VIROLOGYVIROLOGY

VIROLOGY: THE STUDY OF VIROLOGY: THE STUDY OF VIRUSESVIRUSES

(1) What is a virus? (1) What is a virus? (2) What is the structure of a virus?(2) What is the structure of a virus? (3) How do we classify viruses?(3) How do we classify viruses? (4) What are typical viral diseases?(4) What are typical viral diseases? (4) What are various types of viral transmission?(4) What are various types of viral transmission? (5) How can viral infections be prevented? (5) How can viral infections be prevented?

What is a virus? What is a virus?

A virus is a microscopic particle that A virus is a microscopic particle that can infect the cells of a biological can infect the cells of a biological organism (for example, bacterial or organism (for example, bacterial or animal cell animal cell

By the early1900s, some diseases in animals and plants By the early1900s, some diseases in animals and plants were shown to be caused by agents that could pass were shown to be caused by agents that could pass through a filter. These were termed “filterable viruses” and through a filter. These were termed “filterable viruses” and the term "the term "VIRUSESVIRUSES" was given to this type of particle." was given to this type of particle.

Viruses, however were not "seen" until the electron Viruses, however were not "seen" until the electron microscope was developed in the late 1930s. They are microscope was developed in the late 1930s. They are “seen” by what is called “negative staining”“seen” by what is called “negative staining”

Negative staining is staining of a background and in Negative staining is staining of a background and in electron microscopy is done with heavy metals.electron microscopy is done with heavy metals.

HISTORICAL INFORMATION3

What is the structure of a What is the structure of a virus?virus?

A virion, or virus particle, consists of A virion, or virus particle, consists of genetic material (nucleic acid, that is genetic material (nucleic acid, that is RNA or DNA) contained with in a coat RNA or DNA) contained with in a coat of protein or capsid; many viruses of protein or capsid; many viruses also have a lipid membrane, or also have a lipid membrane, or envelope.envelope.

What is the typical structure of What is the typical structure of a virus?a virus?

A virion, or virus particle, consists of genetic A virion, or virus particle, consists of genetic material (nucleic acid, that is RNA or DNA) material (nucleic acid, that is RNA or DNA) contained with in a coat of protein or capsid; contained with in a coat of protein or capsid; many viruses also have a lipid membrane, or many viruses also have a lipid membrane, or envelope.envelope.

Viruses have many shapes: from spiders to Viruses have many shapes: from spiders to popcorn balls to satellite-like structurepopcorn balls to satellite-like structure

Have many fewer enzymes than bacteria or Have many fewer enzymes than bacteria or animal cells. Viruses carry only one or two animal cells. Viruses carry only one or two enzymes that decode their genetic instructions. enzymes that decode their genetic instructions.

A virus must have a host cell (whether human, A virus must have a host cell (whether human, bacteria, or other animal) to reside in and bacteria, or other animal) to reside in and produce more virus particles.produce more virus particles.

Viral StructureViral Structure

““Naked” VirusNaked” Virus Enveloped VirusEnveloped Virus

                                           

Classification, etc.Classification, etc.

For our purposes, we can know that there are at For our purposes, we can know that there are at present 20 recognized families of viruses that present 20 recognized families of viruses that contain viruses of humans or animals.contain viruses of humans or animals.

Historically, properties used most often in Historically, properties used most often in classification derive from electron microscopic classification derive from electron microscopic examination e.g. virion morphology, structure and examination e.g. virion morphology, structure and dimensions, and presence or absence of an dimensions, and presence or absence of an envelope. Additional characterization is supplied by envelope. Additional characterization is supplied by the type and nature of the genomic nucleic acid. the type and nature of the genomic nucleic acid.

