CSIM1.16: Viruses and disease Flashcards
What are the 3 main modes of viral transmission?
- Horizontal transmission (one human to another)
- Vertical transmission (mum to offspring)
- Zoonotic (animal to human)
What are the 6 types of horizontal transmission?
Common:
- Respiratory
- Fecal
Less common:
- Sexual
- Mechanical (skin related cuts/abrasions)
- Urine
- Conjunctiva
What are examples of respiratory transmission related viruses that can cause localised infections?
- Rhinoviruses (common cold)
2. Influenza (flu)
What are examples of respiratory transmission related viruses that can cause generalised (elsewhere) infections?
- Chicken pox (varicella zoster virus)
- Measles (paramyxoviridae)
- Small pox (variola virus)
What are the factors that influence the efficiency of respiratory transmission of viruses?
The size of the water droplets that humans emit: most efficient for transmission would be MIDDLE RANGE DROPLETS
LARGE DROPLETS (>10µm [micrometer ^(-6)]) rapidly fall to the ground
SMALL DROPLETS (
What are some examples of viruses that get transmitted through the fecal-oral route?
Picornaviruses like
- Polio
- Hep A
Norovirus
What makes faeces good virus carriers?
They contain 1000 infection units (IU) per microliter
What does NOROVIRUS cause?
It is the most common cause of viral gastroenteritis
What are some examples of viruses that get transmitted through vertical transmission?
- Rubella (usually spread via respiratory route and if patient is pregnant, this crosses placenta causing foetal death/malformations)
- HIV-1
What are some examples of viruses that get transmitted through zoonotic transmission?
Usually by arthropods
Arboviruses like:
- Dengue fever
- Yellow fever
- Japanese encephalitis
How can a human infect another human indirectly with a virus that is transmitted via zoonosis?
An infected arthropod infects a human -> an uninfected arthropod bites infected human -> now infected arthropod bites healthy human
What is pathogenicity?
The severity of the disease caused by DIFFERENT viruses
e.g. effects of RABIES vs INFLUENZA
What is virulence?
The severity of disease caused by strains of the SAME virus.
e.g. 10 virions of HSV-1 A to kill a mouse vs 10000 virions of HSV-1 B to kill a mouse
What are pathogenicity factors?
Characteristics viruses possess to allow them to be pathogenic
What are pathogenic factors?
- Entry
- Initial replication
- Immune evasion
- Dissemination
- Further replication
- Shedding (infect others)
Describe the pathogenicity of localised infections
Only go through entry -> initial replication -> shedding as infection is localised so sheds to localised area
Describe the pathogenicity of generalised infections
Upon entry, primary viraemia occurs and on further multiplication, secondary viraemia occurs with further entry to bloodstream to finally cause onset of disease
e.g. Primary viraemia from blood to lymph nodes; secondary from blood to blood near brain causing rare encephalitis in measles
What is incubation period?
The time between VIRAL EXPOSURE and ONSET OF ILLNESS (symptoms becoming apparent)
e.g. Localised infections have short incubation periods
What is generation time?
Time between VIRAL EXPOSURE (infection) to ONSET OF INFECTIOUSNESS
What is reproduction number (r0)?
The number of subsequent infections in a susceptible population caused by a viral illness in one individual during its INFECTIOUS PERIOD?
What is a subclinical infection?
Asymptomatic
What is a latent infection?
Virus cells lie dormant in host cells until immune system is compromised/suppressed [usually a slowly progressive disease like shingles after VPV]
