1 Seasonal Diseases and Control Measures

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Epidemiology of Influenza – Seasonal, Avian and Pandemic:

Epidemiology of Influenza – Seasonal, Avian and Pandemic

What is Influenza?:

What is Influenza? An acute Respiratory Tract Infection (RTI), caused by Influenza virus, characterised by sudden onset of: Fever/chills Headache, myalgia Sore throat Cough Coryza Prostration Range of symptoms differs by age Vomiting & diarrhea in children/elderly Fever alone in infants May be atypical in elderly Serious complications can occur among high risk groups

Influenza Virus – 3 Types :

Influenza Virus – 3 Types Causes significant disease: epidemics; pandemics Causes significant disease: milder epidemics Does not cause significant disease Infects both humans and other species Limited to humans Limited to humans Frequent antigenic variations Infrequent antigenic variations! Antigenically stable RNA virus Antigenically distinct types No cross-immunity between different types Type A Type B Type C

Influenza A – Important Feature:

Influenza A – Important Feature 2 surface antigens: Haemagglutinin (HA) Initiates infection following attachment of virus to susceptible cells Neuraminidase (NA) Release of virus from infected cell 16 ‘H’ antigens (1-16) 9 ‘N’ antigens (1-9) Different combinations of H and N antigens Influenza Virus HA NA

Influenza A – Antigenic Variations :

Influenza A – Antigenic Variations Antigenic drift: gradual antigenic change over a period; Involves ‘point mutations’ in genes owing to selection pressure by immunity in host population Responsible for frequent influenza epidemics; necessitates reformulations of seasonal influenza vaccines Antigenic shift: sudden, complete or major change; Results from genetic recombination of human with animal/ avian virus Leads to a novel subtype different from both parent viruses If ‘novel subtype’ has sufficient genes from HI viruses which make it readily transmissible from person to person, it may cause pandemics Evidence suggests that human influenza viruses responsible for last 3 pandemics and current H1N1 pandemic contained gene segments closely related to avian influenza viruses

PowerPoint Presentation:

Different Species Infected by Influenza A Subtypes N9 N8 N7 N6 N5 N3 N4 N2 N1 H15,16 H14 H13 H12 H11 H10 H3 H2 H1 H9 H8 H7 H6 H5 H4 All 16 H subtypes infect birds Most widespread epidemics & all pandemics: H1N1, H2N2, H3N2

Influenza Terminology - 1:

Influenza Terminology - 1 Human seasonal influenza Avian influenza Pandemic influenza

Influenza Terminology - 2:

Influenza Terminology - 2 Seasonal influenza: Occurs every year with gradual variations in previous year’s virus surface proteins ( antigenic drift ) Spreads around the world in seasonal epidemics, affecting 10 - 20% of total population Annual epidemics thought to result in 3-5 million cases of severe illness and 2.5-5 lakh deaths

Influenza Terminology - 3:

Influenza Terminology - 3 Avian Influenza: Primarily a disease of birds due to large group of different influenza A viruses Rarely jumps species and infects humans An influenza pandemic happens when a new subtype emerges that has not previously circulated in humans and is adapted to human to human transmission Viruses in wild water fowl is the ultimate source of new viruses in humans causing pandemics

Influenza Terminology - 4:

Influenza Terminology - 4 Pandemic Influenza: A worldwide surge in cases caused by the introduction of a new influenza type A surface protein (antigenic shift).

Seasonal Epidemics vs. Pandemics:

Seasonal Epidemics vs. Pandemics Seasonal Influenza Influenza Pandemics A public health problem each year Appears in the human population rarely and unpredictably Usually some immunity built up from previous exposures to the same subtype Human population lacks any immunity. Virulence and mortality not entirely linked to immunity Infants and elderly most at risk All age groups, including healthy young adults, may be at increased risk for serious complications Result of Antigenic Drift Result of Antigenic Shift

Magnitude of Disease Burden (Seasonal Influenza):

Magnitude of Disease Burden (Seasonal Influenza) World-wide in distribution: Sporadic cases every season/year round Outbreaks (primarily Influenza A): occur every year Major epidemics: at interval of 2-3 years Pandemics: rare; 10-15 years or more Attack rates during epidemics: 10-20% in general community; > 50% in closed populations Epidemics generally last 3-6 weeks

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Influenza Pandemics 1918: “Spanish Flu” 50 million deaths A(H1N1) 1968: “Hong Kong Flu” 1 - 4 million deaths A(H3N2) 1957: “Asian Flu” 1 - 4 million deaths A(H2N2) 2009: “Swine Flue” A (H1N1) 77201 human cases 332 deaths in 120 countries* *Data as on 1st July 2009

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Recorded Influenza Pandemics

Influenza: Key Characteristics— Agent Factors:

Influenza: Key Characteristics— Agent Factors Reservoir of Infection: Humans primary reservoir for human infections Major reservoir – animals & birds (swine, horses, dogs, cats, domestic poultry, water birds, wild birds etc.) Source of Infection: Usually a case or sub-clinical case Communicability: 3-5 days from clinical onset in adults; Up to 7 days in young children Peak viral shedding occurs on day 1 of symptoms

Influenza: Key Characteristics— Host Factors:

Influenza: Key Characteristics— Host Factors Age & Sex: All ages, both sexes Attack rates lower among adults High Case Fatality Ratio (CFR) during epidemic in high risk cases: (old people; children; persons with diabetes, ch. heart disease, renal & resp. diseases) Human Immunity Antibodies to ‘H’: neutralises the virus Antibodies to ‘N’: modifies the infection Antibodies appear in 7 days after an attack; reach maximum. Level in 2 weeks; drops to pre-infection level in 8-12 months

Influenza: Key Characteristics— Environmental Factors:

Influenza: Key Characteristics— Environmental Factors Seasonality: Temperate zones: epidemics occur in winter Tropics: epidemics occur in rainy season Sporadic cases: any month Overcrowding: Enhances transmission Higher attack rates in closed popn. groups (schools, institutions, ships etc.)

