Influenza Influenza virus A,B,C Sudden onset of chills, fever, malaise, muscular pains and cough Manifests in several forms from sub-clinical infection to pandemics Epidemics in between the pandemics Periodicity of epidemics is irregular due to circulation of many strains

Causes of rapid spread Short incubation period Large number of sub-clinical cases High proportion of susceptibles Short duration of immunity Absence of cross immunity

Epidemiology Influenza A(H1N1),A(H3N2) and B Children and old age has more risk of mortality Epidemics are more common in winters due to overcrowding Transmission is person to person due to droplet infection while sneezing, coughing and talking Incubation period 18-72 hours

Antigenic shift and drift H (Haemagglutinin ): Initiates infection following attachment of virus to susceptible cell N(Neuraminidase) : Responsible for release of virus from infected cell Shift-Sudden and complete major change in antigenic components because of genetic recombination of human with animal/avian virus Drift: Gradual change over a period of time because of point mutation

Avian influenza Type A influenza virus can infect several animal species(Birds, Pigs, Horses, Seals and whales) Influenza viruses that infect birds are called “Avian influenza viruses” All known subtypes of influenza A viruses circulate amongst wild birds Avian influenza viruses do not directly infect humans

Avian influenza cont. Out of 16 known sub-types of HA in birds, 3 are circulating in humans (H1,H2,H3) Two subtypes of NA in humans(N1 and N2)

Characteristics of Avian Influenza in birds NO or mild symptoms in wild birds Other bird species including domestic poultry develop disease when infected Two distinctly different form of disease-Common and mild /Rare and lethal Mild form expressed as ruffled feathers, reduced egg production or mild effects on respiratory system

Characteristics of Avian Influenza in birds cont. Highly pathogenic avian influenza is characterized by sudden onset of severe disease, rapid contagion and mortality rate that can approach 100% within 48 hours The virus not only affects respiratory tract but also involve multiple organs and tissues resulting in massive internal haemorrhages (Chicken Ebola)

Characteristics of Avian Influenza in birds cont. Out of 16 HA and 9 NA subtypes all outbreaks of avian influenza have been caused by viruses of H5 and H7 subtypes Some species of migratory waterfowl are thought to be carrying the H5N1 in its highly pathogenic form and introducing it to new geographic areas

Characteristics of Avian Influenza in birds cont. Avian influenza viruses are readily transmitted from farm to farm by the movement of live birds, people (through contaminated shoes and clothing), contaminated vehicles, equipment, feed and cages Can survive for 6-35 days in bird faeces

Control Measures Rapid culling of all infected or exposed birds Proper disposal of carcasses Quarantining and rigorous disinfection of farms Implementation of strict sanitary measures Restriction of movement of live poultry both within and between countries Vaccination of poultry in high risk area

Human exposure and infection The domestic birds usually roam freely and mingle with wild birds Domestic birds enter household and share areas where children play or sleep Due to poverty household consume poultry when death or the symptoms of illness appear in them High risk of exposure to the virus during slaughtering, defeathering, butchering and preparation of poultry meet for cooking Deaths not reported as they are common in adverse weather

Role of migratory birds Scientists are convinced that migratory waterfowl are carrying H5N1 virus Evidence regarding this started appearing in mid 2005 Scientific studies have found that viruses from the most recently affected countries all of which lie along migratory routes

The disease in Humans Influenza viruses are highly species specific Since 1959, instances of human infection with an avian influenza virus have occurred on10 occasions Of the hundreds of strains of avian influenza viruses, four are known to cause human infections H5N1,H7N3, H7N7,H9N2 Human infection is mild except with H5N1 H5N1 is of concern for two main reasons-firstly as it has caused higher number of cases of severe disease and secondly it has crossed species barrier at least three occasions in recent years – in Hong Kong 2003, Hong Kong 2003 and in current outbreak which began in Dec.2003

