Influenza Dr Ubaid N P Acute respiratory tract

Influenza Dr Ubaid N P

�Acute respiratory tract infection � 3 types – A, B & C �Sudden onset of chills, fever, malaise, muscular pain and cough �International disease �Occurs in several forms – subclinical, epidemics(2 -3 years & 4 -7 years), pandemics (10 -40 years) �Pandemics – 1918(Spanish influenza), 1957(Asian influenza), 1968 (Hong Kong influenza)

� Characteristics of epidemic : 10 -50% attack rate �At present three types of influenza viruses are circulating in the world : A (H 1 N 1), A (H 3 N 2) and B viruses �H 5 N 1(1997 – Hong Kong) doesn't easily transmit between humans

Epidemiological determinants Agent factors (a) AGENT : family Orthomyxoviridae, three viral subtypes - influenza type A, type B and type C �No cross immunity �Influenza A and B responsible for epidemics of disease throughout the world �Influenza A virus has 2 distinct surface antigens - the haemagglutinin (H) and the neuraminidase (N) antigens. �H antigen initiates infection following attachment of the virus to susceptible cells. �The N antigen is responsible for the release of the virus from the infected cell. � 16 HA & 9 NA subtypes have been identified currently

Antigenic shift: �Occurs when the antigenic change is sudden complete or major change �result from genetic recombination of human with animal or avian virus, providing a major antigenic change. �Can cause a major epidemic or pandemic involving all age groups. Antigenic drift: �when the antigenic change is gradual over a period of time �Antigenic drift involves "point mutation" in the gene

�Since the isolation of the virus A in 1933, major antigenic changes have occurred twice - once in 1957 (H 2 N 2) and again in 1968 (H 3 N 2). �Strains occurring between 1946 and 1957 have been called (H 1 N 1) strains. �The shift in 1968 involves only the H antigen. �Antigenic changes occur to a lesser degree in the B group influenza viruses. �Influenza C appears to be antigenically stable.

(b) RESERVOIR OF INFECTION – Animals & birds (c) SOURCE OF INFECTION: Usually a case or subclinical case. The secretions of the respiratory tract are infective. (d) PERIOD OF INFECTIVITY: Virus is present in the nasopharynx from 1 to 2 days before and 1 to 2 days after onset of symptoms.

Host factors (a) AGE AND SEX : � Affects all ages and both sexes. �Mortality higher in certain high-risk groups in the population such as old people (generally over 65 years of age), children under 18 months, and persons with diabetes or chronic heart disease, kidney and respiratory ailments (b) HUMAN MOBILITY: important factor in the spread of infection.

(c) IMMUNITY: � Immunity to influenza is subtype - specific. �Antibodies against HA and NA are important in immunity to influenza. � Resistance to initiation of infection is related to antibody against HA, which neutralizes the virus �Decreased severity of disease and decreased ability to transmit virus to contacts are related to antibody directed against the NA. �Immunity can be incomplete as reinfection with the same virus can occur.

Environmental factors: �Season: epidemics usually occur in winter months in the Northern Hemisphere and in the winter or rainy season in the Southern Hemisphere. ln India, epidemics have often occurred in summer. �Over crowding: Enhances transmission. The attack rates are high in close population groups, e. g. , schools, institutions, ships, etc. Mode of transmission: �droplet infection or droplet nuclei - sneezing, coughing or talking Incubation period: 18 to 72 hours.

features The virus enters the respiratory tract inflammation and necrosis of superficial epithelium of the tracheal and bronchial mucosa Secondary bacterial invasion. Symptoms - fever, chills, aches, coughing and generalized weakness. Fever lasts from 1 -5 days, averaging 3 days in adults. The most dreaded complication is pneumonia, which should be suspected if fever persists beyond 4 or 5 days or recurs abruptly after convalescence Other complications are acute sinusitis, otitis media, purulent bronchitis, reye syndrome

Laboratory diagnosis (a) VIRUS ISOLATION: Nasopharyngeal secretions - indirect fluorescent antibody technique (b) SEROLOGY: Haemagglutination Inhibition(HI), ELISA, Paired Sera

