diease

Arbovirus encephalitis


OVERVIEW OF Arbovirus encephalitis :

Arbovirus is not an virus.It refers to the virus which spreads by athropods or zoonotic infections.The vector are mosquito,ticks and sandflies.

Arboviruses, are usually seen in birds or small rodents,that are transmitted to humans by the bite of an infected mosquito carrying the virus; Human to human spread is not seen in arbovirus. Arboviral infections are most common in the summer and humid climate.

The incubation period – between 2 and 15 days for arboviruses.


STRUCTURE of Arbovirus encephalitis :

Structure of virus:

The family of arbovirus include toga virus,

Flavi virus

Bunya virus

Reovirus

Rhabdeovirus

Orthomyxiviridae

Togaviridae

  1. Morphology
    • Viruses of Togaviridae family are Spherical, Enveloped virus with icosahedral
    • Size: 60 – 70 nm in diameter.
    • Genetic Material :- (+) ssRNA.
  2. Classification
    • Togaviridae contains two Genera: Alphavirus & Rubivirus.
    • Viruses of Togaviridae are transmitted principally by Mosquitoes.
    • Genus Rubivirus contains Rubella virus, is not Arthropod borne.
    • The genus Alphaviruses includes:-
      1. Encephalitis Group
        1. Western equine encephalitis (WEE)
        2. Eastern equine encephalitis (EEE)
        3. Venezuelan equine encephalitis (VEE)
      2. Febrile Illness Group
        1. Chikungunya virus
        2. O’nyong-nyong virus
        3. Sindbis Virus
        4. Ross river virus

Flaviviridae

 

    1. Morphology
      • Viruses of Flaviviridae family are Spherical viruses.
      • Size: 40 – 50 nm in diameter.
      • Genetic Material :- (+) ssRNA.

            Classification

    • Some members of Flaviviridae are Mosquito-borne while others are Tick-borne
    • Hepatitis C virus is neither mosquito nor tick-borne.
    • Mosquito-borne Flaviviruses
      1. Encephalitis viruses
        1. St. Louis Encephalitis Virus
        2. Ilheus Virus
        3. West Nile Virus
        4. Murray Valley Encephalitis Virus
        5. Japanese B Encephalitis Virus
      2. Yellow Fever
      3. Dengue
    • Tick-borne Flaviviruses
      1. Tick-borne Encephalitis viruses
        1. Russian Spring-Summer Encephalitis
        2. Powassan Virus
      2. Tick-borne Hemorrhagic Fevers
        1. Kyasanur Forest disease (KFD)
        2. Omsk Hemorrhagic fever

Bunyaviridae

  1. Morphology
    • Viruses of Bunyaviridae family are Spherical, enveloped viruses with glycoprotein peplomers.
    • Size: 90 – 100 nm in diameter.
    • Genetic Material :ssRNA.
  2. Classification
    • Bunyaviridae contains four genera :
      1. Bunyavirus – Mosquito-borne
      2. Phlebovirus – Phlebotomus or Mosquito-borne
      3. Nairovirus – Tick-borne
      4. Hantavirus – Non-Arthropod-borne
  3. Viruses of Bunyaviridae
    • Bunyavirus
      1. California encephalitis virus
      2. La Crosse virus
      3. Chittor virus
    • Phlebovirus
      1. Sandfly fever (Phlebotomus fever)
      2. Rift valley fever
    • Nairovirus
      1. Crimean Congo hemorrhagic fever virus
      2. Ganjam virus
    • Hantavirus
      1. Hantaan virus
      2. Belgrade virus
      3. Seoul virus
      4. Puumala virus
      5. Muerto Canyon virus
      6. Sin Nombre virus

Reoviridae

  1. Morphology
    • Viruses of Reoviridae family are cubic shaped.
    • Size: 60 – 80 nm.
    • Genetic Material:- dsRNA.
  2. Classification
    • Reoviridae contains four genera – Orthoreovirus, Coltivirus, Orbivirus, and Rotavirus. Of which the only Orbivirus causes Arthropod-borne infections.
    • Colorado tick-borne virus is the only recognized pathogen in Orbivirus, causes Colorado tick fever & is spread by the wood tick.

