Avian Influenza(Bird Flu)
Md. Shaifur Rahman Biotechnology and Genetic Engineering Discipline Khulna University Khulna-9208 Bangladesh Email: [email protected]
Introduction Avian influenza influenza is an infection caused by avian (bird) influenza influenza (flu) viruses. viruses. These influenza viruses occur naturally among birds. Wild birds carry the viruses in their intestines, but usually do not get sick from them. However, avian influenza is very contagious among birds and can make some domesticated birds, including including chickens, chickens, ducks and turkeys, turkeys, very sick and and kill them. Infected Infected birds shed influenza virus in their saliva, nasal secretions, and feces. Domesticated birds may become infected with avian influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact contact with with surfaces surfaces (such (such as dirt dirt or cages) cages) or material materials s (such as water water or feed) that have been contaminated with the virus. Infection with AIV in domestic domestic poultry causes causes two main forms forms of disease that are distinguished by low and high extremes of virulence. The “low pathogenic” usually causes only mild symptoms (such as ruffled feathers and a drop in egg production). However, the highly pathogenic form spreads more rapidly through flocks of poultry which cause disease that affects multiple internal organs and has a mortality rate that can reach 90-100% often within 48 hours. The risk from avian influenza is generally low to most people, because the viruses do not usually infect humans
Historical Background H5N1, Hong Kong, Special Administrative Region, 1997 : Highly pathogenic avian influenza A (H5N1) infections occurred in both poultry and humans. This was the first time an avian influenza A virus directly transmitted from birds to humans.
H9N2, China and Hong Kong, 1999: Low pathogenic avian influenza influenza A (H9N2) virus infection was confirmed.
H7N2, Virginia, 2002: 2002 : one person was found to have serologic evidence of infection with H7N2.
H7N7, Netherlands, 2003: 2003 : 89 people were confirmed to have H7N7 influenza virus infection associated with this poultry outbreak. These cases occurred mostly among poultry workers.
H7N3, Canada, 2004: 2004: human infections of highly pathogenic avian influenza A (H7N3) among poultry workers were found.
Cambodia, China, Indonesia, Thailand and Vietnam, 2005 :
Azerbaijan, Cambodia, China, Djibouti, Egypt, Indonesia, Iraq, Thailand, Turkey, 2006: 2006 :
The recent outbreaks of the Highly Pathogenic Avian Influenza viruses among poultry in many countries, with human infection and deaths, have prompted the World Health Organization to strongly recommend its member states to rapidly prepare themselves in dealing with influenza pandemic. Therefore, it is necessary for Bangladesh Bangladesh to take the necessary steps against Influenza pandemic.
The major objectives of this study are as follows: follows: 1. To To know know the phys physical ical and genet genetical ical char characteri acteristics stics of Avian Influenza Virus (AIV) 2. To prevent the outbreak of an influenza pandemic. 3. To reduce the morbidity and mortality from influenza. 4. Make a national strategic plan to face Influenza pandemic.
Types, Subtypes, and Strains I.
Influenza Type A and It Its Su Subtypes
Infl Influe uenz nzaa A (H5 (H5N1 N1)) vir virus us – also also cal calle led d “H5 “H5N1 N1 vir virus us”” – is an influenza A virus subtype that occurs mainly in birds, is highly contagious among birds, pigs, horses, and other animals and can be deadly to them.
Influenza type A viruses are divided into subtypes and named on the basis of two proteins on the surface of the virus: hem agglutinin (HA) and neuraminidase(NA).
For exampl example, e, an an “H7N2 “H7N2 virus” virus” design designate atess infl influen uenza za a subtype that has an HA 7 protein and an NA 2 protein. Similarly Similarly an “H5N1” “H5N1” virus has an an HA 5 protein protein and an NA NA 1 protein.
are 16 known HA subtypes and 9 known NA
different combinations of HA and NA proteins are
possible. Only some influenza A subtypes (i.e., H1N1, H1N2, and H3N2) are currently in general circulation among people. Other
subtypes are found most commonly in other animal
species. For example, H7N7, which has unusual zoonotic potential and killed one person. H3N8 viruses cause illness in horses, and H3N8 also has recently been shown to cause illness in dogs. H5N1 virus does not usually infect people, but infections with these viruses have occurred in humans. Most of these cases have resulted from people having direct or close contact with H5N1-infected poultry or H5N1-contaminated
Three prominen prominentt subtypes subtypes of the avian influenz influenzaa A virus that are known to infect infect both birds and people are: i. Influenza A H5 Nine potential subtypes of H5 are known and can be highly pathogenic or low pathogenic. H5
infections, such as HPAI H5N1 H5N1 viruses have been documented among humans and sometimes cause severe illness or death. ii. Influenza A H7 Nine potential subtypes of H7 are known. H7 infection in humans is rare but can occur among persons who have direct contact with infected birds. 7
viruses viruses have been been associate associated d with both both LPAI (e.g., (e.g., H7N2, H7N2, H7N7) H7N7) and HPAI (e.g., H7N3, H7N7), and have caused mild to severe and fatal illness in humans.
