Types of Myxoviruses: Orthomyxoviruses and Paramyxoviruses

The following points highlight the two types of myxoviruses. The two types of myxoviruses are: 1. Orthomyxoviruses (Influenza Virus Type A, B, and C) Influenza and 2. Paramyxoviruses (Respiratory Infection; Mumps; Measles).

Myxovirus Type # 1. Orthomyxoviruses (Influenza Virus Type A, B, and C) Influenza:

Description:

These viruses are spherical or filamentous. From the viral envelope project spikes or haemagglutinin which are protein molecules. Be­tween these spikes, there is neuraminadase. Influ­enza viruses of type A were recovered from men, pigs, horses. All the strains of type A share the com­mon antigen (S antigen), while strains of Type B share a different one. influenza Type C is distinct from both A and B.

They remain viable in a dried state and at low temperature for longer period. They withstand expo­sure to glycerin for 3 months and they are killed at 65°C in 5-40 minutes. They are sensitive to drying, rapidly destroyed in both alkaline and acidic media and they are inactivated by ail disinfectants and de­stroyed by ultraviolet irradiation.

Pathogenesis and Disease in Man:

The virus is inhaled and penetrates the cells of the surface epi­thelial layer of the respiratory tract mucosa. Influenza virus is strictly pneumotropic and multiplies only in the cells of the respiratory tract epithelium. As the virus multiplies and the infection develops, the trachea, bronchi, bronchiole and alveo­lar epithelial cells gradually become involved in the process. The injured ciliated epithelium loses its cilia and as a result of this becomes deprived of its de­fence function.

It serves as a favourable medium or the penetration of secondary bacterial flora (strepto­cocci, pneumococci, Haemophilus influenzae etc.) which give rise to complications (pneumonia, en­cephalitis, influenzal meningitis and otitis media).

Immunity:

After an attack of influenza, the en­suing immunity persists for a year or more and con­fers resistance to the virus strain concerned.

Treatment:

Recent findings indicate that L-amantadine hydrochloride is useful because it can block the entry of influenza virus and if given very early after exposure to the virus can prevent viral replica­tion. Transmission, influenza virus is spread by the air droplet route. The source of infection is the influenza patient who may infect healthy people when sneez­ing, coughing and talking. Influenza is highly contagious, it causes epidem­ics and pandemics.

Prophylaxis:

Spread of infection is prevented by isolating the patient, regularly ventilating the room and cleaning the room with a damp cloth (soaked in chloramine solution). Physical exercise and sports serve to strengthen the body. A vaccine prepared from various strains of given types or influenza is used. Liquid and dry vaccines are available as monovalent or polyvalent forms. The vac­cine can be introduced intranasally or into the upper respiratory tract with a pulverize.

Myxovirus Type # 2. Paramyxoviruses (Respiratory Infection; Mumps; Measles):

Although the paramyxo viruses resemble orthomyxo viruses in morphology and symmetry, they are, as a rule, larger and more pleomorphic. This group includes the para-influenza viruses types 1 to 4 which are responsible for respiratory illness, mumps.

Resistance:

They are quickly killed by heating and exposure to the action of disinfection. Pathogenesis and disease in man. Para-influenza virus Types 1, 2 and 3 are more frequently recovered from children suffering from upper respiratory tract lesions (rhinitis, pharyngitis and bronchitis) which are accompanied by a rise of temperature. They produce mild disease in adults.

It has been proved recently that other viruses (over 70 in numbers) may also produce acute respi­ratory diseases. They include the reo-viruses, ECHO (Enterocytopathogenic Human Origin) viruses, rhinoviruses, coxsachie A and B viruses.