Influenza Virus – Morphology, Resistance, Antigenic Properties, Cultivation, Pathogenicity, Clinical Features, Laboratory Diagnosis, Prophylaxis & Treatment

INTRODUCTION TO INFLUENZA VIRUS

⇒ Influenza virus is an Orthomyxovirus, belongs to family orthomyxoviridae; causes influenza, an Acute Respiratory illness.

⇒ Orthomyxoviruses are spherical or filamentous, enveloped viruses with single-stranded RNA genome, that causes Respiratory illness.

⇒ Orthomyxoviruses have the ability to adsorb onto mucoprotein receptors on RBCs, causing haemagglutination.

MORPHOLOGY OF INFLUENZA VIRUS

⇒ Influenza virus is a Spherical or Pleomorphic or Filamentous, Enveloped virus having a helical nucleocapsid.

⇒ Size –  80 – 120 nm in diameter.

⇒ Genetic material – (-) ssRNA, segmented & exists in eight pieces.

⇒ In the envelope, two types of glycoprotein spikes are present – the Haemagglutinin (HA) and the Neuraminidase (NA).

RESISTANCE SHOWN BY INFLUENZA VIRUS

⇒ Influenza virus is inactivated by heating at 50^oC for 30 minutes, remains viable at 0-4^oC for about a week, can be preserved for years at -70^oC or by freeze drying.

⇒ It is sensitive to Ether, Formaldehyde, Phenol, Salts of Heavy metals and particularly to Iodine.

ANTIGENIC PROPERTIES OF INFLUENZA VIRUS

⇒ The influenza virus has three serotypes type A, type B and type C, of which Influenza A virus causes widespread epidemics & pandemics.

⇒ The characteristic feature of this virus is its ability to undergo antigenic variation due to frequent changes in the antigenicity of HA & NA.

⇒ Hemagglutinin (HA) is a strain-specific glycoprotein composed of two polypeptides – HA1 & HA2, Responsible for the Hemagglutination & Hemadsorption.

⇒ Neuraminidase (NA) is also a strain-specific glycoprotein, present in neuraminidase spikes, facilitates infection.

HOST RANGE & CULTIVATION OF INFLUENZA VIRUS 

⇒ The human influenza virus, especially type A influenza, can cause infection in a large number of animal species, due to its high Antigenic variability & adaptability.

⇒ It can grow in the Amniotic cavity, after few egg passages, influenza virus type A & B can grow well in the Allantoic cavity, growth is detected by Hemagglutination test performed with Amniotic & Allantoic fluid.

⇒ It can also be isolated n primary monkey kidney or the human embryonic kidney cell.

PATHOGENICITY OF INFLUENZA VIRUS

⇒ Influenza virus causes influenza, is an acute respiratory disease.

The virus enters the host body via respiratory tract (RT)

⇓

Viral neuraminidase facilitates infection by reducing

the viscosity of mucus lining the RT, exposing the

cell surface receptors for virus adsorption.

⇓

Ciliated cells of RT are the main sites of viral infection,

damages the cells, laying bare the basal cells in

trachea and bronchi.

⇓

This renders the RT highly vulnerable to bacterial invasion.

CLINICAL FEATURES OF INFLUENZA VIRUS INFECTION

⇒ The incubation period of influenza virus varies from 1-4 days.

⇒ The clinical features vary from mild coryza to fulminating & rapidly fatal pneumonia.

⇒ Initial symptoms include fever, headache, and generalized Myalgia.

⇒ The uncomplicated disease usually resolves within 7 days.

⇒ In severe cases, viral pneumonia is seen, associated with –

• Hyperemia
• Alveolar wall thickening
• Intestinal infiltration with leucocytes
• Capillary thrombosis
• Leucocytic exudation
  

⇒ It especially affects young children & is characterized by acute degenerative changes in Brain, Liver, and Kidney.

LABORATORY DIAGNOSIS OF INFLUENZA VIRUS

⇒ Specimen: Nasal secretions, Nasal or Throat swab & throat Garglings can be collected using buffered salt solution.

⇒ Demonstration of viral Antigens: Rapid detection of viral antigen can be done by Immunofluorescence; detection of viral RNA by RT PCR is highly sensitive.

⇒ Isolation of the virus: virus isolation is obtained readily during the first 2-3 days of the illness. The specimens should be treated with antibiotics to destroy bacteria. Isolation may be made in eggs or in monkey kidney cell culture.

⇒ Serology: routinely employed serological tests includes – Complement fixation Test (CFT), Hemagglutination Inhibition Test (HAI test) & Radial Immunodiffusion Test.

PROPHYLAXIS OF INFLUENZA VIRUS

⇒ Vaccination is the primary means of prevention of influenza but is quite difficult due to the frequent change in the antigenic stricture of influenza.

⇒ Two types of vaccines are available for influenza virus – Inactivated vaccine-administered Parenterally; Live attenuated vaccine-administered intranasally or by aerosol spray.

⇒ Rimantadine or Amantadine may be given orally as chemoprophylaxis, to unimmunized people during a major epidemic of Influenza A virus.

TREATMENT OF INFLUENZA INFECTION

⇒ Amantadine & the Rimantadine are useful in the treatment of influenza.

⇒ They cause symptomatic improvement but virus shedding and antibody response are unaffected.

⇒ Zanamivir & Oseltamivir, new drugs designed to block viral neuraminidase, have been found effective in the treatment & prevention of influenza when administered as a nasal spray.

SAHIL BATRA

Hi, I’m the Founder and Developer of Paramedics World, a blog truly devoted to Paramedics. I am a Medical Lab Tech, a Web Developer and Bibliophiliac. My greatest hobby is to teach and motivate other peoples to do whatever they wanna do in life.