iii. Influenza A H9 Nine potential subtypes of H9 are known; influenza A H9 has rarely been reported to infect humans (At least three H9 infections in humans have been confirmed). However,
this subtype has been documented only in a low pathogenic form. II. Influenza Type B Influenza B viruses are usually found only in humans. These viruses are not classified according to subtype. Influenza B viruses can cause morbidity and mortality among humans, but in general are associated with less severe than influenza A viruses. III. Influenza Type C Influenza type C viruses cause mild illness in humans. These viruses are not classified according to subtype.
IV. Strains Influenza
B viruses and subtypes of influenza A virus are further characterized characterized into strains. There
are many different strains of influenza B viruses and of influenza A subtypes. New
strains of influenza viruses appear and replace older strains.
process occurs through antigenic drift. When a new strain of human influenza virus emerges, antibody protection that may have developed after infection or vaccination with an older strain may not provide protection against the new strain.
Therefore, the influenza vaccine is updated on a yearly basis to keep up with the changes in influenza viruses.
How Influenza Viruses Change: Drift and Shift Influenza
viruses are dynamic and are continuously
viruses can change in two different ways: antigenic drift and antigenic shift. Influenza viruses are changing by antigenic drift all the time, but antigenic shift happens only occasionally. Influenza
type A viruses undergo both kinds of changes; influenza type B viruses change only by the more gradual process of antigenic drift.
ANTIGENIC DRIFT Antigenic
drift refers to small, gradual changes that occur through point mutations in the two genes that contain the genetic material to produce the main surface proteins, hemagglutinin, and neuraminidase.
point mutations occur unpredictably and result in minor changes to these surface proteins.
Antigenic drift produces new virus strains that may not be recognized by antibodies to earlier influenza strains.
process works as follows: a person infected with a particular influenza virus strain develops antibody against that strain. As newer virus strains appear, the antibodies antibodies against the older strains strains might not recognize recognize the "newer" "newer" virus, and infection with a new strain can occur. This is one of the main reasons why people can become infected with influenza viruses more than one time and why global surveillance is critical in order to monitor the evolution of human influenza virus stains for selection of which strains should be included in the annual production of influenza vaccine. In most years, one or two of the three virus strains in the influenza influenza vaccine vaccine are updated to keep up with the the changes changes in the circulating circulating influenza viruses. For this reason, people who want to be immunized against influenza need to be vaccinated every year.
ANTIGENIC SHIFTS Antigenic
shift refers to an abrupt, major change to produce
a novel influenza A virus subtype in humans that was not currently circulating among people.
shift can occur either through direct animal
(poultry)-to-human transmission or through mixing of human influenza A and animal influenza A virus genes to create a new human influenza A subtype virus through a process called genetic reassortment. Antigenic shift results in a new human influenza A subtype.
Genetics and diversity of the viral strains Genetic structure and related subtypes
Fig. The H in H5N1 stands for "Hemagglutinin", as depicted in this molecular model.
Fig. The N in H5N1 stands for "Neuraminidase", as depicted in this ribbon diagram.
H5N1 is a subtype of the species Influenza A virus of the Inf Influ luen enzav zavir irus us A genus of the Orthomyxoviridae family.
The H5N1 subtype is an RNA virus.
It has a segmented genome of eight abbreviated as PB2, PB2, PB1, PA, HA, NP, NA, M and NS.
HA codes for hemagglutinin, an antigenic glycoprotein found on the surface of the influenza viruses and are responsible for binding the virus to the cell that is being infected.
NA codes for neuraminid neuraminidase, ase, an antigenic antigenic glycosylated glycosylated enzyme enzyme found on the surface of the influenza viruses. It facilitates the release of progeny viruses from infected cells cells (Couc (Couch, h, R.1996).
HA and NA are also used as the basis for the naming of the different subtypes of influenza A viruses. This is where the H and N come from in H5N1.