Organization involved: Organization involved: International Committee on International Committee on Taxonomy of Viruses and its database -- ICTVdBTaxonomy of Viruses and its database -- ICTVdB

Discussion that follows organized viruses not by the Discussion that follows organized viruses not by the ICTVdb classification but by a more readily ICTVdb classification but by a more readily accessible classification by diseaseaccessible classification by disease

EnterovirusesEnteroviruses

EnterovirusesEnteroviruses are among the most important viral are among the most important viral pathogens of humans. pathogens of humans.

Mild to severe illnessesMild to severe illnesses Polio, aseptic meningitis, encephalitis), Polio, aseptic meningitis, encephalitis),

respiratory (common cold, tonsillitis, pharyngitis, respiratory (common cold, tonsillitis, pharyngitis, rhinitis) cardiovascular (myocarditis, pericarditis), rhinitis) cardiovascular (myocarditis, pericarditis),

Natural Host: HumanNatural Host: Human Spread by oral-fecal , maybe respiratorySpread by oral-fecal , maybe respiratory Unproven: juvenile diabetes, ALS (“Lou Gehrig’s Unproven: juvenile diabetes, ALS (“Lou Gehrig’s

disease”)disease”)

EnterovirusEnterovirus

In addition to the known and documented In addition to the known and documented enteroviral infections, these viruses have enteroviral infections, these viruses have also been implicated in (but definitive also been implicated in (but definitive proof is lacking) several chronic diseases, proof is lacking) several chronic diseases, some of which are: juvenile onset of some of which are: juvenile onset of diabetes mellitus, chronic fatigue diabetes mellitus, chronic fatigue syndrome, and amyotrophic lateral syndrome, and amyotrophic lateral sclerosis (Lou Gehrig's Disease).sclerosis (Lou Gehrig's Disease).

Negatively stained preparation of a typical Negatively stained preparation of a typical Enterovorus, coxsackie B, and seen by Enterovorus, coxsackie B, and seen by transmission electron microscopytransmission electron microscopy

EnterovirusesEnteroviruses

•Negatively stained preparation of a typical Enterovirus, coxsackie B, and seen by transmission electron microscopy.

HerpesvirusesHerpesviruses

Herpesviruses can infect Herpesviruses can infect neonates, children and neonates, children and adults causing a wide adults causing a wide spectrum of diseases. Initial spectrum of diseases. Initial infection with the virus infection with the virus establishes a viral "latency", establishes a viral "latency", which allows for subsequent which allows for subsequent potential of reactivation of potential of reactivation of the virusthe virus

Includes cytomegalovirus, Includes cytomegalovirus, varicella (chicken pox) and varicella (chicken pox) and herpes zoster (shingles)herpes zoster (shingles)

Influenza VirusesInfluenza Viruses Influenza A is an important respiratory pathogenInfluenza A is an important respiratory pathogen of humans. It re-emerges of humans. It re-emerges

annually, causing significant morbidity and mortality in the world's annually, causing significant morbidity and mortality in the world's population. In addition to humans, Influenza A also infects species such as population. In addition to humans, Influenza A also infects species such as birds, pigs, horses and marine mammals.birds, pigs, horses and marine mammals.

Influenza A virus has a heterogeneous morphology, giving it a diverse Influenza A virus has a heterogeneous morphology, giving it a diverse structural appearance. structural appearance.

Some viruses are spherical while others have a filamentous shape.Some viruses are spherical while others have a filamentous shape. Two surface glycoproteins known as the hemagglutinin (H or HA) and Two surface glycoproteins known as the hemagglutinin (H or HA) and

neuraminidase (N or NA) are embedded in a lipid membrane and radiate from neuraminidase (N or NA) are embedded in a lipid membrane and radiate from the particle. These are the protruding white spikes that are most easily seen the particle. These are the protruding white spikes that are most easily seen on the magnified spherical particles (left). on the magnified spherical particles (left).

The HA and NA are major targets of our immune system. The HA and NA are major targets of our immune system.

