3.5 Viruses Transmitted via Air, Food or Water I

airborne virus - picornaviridiae

rhinoviruses, enteroviruses, cold

airborne virus - paramyxoviridiae

parainfluenza, metapneumoviruses, respiratory syncytial viruses, cold

airborne virus - orthomyxoviridiae

flu viruses, flu

airborne virus - adenoviridiae

adenoviruses, flu

airborne virus - coronaviridiae

coronaviruses, cold, sars, mers, cov19

which airborne viruses have an RNA genome

all but adenoviruses

short-range transmission

droplet/aerosol inhalation → aerosol can fill a room, not affected by gravity, physical contact, fomite contact

long range transmission

aerosol inhalation, fomite contact

determinants of successful viral transmission

viral-dependent factors → physical properties influence infectivity, environmental factors → determine fate of the virus during transmission, host factors → individual and population levels, infected persons and infectees

virus-dependent factor - capsid/envelope

surface protein expression/modification → determine infection site, host receptor binding specificity and affinity, formation of aggregates = more efficient infection

virus-dependent factors - internal proteins/viral genomes

densely packaged = viral stability, mutability = host adaptation, transmissibility

environmental factors

ventilation/airflow, temperature, humidity, pH, UV radiation, salinity, surface materials

host factors - infected person

tissue and cellular tropism → determine site of viral release = many sites, many viruses, highly contagious. variability in symptom presentation → pre-symptomatic, asymptomatic, symptomatic. lung function → exhaled particle number and size distribution

host factors - exposed person/infectee

tissue specific receptor expression, glycosylation, and glycan expression → site of infection, risk of infection. pre-existing immunity → risk of infection. lung anatomy → virus laden particle deposition

host factors - populations

social contact patterns → mode of transmission. Age related mixing patterns → age-specific risk of infection

Influenza A overview

pandemics/epidemics most severe, infects swine, birds, humans, A is H1N1/H3N2, seasonal

Influenza B overview

epidemics, only infects humans, seasonal

influenza c/d

c = mild illness, like cold. d = only infects cows, so far

influenza a anatomy

hemagglutinin (HA) attachment → 18 subtypes, H1-18, neuraminidase (NA) → 11 subtypes, N1-N11, 8 negative sense ssRNA segments → 8 separate strands, 11 proteins, envelope → lipid bilayer, M1 protein - budding → coat inside envelope

Flu a subtypes

HxNx, most combinations found in birds, H1
N1 and H3N2 currently

RhinoV general characteristics

nose, causes 30-50% of common colds, replicates at temperature in the nose, symptoms= nasal congestion, runny nose, sore throat, sneezing

RhinoV physical characteristics

+ssRNA, encodes 11 proteins, capsid proteins (VP1-VP4) → responsible for cellular tropism, genome protection, antigenicity. non structural proteins → proteases, RNA polymerase, inhibitors of host cell functions

rhinovirus types

1000 known serotypes within the species a/b/c

rhinov human receptors

3 human receptors, ICAM-1 (intercellular adhesion molecule) main receptor, LDLR, CDHR3

corona general characteristics

named for the crown-like spikes, 4 main sub-groups (alpha/beta/gamma/delta), large, enveloped, +ssRNA

corona infection and types

human coronaviruses = 229E (alpha), NL63 (alpha), OC43 (beta), HKUI (beta), animal → human coronaviruses = SARS-CoV-2 (covid19), MERS-CoV, SARS-CoV

SARS-CoV-2 structure and proteins

S (spike) protein → binds to ACE2 receptor for cell entry, E (envelope) protein → involved in viral assembly and release, M (membrane) protein → most abundant structural protein, N (nucleocapsid) protein → binds to viral RNA genome

SARS-CoV-2 mechanism of cell entry

uses ACE2 receptor for cell entry, in synergy with hosts TMPRSS2, similar to viral activtion and cell entry of other coronaviruses and flus

Why are bats major virus reservoirs?

20% of all mammals are bats, bat antiviral immune responses are dampened, bats live long lives