The hemagglutinin hemagglutinin (HA) and neuraminida neuraminidase se (NA) RNA strands specify specify the structure of proteins.
PROPERTIES of H5N1 Infectivity H5N1
is easily transmissible between birds facilitating a potential global spread of H5N1. While H5N1 undergoes specific mutations and reassorti reassorting ng creating creating variatio variations ns which which can infect infect specie speciess not not previously known to carry the virus, not all of these variant forms can infect humans. H5N1
as an avian virus preferentially binds to a type of galactose receptors that populate the avian respiratory respiratory tract from the nose to the lungs and are virtually absent in humans, occurring only in and around the alveoli, structures deep in the lungs where oxygen is passed passed to the blood. blood. Therefore, Therefore, the the virus virus is not easil easily y expelled expelled by coughing and sneezing, the usual route of transmission (Shinya K. et. al., 2006 and Van Riel D. et. al., 2006).
has mutated into a variety of strains with differing pathogenic profiles, some pathogenic to one species but not others, some pathogenic to multiple species. species. Each specific specific known genetic genetic variation variation is traceable to a virus isolate of a specific case of infection. Through
antigenic drift, H5N1 has mutated into dozens of highly pathogenic varieties varieties divided into into genetic clades clades which are known known from specific isolates, isolates, but all currently belonging to genotype Z of avian influenza virus H5N1, now the dominant genotype (Kou Z.et. al., 2005). H5N1 isolates found in Hong Kong in 1997 and 2001 were not consistently transmitted efficiently among birds and did not cause significant disease in these animals.
In 2002 new isolates of H5N1 were appearing within the bird population of Hong Kong. These new isolates caused acute disease, including severe neurological dysfunction and death in ducks. This was the first reported case of lethal influenza virus infection in wild aquatic birds since 1961(Sturm-Ramirez K.M.et. al.,2004). Genotype Genotype Z emerged emerged in in 2002 through reassortmen reassortmentt from earlier highly pathogenic genotypes of H5N1 that first infected birds in China in 1996, and first infected humans in Hong Kong in 1997.
Transmission and host range Infected
birds transmit H5N1 through their saliva, nasal secretions, feces and blood. Other animals may become infected with the virus through direct contact with these bodily fluids or through contact with surfaces contaminated with them. H5N1 remains infectious after over ove r 30 days at 0 °C (32.0 °F) °F) over one on e month at freezing fr eezing temperatu te mperature re or 6 days at a t 37 °C (98.6 °F) °F) and one on e week at human hu man body temperatu t emperature. re. So at ordinary o rdinary temperatures temperat ures it lasts in the environment for weeks. In arctic temperatures, it doesn't degrade at all.
Fig.1.1 Influenza A virus, the virus that causes Avian flu. Transmission electron micrograph of negatively stained virus particles in late passage. (Source: Dr. Erskine Palmer, Centers for Disease Control Control and Prevention Prevention Public Health Image Library Library ))
High mutation rate Influenza
viruses have a relatively high mutation rate that is characteristic of
RNA viruses. The segmentation of the influenza genome facilitates genetic recombination recombination by segment segment reassort reassortment ment in hosts who are are infected infected with with two different influenza viruses at the same time (Kou Z. et. al., 2005). H5N1 viruses can reassort reassort genes with with other strains strains that that co-infect co-infect a host host organism, organism, such as a pig, bird, or human, human, and mutate into a form that that can pass easily among humans. humans.
ability of various influenza strains to show species-selectivity is largely
due to to variati variation on in the the hemaggl hemaggluti utinin nin genes. genes. Gene Genetic tic mutat mutations ions in in the hemagglutinin hemagglutinin gene that that cause single single amino acid acid substitutions substitutions can significantly significantly alter the ability ability of viral viral hemagglut hemagglutinin inin proteins proteins to bind bind to receptor receptorss on the surface of host cells. Such mutations in avian H5N1 viruses can change virus strains from from being ineffic inefficient ient at infecting infecting human human cells cells to being as efficient efficient in causing human infections as more common human influenza virus types (Gam (Gamba bary ryan an A. et. al., 2006).
Human health risks during the H5N1 outbreak
Few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 has caused the largest number of detected cases of severe disease and death in humans.
In human cases associated with the ongoing H5N1 outbreaks in poultry and wild birds in Asia and parts of Europe, the Near East and Africa, more than half of those people reported infected with the virus have died. Most cases have occurred in previously healthy children and young adults and have resulted from direct or close contact with H5N1-infected poultry or H5N1contaminated surfaces. In general, H5N1 remains a very rare disease in people. The H5N1 virus does not infect humans easily, and if a person is infected, it is very difficult for the virus to spread to another person.
