Influenza

Influenza The one of the most significant acute upper respiratory tract infections A broad array of respiratory illnesses responsible for significant morbidity and mortality in children Epidemic disease (influenza virus types A and B) and sporadic disease (type C) in humans

Pandemics the 1918-1919 Spanish pandemic (influenza virus subtype H1N1) the 1957 pandemic (subtype H2N2) the 1968-1969 pandemic (Hong Kong subtype H3N2) and, to a lesser extent, the Russian pandemic in 1977 (subtype H1N1)

the family Orthomyxoviridae single-stranded RNA viruses 3 basic types of virus A, B, C structural and biological similarities but vary antigenically

the most significant surface proteins are hemagglutinin and neuraminidase The viruses are typed based on these proteins For example, influenza A subtype H3N2 expresses hemagglutinin 3 and neuraminidase 2

The most common prevailing human influenza A subtypes are H1N1 and H3N2 The trivalent vaccine contains A strains from H1N1 and H3N2, along with an influenza B strain

Influenza A is generally more pathogenic than influenza B Influenza A is a zoonotic infection, and more than 100 types of influenza A infect most species of birds, pigs, horses, dogs and seals

H5N1 bird flu In 1997, an avian subtype,H5N1, was first described in Hong Kong The H5N1 flu is transmitted to humans from birds more than 240 human cases have been documented and more than 140 persons have died

Experts are concerned that a slight mutation could convert H5N1 to a strain that would be easily transferred from human to human Such a strain could potentially spread rapidly and precipitate a catastrophic worldwide pandemic

Pathophysiology Respiratory transmission The virus attaches to and penetrates respiratory epithelial cells in the trachea and bronchi Viral replication occurs, which results in the destruction of the host cell Viremia does not occur The virus is shed in respiratory secretions for 5-10 days

Epidemiology Highly contagious Is spread when an individual inhales infected air-borne droplets or comes in direct contact with an infected person's secretions In the winter and spring Typical symptoms begin 2-3 days after exposure to the virus

Clinical manifestations Abrupt onset of illness Fever 39 – 40 C, chills Severe headache Weakness, severe fatigue Myalgias Ocular symptoms (photophobia, burning sensations, pain upon motion) Sore throat (pharyngitis) Tachycardia resulting from hypoxia, fever

Subsequent catharal and respiratory symptoms Nasal congestion Rhinitis Nonproductive cough Cough-related pleuritic chest pain Dyspnea Wheezing, rhonchi Cervical lymphadenopathy

Influenza in infants Conjunctivitis, rhinitis, and gastrointestinal tract symptoms are reported more commonly In young infants, influenza may produce a sepsislike picture with shock Occasionally, influenza viruses can cause croup or pneumonia

Complications Primary influenza viral pneumonia Secondary bacterial pneumonia Croup Myositis Myocarditis Toxic shock syndrome Reye syndrome

Reye syndrome Acute noninflammatory encephalopathy and hepatic failure The etiology of Reye syndrome is unknown Occurs after a viral illness (upper respiratory tract infection, influenza, varicella, or gastroenteritis), and the use of aspirin during the illness Decrease in the use of aspirin among children have made the diagnosis and occurrence of Reye syndrome rare

Lab Studies Findings of standard laboratory studies are nonspecific Viral culture of nasal-pharyngeal samples, throat samples, or both Direct immunofluorescent tests Serologic studies Chest radiography - to exclude pneumonia

Treatment Etiological : Antiviral drugs α - Interferons Interferon's inductors Symptomatic – detoxication - antipyretics (paracetamol 10-15 mg/kg) - antihistamins (clemastin, loratadin) - mucolythics (ambroxol) - anticongestants (oxymetazolin)

Antiviral medications Influenza antiviral medications should be started as soon as possible after symptom onset These medications have not been shown to be effective if administered more than 48 hours after onset They can reduce illness severity and shorten duration of illness They may also prevent serious influenza-related complications (e.g., pneumonia or exacerbation of chronic diseases)

Antiviral Drugs RNA mutagen Broad spectrum Ribavirin Neuraminidase Inhibitor Influenza strains A and B Oseltamivir and Zanamivir Matrix protein / haemagglutinin Influenza A strains Amantadine / Rimantadine Target Virus Drug

Antiviral Drugs Amantadine 4,5-5 mg/kg, not > 150 mg/day Rimantadine 7-10 years - 50*2 times/day 11-14 years - 50*3 times/day Ribavirin 10 mg/kg/day (RSV-infection – 20mg/ml/12 hours inhalations)

Oseltamivir Oseltamivir is approved for treatment among persons aged 1 year and older and for chemoprophylaxis among persons aged 13 years and older. Recommended treatment dosages for children vary by the weight of the child: 15 kg or less - is 30 mg twice a day >15-23 kg the dosage is 45 mg twice a day; >23-40 kg the dosage is 60 mg twice a day; >40 kg the dosage is 75 mg twice a day. Dosages for chemoprophylaxis are the same for each weight group, but doses are administered only once per day.

Zanamivir Zanamivir is approved for treatment among children aged 7 years and older The recommended dosage of zanamivir for treatment of influenza is two inhalations (one 5-mg blister per inhalation for a total dose of 10 mg) twice daily (approximately 12 hours apart) Zanamivir is approved for chemoprophylaxis of influenza among children aged 5 years and older - the dosage is 10 mg (2 inhalations) once a day

Chemoprophylaxis Vaccination is the best way to prevent influenza - safe and effective immunity throughout the influenza season Antiviral medications are useful adjuncts to vaccination To be effective as prophylaxis, the drug must be taken each day for the duration of potential exposure to influenza or until immunity after vaccination develops

WHO determines influenza vaccine contents annually Typically, 3 live attenuated virus strains, which antigenically represent the influenza strains likely to circulate the next flu season, are included in the formulation each year

For the 2006-2007 season, the trivalent vaccine contained the following antigenic strains: influenza A - H1N1: New Caledonia/20/1999 influenza A - H3N2: Wisconcin/67/2005 or equivalent; and influenza B: Malaysia 2506/2004 or equivalent

Vaccination is recommended Persons older than 65 years Patients with chronic pulmonary, cardiac, metabolic , renal disease, immunosuppression Children and teenagers with long-term use of aspirin Pregnant women in their second or third trimester during influenza season Physicians, nurses, and other health care providers Employees and residennts of nursing homes Household members of persons at high risk Providers of essential community services (police, fire) Students and dormitory residents Anyone wishing to reduce risk of influenza

Vaccination Influvac (Netherlands) Fluarix (England) Agrippal S1 (Germany) Begrivac (Germany) Vaxigrip (France) Grippol (Russia)

Child with croup. Note the steeple or pencil sign of the proximal trachea evident on this anteroposterior film.

Influenza

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Influenza