Rhabdoviridae

  1. Morphology
    • Viruses of Rhabdoviridae family are Bullet-shaped.
    • Size :- 170*100 nm.
    • Genetic Material :ssRNA.
  2. Classification
    • The chandipura virus, belonging to the genus Vesiculovirus of family Rhabdoviridae was isolated in Nagpur (INDIA) in 1967.
    • The vectors are sandflies and Aedes mosquitoes, in which the virus multiplies.
    • The pathogenic significance of this virus has not been found.


CAUSES :

It is a vector borne virus

Blood transfusion from an infected persons

Organ transplantation

Vertical transmission(from mother to the child)

Routes of transmission:

Coming into contact with the contaminated objects

Sexual contact.


PATHOPHYSIOLOGY :

Arbovirus enter cells by receptor-mediated endocytosis and exit by budding from

the plasma membrane.

Arbo viruses enter the body via mosquito bites and replicate in various tissues,

including Langerhans cells, which then migrate to lymph nodes, causing viremia.

Viremia results in invasion of the central nervous system (CNS) by arbovirus that

cause encephalitis and meningitis or of the joints and internal organs by viruses that cause fever,

arthralgia, and rash.

All arbovirus suppress the innate immune response by inhibiting JAK/STAT

signaling, a major early determinant of disease severity.

At later times, recovery is mediated by virus-neutralizing antibodies and cytotoxic T cells.

The viruses are capable of boosting the immune system of the host cell and aids in the production of interferons.


COMMON CLINICAL SIGNS AND SYMPTOMS :

Headache

Vomiting

Fatigue

Sleepiness


DIAGNOSTIC :

Detection of virus-neutralizing antibodies in combination with recent travel history to an

endemic area may be meaningful.

Immunosorbent assay- detect the virus specific IgM or IgG antibodies.

Greater than fourfold rise in titer between acute and convalescent sera and cerebo spinal

fluid containing virus specific IgG or IgM or both are the diagnostic features.

Real-time polymerase chain reaction (RT-PCR)- is valuable in the early confirmation of

arbovirus infections, particularly chikungunya. However, the value of RT-PCR is limited to

diagnosis in the viraemic phase, with later infection requiring serology.

Direct immunofluorescence assay -to detect chikungunya IgM has a high sensitivity and

specificity and is used in the latter. stages.However, the use of these tests in the tropics may be limited to the financial strains.

Detection of virus-neutralizing antibodies in combination with recent travel history to an

endemic area may be meaningful.

Immunosorbent assay- detect the virus specific IgM or IgG antibodies.

Greater than fourfold rise in titer between acute and convalescent sera and cerebo spinal

fluid containing virus specific IgG or IgM or both are the diagnostic features.

Real-time polymerase chain reaction (RT-PCR)- is valuable in the early confirmation of

arbovirus infections, particularly chikungunya. However, the value of RT-PCR is limited to

diagnosis in the viraemic phase, with later infection requiring serology.

Direct immunofluorescence assay -to detect chikungunya IgM has a high sensitivity and

specificity and is used in the latter. stages.However, the use of these tests in the tropics may be limited to the financial strains.

 

A normal erythrocyte sedimentation rate- and a negative rheumatoid factor are useful to

differentiate chikungunya arthritis from rheumatoid arthritis. Extensive, symmetrical joint

involvement, particularly of the metacarpophalangeal and proximal joints, the presence

of rheumatoid nodules or anti-cyclic citrullinated peptide (anti-CCP) antibodies favours

rheumatoid arthritis over chikungunya with chronic arthropathy. The presence of lower limb

asymmetrical joint involvement with axial skeletal affliction favours the diagnosis

of spondyloarthropathy over chikungunya.

A complement fixation test:which provides antigen to antibody reactions.

Isolation of Virus:

Mouse suckling:

This test involve sthe injection of arbovirus in to the mice cell by suckling action.later the mice develops the encephalitis.


TREATMENT AND PROGNOSIS :

infusion of fluids to balane the electrolyte

antiviral medications.


PREVENTION :

  • Clean the stagnant area which host for multiplication of virus.
  • Wear clothing that covers the arms, legs, and feet whenever you are outdoors.
  • Use mosquito repellents sparingly on exposed skin. An effective repellent will contain 20% to 30% DEET (N,N-diethyl-meta-toluamide).
  • Spray clothing with repellents containing permethrin or DEET as mosquitoes may bite through thin clothing.
  • Minimize outdoor activities at dawn, dusk, and in the early evening when mosquitoes are most active.
  • Inspect window and door screens and repair any holes found.


REFERENCE :

www.healthline.com

www.nhs.uk

http://www.cdc.gov.in