survey of viruses 3

many viruses are limited…

to a single species (human only)

what are some viruses

zoonoses

zoonoses

diseases that are naturally transmitted between humans and other vertebrates

for zoonoses what may human host be 

human host may be an integral part of the virus life cycle or an accidental host 

arboviruses 

viruses transmitted by arboviral vectors

in arboviruses what are humans

usally dead end hosts

• cant send it to anything else 

what does the route of virus transmission depend on

• source of the virus (target tissue and secretion)

• the stability of the virus in environmental (enveloped or not, seasonaloty )

• portal of entry of the virus in the new host 

what plays a major role in the mode of transmission

wheater or not a virus is enveloped plays a major role in the mode of transmission due to reduced stability in the environment 

what type of virus tends to be more environmentally stable

non- enveloped viruses

what are non enveloped viruses resistant to

drying, detergent, exposure, extremes of pH and temp ( stomach acid, bile, mild sewage treatment)

• these types of viruses can cause foodborne illnesses 

what must enveloped viruses remain

wet

• respiratory droplets, bodily secretions, semen, blood

• most are susceptible to acids and detergents 

other transmission factors

• seasonality

• immunity in the population

• environmental factors (temp, humidity (water), vector life cycles)

• social and economic factors that enhance transmissions of a virus 

• nosocomical infections 

• asymptomatic carrier population

• age

• travel

• occupation/ activities

nosocomical infections 

an infection you get while you are in the hospital for another reason 

what are most viruses limited to 

a particular host or cell because of receptors 

what do viral infections range from 

asymptomatic to mild to life- threatening 

• depending on the population and people 

majority of viral infection are

asymptomatic

common manifestations of infection at the organism level

respiratory involvement, rashes, fever, muscle aches, swollen lymph nodes, diarrhea

what does common symptoms result from

immune activation

resolution of infection

the combined action of innate and adaptive immunity

the combined action of innate and adaptive immunity results in 

lifelong immunity, however this does not equal to prevention of re-infection 

many viral infections have a

rapid course (lytic cycle)

• uses lysis as mechanism 

• rapid course of infection and big immune response

what do some viruses produce

biphasic infection

biphasic infection

initial acute infection, recovery, secondary infection

• weak months or year later 

what do some viruses establish 

long term persistent infections that may last many years or a lifetime

how many types of persistent infections are there

2

chronic infections

virus is detectable in tissue samples

• multiplying at a slow rate 

• symptoms are mild or absent 

latent infections

after a lytic cycle, virus enters a dormant phase and is generally not detectable

• no symptoms 

• can reactivate and result in recurrent infections 

sterilization

completely clean surface

disinfection

misses something on surfaces

what type of virus can survive disinfection

naked virus surface could survive this

antivirals

proper treatment of infected individuals to kill the virus at its source

measures irected at the reservoir

cases, carriers, animal reservoir

case finding

reporting to the local health authority in order to apply the appropriate control measures for contact and the environment (covid- 6 feet apart regulation) 

isolation 

( strict isolation or discharge/ body fluid isolation) for the whole period of communicability and treatment

surveilance 

for the longest incubation period 

carriers

identification, treatment, and exclusion

treatment and exclusion

from work til the organism is eliminated especially food handlers or working with children

animal reservoir

adequate animal husbandry

immunization of animals

treatment of infected animals and killing if treatment is not feasible

animal husbandry 

if an animal can trasnfer virus to humans or vice versa 

measures directed at portal of entry- house

using bed nets

measures directed at portal of entry- healthcare

wearing masks and gowns to prevent entry of infected body secretion or droplets through skin or mucous membrane

measures directed at portal of entry- people

covering skin and using insect repellents

how to stop viruses from spreading

health education, adequate personal hygiene, sound nutrition, immunization, chemoprophylaxis

chemoprophylaxis

administration of a mediciation for the purpose of preventing disease or infection

benefits of complete immunization in a community 

complete immunization coverage can help prevent the agent from reaching a susceptible host 

herd immunity

if a high proportion of individual in the community are resistant to an agent, them susceptible people will also be protected by the resistant majority 

when does level of susceptibility increase 

as new infants are born 

when will an epidemic develop

after accumulation of susceptible individuals