The disease in Humans cont. H5N1 if given enough opportunities will develop characteristics it needs to cause pandemic The virus has met all the prerequisites for start of a pandemic save one: an ability to spread efficiently and sustainably among humans Studies of human cases determined that direct contact with live poultry was source of infection Very limited evidence of person to person transmission

Transmission of disease to Humans Close contact with dead or sick birds Slaughtering, defeathering, butchering and preparation for consumption of infected birds Exposure to chicken faeces Swimming in water bodies containing carcasses of dead infected birds Yet unknown environmental factor Role of peri-domestic birds like pigeons or use of untreated bird faeces as fertilizers

Clinical Features Unusually aggressive clinical course with rapid deterioration and high fatality Disease in humans is still poorly understood Incubation period for H5N1 Avian influenza is longer than seasonal influenza ranging from 2-8 days may be up to 17 days WHO currently recommends incubation period of 7 days for field investigations and monitoring of patients contacts

Clinical Features cont. Initial symptoms include -High grade fever with temperature >38 C -Influenza like symptoms -Diarrhea,Vomiting,abdominal pain -Chest pain -Bleeding from nose and gums -Manifestation in lower respiratory tract early in illness -Blood stained sputum

Clinical Features cont. Primary viral pneumonia with bacterial super infection Acute respiratory distress (develops at around 6th day and range is 4 to 13 days ) Respiratory failure after 3 to 5 days Multi-organ dysfunction involving kidney and heart Lymphopenia,leukopenia,elevated aminotransferases,mild to moderate thrombocytopenia and DIC

Role of anti-viral drugs Oseltamivir should be prescribed as early as possible ideally within 48 hours Due to associated high mortality and prolonged viral replication administration of drug is considered in those presenting late in illness Dose in adults and >13 years age is 150mg / day, given as 75 mg twice a day for 5 days (Not recommended in <1 Year) Treatment may be prolonged to 7-10days in those not showing clinical response

Countries with Human cases in the current outbreak Six countries -Cambodia -China -Indonesia -Thailand -Turkey -Viet Nam More than half of the laboratory confirmed cases have been fatal but avian influenza in humans is still a rare disease

Reasons for panic The H5 antigen of H5N1 virus is totally new amongst human population with no herd immunity It causes severe disease in most cases with involvement of multiple organs The mortality is more than 50% amongst those who gets infection The virus H5N1 has crossed species barrier several times No vaccine becomes available unless the circulating stains and its antigens are identified No definite mode of transmission is known The drugs for treatment are not yet available everywhere Migration of birds is a regular process Birds that survive infection excretes virus for 10days orally and in faeces H5N1 can survive in bird faeces for 6-35 days The spread of infection in birds increases opportunities of direct human contact

Reasons for no panic Most human cases had direct contact with poultry No transmission from person to person The disease is rare The number of cases was so far few whenever it occurred Despite infection of tens of millions of poultry fewer than 200 human cases have occurred so far Very few cases have been detected in presumed high risk groups like commercial poultry workers, workers at live poultry markets, cullers and veterinarians

Influenza pandemics- Can they be averted ? Based on historical patterns, influenza pandemics can be expected to occur on average 3-4 times each century(1918Spanish Influenza, 1957Asian Influenza, 1968 Hong Kong Influenza) Experts agree that another influenza pandemic is inevitable

Measures to minimize global public health risk Halt further spread of epidemics in poultry population Vaccination of persons at high risk of exposure to infected poultry using existing vaccines effective against currently circulating influenza strains to avoid co-infection with avian and influenza strains Protection of workers involved in culling of poultry by proper clothing and equipment against infection Anti-viral drugs as prophylactic measure in these workers

Measures to minimize global public health risk When cases of avian influenza in humans occur, information on extent of influenza infection in animals as well as humans and on circulating influenza viruses is urgently needed to aid the assessment of risk to public health Thorough investigation of each case WHO and other international agencies assist in these activities Epidemiological and laboratory surveillance

All these activities can reduce the likelihood that a pandemic strain will emerge

The question of whether another influenza pandemic can be averted can not be answered with certainty

Thank you