microbio 2125 unit 6 part 8 - Influenza A

Etiological Agent

Orthomyxovirus (Influenza A virus)

Distinguishing Characteristics of Etiological Agent:

• Enveloped virus with segmented RNA genome (8 segments, 10 genes)

• Contains glycoprotein spikes: Hemagglutinin (H) and Neuraminidase (N)

• Undergoes antigenic drift (minor changes) and antigenic shift (major changes via reassortment)

ssRNA virus

Virulence Factor(s):

• Hemagglutinin: binds to host cells

• Neuraminidase: hydrolyzes mucus, assists budding and release

Predisposing Factors:

• Elderly and small children at higher risk

• Weakened immune defenses increase risk for secondary infections

Transmission:

• Inhalation of aerosols and droplets

• Contact with contaminated fomites

Syndrome (Signs + Symptoms):

• Acute respiratory illness

• Fever, headache, myalgia, pharyngeal pain

• Shortness of breath, coughing

• Severe inflammation and stripping of respiratory epithelium

Affected Body Region/System:

Respiratory tract (upper and lower)

Treatment:

• Symptom control

• Antivirals: amantadine, rimantadine, zanamivir (Relenza), oseltamivir (Tamiflu)

• Note: Resistance to amantadine and rimantadine is high

Prevention:

Annual trivalent vaccine recommended

Other Notes:

• Major cause of seasonal flu and pandemics

• High mutation rate complicates long-term immunity

• Diagnosis: Rapid immunofluorescence tests to detect antigens in pharyngeal specimen; serological testing to screen for antibody titer