Spherical viruses



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Spherical viruses

  • Spherical viruses

    • Capsid, Membrane protein, and Envelope protein
  • Capsid (C protein)

    • Structural Protein
    • Houses the RNA and the viral RNA polymerase
  • Membrane protein (prM/M)

    • Helps the capsid pass through the cell membrane.
  • Nonstructural proteins (NS)

    • Nonstructural protein 1 (NS1) is a glycosylated protein found on an infected cell’s surface and is involved in viral assembly and release. This protein induces protective antibodies.
    • Nonstructural protein 5 is a viral RNA polymerase.


Carlos Finlay

  • Carlos Finlay

    • Cuban physician and scientist.
    • Pioneered the early research on YF.
      • Hypothesized that YF was spread by mosquitoes.
  • Walter Reed

    • Appointed by the government to head the Yellow Fever Commission.




Three types of transmission to humans:

  • Three types of transmission to humans:

      • Sylatic or jungle YF
      • Intermediate YF
      • Urban YF
  • Vertical and Horizontal Transmission

    • Vertical transmission is mosquito to mosquito.
    • Horizontal transmission is when an infected mosquito bites a non-infected human or monkey.


One is jungle fever that is spread from monkeys to people by mosquitoes.

  • One is jungle fever that is spread from monkeys to people by mosquitoes.



Acute phase

  • Acute phase

    • Fever
    • Muscle pains (prominent backaches)
    • Headaches
    • Shivers
    • Nausea, vomiting
      • These symptoms are also closely related to the flu and common cold.
  • Usually recover in 3-4 days



Toxic phase

  • Toxic phase

    • Fever
    • Jaundice
      • Yellowish color develops in the patients face and eyes
      • This gives Yellow fever its name
    • Complains of abdominal pain with vomiting.
    • Bleeding can occur from the mouth, nose, eyes and/or stomach.
      • Once this happens, blood appears in the vomit and faeces.
    • Kidney function deteriorates; this can range from abnormal protein levels in the urine (albuminuria) to complete kidney failure with no urine production (anuria).
    • Half of the patients in the "toxic phase" die within 10-14 days. The remainder recover without significant organ damage.


This disease is caused by Yellow Fever virus that can not be cured.

  • This disease is caused by Yellow Fever virus that can not be cured.

  • But it can be prevented by a yellow fever vaccination.





SS-RNA arbovirus (Flavivirus)

  • SS-RNA arbovirus (Flavivirus)

  • 4 serotypes (DEN-1, 2, 3, 4)

    • Based on envelop glycoprotein
    • DEN-1 and 3 are more closely related
    • DEN-4 less closely related to others
    • Virulent variants (genotypes) within serotype
  • Infection with any serotype confers specific lifelong immunity

  • Transient cross-protection to other serotypes

  • Any serotype can cause severe / fatal disease



Dengue viruses – 4 flavours cause it

  • Dengue viruses – 4 flavours cause it

  • It is transmitted by a mosquito- the Aedes aegypti

  • It is generally an animal virus

  • Man is accidentally infected

  • Other vertebrates are the reservoirs





Dengue is spread when the female Aedes aegypti mosquito bites an infected person, it sucks up the blood with the virus and passes this virus onto the next person she bites for more blood. In this way the mosquito becomes a carrier of the dengue virus. We call these carriers of disease and illness “vectors”

  • Dengue is spread when the female Aedes aegypti mosquito bites an infected person, it sucks up the blood with the virus and passes this virus onto the next person she bites for more blood. In this way the mosquito becomes a carrier of the dengue virus. We call these carriers of disease and illness “vectors”



Mosquito bite  virus injected into blood

  • Mosquito bite  virus injected into blood

  •  Virus replicates in lymphocytes

  •  Fever, myalgia, arthralgia, rash

  •  Slow recovery

  •  Immunity to the virus (Serotype)

  • Mosquito bite

  •  Second serotype injected into blood

  •  Enhanced replication, severe disease,

  • hemorrhage, cardiovascular shock



2–7 days after the mosquito had its dinner on us we may develop

  • 2–7 days after the mosquito had its dinner on us we may develop

  • Sudden onset of fever, chills, headache

  • Back pain with severe muscle and joint pains

  • Pain behind the eyes and on moving the eyes

  • Nick name - Break bone fever- pains so severe

  • Red patches or spots on the skin

  • Mild nose bleeds

  • This is the ordinary classical

  • Non dangerous form!