Influenza: Key Characteristics— Disease Transmission:

Influenza: Key Characteristics— Disease Transmission Mainly airborne: Droplet infection Droplet nuclei Through direct contact Transmission from objects possible Incubation period: 18 to 72 hours

Epidemiology Terms:

Epidemiology Terms Endemic A disease that occurs at an expected constant level in a population “Background” level Cécile Viboud, et al. Emerg Infect Dis [serial on the Internet]. 2006 Apr. Available from http://www.cdc.gov/ncidod/EID/vol12no04/05-0695-G2.htm Red line: Expected deaths each year

Epidemiology Terms:

Epidemiology Terms Epidemic When the cases of a disease exceed what is normally expected Pandemic An epidemic that occurs over a large geographic area, or across the whole world

When does the pandemic start? :

When does the pandemic start? Usually not known H5N1 is not the only avian influenza A virus to worry about Circulation of H5N1 viruses among poultry must be controlled WHO Pandemic alert period: Phase 3 (Avian H5N1 influenza) Phase 6 (Novel H1N1 influenza)

PowerPoint Presentation:

Recent Human Infections: Avian Influenza * As of 1 st July 2009 Year Place Subtype Cases Deaths 1997 Hong Kong H5N1 18 6 1999 Hong Kong H9N2 2 0 2003 Hong Kong H5N1 2 1 2003 Netherlands H7N7 83 1 2003 Hong Kong H9N2 1 0 2004 - Feb . 2009 * Azerbaijan, China, Cambodia, Djibouti, Egypt, Indonesia, Iraq, Lao’s PD R, Myanmar, Nigeria, Pakistan, Thailand, Turkey, Vietnam Bangladesh H5N1 436 2 62

Emergence of Avian Influenza (H5N1) 2003 - Feb’ 09: 436 human cases, 262 deaths, CRR > 60%:

Emergence of Avian Influenza (H5N1) 2003 - Feb’ 09: 436 human cases, 262 deaths, CRR > 60%

Epidemiology of Avian Influenza in Humans (H5N1) Demographic characteristics:

Epidemiology of Avian Influenza in Humans (H5N1) Demographic characteristics Despite widespread exposures to avian influenza (H5N1) infected poultry, disease in humans remains rare Since May 2005, number. of both affected countries and confirmed cases of H5N1 infection (408 cases) have increased, in part because of the spread of clade 2.2 viruses across Eurasia and Africa Median age of patients with H5N1 infection is approximately 18 yrs; 90% patients 40 years or younger

Epidemiology of Avian Influenza in Humans (H5N1) Demographic characteristics:

Overall Care Fatality Ratio (CFR): 63%; highest among 10 -19 yrs; lowest among persons 50 years or older: pre-existing immunity differences in exposure or other factors Increased H5N1 human cases during cooler months: associated with increased poultry outbreaks Cases occur year-round: clinicians must be alert at any time, especially in countries with H5N1 poultry outbreaks Epidemiology of Avian Influenza in Humans (H5N1) Demographic characteristics

Epidemiology of Avian Influenza in Humans (H5N1) Seasonality:

Epidemiology of Avian Influenza in Humans (H5N1) Seasonality Source: NEJM, 2008

Epidemiology of Avian Influenza in Humans (H5N1) Transmission:

Direct avian-to-human transmission: predominant route Most common risk factor: Handling of sick/dead poultry (week before the onset of illness) Potential risk factors: Slaughtering, defeathering, or preparing sick poultry for cooking Playing with or holding diseased/dead poultry Handling fighting cocks/ducks that appear healthy Consuming raw or undercooked poultry (products) Epidemiology of Avian Influenza in Humans (H5N1) Transmission

Epidemiology of Avian Influenza in Humans (H5N1) Transmission:

Human clusters: at least 2 epidemiologically linked cases of H5N1 illness; identified in 10 countries - approximately 25% of reported cases. Cluster size: mostly 2-3; largest 8 persons Possible genetic susceptibility: more than 90% of clusters among blood-related family members; might be chance alone Epidemiology of Avian Influenza in Humans (H5N1) Transmission

Epidemiology of Avian Influenza in Humans (H5N1) Transmission:

Transmission in clusters: Mostly common-source exposure to poultry, but limited, non-sustained H-to-H transmission probably occurred during very close, unprotected contact with a severely ill patient Largest cluster: probable transmission from index case to 6 blood-related family members; subsequently to another family member Respiratory secretions, all body fluids, incld. feces considered potentially infectious Epidemiology of Avian Influenza in Humans (H5N1) Transmission

Epidemiology of Avian Influenza in Humans (H5N1) Transmission:

In 25% patients, source of exposure is unclear; environment-to-human transmission possible For some patients, only identified risk factor was visiting a live-poultry market contact with virus-contaminated fomites or fertiliser containing poultry feces Drinking potable water and eating properly cooked food not considered to be risk factors, but ingestion of virus-contaminated products or swimming or bathing in virus-contaminated water might be risky Epidemiology of Avian Influenza in Humans (H5N1) Transmission

Epidemiology of Avian Influenza in Humans (H5N1) Incubation period:

After exposure to infected poultry: Generally 7 days or less 2-5 days in many cases Clusters with limited H-to-H transmission: Approximately 3-5 days Estimated 8-9 days in one cluster Epidemiology of Avian Influenza in Humans (H5N1) Incubation period

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