Prevention of influenza �Good ventilation of public buildings �Avoidance of crowded places during epidemics. �Encouraging sufferers to cover their faces with a handkerchief when coughing and sneezing, �To stay at home at the first sign influenza �Hygienic practices during handling of poultry products, including handwashing and prevention of cross – contamination �Thorough cooking, to more than 70°C, of poultry products �The vaccine is not recommended to control spread in the general population. �To be effective the vaccine must be administered at least two weeks before the onset of an epidemic, or

�Since epidemics of influenza are unpredictable, the hope of preventing influenza epidemics by prophylactic mass vaccination is remote. �Since influenza vaccines will not control epidemics, they are recommended only in certain selected population groups �E. g. in industry to reduce absenteeism, and in public servants to prevent disruption of critical public services, such as the police, fire protection, transport and medical care. �Also, certain groups e. g. the elderly and individuals in any age group who have a known underlying chronic or debilitating disease are selectively immunized

Influenza vaccines (a) KILLED VACCINES �Formulated in aqueous or saline suspension �Subcutaneous or intramuscular route. � A single inoculation (0. 5 ml for adults and children over 3 years and 0. 25 ml for children from 6 months to 36 months of age) �In unprimed individuals, 2 doses of the vaccine, separated by an interval of 3 to 4 weeks

� The protective value : 70 -90% � immunity lasts for only 6 -12 months. � Revaccination on an annual basis is recommended. � Can produce fever, local inflammation at the site of injection, and very rarely Guillain-Barre syndrome (an ascending paralysis). � Persons allergic to eggs may develop symptoms and signs of hypersensitivity (b) LIVE ATTENUATED VACCINES: � Administered as "nose drops" into the respiratory tract. � Stimulate local as well as systemic immunity

Antiviral drugs �Prophylactic & therapeutic �Zanamivir & Oseltamivir – Neuraminidase inhibitors �amantadine and rimantidine

Avian influenza �large group of different influenza viruses that primarily affect birds �On rare occasions - pigs and humans �Avian H 5 N 1, strain with pandemic potential �Ultimately adapt into a strain that is contagious among humans - human influenza virus. �The H 5 N 1, strain first infected humans in Hong Kong in 1997, causing 18 cases including six deaths. �Since then – 478 cases, 286 deaths, 15 countries �Most cases have occurred in previously healthy children and young adults.

Pandemic Influenza A(H 1 N 1) 2009 �Can infect lower respiratory tract and cause pneumonia �Emergence – March 2009, declared pandemic by WHO on 11 th June 2009 �Incubation period : 2 -3 days, could range upto 7 days

Case definitions Suspected case: A person with acute febrile illness (Fever ≥ 38°C) with onset (a) Within 7 days of close contact with a person who is a confirmed case of influenza A(H 1 N 1) 2009 virus infection; or (b) Within 7 days of travel to areas where are confirmed cases; or (c) resided in a community where there are confirmed influenza A(H 1 N 1) 2009 cases

Probable case: A person with acute febrile illness who (a) Is positive for influenza A, but unsubtypable; or (b) Is positive for influenza A by an influenza rapid test or an influenza Immunoflurescence Assay (IFA) & meets the criteria for a suspected case; or (c) Person who died of an unexplained acute respiratory illness whos is considered to be epidemiologically linked to a probable or confiremd case

Confirmed case: A person with acute febrile respiratory illness with lab confirmed influenza A(H 1 N 1) 2009 virus infection at WHO approved lab by one or more of the following test (a) Real Time PCR (b) Viral Culture (c) Four fold rise in influenza A (H 1 N 1) virus specific neutralizing antibodies

Clinical features (a) Uncomplicated influenza (i) ILI symptoms – no shortness of breath (ii) GI symptoms - no dehydration (b) Complicated influenza (i) RT, CNS involvement, severe dehydration, renal failure, multi organ failure, septic shock etc (ii) Exacerbation of underlying chronic disease – COPD, Asthma, hepatic or renal failure, diabetes etc (iii) Hospitalization requiring presentations (iv) Any of the signs of progressive illness

�Risk factors for severe disease �Laboratory diagnosis : Need for it? RT – PCR, sample collection �Infection control : Community, Hospital, Immunocompromised patients

Vaccine