Influenza viruses continually change the amino acids and carbohydrates that Influenza viruses continually change the amino acids and carbohydrates that make up these glycoproteins to evade the antibodies produced against make up these glycoproteins to evade the antibodies produced against previously circulating strains of the virus. This process is known as "antigenic previously circulating strains of the virus. This process is known as "antigenic drift" and it is the primary reason we have to annually modify the influenza drift" and it is the primary reason we have to annually modify the influenza vaccine.vaccine.

The Influenza A virus (electron The Influenza A virus (electron micrograph)micrograph)

Additional viruses*Additional viruses*

Parvovirus B19 –Parvovirus B19 – Usually a Usually a mild infection but can be mild infection but can be more serious in more serious in immunocompromised patientsimmunocompromised patients

..

LaCrosse Virus: An LaCrosse Virus: An “arbovirus” meaning that it “arbovirus” meaning that it is transmitted by insects – is transmitted by insects – may cause encephalitismay cause encephalitis

Source: Wadsworth Center, NYS Dept. of Health*

Additional viruses (cont’d)Additional viruses (cont’d)

Norwalk virus (causes Norwalk virus (causes occasionally severe occasionally severe gastroenteritis)gastroenteritis)

Rabies Virus: causes a fatal Rabies Virus: causes a fatal infection of the central infection of the central nervous system acquired nervous system acquired through the bite of an through the bite of an

infected animal.infected animal.

Additional viruses - Additional viruses - continuedcontinued

Rotavirus – causes Rotavirus – causes gastroenteritisgastroenteritis

Vaccinia: includes Vaccinia: includes smallpox, best known for smallpox, best known for the successful eradication the successful eradication campaign of the 1960s and campaign of the 1960s and

1970s1970s

HIVHIV

Because of the success of anti-HIV drugs, Because of the success of anti-HIV drugs, it is becoming less common for people it is becoming less common for people with AIDS to actually die of causes related with AIDS to actually die of causes related to the disease, according to a New York to the disease, according to a New York study. study.

Variety of drug “cocktails” now available Variety of drug “cocktails” now available for treatmentfor treatment

HIV testing recommended if at risk since HIV testing recommended if at risk since treatments now availabletreatments now available

Complacency or Action?Complacency or Action?

HIV – 1981 – small HIV – 1981 – small group of gay men with group of gay men with similar immune-similar immune-related symptomsrelated symptoms

1987 – on of the first 1987 – on of the first chronicles of HIVchronicles of HIV

Discusses what it Discusses what it alleges were the slow alleges were the slow and inadequate and inadequate responses of responses of politicians and the politicians and the health rhealth r

What did happen?What did happen?

1980s:1980s: Slow responses by politicians and research Slow responses by politicians and research

community until it touched their own community until it touched their own “backyards” – e.g., for Ronald Reagan it was “backyards” – e.g., for Ronald Reagan it was Rock Hudson, etc.Rock Hudson, etc.

By mid-1980s, pharma companies and the By mid-1980s, pharma companies and the Catholic Church start to respondCatholic Church start to respond

““Moral majority” continues to allege that the Moral majority” continues to allege that the community as a whole lacks response for the community as a whole lacks response for the “gay disease“gay disease

What are the three fallacies of this approach ?What are the three fallacies of this approach ? AZT (Burroughs-Wellcome) was one of the first AZT (Burroughs-Wellcome) was one of the first

drugs developeddrugs developed

1990s - present1990s - present

HIV is now a treatable diseaseHIV is now a treatable disease Testing recommendedTesting recommended ““Drug Cocktails” including 2-3 Drug Cocktails” including 2-3

different types of HIV deemed different types of HIV deemed effectiveeffective

Where does this approach become Where does this approach become problematical problematical Developing world – expense becomes a Developing world – expense becomes a

problemproblem

HIV VirusHIV VirusHIV virus and an immune cell it has HIV virus and an immune cell it has

infectedinfected

Prevention of VirusesPrevention of Viruses

VaccinesVaccines Hygiene Measures (handwashing, Hygiene Measures (handwashing,

avoidance of respiratory infection)avoidance of respiratory infection) Tracking viral IllnessesTracking viral Illnesses

How do vaccines work?How do vaccines work?

