside the cell Tc cells – kill infected cells. Antibody assisted clearance: After the host has developed circulating antibody, plasma virus is rapidly neuralized in the circulation, and virus-antibody complexes bind to Fc receptors, facilitating removal by sessile macrophages lining the vessels. |
