Human Infectious Diseases
Lecture 1 + 2: Course overview and introduction to Virology
Living and non living pathogens.
Focus on protozoa, bacteria (cellular, living) and viruses (acellular, non-
living).
Learning goals:
- Know the characteristics of selected viral diseases
- Understand how viruses enter cells, replicate and cause disease
- Know the general building plan of viruses
- Apply the concept of triangulation, make simple calculations.
The Spanish flu 1918:
- Death toll estimated at 50 million to 100 million worldwide (covid: 6
million).
- Death rate highest among young, healthy adults. Roughly 2.5% of
infected people died.
- Death sometimes swift, within hours of the start symptoms.
- Caused by an H1N1 flu virus
- Milder first wave reported in late winter, early spring of 1918.
- Vicious second wave starts in late August, early September.
Other examples of viruses and disease:
- Smallpox virus: eradicated in the 70’s due to vaccination
programmes
o Famous for its devastating effect for human health. Easily
transmitted.
- Poliovirus: eradication ongoing: (>2020)
o Virus of the central nervous system partially paralyzed. We
do not see these cases in the Netherlands anymore (DTKP
vaccination).
- Measles: we want to get it eradicated but it isn’t yet.
Measles: often mild but sometimes not!
- Common complications:
o Ear infections: occur in about one out of every 10 children with
measles.
o Diarrhea: is reported in less than one out of 10 people with
measles.
- Severe complications in children and adults:
o Pneumonia: infections of the lungs
o Encephalitis: swelling of the brain, inflammation in the brain.
o People may require hospitalization and could die.
- Long-term complications:
o Subacute sclerosing panencephalitis (SSPE), measles can
persist in people who have recovered. The virus mutates a bit
and later in life people suffer from SSPE , a kind of encephalitis
which kills children.
, o Very rare but fatal disease of the central nervous system. SSPE
generally develops 7 to 10 years after a person has measles,
even though the person seems to have fully recovered from
the illness. Vaccination prevents this.
- Recurring measles outbreaks due to poor vaccination
Human papillomavirus HPV genital warts:
- Mostly a benign virus.
- Sexually transmitted.
- Some variants however cause (cervical) cancer
(baarmoederhalskanker), that is dangerous later in life, can kill the
woman.
- Starting 2009, HPV vaccine against cervical cancer is included in
national vaccination programme.
- Concerns over failing vaccination coverage within National
Immunisation Programme. Measle vaccination needs to be 95%, it is
only dropping so it bad. Any time there can be a measle outbreak.
- First only in girls but now also in boys.
Virus infections often dictate population dynamics:
- Phocine distemper virus, it is a relative of measles
- 2002 epidemic killed, 21.700 seals (ong 50% population) seals
population is healthy because after this virus the amount of seals
goes back to normal.
- Every decade in the dutch wadden sea
Foot-and-mouth Disease Virus
- FMDV, life-stock animals
- Extremely infectious picornavirus (pico=small), small RNA virus.
Herpes simplex virus (HSV)
- Koortslip , lip sores, when immunity drops.
- Reactivated out of the latent state. You will remain infected for life.
Chicken pox and shingles (gurdle herpes):
- Caused by varicella zoster virus (a herpesvirus)
- Gordelroos, later in life.
- They called it pox because it looks like pox but it is a different family
of viruses.
- There is a shingles vaccine and a chicken pox vaccination.
HIV-infection can lead to AIDS:
- Acquired Immuno Deficiency Syndrome: virus targets the immune
system
- It replicates in the CD4-T helper cells and kills them in the end. So
your immune system will be broken down.
- Breaks down the immune system: opportunistic infections such as
by Candida lead to 100% mortality.
,The zika virus epidemic:
- By the bite of an infectious mosquito.
- Zika baby: baby with microcephaly, the virus travels through the
placenta to the baby. The skull remains small because the brain is
underdeveloped. These babies need care for the rest of their life.
Routes of virus transmission:
- Air (Influenza and Sars-CoV-2)
- Water(polio and diarrhea)
- Contact (HIV, Ebola, Herpes)
- Food (norovirus), a cook who did not wash hands.
- Vertical(plant virus), transmit through seed through the germ line.
- Mosquito vectors (West Nile, Chikungunya, Zika)
- Bats as virus reservoir hosts: SARS, Hendra, Rabies, Ebola.
What is a virus:
- The smallest genetic entities.
- Poliovirus only visible by electron microscopy because of small
wavelengths (smaller than visible light).
- RNA or DNA genome with a protecting protein coat. (in the cell there
is uncoating from the coat so it can replicate).
- Poliomyelitis: kinderverlamming
Characteristics of viruses:
- Genetic entity: the RNA inside.
- They have infectivity (property to penetrate a cell, to multiple in the
cell and to leave that cell)
- Obligate, intracellular parasite (it needs a host cell for energy and
synthesising)
o No protein synthesizing machinery
o No energy producing machinery
- Property to survive outside a living cell (in an inert state or via
carrier)(permafrost defrost and virus can become back).
Historical connotation:
- Adolf Mayer: 1882
, - Marinus Beijerinck 1898
o Both Tobacco mosaic virus (he observed contagium vivum
fluidum (soluble living germ, smaller than a bacteria.)) studied
tabacco. He was the first person that named something a
virus.
Tobacco mosaic virus (TMV):
- Example of a rod-shaped virus
- Coiled RNA within protein subunit
Composition of viruses:
- Definition of a virus: a piece of genetic information (RNA or DNA),
protected by a protein coat and sometimes a lipid membrane.
Which, upon infection of a living cell, will replicate to vast amounts,
coinciding with pathological effects on the host.
- A virus is composed of: nucleic acid (RNA or DNA, ss or ds,
segmented or non-segmented) protein shell (assembled from
smaller subunits: the coat proteins) lipid membrane (some viruses).
The ‘minimal’ virus:
-
- Gene 1 is always a polymerase: copies the genome into another
genome (DNA or RNA)
- Gene 2: coat protein to protect.
- Some insect viruses: 2 genes on 2500 bases-long RNA + ve strand
RNA genome
- Most complex viruses: 100-500 genes on 10^6 bp DNA genome,
huge genome, lots of diversity.
Most viruses are found in surface waters:
- Oceans and fresh water lakes contain 5-150 * 10^6 viruses per ml.
- Hosts: cyanobacteria and phytoplankton, not human infectious.
- This correspondents with 10^27 virus particles in total
- If you make a single string of these viruses: 16 times the milky way
- Total organic mass corresponds with 75 million whales.
Biodiversity of viruses:
