Avian Influenza Virus September 18, 2005

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1 Avian Influenza Virus September 18, 2005 Influenza Virus Influenza viruses are RNA viruses in the family Orthomyxoviridae and are comprised of 8 separate gene segments. The segmented genome allows viruses from different species to mix and create new viruses. There are three types of influenza viruses: A, B and C. Type A viruses can infect people, birds and other animals including pigs and horses. Wild birds are the natural hosts for Type A viruses. Types B and C viruses normally are found only in humans. Type A viruses are subtyped according to two surface proteins (glycoproteins): hemagglutinin (HA) and neuraminidase (NA). There are 16 HA subtypes and 9 NA subtypes and the combinations result in subtypes generally found only in humans, e.g., H1N1, H1N2 and H3N2, and those most commonly associated with animals, e.g., H7N7 and H3N8 in horses. It appears that virulence (pathogenicity) is linked to the ability of trypsin to cleave the HA molecule into 2 subunits. Influenza B viruses and subtypes of influenza A virus are further characterized into strains. Strains emerge over time through a process referred to as drift; the drift can be defined as antigenic drift that occurs slowly over time or antigenic shift that occurs abruptly and in a relative major fashion to create a new influenza A subtype. Type A viruses undergo both types of drift, whereas Type B viruses change only by the more gradual antigenic drift. Humans can be infected with Types A, B and C; birds are infected by Type A (causing bird flu). In those rare occasions when humans get bird flu, symptoms range from typical flu-like symptoms such as fever, sore throat and muscle aches, to eye infections, pneumonia and severe respiratory distress. Avian Influenza Virus Influenza viruses that infect birds (causing bird flu) are called avian influenza (AI) viruses and are Type A influenza viruses. These flu viruses occur naturally among birds and have been recognized as a highly lethal generalized disease of poultry since The viruses are carried in the intestines of wild birds that are generally asymptomatic. Bird flu is very contagious and can make domesticated birds, including chickens, ducks and turkeys very sick. It is impossible to generalize on the host range for specific strains of AI viruses, since each strain may infect only selected avian species of fowl, ducks, geese, turkeys, guinea fowl, quail and pheasants. H5 and H7 subtypes (not all of which are virulent for poultry) of AI viruses can be further classified as either highly pathogenic (HP) or low pathogenic (LP). H9 subtype has only been identified in a LP form. Each of these AI viruses, H5, H7 and H9, can be partnered with any one of the 9 NA proteins. For example, influenza A (H5N1) virus, or H5N1 virus, was first isolated from birds (terns) in South Africa in H5N1 virus circulates among birds worldwide, is very contagious and can be deadly. Influenza caused by H5N1 has proven itself to be a zoonotic disease, which means an illness that is capable of moving from animals to infect humans. Lethal H5 infections have been documented among humans; H7 and H9 infections also have occurred in humans, but these infections are rare and less severe. The incubation period is usually 3 to 7 days depending on the isolate, the dose, the species and the age of the bird. Clinical signs are variable and are influenced by factors such as the virulence,

