Exam 1: Mechanisms of Infection Flashcards
What viruses use the minor abrasion route?
Family: poxviridae
Cowpox, orf
What viruses use the arthropod (mechanical) route?
Family: poxviridae
Fowlpox, swinepox
What viruses use the arthropod (biological) route?
Family: rhabdoviridae
Bovine epheremal fever
What viruses use the bite of vertebrate route?
Family: rhaboviridae
Rabies
What viruses use the genital tract route?
Family: herpesviridae
Many species
What viruses use the conjunctiva route?
Family: adenoviridae
Canine adenovirus 1 and 2
What viruses initiate infection in the respiratory tract?
Adenoviridae and herpesviridae: many species
Parvoviridae: feline panleucopenia virus, canine parvovirus
What viruses produce respiratory disease?
Adenoviridae and herpesviridae
Many species
What viruses produce systemic disease, usually without initial respiratory signs?
Parvoviridae
Feline panleucopenia virus, canine parvovirus
What viruses initiate infection in the intestinal tract?
Coronaviridae and toroviridae: some coronaviruses, Breda and Berne viruses
Calciviridae and picornaviridae: vesicular exanthema of swine virus, some enteroviruses
What viruses produce diarrhea?
Coronaviridae and toroviridae
Some coronaviruses, Breda and Berne viruses
What viruses produce systemic disease, usually without diarrhea?
Calciviridae and picornaviridae
Vesicular exanthema of swine virus, some enteroviruses
What are the mechanisms of spread in the body?
Local spread on epithelial surfaces
Subepithelial invasion and lymphatic spread
Spread by the bloodstream: viremia
Describe local spread on epithelial surfaces with pox virus
Produce infection via the skin
Local subepithelial and lymphatic spread
Describe local spread on epithelial surfaces with paramyxoviruses and influenza virus
Do not invade subepithelial tissues
Enter lymphatic and spreaf
Describe local spread on epithelial surfaces with rotaviruses or coronaviruses
Do not invade subepithelial tissues
Enter lymphatic and spread
Where does canine distemper virus replicate?
Macrophages
What is the most important route for virus shedding?
Respiratory secretions
Which viruses have virus shedding in the skin?
FMD
Vesicular stomatitis
Pox
Herpes
What viruses have virus shedding in saliva?
Rabies and feline immunodeficiency viruses
What viruses have virus shedding in feces?
Poliovirus and rotaviruses
What viruses have virus shedding in genital secretions?
Herpes and immunodeficiency viruses
What viruses have virus shedding in urine (viruses that replicate in the kidney)?
Rinderpest
Infectious canine hepatitis
FMD
What viruses have virus shedding in milk (replicate in mammary gland)?
Caprine arthritis-encephalitis
Tick-borne flaviviruses
What happens to viruses that don’t shed?
Replicate in CNS
What viruses shed in the respiratory tract mucous membrane?
Canine distemper
Rinderpest
What viruses shed in the skin?
Lumpyskin disease
What viruses are in the brain, but no shedding?
Arbovirus
Canine distemper encephalitis
What viruses shed in the salivary gland or kidney?
Rabies (salivary gland only)
Arenaviruses
Cytomegaloviruses
What are persistent infections?
Infection that persist for the life of the animal, although episodes of clinical disease might occur infrequently
What are examples of persistent infection?
Classical: herpesvirus
Unclassical: canine distemper virus
Why are persistent infections are important?
Serves as a source of infection for other animals
Can be reactivated and cause recurrent acute episodes of disease
Lead to immunopathologic disease
Associated with neoplasms
What are latent infections?
Virus is not demonstrable except when reactivation occurs
What are chronic infections?
Virus always demonstrable and often shed and disease may be absent, chronic, or may develop late
What are slow infections?
Virus gradually increases during a very long preclinical phase, leading to a slowly progressive lethal disease
Where does the viral genome for infectious bovine rhinotracheitis virus persist?
Latently in neurons, probably as an episome
What happens when the episome for infectious bovine rhinotracheitis virus reactivates?
Infectious virus is produced and moves down the sensory nerves and reaches the nasal mucous membrane or the skin
Where does proliferation of infectious bovine rhinotracheitis virus occur?
Epithelial cells, with virus shedding
What is an episome?
Like an extracellular plasmid
What does FMD persist in?
The pharynx in cattle, sheep, goats, and other ruminants
What is lymphocytic choriomenigitis in mice caused by?
Arenavirus
How is lymphocytic choriomenigitis in mice transmitted?
Horizontally and in utero
What is vertical transmission?
Offspring becomes immunologically tolerant (in presence of virus but in absence of antibody)
What is immunological tolerance (incomplete)?
The presence of virion-IgG-complement and the complexi is infectious
What is subacute spongiform viral encephalopathies?
Scrapie in sheep and goats
Bovine spongiform encephalopathy (Mad cow)
What are prions?
Proteinaceous infectious particles
Misfolded protein that concentrates in the tissues of CNS
Where do prions concentrate?
In brain and spinal cord
What are prions resistant to?
Steam sterilization
What do prions do?
Persuades other proteins to copy it
What is canine distemper?
Acute systemic infection in which the majority of dogs recover completely within 1 month
What can happen with dogs that have recovered from canine distemper?
They can harbor the virus in brain cells where it replicates slowly and eventually produces old dog encephalitis
What is the pathogenesis of persistent infections?
Unique properties of the virus: Nonimmunogenic agents Integrated genomes Growth in protected sites Antigenic variation
Describe nonimmunogenic agents-prions
Do not induce interferon
No immune responses, therefore host cannot restrict the replication and pathologic effects
What are integrated genomes?
Retroviruses whose proviral DNA is integrated are maintained indefinitely, from one generation to the next, as a part of the genome of the host
Describe how alphaherpeeviruses grow in protected sites
Avoid immune elimination by remaining within cells of the nervous system
As episomal DNA in ganglion cells during the intervals between disease episodes
As viral DNA, subviral particles, or virions within axons prior to acute recurrent episodes
Describe how betaherpeeviruses and gammaherperviruses grow in protected sites
Avoid immune elimination by maintaining serial infection by cell-to-cell contact
What are mechanisms of modification of host defense?
Defective antibody response
Defective cell-mediate immunity
Growth in macrophages
In defective antibody responses, what do viruses that replicate in lymphoid tissue and macrophages do?
Induce non-neutralizing antibodies
What does the antibody do in defective antibody response?
Combines with viral antigens and virions in the serum to form immune complexes which may produce immune complex disease
What do viruses in macrophages do?
Avoid host immune responses
Describe defective cell-mediated immunity
Immunosuppresion by the causative virus
Immunological tolerance
The presence of virus-antibody complexes
Filaure of immune lymphocytes to reach target cells
Decrease in the numbers of Th lymphocytes
What is the target of receptor analogs?
Attachment of virion to cell receptor
What is the target of transcriptase inhibitor?
Primary transcription
What is the target of AZT?
Reverse transcription
What is the target of interferons?
Translation of viral mRNA into protein
What is the target of protease inhibitors?
Post-translational cleavage of proteins
What is the target of replicase inhibitors?
Replication of RNA viral genome