A vaccine is given by shot or as a liquid by A vaccine is given by shot or as a liquid by mouth--vaccines contain a weak (“attenuated”) or mouth--vaccines contain a weak (“attenuated”) or dead (“killed”) disease germ. dead (“killed”) disease germ.

A body produces antibodies A body produces antibodies These antibodies develop ways of responding to These antibodies develop ways of responding to

the weak germs so when the real, strong disease the weak germs so when the real, strong disease germs--which can be lurking all around--invade germs--which can be lurking all around--invade the child's body, the antibodies will know how to the child's body, the antibodies will know how to destroy them and the child will not become ill. destroy them and the child will not become ill.

Protective antibodies stay on guard in the body to Protective antibodies stay on guard in the body to safeguard it from the real disease germs.safeguard it from the real disease germs.

How do antviral drugs work?How do antviral drugs work?

Antiviral DrugsAntiviral DrugsFour antiviral medications (amantadine, rimantadine, zanamavir and Four antiviral medications (amantadine, rimantadine, zanamavir and

oseltamivir) have been approved by the U.S. Food and Drug oseltamivir) have been approved by the U.S. Food and Drug Administration (FDA) for Administration (FDA) for treatmenttreatment of influenza.). of influenza.).

Tamiflu (oseltamivir)Tamiflu (oseltamivir) Relenza (zanamivir)Relenza (zanamivir) Symmetrel (amantadine) blocks viral entry Symmetrel (amantadine) blocks viral entry Relenza and Tamiflu prevent the release of viral particles by Relenza and Tamiflu prevent the release of viral particles by

blocking a molecule named neuraminidase that is found on the flu blocking a molecule named neuraminidase that is found on the flu virus surfacevirus surface

Interferons encourage the immune system rather than attacking Interferons encourage the immune system rather than attacking viruses directly..viruses directly..

For amantadine, Tamiflu, and Relenza, one needs to take For amantadine, Tamiflu, and Relenza, one needs to take medication within 2 days after becoming sick. These medications medication within 2 days after becoming sick. These medications can diminish flu symptoms and may shorten the time you are sick can diminish flu symptoms and may shorten the time you are sick by 1 or 2 days and may make you less contagious. A 3-5 day by 1 or 2 days and may make you less contagious. A 3-5 day course, prescribed by a physiciancourse, prescribed by a physician

How can major How can major viral pandemics viral pandemics be prevented?be prevented?

Vaccine TechnologiesVaccine Technologies

Why can’t we develop flu vaccines Why can’t we develop flu vaccines more rapidly?more rapidly?

The scientific problem: The scientific problem: The technology problem:The technology problem: The money problem:The money problem: The societal problem The societal problem

Avian fluAvian flu

Historical: The 1918 flu epidemic was Historical: The 1918 flu epidemic was originally an avian-type influenza. originally an avian-type influenza. This epidemic killed more people This epidemic killed more people than did World War I.than did World War I.

Avian flu in 2004 – Successful Avian flu in 2004 – Successful “temporary” control measures - “temporary” control measures -

George Bush’s report to the George Bush’s report to the NationNation

On May 3, 2006, the George W. Bush White House "unveiled a On May 3, 2006, the George W. Bush White House "unveiled a foreboding report on the nation's lack of preparedness for a bird foreboding report on the nation's lack of preparedness for a bird flu pandemic, warning that such an outbreak could kill up to 2 flu pandemic, warning that such an outbreak could kill up to 2 million people. million people.

"In the government's first detailed look at the potential impact on "In the government's first detailed look at the potential impact on public health and U.S. society, the report said a full-blown public health and U.S. society, the report said a full-blown pandemic could lead to travel restrictions, mandatory quarantines, pandemic could lead to travel restrictions, mandatory quarantines, massive absenteeism, an economic slowdown 'and civil massive absenteeism, an economic slowdown 'and civil disturbances and breakdowns in public order," disturbances and breakdowns in public order,"

The report "warned that the health-care system cannot meet the country's The report "warned that the health-care system cannot meet the country's needs in a flu pandemic." needs in a flu pandemic."

