infectious diseases viral diseases

virus

• small infectious agent that can multiply only in living cells of animals, plants, or bacteria; cant reproduce or conduct metabolic processes without a host cell

  • parasites

  • vector-borne viruses multiply in both the invertebrate vector and the vertebrate host

virion

• a complete virus particle that is the extracellular infective form of the virus; includes the capsid (outer protein shell), the RNA or DNA core, and sometimes external envelopes

virus classification

• DNA

• RNA

  • retroviruses such HIV

  • RNA viruses, especially retroviruses, are prone to mutate

• can be single or double stranded

• can be linear or circular

• can very in length

• Baltimore classification system classifies viruses based on replication method and type of nucleic acid genome

Retroviruses

• use RNA for their genetic material and after infecting the cell, the retrovirus converts its RNA to DNA, then integrates viral DNA into host cell DNA so its replicated

viral interaction with host

• viruses typically affect one type of cell

  • common cold viruses affects cells of upper respiratory tract

• penetrate host cell membrane or cell wall & inject its genome into host cell

• forces the host cell machinery to replicate the viral genome

• the new viruses emerge from host cell (this kills the host cell)

latent infections

• viral DNA or RNA remains in hosts cells but doesnt replicate or cause disease for extended time

• transmissible during the asymptomatic period so spread still occurs

• ex: herpes viruses

chronic viral infections

• continuous viral shedding with persistent hep B or C

cancer

• some viruses dont kill the cells they infect, but instead change cell function

• if this includes changing cell division can cause cancer

common viral infections include infections of

• respiratory tract

  • common cold, flu, pneumonia

• GI Tract

  • norovirus

• Liver

  • hep A,B,C

• Nervous system

  • rabies, west nile, polio

• Skin

  • warts, chickenpox

• Placenta & Fetus

  • zika virus, rubella, cytomegalovirus

• multiple body systems

  • enteroviruses

how viruses are transmitted

• inhaled

• swallowed (in food)

• insect bites (vector borne)

• sexual activity

• exposure to blood

• etc.

viral disease management

• viral diseases - not treatable with antibiotics

• vaccines for viral infections include:

  • hep A

  • hep B

  • human papillomavirus

  • influenza

  • japanese encephalitis

  • measles, mumps, rubella

  • polio

  • rabies

  • shingles

  • yellow fever

  • Covid 19

use of fetus cells to produce vaccines against viruses

• grow the viruses in fetal embryo fibroblast cells

  • varicella (chickenpox)

  • rubella

  • hep A

  • one version each of shingles and rabies

• cells r descended from cells from 2 fetuses whose mother decided to have legal abortions 1 in eng on in sweden

influenza risk factors for serious complications from seasonal flu

• under 2 over 65

• living in nursing home/long term care facility

• underlying health conditions

  • asthma

  • chronic lung disease

  • blood disorders (sickle cell disease)

  • diabetes

  • heart disease

  • kidney disorders

  • liver disorders

  • bmi > 40

  • weakened immune system

• pregnant ppl & up 2 weeks after end of pregnancy

4 types of influenza viruses

• A and B viruses - cause seasonal flu

• a new influenza A can cause pandemic when it:

  • infects humans & causes illness

  • spreads easily and continues among humans

  • is diff enough so ppl have little to no immunity to it

• C - generally mild illness

• D - mostly affect cattle: not known to cause illness in humans

pandemic flu risk with influenza A viruses

• broad host range including birds, humans, other mammalian hosts

  • potential for zoonotic disease

  • difficult to control spread of diseases in wild animals

• reassortment: when two influenza viruses infect the same host cell at same time & exchange genetic material

Bird Flu

• hard to control cuz it can be carried long distances & transmitted by wild birds

how infected backyard poultry could spread bird flu to ppl

1. direct contact

2. contaminated surfaces

3. bird flu virus in the air (droplets or dust)

viral host jump: disease transmission to new species

• virus moves from one species to another

• come into contact with the new species, enter their cells, replicate, and spread between individuals.

• It’s rare, but more likely when:

  • Humans have close contact with animals

  • The virus mutates quickly (like RNA viruses)

  • Environmental changes force animals and humans closer

pandemic influenza

• conditions that initiate a flu pandemic

  • new virus emerges (no human immunity)

  • infects humans and causes illness

  • spreads easily and continues without interruption among humans