Nnamani

• Measles virus


  Enveloped RNA virus belonging to genus Morbillivirus of the family Paramyxoviridae
• Measles virus


  • Single stranded virus of negative polarity surrounded by the nucleoprotein (NP), the phosphoprotein (P), matrix protein (M) and a large protein with polymerase function (L)
  • Envelope contains 2 viral glycoproteins: heamaglutinin (H) for binding the virus to cells and fusion protein (F) for uptake of virus into cells
  • Antibodies to H correlate with protection against the disease
• Transmission/Incubation Period


  • Transmitted from respiratory secretions by direct contact, droplets or airborne transmission with inoculation onto mucous membranes
  • Incubation period is 10 (8-15) days
• Symptoms and Signs


  • Local: Rash, cough, conjuctivities, koplick spots
  • Systemic: Fever, Malaise, Diarrhae
  • Complications: Otitis media, croup, pneumonia, encephalitis, SSPE (Subacute sclerosing panencephalitis)
• Epidemiology


  • Most cases occur in late winter and early spring in temperate regions, and in the dry season in the tropics
  • In non-immune population, 90-100% become infected and get clinical measles
  • Epidemics occur every 2-4 years when 30-40% of children are susceptible
  • Immunity is lifelong after introduction of effective vaccine, case reports have fallen by over 90%
  • Measles is now nearly eliminated in most European and Latin American countries with widespread implementation of two-dose vaccination strategies
• Laboratory Diagnosis


  • Antigen captured measles-specific IgM Antibodies assays (ELISA) are highly sensitive and specific
  • Confirmation of diagnosis - Demonstration of 4-fold rise of the above IgM antibodies in acute and convalescent
• Differential Diagnosis


  • Parvovirus B19
  • Rubella
  • Enterovirus
  • Dengue Virus
  • Adenoviruses
  • EBV
• Varicella-Zoster Virus (Chickenpox)


  • Primary infection causes varicella (chickenpox), a common, usually mild exanthematous childhood disease
  • Infection is more serious in adults and may be prolonged and life-threatening in newborns and individuals with immunodeficiency
  • Zoster, 'herpes zoster', is the clinical manifestation of reactivation of latent VZV
• Varicella-Zoster Virus


  • It is one of the herpesviruses and a double-stranded DNA virus
  • VZV is quickly inactivated outside the host cell
  • Haematogenous spread by mononuclear cells, secondary viraemia, occurs 4-5 days before and 1-2 days after onset of symptoms
  • Man is the only natural host
• Transmission/Incubation Period


  • Varicella is most infectious 2 days before and 3-4 days after eruption
  • VZV is spread by direct contact or by droplets, but may also be airborne in institutions
  • Incubation period is usually 14-16 days
• Clinical Features


  • Local: Vesicular, Pruritic Rash on the mucous Membranes and skin
  • Systemic: Variable fever and generalized Malaise for 2-4 days
  • Secondary staphylococcus or streptococcus skin infection with impetigo or erysipelas
  • Septicaemia with distant arthritis or osteomyelitis focus can be seen
  • Multiple organ spread of VZV can occur including brain, lungs, liver, pancreas, heart and kidneys
  • Meningoencephalitis can occur due to direct VZV infection
• Viral Haemorrhagic Diseases


  • Acute infection: fever, myalgia, malaise; progression to prostration
  • Small vessel involvement: increased permeability, cellular damage
  • Multisystem compromise (varies with pathogen)
  • Hemorrhage may be small in volume (indicates small vessel involvement, thrombocytopenia)
  • Characteristically, the overall vascular system is damaged, and the body's ability to regulate itself is impaired
  • Poor prognosis associated with: shock, encephalopathy, extensive hemorrhage
• Viral Families of Viral Haemorrhagic Fevers

  • Arenaviridae
  • Filoviridae
  • Bunyaviridae
  • Flaviviridae
• Characteristics of Haemorrhagic Viruses

  • They are all RNA viruses, which are enveloped, in a fatty (lipid) coating
  • Their survival is dependent on a mammalian or invertebrate host: the natural reservoir
  • The viruses are geographically restricted to the areas where their host species live
  • Viruses associated with most VHFs are zoonotic. They are totally dependent on their hosts for replication and overall survival
  • For the most part, rodents and arthropods are the main reservoirs for viruses causing VHFs
  • Humans are not the natural reservoir for any of these viruses. Humans are infected when they come into contact with infected hosts
• Classification of VHF based on Viral Families

  • Arenaviridae: Lassa fever, Junin, Machupo
  • Filoviridae: Ebola, Marburg
  • Flaviviridae: Yellow fever, Dengue, Kynasanaur
  • Bunyaviridae: Rift valley fever, Crimean congo, Hantavirus
• Transmission of Hemorrhagic Fever Viruses


  • Overlap of the activities of infected reservoir hosts or vectors and humans
  • Transmission when humans have contact with urine, fecal matter, saliva, or other body excretions from infected rodents
  • Bites of the vector mosquito or tick
  • Some vectors may spread virus to animals, livestock, and humans then become infected when they care for or slaughter the animals
  • Secondary transmission of the virus can occur directly, through close contact with infected people or their body fluids, or indirectly, through contact with objects contaminated with infected body fluids
• Geographical Distribution of Viral Hemorrhagic Fever

  • The virus and the disease it causes are usually seen only where the host species live(s)
  • Some hosts, such as the rodent species carrying several of the New World arenaviruses, live in geographically restricted areas. Therefore, the risk of getting VHFs caused by these viruses is restricted to those areas
  • Other hosts range over continents, such as the rodents that carry viruses which cause various forms of hantavirus pulmonary syndrome (HPS) in North and South America, or the different set of rodents that carry viruses which cause hemorrhagic fever with renal syndrome (HFRS) in Europe and Asia
• Symptoms of Viral Hemorrhagic Fever Illnesses


  • Marked fever
  • Fatigue
  • Dizziness
  • Muscle aches
  • Loss of strength
  • Exhaustion
  • Bleeding under the skin, in internal organs, or from body orifices
  • Shock
  • Nervous system malfunction
  • Coma
  • Delirium
  • Seizures
  • Renal failure
• Pathophysiology


  • The diversity of clinical features seen among the VHF infections probably originates from varying mechanisms of pathogenesis
  • An immunopathogenic mechanism has been identified for dengue haemorrhagic fever, which usually occurs among patients previously infected with a heterologous dengue serotype
  • The reasons for variation among patients infected with the same virus are unknown but stem from a complex system of virus-host interactions
• Host species


  • Some hosts live in geographically restricted areas
  • Other hosts range over continents
• The risk of getting VHFs is restricted to the areas where the host species live(s)
• Symptoms of viral hemorrhagic fever illnesses


  • Marked fever
  • Fatigue
  • Dizziness
  • Muscle aches
  • Loss of strength
  • Exhaustion
  • Bleeding under the skin
  • Bleeding in internal organs
  • Bleeding from body orifices like the mouth, eyes, or ears
  • Shock
  • Nervous system malfunction
  • Coma
  • Delirium
  • Seizures
  • Renal failure
• Pathogenesis


  The mechanisms that cause the disease
• The diversity of clinical features seen among the VHF infections probably originates from varying mechanisms of pathogenesis
• Immunopathogenic mechanism


  A mechanism identified for dengue haemorrhagic fever, which usually occurs among patients previously infected with a heterologous dengue serotype
• Antibody-dependent enhancement


  An influential theory explaining the immunopathogenic mechanism in dengue haemorrhagic fever
• The reasons for variation among patients infected with the same virus are unknown but stem from a complex system of virus-host interactions
• Some infected persons develop full-blown VHF while others do not: an unresolved issue
• Virulence of the infecting agent clearly plays an important role
• VHF syndrome


  • Capillary leak
  • Bleeding diathesis
  • Hemodynamic compromise leading to shock
• The "VHF syndrome" occurs in a majority of patients manifesting disease from filoviruses, CCHF, and the South American hemorrhagic fever viruses, while it occurs in a small minority of patients with dengue, RVF and Lassa fever
• Signs and symptoms of VHFs

  • Fever
  • Bleeding diathesis
  • Flushing of face and chest
  • Petechiae
  • Frank bleeding
  • Oedema
  • Hypotension
  • Shock
• Incubation period


  • Varies with different viruses
  • May be insidious or abrupt
• Clinical features


  • Bradycardia often occurs in Lassa fever, Marburg, Ebola and YF
  • Erythematous rash appears in Marburg and Ebola fevers
  • Pharyngitis is prominent in Lassa fever
  • Abdominal pain is present in C-CHF, Lassa fever and Ebola
• Findings of laboratory investigation

  • Decrease in total white cell count particularly the lymphocytes
  • Decrease in platelet count, absent or moderate in Lassa fever
  • Increase in serum liver enzymes, clinical jaundice present only in YF and RVF
  • Prolonged prothrombin (PT) and activated partial thromboplastin times (PTT), marked in YF, C-CHF and RVF
  • Elevated haematocrit
  • Raised serum urea and creatine, dependent on hydration status
  • Prolonged bleeding time
  • Proteinuria, severe in Lassa, Marburg and Ebola
• Laboratory diagnosis


  • Serology, Virus isolation, Antigen detection and Nucleic acid amplification techniques are useful
  • Electron microscopy can be used for the filoviruses
  • Virus isolation requires a BSL-4 facility
• Medical management


  • May require intensive supportive care
  • Antiviral therapy with intravenous ribavirin may be useful in Bunyaviridae and Arenaviridae infections
  • Interferon may be effective in Argentine or Bolivian hemorrhagic fevers
  • Experimental vaccines for other VHFs are not readily available
  • Prophylactic (preventive) ribavirin may be effective for some Bunyaviridae and Arenaviridae infections
• Yellow fever


  • An acute viral haemorrhagic disease transmitted by infected mosquitoes
  • 50% of those severely affected may die without treatment
  • Africa has 90% of the disease burden
  • Caused by a flavivirus
  • The severity of the illness varies making the illness under reported
  • Rare in Asia despite the fact the vector Aedes aegypti is common there
• Cycles of yellow fever transmission

  • Jungle cycle/sylvatic
  • Intermediate/savannah form
  • Urban/epidemic form
• Jungle cycle/sylvatic


  • The Aedes mosquito infects the monkeys and some birds in the high forest canopy at sunset and after sunrise the infected mosquitoes descend to ground level and bite humans
  • Primarily a disease of adults whose work brings them into close contacts with the forests- hunters and forestry workers
  • Aedes africanus is the main vector