"In the event of multiple simultaneous outbreaks, there may be insufficient "In the event of multiple simultaneous outbreaks, there may be insufficient medical resources or personnel to augment local capabilities." medical resources or personnel to augment local capabilities."

The report said "state, local and tribal governments should 'anticipate that The report said "state, local and tribal governments should 'anticipate that all sources of external aid may be compromised during a pandemic,' ... all sources of external aid may be compromised during a pandemic,' ...

""

Report to the Nation (George Report to the Nation (George Bush - cont’d)Bush - cont’d)

The strategy is built around three elements: preparation, The strategy is built around three elements: preparation, surveillance and detection, and containment. surveillance and detection, and containment. Quarantine: Quarantine: Executive OrdersExecutive Orders

Federal Register page and date: 70 FR 17299, April 5, 2005: Federal Register page and date: 70 FR 17299, April 5, 2005: Executive Order 13295: "Revised List of Quarantinable Executive Order 13295: "Revised List of Quarantinable Communicable Diseases," April 4, 2003. Amended April 1, Communicable Diseases," April 4, 2003. Amended April 1, 2005, with Executive Order 13375: "Amendment to 2005, with Executive Order 13375: "Amendment to Executive Order 13295 Relating to Certain Influenza Viruses Executive Order 13295 Relating to Certain Influenza Viruses and Quarantinable Communicable Disease": "Section 1. and Quarantinable Communicable Disease": "Section 1. Based upon the recommendation of the Secretary of Health Based upon the recommendation of the Secretary of Health and Human Services, in consultation with the Surgeon and Human Services, in consultation with the Surgeon General, and for the purpose set forth in section 1 of General, and for the purpose set forth in section 1 of Executive Order 13295 of April 4, 2003, section 1 of such Executive Order 13295 of April 4, 2003, section 1 of such order is amended by adding at the end thereof the following order is amended by adding at the end thereof the following new subsection: "'(c) Influenza caused by novel or new subsection: "'(c) Influenza caused by novel or reemergent influenza viruses that are causing, or have the reemergent influenza viruses that are causing, or have the potential to cause, a pandemic.'" potential to cause, a pandemic.'"

Why?Why?

Is the science hard – yes, but not that Is the science hard – yes, but not that hard. Some companies are hard. Some companies are developing technologies – check the developing technologies – check the web for faster vaccine technologiesweb for faster vaccine technologies

Is this a problem with the market Is this a problem with the market system?system?

Is this a problem with academia?Is this a problem with academia? Whose problem is it?Whose problem is it?

Biotech and Pharma - Biotech and Pharma - TechnolgiesTechnolgies

Newspaper articles in 2004 Newspaper articles in 2004 and 2005 describe the and 2005 describe the vaccine industry as “long-vaccine industry as “long-dormant”dormant”

Need alternatives to an egg-Need alternatives to an egg-based system that takes based system that takes months to turn out flu months to turn out flu vaccine. vaccine.

Have membrane capsules for Have membrane capsules for large molecule applications large molecule applications compared to conventional compared to conventional resin- or gel-based column resin- or gel-based column chromatographychromatography

Use cell culture (animal Use cell culture (animal cells) or bacteria to grow flu cells) or bacteria to grow flu virusvirus

Adenovirus to carry antigensAdenovirus to carry antigens

CNN – September 22, 2006CNN – September 22, 2006

(1)) The H5N1 strain of bird flu has (1)) The H5N1 strain of bird flu has

killed at least 144 people worldwide killed at least 144 people worldwide since it started ravaging poultry stocks since it started ravaging poultry stocks in Asia three years ago, according to the in Asia three years ago, according to the World Health OrganizationWorld Health Organization(2) An additional fatality of an 11-year-(2) An additional fatality of an 11-year-old Indonesian young man, has been old Indonesian young man, has been reported.reported.

