Avian Influenza(bird Flu)

Avian Influenza(Bird Flu)

Md. Shaifur Rahman Biotechnology and Genetic Engineering Discipline Khulna University Khulna-9208 Bangladesh Email: [email protected]

Introduction Avian influenza is an infection caused by avian (bird) influenza (flu) 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 chickens, ducks and turkeys, very sick and kill them. 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 with surfaces (such as dirt or cages) or materials (such as water or feed) that have been contaminated with the virus. Infection with AIV in domestic poultry causes two main 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 A (H9N2) virus infection was confirmed. ‰ H7N2, Virginia, 2002: one person was found to have serologic evidence of infection with H7N2. ‰ H7N7, Netherlands, 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: human infections of highly pathogenic avian influenza A (H7N3) among poultry workers were found. ‰H5N1, Cambodia, China, Indonesia, Thailand and Vietnam, 2005: ‰H5N1, Azerbaijan, Cambodia, China, Djibouti, Egypt, Indonesia, Iraq, Thailand, Turkey, 2006: ‰H5N1, India, Bangladesh,2007

Objectives

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 to take the necessary steps against Influenza pandemic.

The major objectives of this study are as follows: 1. To know the physical and genetical characteristics 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 Its Subtypes

™ Influenza A (H5N1) virus – also called “H5N1 virus” – 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 example, an “H7N2 virus” designates influenza a subtype that has an HA 7 protein and an NA 2 protein. Similarly an “H5N1” virus has an HA 5 protein and an NA 1 protein.

™There are 16 known HA subtypes and 9 known NA subtypes. ™Many 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 surfaces.

Three prominent subtypes of the avian influenza A virus that are known to 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 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 have been associated with both LPAI (e.g., H7N2, 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 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. ™This 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 evolving. ™Influenza 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. ™These 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. ™This 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 against the older strains might not recognize the "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 vaccine are updated to keep up with the changes in the 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. ™Antigenic 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 Influenzavirus A genus of the Orthomyxoviridae family.

™

The H5N1 subtype is an RNA virus.

™

It has a segmented genome of eight abbreviated as 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 neuraminidase, an antigenic glycosylated enzyme found on the surface of the influenza viruses. It facilitates the release of progeny viruses from infected cells (Couch, 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 (HA) and neuraminidase (NA) RNA strands 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 reassorting creating variations which can infect species 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 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 to the blood. Therefore, the virus is not easily expelled by coughing and sneezing, the usual route of transmission (Shinya K.et. al., 2006 and Van Riel D. et. al., 2006).

Virulence ™H5N1 has mutated into a variety of strains with differing pathogenic profiles, some pathogenic to one species but not others, some pathogenic to multiple species. Each specific known genetic 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 divided into genetic clades which are known from specific 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 Z emerged in 2002 through reassortment 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 30 days at 0 °C (32.0 °F) over one month at freezing temperature or 6 days at 37 °C (98.6 °F) and one week at human body temperature. So at ordinary temperatures 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 and Prevention Public Health Image 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 by segment reassortment in hosts who are infected with two different influenza viruses at the same time (Kou Z. et. al., 2005). H5N1 viruses can reassort genes with other strains that co-infect a host organism, such as a pig, bird, or human, and mutate into a form that can pass easily among humans. ™The ability of various influenza strains to show species-selectivity is largely due to variation in the hemagglutinin genes. Genetic mutations in the hemagglutinin gene that cause single amino acid substitutions can significantly alter the ability of viral hemagglutinin proteins to bind to receptors on the surface of host cells. Such mutations in avian H5N1 viruses can change virus strains from being inefficient at infecting human cells to being as efficient in causing human infections as more common human influenza virus types (Gambaryan 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 haemaglutinin (H) protein on the surface of the flu virus binds to sialic acid, a suger 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 RNAs inside 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 RNAs are made.

6. New viral surface proteins – haemaglutinin, neuraminidase and the M2 channel- migrate to the cell membrane as they are produced. Here, the neuraminidase slashes off any sialic acids protruding from the cell surface, so new viruses do not stick to it and can float free to infect other cells.

7. The M1 matrix protein helps pack up new sets of the viral RNAs and internal proteins and transport them to the cell membrane to join the viral surface proteins. New viruses start budding off from the cell surface – a single infected 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, 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, Glu289, and Phe154 are not 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) Structural comparison of the Viet04 monomer (olive) with duck H5 (orange) and 1918 H1 (red) HAs. Structures were first superimposed on the HA2 domain of Viet04 through the following residues: Viet04, Gly1 to Pro160; 1918 H1 (PDB: 1rd8), Gly1 to 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 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 the two structures.