While there has been some human-to-human spread of H5N1, it has been limited, inefficient and unsustained.
How flu virus invades cells and multiplies
1.The haem 1.The haemagl agluti utinin nin (H) protein on the surface of the flu virus binds to sial si alic ic ac acid id,, a sug uger er found on cell surface proteins in the virus’s host. Most birds have a different type of sialic acid to people, but the H on H5N1 has a mutation that allows it to bind to both types.
2. The cell engulfs the virus to destroy it and also traps a protease, a protein-destroying enzyme found in fluid outside cells. The protease attacks haemagglutinin, but flu has evolved to exploit this. In chickens, H can usually be activated only by a protease found in the lungs. But a common mutation in the H allows it to be activated by a wider variety of protease, enabling the virus to attack all the bird’s organs.
3. The cells pump in acid to destroy the virus. But again, the virus exploits this. When the acid enters the virus through the M2 ion channel, it triggers an extraordinary change in any H activated by protease. The globular heads of the protein fold back and the exposed innards bind to the cell membrane around the virus, making it fuse with the viral membrane.
4. The fusion of the cell and virus membranes opens up a pore, and the RN RNAs inside th the virus spill out into the cell and migrate to the cell’s nucleus.
5. Polymerase enzymes packaged with the RNAs churn out messenger RNA copies of viral genes, so the cell makes many thousands of copies of the 10 flu proteins. Once lots of proteins have been made, new copies of the viral viral RNAs RNAs are made. made.
6. New viral surface proteins – haemaglutinin, neuraminidase and the M2 channel channel-- migrat migrate e to the cell membrane as they are produced. Here, the neuraminidase slashes off any an y si sialic alic acid acids s pr protru otrudi ding ng from the cell surface, so new viruses do not stick to it and can float free to infect other cells.
7. The M1 M1 matrix protein protein helps helps pack up new sets sets of the viral viral RNAs and internal internal proteins and transport them to the cell membrane to join the viral surface proteins. New viruses viruses start start budding budding off from the the cell surface surface – a single infected infected cell cell can produce 10,000 viruses.
Fig. Crystal structure of Viet04 HA and comparison with 1918 human H1, duck H5, and 1968 human H3 HAs. (A) Overview of the Viet04 trimer, trimer, represented as a ribbon diagram. For clarity, each monomer has been colored differently. Carbohydrates observed in the electron-density maps are colored orange, and all the asparagines that make up a glycosylation site are labeled. Only Glu20, Glu20, Glu289, and Phe154 are not labeled, labeled, as these are on the back of the molecule. The location of the receptor binding, cleavage, and basic patch sites are highlighted only on one monomer. (B ( B) Structural comparison of the Viet04 monomer (olive) with duck H5 (orange) and 1918 H1 (red) HAs. Structures Structures were first superimposed on the HA2 HA2 domain of Viet04 through the following residues: Viet04, Gly1 to Pro160; 1918 H1 (PDB: 1rd8), Gly1 to Pro160; Pro160; H3(PDB:2hmg), Gly1 to Pro160; H5 (PDB: 1jsm ), Gly1 to Pro160. Orientation of the overlay approximates to the blue monomer in (A). (C) Superimposition of the two long -helices of HA2 for 1918 H1 (PDB: 1rd8), avian H5 (PDB: 1jsm), human H3 (PDB: 2hmg), and Viet04 Viet04 reveal that the extended interhelical loop of Viet04 is more similar to the 1918 H1 than to the existing avian H5 structure. The side chain of Phe63 is illustrated as an example of the close proximity of
Symptoms Symptoms in Bird
Symptoms in Human
Change in wing color
Reduction in egg production
Treatment & Vaccination
Antiviral drugs: amantadine, rimantadine, oselatmivir, and zanamivir.
Recombinant Recombinant vaccine: vaccine: sanofisanofi-pasteu pasteur’s r’s candidate candidate vaccine, vaccine, Omniv Omnives estt vacc vaccin ine e.
