Virology Flashcards
Virus unique characteristics
Are smallest infectious particles
Range from 18 - 300 nm in size 100 nm
Consist of either DNA or RNA (but not both) and proteins with or without a lipid membrane coat
Lack an independent metabolic system
Require host cells for replication: true parasites
Consist of an intracellular reproductive cycle, and an extracellular transmissive cycle
Unicellular organisms
Protozoa, fungi, bacteria, rickettsiae, mycoplasmas, chlamydiae
Unicellular, both DNA and RNA, binary fission
Viruses
Obligate intracellular, either DNA or RNA (not both)
Two life cycles: extracellular (transmissive, inert), intracellular (reproductive)
Prions
Proteins only, a small proteinaceous infectious particle (no nucleic acid genome). Prion diseases–Spongiform encephalitides
High resistance to heat, UV, irradiation, chemicals
Prion proteins:
Present in normal cells (PrPc)
Abnormal, conformational aberration: amyloid formation (PrPsc)
Non-enveloped viruses
Protein subunit
Structure unit
Capsomer
Capsid (coat or shell)
Nucleocapsid
Only nucleocapsid protein (“naked”, no envelope)
More resistant: longer survival in environment, not seasonal disease, difficult to inactivate
Pathogenesis: lytic cell infection: often associated with acute disease, less chronic
Enveloped viruses
Building blocks of non-enveloped viruses plus
Envelope: peplomer/spike, matrix proteins, lipids
Epidemiology: short survival in environment, labile, “easier” to inactivate, often associated with seasonal diseases
Pathogenesis: budding through infected cells, chronic/persistent infections
Immunology: Glycoprotein antigens: VN, CMI, vaccine immunity
prevalence
photograph/snapshot
Insidious onset with unknown initial date
Chronic, long duration diseases
No time parameters only number of cases in defined number of subjects
Incidence
Number of cases over number of subjects over a period of time (case:population ratio).
Acute, short duration diseases.
Denominator: population in a time frame: thus person- years or subject-weeks
Enzootic
Multiple, continuous transmissions, disease presence in a defined population/region/time
Epizootic
Peaks in incidence exceeding the endemic baseline. Nature and degree of expected damage defines whether it is called epidemic (high damage) or not (low damage)
Panzootic
Worldwide outbreak
incubation period
Moment of infection to onset of clinical signs
Short? long? variable?
generation time
From moment of infection to first day virus shedding
Mostly shorter than incubation period. Influence in spreading disease
period of infectivity
From first day to last day of virus shedding
May or may not be longer than clinical signs
Great influence in spreading disease
Horizontal transmission
viruses are transmitted among individuals of the same generation
Vertical transmission
occurs from mothers to their offspring
Zoonotic transmission
an infectious disease that has jumped from a non-human animal to humans
Viral diseases transmissible under natural conditions from vertebrate animals to humans
Vector-borne transmission
one in which transmission of infection in a population (the host population) occurs only via a second population (vectors). Vectors are usually haematophagous (blood-feeding) arthropods such as mosquitoes, sandflies or ticks
Iatrogenic transmission
refers to the spread of a pathogen, (bacteria or virus) through a medical procedure or treatment such as a blood transfusion, reuse of needles or IV sets, or by touching a wound on an infected horse and then handling another horse
Nosocomial transmission
an infection that is acquired in a hospital or other health care facility????
Arbovirus transmission
Biological vector: virus replicate, magnify in vectors,
efficient transmission
Mechanical vector: no virus replication in vectors,
not efficient for transmission
Transmitted by mosquitoes, ticks, and sandflies
Arbovirus transmission
Biological vector: virus replicate, magnify in vectors,
efficient transmission
Mechanical vector: no virus replication in vectors,
not efficient for transmission
Transmitted by mosquitoes, ticks, and sandflies
acute virus infections
Rapid production of infectious viruses
Rapid resolution and elimination of the infection (virus clearance) by the host
Acute infections do not always produce disease
Persistent virus infections
Infection not cleared efficiently
Virus particles are produced for a long period of time either continuously or intermittently for months or years
Latent virus infections
Viral genomes integrated into cellular genomes, not expressed
no infectious progeny
Host Range
receptors on animal tissues/cells; susceptible for wide range of infections or restricted infections
Susceptibility
ability to become infected
Permissivity
ability to replicate and produce progeny viruses
Skin (routes of virus shedding)
Not a major route
Contact, abrasions, wounds
Respiratory Secretions (routes of virus shedding)
Very important
Numerous diseases, local, systemic
Shedding occur before, during, after clinical signs
Saliva (routes of virus shedding)
Salivary gland, oral cavity
Rabies, FIV
Genital secretions (routes of virus shedding)
Sexual activity, semen, mucus
Urine (routes of virus shedding)
Rinderpest, FMD, canine hepatitis in kidneys
Hantaviruses: mice to humans
Milk: Not an important route
(routes of virus shedding)
Mammary gland replication, caprine arthritis-encephalitis