2 species affected, age, sex, concurrent disease and the environment. HPAI infections appear suddenly in a flock and many birds die either without premonitory signs or with minimal signs of depression, inappetence, ruffled feathers and fever. Other birds show weakness and a staggering gait. Hens may at first lay soft-shelled eggs, but soon stop laying. Sick birds often sit or stand in a semi-comatose state with their heads touching the ground. Combs and watties are cyanotic and oedematous, and may have petechial or ecchymotic haemorrhages at their tips. Profuse watery diarrhea is frequently present and birds are excessively thirsty. Respiration may be labored. Haemorrhages may occur on unfeathered areas of the skin. The mortality rate varies from 50 to 100%. In broilers, the signs of disease may be less obvious with severe depression, inappetence and a marked increase in mortality being the first abnormalities observed. The disease in turkeys is similar to that seen in layers, but it last 2 to 3 days longer and is occasionally accompanied by swollen sinuses. In poultry, LPAI viruses cause respiratory disease with ocular and nasal discharges; laying hens will show decreased production with eggs becoming misshapened and thin-shelled; and yolks often rupture within the shell. Transmission of Avian Influenza Virus Infected birds shed flu virus in their saliva, nasal secretions and feces. Fecal-to-oral transmission is the most common mode of spread between birds. Infected birds excrete virus in high concentrations. Once introduced into a flock, the virus is spread by numerous activities including the movement of birds, contaminated equipment, egg flats, feed trucks and service crews. Airborne transmission occurs easily as birds are readily infected via instillation of virus into the conjunctival sac, nares or trachea. Virus can be recovered from the yolk and albumen of eggs laid by hens at the height of the disease. Outbreaks of Avian Influenza Virus From 1959 to 2005 there have been over 25 outbreaks caused by AI. The progenitor virus for the more serious HPAI was from Guaungdong, China and originated in Prevalence of H5 and H7 AI in the U.S. was % in 2004 (USDA does extensive monitoring, particularly in live markets in the NE corridor). Over 200 million poultry have been killed and there are reportedly about 62 human fatalities from HPAI. Major problems are the domestic reservoirs in village poultry industries and domestic ducks and geese (typically raised in rice fields), where HPAI is endemic. Fighting cocks also serve as traveling vectors. Outbreaks of HPAI (H5N1) occurred among poultry in 8 countries in Asia during late 2003 and 2004, resulting in the death or culling of over 100 million birds (overall, nearly 140 million domestic poultry have either died or been destroyed as of August, 2005, with economic losses to the Asian poultry sector estimated at $10 billion). Outbreaks of AI among poultry in the U.S. occur from time to time. Some examples of outbreaks occurring in 2004 include the following: Texas (HPAI, H5N2), Maryland, (LPAI, H7N2), Pennsylvania (LPAI, H2N2), Delaware (LPAI, H7N2). Human cases of AI in North America were first detected in February, 2004, in association with an outbreak of AI H7N3 in the Fraser Valley region of British Columbia. Two persons in close

3 contact with the poultry operations developed conjunctivitis and flu-like symptoms and were confirmed to be infected with influenza A (H7) virus. In November 2003, a person in New York was confirmed to be infected with AI H7N2 virus. Outbreaks of HPAI in Asia & Europe* Korea H5N1 2003, 2004 Cambodia H5N1 2004, 2005 China H5N1 2004, 2005 Hong Kong H5N1 2004, 2005 Indonesia H5N1 2004, 2005 Japan H5N Laos H5N Malaysia H5N1 2004, 2005 Pakistan H7N Thailand H5N1 2004, 2005 Vietnam H5N1 2004, 2005 Kazakhstan H5N Mongolia H Romania H5N Russia H5N Turkey H5N * The data for outbreaks of HPAI are constantly being updated, but these data illustrate some of the historical outbreaks of HPAI. HPAI (e.g., H5N1, H5N2, H3N2, H7N3) also has been reported in the U.S.A., Canada, and South Africa). LPAI (e.g., H2N2, H5N2, H7N2, H7N3, H9N2, H10N7) also has been reported in Korea, Japan, Taiwan, Pakistan, the Philippines, the U.S.A., Canada, Mexico, South Africa, Egypt, and Italy. Human Infections Related to Bird Flu Influenza A viruses are found in many different animals. Certain subtypes of influenza A virus are specific to certain species, except for birds which are hosts to all subtypes of influenza A. Subtypes that have caused widespread illness in people either in the past or the current period are H3N2, H2N2, H1N1 and H1N2. H1N1 and H3N2 subtypes have caused outbreaks in pigs and H7N7 and H3N8 viruses have caused outbreaks in horses. AI viruses may be transmitted to humans in two main ways: (1) directly from birds or from avian virus-contaminated environments to people, and (2) through an intermediate host such as a pig. The H5N1 virus usually does not infect humans. The first case of bird-to-human transmission was seen in Hong Kong in 1997 during an outbreak of HPAI bird flu in poultry; 6 of 18 people with confirmed infection died. During 2003 and 2004, 12 confirmed human cases of AI (H5N1) were reported in Thailand and 23 in Vietnam, resulting in 23 deaths. Beginning in late June 2004, new lethal outbreaks of AI (H5N1) in poultry were reported across Asia from Indonesia to North Korea; additional human cases were reported in Vietnam and Thailand. In 2005, human infections were reported in Cambodia and Indonesia. As of September 18, 2005 there have been at least 117 human cases of AI Type A (H5N1) in Vietnam (91, with 41 deaths), Thailand (17, with 12 deaths), Cambodia (4, with 4 deaths) and Indonesia (5, with 3 deaths), resulting in 61 deaths. While the infection in most instances resulted from contact with infected poultry or contaminated surfaces, human-to-human transmission can not be ruled out as a means of transmission.

