Virus Tissue Tropism

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Virus Tissue Tropism

• Targeting of the virus to specific tissue and
  cell types
• Receptor Recognition
• CD4 cells infected by HIV
• CD155 acts as the receptor for poliovirus

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DNA Viruses

• Herpesviridae
• Poxviridae

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Herpesviridae

• Causes diseases in animals
• The family name is derived from the Greek word
  herpein ("to creep"), referring to the latent,
  recurring infections typical of this group of
  viruses. (Can cause lytic or latent infections)

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• Causes diseases in animals
• The family name is derived from the Greek word
  herpein ("to creep"), referring to the latent,
  recurring infections typical of this group of
  viruses. (Can cause lytic or latent infections)

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• More than 90 of adults have been infected with
  at least one of these, and a latent form of the
  virus remains in most people.

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• All herpesviruses are enveloped viruses composed
  of relatively large double-stranded, linear DNA
  encoding 100-200 genes encased within an
  icosahedral capsid.

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Poxviridae

• Causes diseases in vertebrates and invertebrates

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• Causes diseases in vertebrates and invertebrates
• Five species of Herpesviridae
• HSV-1 and HSV-2 (both of which can cause
  orolabial herpes and genital herpes),
• Varicella zoster virus (which causes chicken-pox
  and shingles),
• Epstein-Barr virus (which causes mononucleosis)
• Cytomegalovirus

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Smallpox

• Variola is a large brick-shaped virus measuring
  approximately 302 to 350 nm by 244 to 270 nm,
  with a single linear ds DNA of 186 (kbp) in size.

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• The life cycle of poxviruses is complicated by
  having multiple infectious forms, with differing
  mechanisms of cell entry.
• Poxviruses are unique among DNA viruses in that
  they replicate in the cytoplasm of the cell
  rather than in the nucleus.

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• In order to replicate, poxviruses produce a
  variety of specialized proteins not produced by
  other DNA viruses, the most important of which is
  a viral-associated DNA-dependent RNA polymerase.

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Smallpox in the New World

• In the early 16th century smallpox began to
  imported into the western hemisphere.
• The Spanish inadvertently owe success in
  conquering the Aztec and Incas in Mexico to
  smallpox.
• Smallpox arrived in North America via Canada, and
  Mexico.

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• The disease killed an estimated 400,000 Europeans
  annually during the closing years of the 18th
  century (including five reigning monarchs), and
  was responsible for a third of all blindness.

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• Of all those infected, 2060and over 80 of
  infected childrendied from the disease. Smallpox
  was responsible for an estimated 300500 million
  deaths during the 20th century.
• As recently as 1967, the WHO estimated that 15
  million people contracted the disease and that
  two million died in that year.

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Smallpox as Biological Warfare

• Lord Jeffrey Amherst, Commanding General of
  British Forces in North America during the French
  and Indian War. (1754-1763)
• Used blankets (smallpox blankets) coated with
  smallpox dust as germ warfare to wipe out the
  Native American population.

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RNA viruses

• Poliovirus
• Rhinovirus
• Norovirus
• Influenza
• Rotavirus
• Hantavirus
• Ebola

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• RNA viruses can be further classified according
  to the sense or polarity of their RNA into
  negative-sense and positive-sense, or ambisense
  RNA viruses.

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• Positive-sense viral RNA is similar to mRNA and
  thus can be immediately translated by the host
  cell
• Negative-sense viral RNA is complementary to mRNA
  and thus must be converted to positive-sense RNA
  by an RNA polymerase before translation.

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• Purified RNA of a positive-sense virus can
  directly cause infection though it may be less
  infectious than the whole virus particle
• Purified RNA of a negative-sense virus is not
  infectious by itself as it needs to be
  transcribed into positive-sense RNA each virion
  can be transcribed to several positive-sense
  RNAs.

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• Ambisense RNA viruses resemble negative-sense RNA
  viruses, except they also translate genes from
  the positive strand.

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Poliovirus
Properties of the virus

• Enterovirus.
• stranded RNA virus
• Transmitted by the faecal oral route.
• Cause of gastrointestinal illness and
  poliomyelitis.

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Poliovirus
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Poliovirus Infection
Non-neuronal tissues
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Incidence of Poliomyelitis
Poliovirus vaccines A Salk killed inactivated
vaccine. B Sabin live attenuated
vaccine
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Influenza A virus
Properties of the virus

• Myxovirus
• Enveloped RNA virus
• Infects a wide range of animals other than humans
• Undergoes extensive antigenic variation
• Major cause of respiratory infections

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Weekly consultation rates for influenza and
influenza-like illness Weekly Returns Service of
the Royal College of General Practitioners, 1988
to 1999
Epidemic activity
Higher than expected seasonal activity
Baseline activity
Rate per 100 000 population
Normal seasonal activity
Year
CDR Weekly Report 5th November 1999
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Norovirus

• Genus of genetically diverse single-stranded RNA,
  non-enveloped viruses in the Caliciviridae family
• The known viruses in the genus are all considered
  to be the variant strains of a single species
  called Norwalk virus.