Table 3.1 Confirmed human cases and mortality rate of avian influenza (H5N1) (As of of Mar March ch 28, 28, 2007 2007)) Country
1 00% 10
World Health Organization O rganization Communicable Disease Surveillance Surveillance & Response (CSR)
Summary of the Strategic Plan 3 objectives and 5 targets 3 Objectives • Pandemic prevention • Reduction Reduction of morbidity morbidity and mortality mortality • Development Development of effective effective respond respond systems
5 Targets • Surveillance system • Pandemic Pandemic response response • Stockpile Stockpile of supplies supplies and drugs • Develop Develop vaccine vaccine production production capacity capacity • Public health service system
5 Strategies and 18 measures
1 . Surveillance systems
• Surveillan Surveillance ce systems in humans humans and animals animals • Link surveillance information of humans and animals • Surveillance network of human influenza 3. Pandemic Response Preparedness • Set up standard standard operating operating procedur procedures es • Develop Develop the capacity capacity of staff / volunteers volunteers • Develop Develop preparedn preparedness ess of hospitals hospitals • Develop Develop ca pacity of public public health health emergenc emergency y measures • Develop Develop financia financiall measures measures
2. Stockpile of supplies • sufficient sufficient antiviral antiviral drugs for emergen emergency cy situation • Develop Develop system system for stockpilin stockpiling g and administration of the stock • Research Research and develo development pment on vaccines vaccines and antivirals • Develop Develop criteria criteria for fair distributio distribution n 4. Pubic relations and education
• Informatio Information n dissemin dissemination ation • Develop Develop risk communi communication cation skills skills • Set up multi multi sectoral sectoral working working groups groups • Formulate Formulate communicati communication on strategies strategies
5. Sustainable and integrated management systems • Pandemic Pandemic alert period period Pandem Pandemic ic perio period d
Summary of the Strategic Plan 3 objectives and 5 targets 3 Objectives • Pand Pandem emic ic preve prevent ntion ion • Re Reduc ductio tion n of morbi morbidit dity y and mortality • Development Development of effective effective respond respond systems
5 Targets • Survei Surveilla llance nce system system • Pandem Pandemic ic respon response se • Stockpile Stockpile of supplie supplies s and drugs. drugs. • Develop Develop vaccine vaccine produc production tion capacit capacity y • Public Public health health service service system system
Summary of the Strategic Plan 5 Strategies and 18 measures 1.Surveillance systems Surveillance
systems in humans and
animals Link surveillance information of humans and animals Surveillance network of human influenza
2. Stockpile of supplies and drugs Sufficient
antiviral drugs for emergency
situation Develop system for stockpiling and administration of the stock Research development on vaccines and antiviral drug Develop criteria for fair distribution
3.Pandemic Response Preparedness Set
up standard operating procedures Develop the capacity of staff / volunteers Develop preparedness of hospitals Develop the capacity of public health emergency measures Develop financial measures
4.Pubic relations and education Develop
risk communication skills Information dissemination Set up multi sectoral working groups Formulate communication strategies
5.Sustainable and integrated management systems Pandemic
alert period Pandemic period
Roles & responsibility of concerned agencies Ministry
of public health
of livestock development
of disaster prevention and
mitigation National Public
Conclusion Avian influenza viruses do not usually infect humans; however, several instances of human infections and outbreaks of avian influenza have been reported since 1997. In 2003, influenza A (H7N7) infections occurred in the Netherlands among persons, more than 80 cases of H7N7 illness were confirmed by testing and one patient died. It is believed that most cases of avian influenza infection in humans have resulted from contact with infected poultry or contaminated surfaces. When highly pathogenic influenza H5 or H7 viruses cause outbreaks, between 90% and 100% of poultry can die from infection and then quarantine and depopulation (or culling) and surveillance around affected flocks is the preferred control and eradication option.
The following interim recommendations are based on what are deemed optimal precautions for protecting individuals involved in the care of patients with highly pathogenic avian influenza from illness and for reducing the risk of viral reassortment (i.e., mixing of genes from human and avian viruses). i. Standard Precautions Pay careful attention to hand hygiene before and after all patient contact or contact with with items potentially contaminated with respiratory secretions. ii. Contact Precautions Use gloves and gown for all patient contact, also Use dedicated equipment such as stethoscopes, disposable blood pressure cuffs, disposable thermometers, etc.
iii. Eye protection Wear goggles or face shields when within 3 feet of the patient. iv. Airborne Precautions Place the patient in an airborne isolation room (AIR). v. Vaccination of Health-Care Workers against Human Influenza vi. Surveillance and Monitoring of Health-Care Workers Instruct health-care workers to be vigilant for the development of fever, respiratory symptoms, and/or conjunctivitis (i.e., eye infections) for 1 week after last exposure to avian influenza-infected patients.
THANKS TO ALL