4 H9N2 virus was isolated from 2 children in Hong Kong in 1999; and H7N7 virus infected 89 persons during a simultaneous outbreak in poultry in the Netherlands in In both instances, the infections caused only mild illness. When infected with an unrecognized virus such as H5N1, the human immune system can actually create an immunologic storm with over-production of cytokine that will attack and destroy healthy tissues such as those of the lungs. Influenza Pandemics An influenza pandemic is a global outbreak of a disease that occurs when a new influenza A virus appears or emerges (from antigenic shift) in the human population, causes serious illness, and then spreads easily from person-to-person worldwide. The U.S. Centers for Disease Control and Prevention and the World Health Organization have surveillance programs to monitor and detect influenza viruses around the world, including those capable of causing pandemics. Three notable pandemics are (1) Spanish flu occurring during 1918 and 1919, caused by influenza A H1N1, and killing as many as 50 million people worldwide, (2) Asian flu occurring during 1957 and 1958, caused by influenza A H2N2, and killing as many as 70,000 people in the U.S., and (3) Hong Kong flu occurring during 1968 and 1969, caused by influenza A H3N2, and killing as many as 34,000 people in the U.S.. The Asian and Hong Kong flu pandemics were caused by viruses that were combinations of human and avian influenza viruses. Spread of H5N1 from person-to-person has been minimal to this point. Because H5N1 typically does not infect humans, there is little or no immune protection against the virus in the human population. Because of the capacity for influenza viruses to drift, there is a real concern that H5N1 virus could one day easily infect humans and spread easily throughout the human population, resulting in a influenza pandemic. Treatment of Human Influenza Four different influenza antiviral medications (amantadine, rimantadine, oseltamivir and zanamivir) are approved by FDA for the treatment and prevention of influenza. Although all four appear to work against influenza A viruses, resistance can develop to one or more of these drugs. The H5N1 virus is resistant to amantadine and rimantadine, and the efficacy of oseltamavir and zanamavir is being assessed. Oseltamivir, also known as Tamiflu, is produced by Roche (although there appears to be litigation brought against Roche by Gilead, the U.S. biotech company that apparently originally developed the drug and licensed it to Roche) in Switzerland; and production may be expanded to six U.S. plants in the Fall of The U.S. government reportedly has set a goal of purchasing 20 million treatment courses of 10 pills each. Human vaccines have been developed by such notable researchers as Dr. Robert Webster of St. Jude s Children s Hospital in Memphis, Tennessee, who constructed the H5N1 virus used for vaccine production. According to a BMO Nesbitt Burns Investor s Guide (August, 2005), only nine nations have the capacity to produce flu vaccine on a commercial scale. The only largescale U.S. plant is operated by Sanofi-Pasteur and is working on a new cell culture process for producing a vaccine for H5N1 to replace the more time-consuming (4 to 6 months) chicken eggbased process. Sanofi-Pasteur is working under contract with the U.S. National Institute of Allergy and Infectious Diseases under the direction of Dr. Anthony Fauci. The greatest hurdle is producing sufficient quantities of an effective vaccine for hundreds of millions of people likely to be exposed in a pandemic.