Like any other viral fever- not clear cut

  • Like any other viral fever- not clear cut

  • Dengue Fever with Muscle pains this is classical presentation in 90% cases

  • Dengue Fever with bleeding in 7%

  • Dengue – the dangerous form in 3%







Blood vessels are affected

  • Blood vessels are affected

  • There is severe oozing into tissues

  • Bleeding into all possible parts of body

  • Blood clotting mechanism is disrupted

  • Blood pressure falls and many end in collapse and death

  • In the best centers 5% of this type of Dengue will reach their forefathers











Routine blood test

  • Routine blood test

  • Tests to check the clotting process

  • Special tests to identify the Dengue or its foot marks in our blood

  • Urine to check protein leak





There is no vaccine available as yet

  • There is no vaccine available as yet

  • But we can prevent the disease by preventing ourselves from mosquito bite



















Rift Valley fever

  • Rift Valley fever

  • Crimean Congo hemorrhagic fever





Disease of sheep and cattle

  • Disease of sheep and cattle

  • Humans: Asymptomatic-to-mild

  • Rare VHF, encephalitis, retinitis





478 deaths

  • 478 deaths

  • 115 VHF deaths

  • 9% IgM+

  • ~89,000 cases

  • 70% animal loss



3-7 day incubation, 3-5 day duration

  • 3-7 day incubation, 3-5 day duration

  • Asymptomatic or mild illness

  • Fever, myalgia, weakness, weightloss

  • Photophobia, conjunctivitis

  • Encephalitis

  • <5% hemorrhagic fever

  • 1-10% vision loss (retinal hemorrhage, vasculitis)



Extensive geographic distribution

  • Extensive geographic distribution

  • (Africa, Balkans, and western Asia)

  • Transmission:

    • Tick-borne (Hyalomma spp.)
    • Contact with animal blood or products
    • Person-to-person transmission
  • by contact with infectious body fluids

    • Laboratory worker transmission documented
  • Mortality 15-40%

  • Therapy: Ribavirin





4-12 day incubation after tick exposure

  • 4-12 day incubation after tick exposure

  • 2-7day incubation after direct contact with infected fluids

  • Abrupt onset fever, chills, myalgia, severe headache

  • Malaise, GI symptoms, anorexia

  • Leukopenia, thrombocytopenia, hemoconcentration, proteinuria, elevated AST

  • Hemorrhages may be profuse (hematomas, ecchymoses)





Viremia present throughout disease

  • Viremia present throughout disease

  • IFA becomes positive in patients destined to survive days 4-6, often simultaneously with viremia

  • Recovery may be due to CMI or neutralizing antibodies

  • Patients that die usually still viremic

  • Virus grows in macrophages and other cells

  • DIC often present

  • Poor prognosis signaled by early elevated AST and clotting



Sheep and cattle become viremic without disease

  • Sheep and cattle become viremic without disease

  • Blood and fresh tissues infective by contact

  • Possibility of establishing transmission of CCHF in holding pens by Hyalomma or other tick vectors



DEET repellents for skin

  • DEET repellents for skin

  • Permethrin repellents for clothing –

  • (0.5% permethrin should be applied to clothing ONLY)

  • Check for and remove ticks at least twice daily.

  • If a tick attaches, do not injure or rupture the tick.

  • Remove ticks by grasping mouthparts at the skin surface using forceps and apply steady traction.



Each person is a Book !

  • Each person is a Book !

  • Each Day is a Learning Opportunity!!

  • Learning has More Relevance

  • today than ever !!!



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