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Norovirus

• The viruses are transmitted by fecally
  contaminated food or water, by person-to-person
  contact, and via aerosolization of the virus and
  contamination of surfaces.
• Noroviruses are the most common cause of viral
  gastroenteritis in humans, and affect people of
  all ages.

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Rotovirus

• Genus of dsRNA virus in the family Reoviridae.
• 11 unique double helix molecules of RNA which are
  18,555 nucleotides in total. Each helix codes
  for a protein.
• The RNA is surrounded by a three-layered
  icosahedral protein capsid. Viral particles are
  up to 76.5 nm in diameter and are not enveloped.

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Rotovirus

• Nearly every child in the world has been infected
  with rotavirus at least once by the age of five.
• There are five species of this virus, referred to
  as A, B, C, D, and E. Rotavirus A, the most
  common species, causes more than 90 of rotavirus
  infections in humans.

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Rotovirus

• Transmitted by the fecal-oral route. It infects
  and damages the cells that line the small
  intestine and causes gastroenteritis.

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HIV

• HIV is a member of the genus Lentivirus part of
  the family Retroviridae.
• ss positive-sense, enveloped virus
• HIV is different in structure from other
  retroviruses. It is roughly spherical with a
  diameter of about 120 nm, around 60 times smaller
  than a RBC yet large for a virus.

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• Infection with HIV occurs by the transfer of
  blood, semen, vaginal fluid, pre-ejaculate, or
  breast milk.
• Within these bodily fluids, HIV is present as
  both free virus particles and virus within
  infected immune cells.

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• HIV infects vital cells in the human immune
  system such as helper T cells (specifically CD4
  T cells), macrophages, and dendritic cells.

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Ebola

• Ebolavirions are filamentous particles of ssRNA
  that may appear in the shape of a shepherd's
  crook or in the shape of a "U" or a "6", and they
  may be coiled, toroid, or branched.

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• The current outbreak in west Africa, (first cases
  notified in March 2014), is the largest and most
  complex Ebola outbreak since the Ebola virus was
  first discovered in 1976. There have been more
  cases and deaths in this outbreak than all others
  combined.
• As of Oct 8, 2014
• Total Cases 8400
• Laboratory-Confirmed Cases 4656
• Total Deaths 4033

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Ebola

• Cells lining the inside of blood vessels
  (endothelial cells), macrophages, monocytes and
  liver cells are the main targets of infection.
• After infection, a secreted glycoprotein, known
  as small soluble glycoprotein (sGP) or as the
  Ebola virus glycoprotein (GP), is synthesized

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• Human-to-human transmission occurs only via
  direct contact with blood or body fluid from an
  infected person (including embalming of an
  infected dead body), or by contact with objects
  contaminated by the virus, particularly needles
  and syringes.

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• Other body fluids that may transmit ebolaviruses
  include saliva, mucus, vomit, feces, sweat,
  tears, breast milk, urine, and semen.
• The dried virus can live on doorknobs and
  countertops for several hours
• Entry points include the nose, mouth, eyes, or
  open wounds, cuts and abrasions

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• Humans are not infectious until they develop
  symptoms.
• Symptoms usually begin suddenly with an
  influenza-like stage characterized by fatigue,
  fever, headaches, and pain in the joints,
  muscles, and abdomen.
• Vomiting, diarrhea, and loss of appetite are also
  common.

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• Less common symptoms include sore throat, chest
  pain, hiccups, shortness of breath, and trouble
  swallowing.
• The average time between contracting the
  infection and the start of symptoms (incubation
  period) is 8 to 10 days, but it can vary between
  2 and 21 days

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• In the bleeding phase, which typically begins
  five to seven days after first symptoms,internal
  and subcutaneous bleeding may present itself in
  the form of reddened eyes and bloody vomit and/or
  stools.

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• People remain infectious as long as their blood
  and body fluids, including semen and breast milk,
  contain the virus. Men who have recovered from
  the disease can still transmit the virus through
  their semen for up to 7 weeks after recovery from
  illness

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• The disease is only spread by direct contact with
  the secretions from someone who is showing signs
  of infection
• A person's ability to spread the disease is often
  limited as the individual is often too sick to
  travel during the infectious stages of the
  disease.

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• As transmission via air is generally ruled out,
  the possibility of transmission between
  non-seat-mate airline passengers is generally
  ruled out

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What about pets?

• In the 2001-2002 outbreak in Gabon, scientists
  found signs of the virus in 25 of the dogs
  living near the outbreak. The animals were not
  symptomatic, nor did they die during the time the
  scientists were studying them.

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Pets?

• So..the animals came in contact with Ebola virus
  and their immune systems responded.
• Whether or not dogs shed Ebola once their immune
  systems encounter it remains to be seen.
• Scientists are studying the pets of the infected
  humans currently.
• Cats have not found to contract virus.

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• At this time, there have been no reports of dogs
  or cats becoming sick with Ebola or of being able
  to spread Ebola to people or other animals.
• Even in areas in Africa where Ebola is present,
  there have been no reports of dogs and cats
  becoming sick with Ebola.

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• Why did hospital workers contract virus?
• There are only 5 hospitals that really are
  equipped to handle Ebola patients. The Dallas
  hospital is not one of them.
• Decontamination procedures and the buddy-system
  were not used...