5 Diagnosis and Sampling for Avian Influenza Virus` Diagnosis of AI is by isolation and characterization of the virus. In 1992, the OIE adopted criteria for classifying an AI virus as HP based on pathogenicity in chickens, growth in cell culture and the amino acid sequence for the connected peptide. More rapid reverse transcription (RT) PCR tests also are being used for identification and characterization. Sample collection from live animals requires planning and skill to ensure the appropriate sample is taken and cross contamination does not occur. Samples taken include blood (generally the wing vein in birds), feces (at least 10 g or preferably, a rectal swab), skin (2 g of tissue and vesicular fluid collected separately if vesicles are present), genital tract and semen, eye (conjunctiva swab), nasal discharge, saliva and tears. Sample collection at post-mortem involves samples of tissues from a variety of organs and detailed procedures are written to optimize virus recovery and minimize cross contamination. In more traditional diagnostic tests, suspensions in antibiotic solution of tracheal and cloacal swabs (or feces) taken from live birds, or from feces and pooled samples of organs from dead birds, are inoculated into the allantoic cavity of 9- to 11-day-old embryonic fowl eggs. The eggs are incubated at 35 to 37 C for 4 to 7 days. The allantoic fluid of the eggs containing dead or dying embryos as they arise and all eggs at the end of the incubation period are tested for the presence of haemagglutinating activity. The presence of influenza A virus can be confirmed by an agar gel immunodiffusion test between concentrated virus and an antiserum to the nucleocapsid or matrix antigens common to all influenza A viruses. HP AI viruses are characterized by their ability to cause greater than 75% mortality in susceptible 4 to 8-week-old chicks within 10 days or have an intravenous pathogenicity index (IVPI) of greater than 1.2. Also, all H5 and H7 isolates with a specific amino acid sequence (i.e., the presence of multiple basic amino acids, arginine or lysine, at the cleavage site of the haemagglutinin precursor protein, HA0) characteristic of HP viruses are considered HP regardless of their virulence for chickens. All characterization should occur in a virus-secure laboratory. Serological tests are useful as supplemental tests; but not all birds develop demonstrable precipitating antibodies. ELISA has been used to detect antibodies to influenza A type-specific antigens. Industry Controls to Reduce Risks Vaccination protects against clinical signs and mortality, reduces virus shedding and increases resistance to infection, protects from low and high challenge exposure, and reduces contact transmission of challenge virus. However, the virus is still able to infect and replicate in healthy vaccinated birds. It is imperative that the circulating antigenic AI virus be known and that the vaccine represent this antigenic strain since there is no cross-protection among the 16 known HA subtypes. Vaccination is not the solution to the control of AI; monitoring systems, strict biosecurity and depopulation in the face of infection are necessary. Risk factors for HPAI disease in humans include exposure to live poultry, living in association with a village poultry industry or a live poultry market, exposure to aerosols caused during slaughter, and proximity to poultry fecal material or respiratory secretions. Raw products,