Symptoms Symptoms in Bird ¾ Change in wing color ¾ Reduction in egg production ¾ Feeding problem ¾ Cytokinemia

Symptoms in Human ¾ Fever, ¾ Cough, ¾ Sore throat, ¾ Muscle aches, ¾ Breathing problem, ¾ Pneumonia, ¾ Vomiting, ¾ Headaches etc.

Treatment & Vaccination y

Antiviral drugs: amantadine, rimantadine, oselatmivir, and zanamivir.

y

Recombinant vaccine: sanofi-pasteur’s candidate vaccine, Omnivest vaccine.

Table 3.1 Confirmed human cases and mortality rate of avian influenza (H5N1) (As of March 28, 2007) Country

Report dates

2003 cases

deaths

2004 cases

Total

2005

deaths

cases

2006

deaths

Azerbaijan

cases

2007

deaths

cases

deaths

cases

deaths

8

5

63%

8

5

63%

6

6

100%

23

14

61%

1

0

0%

4

4

100%

2

2

100%

8

5

63%

13

8

62%

Djibouti

1

0

0%

Egypt

18

10

56%

11

3

27%

29

13

45%

56

46

82%

6

5

83%

81

63

78%

3

2

67%

3

2

67%

Cambodia PR China

1

1

100%

Indonesia

19

12

63%

Iraq

1

0

0%

Laos

2

2

100%

2

2

100%

Nigeria

1

1

100%

1

1

100%

Thailand

17

12

71%

5

2

40%

Turkey Vietnam

3

3

100%

29

20

69%

61

19

31%

Total

4

4

100%

46

32

70%

97

42

43%

3

3

100%

25

17

68%

12

4

33%

12

4

33%

93

42

45%

284

169

60%

116

80

69%

21

Source: World Health Organization Communicable Disease Surveillance & Response (CSR)

11

52%

Summary of the Strategic Plan 3 objectives and 5 targets 3 Objectives • Pandemic prevention • Reduction of morbidity and mortality • Development of effective respond systems

5 Targets • Surveillance system • Pandemic response • Stockpile of supplies and drugs • Develop vaccine production capacity • Public health service system

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 3. Pandemic Response Preparedness • Set up standard operating procedures • Develop the capacity of staff / volunteers • Develop preparedness of hospitals • Develop ca pacity of public health emergency measures • Develop financial measures

2. Stockpile of supplies • sufficient antiviral drugs for emergency situation • Develop system for stockpiling and administration of the stock • Research and development on vaccines and antivirals • Develop criteria for fair distribution 4. Pubic relations and education • Information dissemination • Develop risk communication skills • Set up multi sectoral working groups • Formulate communication strategies

5. Sustainable and integrated management systems • Pandemic alert period • Pandemic period

Summary of the Strategic Plan 3 objectives and 5 targets 3 Objectives • Pandemic prevention • Reduction of morbidity and mortality • Development of effective respond systems

5 Targets • Surveillance system • Pandemic response • Stockpile of supplies and drugs. • Develop vaccine production capacity • Public health service system

Summary of the Strategic Plan 5 Strategies and 18 measures 1.Surveillance systems ¾Surveillance systems in humans and animals ¾Link surveillance information of humans and animals ¾Surveillance network of human influenza

2. Stockpile of supplies and drugs ¾Sufficient antiviral drugs for emergency situation ¾Develop system for stockpiling and administration of the stock ¾Research development on vaccines and antiviral drug ¾Develop criteria for fair distribution

3.Pandemic Response Preparedness ¾Set up standard operating procedures ¾Develop the capacity of staff / volunteers ¾Develop preparedness of hospitals ¾Develop the capacity of public health emergency measures ¾Develop financial measures

4.Pubic relations and education ¾Develop risk communication skills ¾Information dissemination ¾Set up multi sectoral working groups ¾Formulate communication strategies

5.Sustainable and integrated management systems ¾Pandemic alert period ¾Pandemic period

Roles & responsibility of concerned agencies ¾ Ministry

of public health ¾ Department of livestock development ¾ Ministry of defense ¾ Department of disaster prevention and mitigation ¾ National police bureau ¾ Public relation department ¾ Ministry of education

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 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