(2) The worry: the 1918 epidemic was (2) The worry: the 1918 epidemic was avian in origin; this epidemic killed more avian in origin; this epidemic killed more people than in World War Ipeople than in World War I..

Are special measures Are special measures indicatedindicated??

What choices will this What choices will this generation make?generation make?

By the 1950s, Albert Einstein publicly By the 1950s, Albert Einstein publicly expressed regrets about encouraging the expressed regrets about encouraging the development of the Atom Bomb in response development of the Atom Bomb in response to the World War II threat posed by Hitlerto the World War II threat posed by Hitler

It is likely that, whatever choices we as a It is likely that, whatever choices we as a community make in relation to controlling community make in relation to controlling epidemics and pandemics – we will continue epidemics and pandemics – we will continue to wonder whether we’ve made the right to wonder whether we’ve made the right onesones

Dateline SJUDateline SJU: : February 5, 2007 H5N1 flu outbreak in UK birdsFebruary 5, 2007 H5N1 flu outbreak in UK birds

HeadlineHeadline: : U.N. sees Europe-wide bird U.N. sees Europe-wide bird flu threat; flu threat; POSTED: 10:41 a.m. EST, February POSTED: 10:41 a.m. EST, February 4, 20074, 2007

HIGHLIGHTS:HIGHLIGHTS:• • European Commission confirms UK bird European Commission confirms UK bird

flu outbreak is deadly H5N1 strainflu outbreak is deadly H5N1 strain• More than 2,000 turkeys killed by avian • More than 2,000 turkeys killed by avian influenza at poultry farm in Englandinfluenza at poultry farm in England• H5N1 strain can be deadly to humans• H5N1 strain can be deadly to humans

An outbreak of the deadly H5N1 bird flu virus strain detected on a An outbreak of the deadly H5N1 bird flu virus strain detected on a British turkey farm is likely a precursor to other outbreaks in British turkey farm is likely a precursor to other outbreaks in Europe, a U.N. bird flu expert said Sunday.Europe, a U.N. bird flu expert said Sunday.

"I think we will have more in Europe in the next month or two," said "I think we will have more in Europe in the next month or two," said David Nabarro, Senior U.N. Coordinator for Avian and Human David Nabarro, Senior U.N. Coordinator for Avian and Human Influenza.Influenza.

Over recent years such outbreaks have been seen between Over recent years such outbreaks have been seen between November and May as infected migrating wild birds come into November and May as infected migrating wild birds come into contact with domesticated stocks, said Nabarro, who is attending contact with domesticated stocks, said Nabarro, who is attending a bird flu conference in Indonesia.a bird flu conference in Indonesia.

The outbreak on a farm near Lowestoft in Suffolk "is the highly The outbreak on a farm near Lowestoft in Suffolk "is the highly pathogenic Asian strain" and is similar to the virus found in pathogenic Asian strain" and is similar to the virus found in Hungary last month, a British government agency said Saturday. Hungary last month, a British government agency said Saturday. The outbreak was discovered Friday night after 2,500 turkeys died The outbreak was discovered Friday night after 2,500 turkeys died on the farm which was holding nearly 160,000 birds, officials said.on the farm which was holding nearly 160,000 birds, officials said.

The remaining birds are being killed -- a process expected to take 36 The remaining birds are being killed -- a process expected to take 36 hours, the agency said.hours, the agency said.

The farm is 120 miles northeast of central London.The farm is 120 miles northeast of central London.Veterinary officials are enforcing a protection zone around the farm Veterinary officials are enforcing a protection zone around the farm

and taking other measures to deal with the issue.and taking other measures to deal with the issue.But the British Department of Environment, Food and Rural Affairs But the British Department of Environment, Food and Rural Affairs

said "there is no reason for public health concern.said "there is no reason for public health concern.