6 handling, cooking and eating cooked poultry are not risk factors. AI can be found in poultry breast and thigh meat; the ability to detect the AI in meat appears to be dose-dependent when doing challenge studies. Pasteurization temperatures for liquid egg processing destroy AI viruses, as does cooking to 70 C. Some poultry operations have implemented control programs. Sunny Fresh Foods, a liquid egg processor with operations in Minnesota, Iowa, Michigan and Ontario, has developed contingency plans to protect human and animal health and ensure their raw material supply, and developed a stepwise approach to risks associated with LP and HPAI. Sun Valley s Thailand operations have implemented a zero tolerance for AI. This tolerance pertains to all flocks within 5 km of any Sun Valley flock. There also is a zone of zero tolerance if there are any open farms within 1 km of their operations. In the event of an outbreak of AI, the zone of zero tolerance extends to 10 km. Sun Valley flocks now have closed houses and closed water systems, pest control, dedicated feed routes, all-in and all-out operations for broilers, single age pullet operations, strict limits on people movement (including shower-in and showerout, complete clothing changes, no work policy for ill employees, and mask requirement for all houses), a clean-fence boundary, super clean zones established for bird houses, examinations required for all deaths, AI tests on all culled birds, a 10-day down time between broiler growouts, and an 80 C treatment for all feed production. Sun Valley also has a robust testing program for hatcheries (30 blood samples/flock), pullets (supplier certification based on cloacal samples taken throughout the growing period), breeders (30 cloacal samples/week for all houses), broiler farms (blood samples), pre-slaughter (tracheal swabs), and processing (incoming birds sampled). Cargill feed operations also have an extensive outreach educational program, HACCP programs, daily reporting and routinely scheduled, global conference calls. Cargill believes that as much as 99% of transmission occurs via contaminated feces and thus, has an extensive educational program on waste management. Perdue also has implemented control programs based on their experiences with outbreaks of AI H7N2 that occurred in the Shenandoah Valley (March, 2002) and Delmarva Peninsula (February, 2004). One of their primary lessons was that if AI is detected, quick depopulation (within 24 hours) is a key to controlling the spread of AI. Other key controls were to stop all movement of birds immediately, do not introduce new hosts until there is confidence in the negative status of a facility, focus on those flocks with the highest mortality, find the epidemiological links to positive flocks and follow them immediately, do not release any positive flocks to processing and be prepared to suffer business disruptions. Perdue operates with a 2 mile-radius quarantine zone (test within 24 hours) and a 6 mile buffer zone (test within 72 hours) around any positive AI finding. Perdue uses a 69-point questionnaire to assess farms and believe that ultimately, certification should be required for A-free flocks and AI-free plants. Decontamination of AI positive areas should be relatively easy since the lipid-enveloped AI is sensitive to generally-used disinfectants (500 ppm quat, 200 ppm peracetic acid, 200 ppm hypochlorite, and 500 ppm phenolics). The difficulty is to remove the organic material that will neutralize the disinfectants. In addition, in the U.S., there are restrictions on the concentrations of disinfectants that can be formulated and used (as declared on the label).

7 Protecting Poultry Workers Poultry workers at risk include poultry growers and their employees, service technicians of poultry processing companies, caretakers, layer barn workers, chick movers at egg production facilities, and workers involved in disease control and eradication activities. The measures for protecting these and other workers include the following: (1) follow biosecurity practices to prevent the introduction of AI into a poultry flock (best practices available from USDA and USPEA), (2) be aware of the signs indicating birds are infected with AI viruses, (3) in the event of an AI outbreak, take antiviral medication and get the current season s influenza vaccine if appropriate (CDC advice should be considered), (4) know the signs and symptoms of human infection with AI virus (e.g., fever, cough, sore throat, conjunctivitis and muscle aches), (5) wear personal protective equipment (e.g., respirator, eye protection, protective clothing), and (6) use proper hand-washing procedures. Regulatory and Food Safety Issues Title 42 U.S. Code Section 264 (Section 361 of the PHS Act) gives the Secretary of HHS responsibility for preventing introduction and spread of communicable diseases (42 CFR Parts 70 and 71). Authorization of quarantine for an AI virus capable of causing a pandemic is specified through an Executive Order of the President. CDC, as well as state and local governments, become the executors of a quarantine operation. On February 4, 2004 CDC and USDA issued an order for a ban on the import of all birds (Class: Aves) from infected areas in SE Asia. On March 10, 2004 CDC, in coordination with USDA, lifted the embargo of birds and bird products from Hong Kong. On September 28, 2004 the list of countries affected by the embargo of birds and bird products was expanded to include Malaysia. While countries that import poultry species and their products have imposed trade restrictions to protect animal health, in accordance with the OIE Terrestrial Code, the OIE and WHO conclude that any poultry products destined for human consumption from countries currently experiencing outbreaks of AI do not pose a risk to public health. AI viruses are killed at temperatures of approximately 70 C.

Avian Influenza (Bird Flu) Fact Sheet

Avian Influenza (Bird Flu) Fact Sheet What is an avian influenza A (H5N1) virus? Influenza A (H5N1) virus also called H5N1 virus is an influenza A virus subtype that occurs mainly in birds. It was first isolated from birds (terns) in South