"Avian influenza is a disease of birds and whilst it can pass very rarely and with "Avian influenza is a disease of birds and whilst it can pass very rarely and with difficulty to humans, this requires extremely close contact with infected difficulty to humans, this requires extremely close contact with infected birds, particularly feces."birds, particularly feces."

Nabarro, the U.N. official in charge of tracking bird flu outbreaks, said that in Nabarro, the U.N. official in charge of tracking bird flu outbreaks, said that in addition to the outbreaks in Britain and Hungary, officials have recently addition to the outbreaks in Britain and Hungary, officials have recently confirmed infections among domestic birds in Japan, and South Korea.confirmed infections among domestic birds in Japan, and South Korea.

Speaking from Jakarta, Nabarro said British health officials are handling the Speaking from Jakarta, Nabarro said British health officials are handling the outbreak "in the proper way, the way that's been required by the European outbreak "in the proper way, the way that's been required by the European Commission and I believe that under these circumstances, we would be Commission and I believe that under these circumstances, we would be unlucky if other farms in the vicinity get affected."unlucky if other farms in the vicinity get affected."

World Health Organization officials have confirmed 271 human cases and 165 World Health Organization officials have confirmed 271 human cases and 165 deaths worldwide from the same strain of bird flu found in Britain. The latest deaths worldwide from the same strain of bird flu found in Britain. The latest case confirmed by laboratory tests was that of a 22-year-old deceased case confirmed by laboratory tests was that of a 22-year-old deceased female from Lagos, Nigeria, WHO officials said Saturday.female from Lagos, Nigeria, WHO officials said Saturday.

"The initial positive test findings from a laboratory in Nigeria were confirmed by "The initial positive test findings from a laboratory in Nigeria were confirmed by the WHO Collaborating Centre for Reference and Research on Influenza in the WHO Collaborating Centre for Reference and Research on Influenza in London," the WHO said in a statement. Tests of those who were in contact London," the WHO said in a statement. Tests of those who were in contact with the woman were negative for bird flu, the WHO said.with the woman were negative for bird flu, the WHO said.

Bird flu cannot be contracted from eating "properly prepared" poultry, the WHO Bird flu cannot be contracted from eating "properly prepared" poultry, the WHO statement said.statement said.

"The H5N1 avian influenza virus is not transmitted to humans through properly "The H5N1 avian influenza virus is not transmitted to humans through properly prepared and cooked food (even if contaminated with the virus prior to prepared and cooked food (even if contaminated with the virus prior to cooking), according the WHO Web site. "However, in a few instances, cases cooking), according the WHO Web site. "However, in a few instances, cases have been linked to consumption of dishes made of raw contaminated have been linked to consumption of dishes made of raw contaminated poultry blood.poultry blood.

"Cases of human infection with H5N1 have frequently been linked to the home "Cases of human infection with H5N1 have frequently been linked to the home slaughter and subsequent handling of diseased or dead birds prior to slaughter and subsequent handling of diseased or dead birds prior to cooking."cooking."

A Gamble?A Gamble?

The avian influenza virus lacks just one trait that The avian influenza virus lacks just one trait that could turn it into a pandemic: transmissibility, the could turn it into a pandemic: transmissibility, the ability to spread easily from person to person. If ability to spread easily from person to person. If the virus acquires that ability, a pandemic could the virus acquires that ability, a pandemic could erupt.erupt.

When will avian influenza become more When will avian influenza become more transmissible to humans?transmissible to humans?

A(H5N1) has existed for over 10 years and the A(H5N1) has existed for over 10 years and the shift has not occurred. shift has not occurred.

Do we want to gamble that it will not?Do we want to gamble that it will not? Probably not: we need to work on better vaccines, Probably not: we need to work on better vaccines,

better methods of infection control, and better methods of infection control, and increasing the supply of antiviral medicationsincreasing the supply of antiviral medications