FAO-OIE-WHO Joint Technical Consultation on Avian Influenza at ...

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<strong>Joint</strong> Writing CommitteeFerret studies suggest that contact and droplet transmissionof H5N1 and other AIVs to mammals are generallyinefficient, although H5N1 has been transmitted to ferretshoused in a room where asymptomatic infected chickenswere slaughtered. Overall, studies show that transmission(as well as pathogenicity and virulence) depend not onlyon animal host species but also on virus subtype and virusstrain, dose, and exposure route.4.2 Exposure risk for human infection with avianinfluenza virusesExposure data on human casesSpecific exposure risks for AI H5N1 infection in humansare not well understood, and likely differ greatly by country.Along with direct contact with sick or infected poultry,indirect contact with poultry, environmental contamination,and contact with healthy infected poultry are alsolikely to be risks. Most humans infected to date were notin ‘‘traditional’’ occupational risk groups, while subpopulationssuch as children and housewives seem to be at greaterrisk in some countries. As well, the risks posed by differenttypes of poultry, and household animals such as cats, arenot yet understood. It was agreed that it is not currentlypossible to globally disentangle data and determine specificrisk activities, and that epidemiological data collection andanalysis should be improved. It was suggested that ecologicalaspects, the species of birds or other animals, the vaccinationstatus of domestic poultry, and the type of poultryproduction system 8 associated with human cases shouldalso be recorded and considered in analysis. It was stressedthat, although it is clear that control of AI in poultry is themost important step in reducing zoonotic risk and pandemicthreat, understanding specific zoonotic risks isimportant to enable development of practical risk reductionmeasures for humans.Representatives from affected countries reported thathuman cases are usually located in areas of poultry cases, andthat exposure history has included household poultry raising(especially poultry living inside the house), poor poultry vaccinationcoverage, exposure to sick or dead poultry, lack ofan indoor water source, visiting LBMs, having an underlyingmedical condition, and in some cases occupational poultryexposure. In many cases, a specific exposure was inconclusiveor unknown despite in-depth investigation.The question of why human H5N1 cases seem to beoccurring only in certain countries and communities wasdiscussed. It was agreed that this reflects primarily the presenceof infected poultry and the amount of virus present,8 Poultry production sectors described in: <strong>FAO</strong> Recommendations onthe Prevention, Control and Eradication of Highly Pathogenic AvianInfluenza in Asia, Sept. 2004, available at http://www.fao.org/docs/eims/upload/165186/<strong>FAO</strong>recommendationsonHPAI.pdfbut might also reflect the surveillance system or other asyet unidentified local ecologic, cultural, genetic, virological,or management factors.Most studies have indicated a very low seroprevalence ofantibodies to AIVs among people in high risk occupations,such as poultry cullers and LBM workers, in affected countries.The many difficulties with the serological tests werementioned, and it was noted that more sensitive and discriminatingsubtype-specific tests need to be developed. Itwas agreed that more seroprevalence studies for AIVs inhumans need to be done and the results from completedstudies need to be shared with the wider scientific communityin a more timely manner. It was noted that solutionsmust be found to improve timely publishing and sharingof study results with the animal and public health communities,to improve the availability of seroprevalence, casecontrol and attack rate data for zoonotic AIVs.Consumption and inactivationAvian influenza is not generally considered a food safetyissue, as complete cooking inactivates the virus and the riskof infection from foods cross contaminated with virus isnegligible.Virus is contained in meat, viscera, blood and eggs frompoultry infected with highly pathogenic AIVs. Consumptionstudies of raw infected chicken meat in ferret and pigmodels suggest that H5N1 viruses initiate infection via thetonsil or pharynx with spread to the upper and lower respiratorytract. However, experimental data in pigs and ferretssuggest that foodborne infection by consumption of rawinfected meat would require higher viral doses than wouldinfection through respiratory tract exposure. Thus, riskreduction measures for humans include pasteurization orthorough cooking of meat and eggs, basic kitchen hygiene,and consuming products derived from vaccinated poultry(as poultry vaccination prevents viremia and localization ofvirus in muscle tissue).Freezing at )70°C preserves the virus, while inactivationat )20°C is inconsistent and unpredictable, and refrigeration(4°C) allows slow virus inactivation in meat due todecreasing pH and enzymatic action. Infectious virus hasbeen detected in frozen raw poultry stored in a householdfreezer.Risk from live bird markets and virus in the environmentMultiple AIV subtypes, including H5N1, H9N2 and H6N1,have been obtained from birds in LBMs in Asia. Interestingly,H7 subtype viruses are not commonly found inLBMs. Isolation rates and virus subtypes differ by speciesof poultry and location, with more frequent virus recoveryfrom aquatic poultry (ducks and geese) than chickens, andhigher isolation rates during the winter. Studies show thatLBMs can maintain, amplify, and allow dissemination of10 ª 2010 <strong>FAO</strong>, <strong>OIE</strong> and <strong>WHO</strong>, Influenza and Other Respiratory Viruses, 4 (Suppl. 1), 1–29
<strong>FAO</strong>-<strong>OIE</strong>-<strong>WHO</strong> <strong>Joint</strong> <strong>Technical</strong> <strong>Consultation</strong> on Avian Influenza at the Human-Animal InterfaceAIVs to farms and are a source for human infection, andare therefore a useful site for targeted surveillance. It wasnoted that, in an affected country, virus concentration isgenerally low at the farm or household level, increases atwholesale markets, and is further amplified and sustainedat LBMs from where virus may be disseminated back tofarms and households.Data from different countries was presented. Risk factorsfor LBM contamination included housing of unsold poultryovernight, presence of Muscovy ducks, presence of a largeduck population, and slaughtering in multipurpose areasand in stalls. Human risk at LBMs was associated with thepresence of restaurants and food stalls in markets, havingfamily members in the market, and the use of traditionalslaughtering processes. Viral burden in LBMs was shown tobe decreased by implementing a rest day, removal of particularspecies (e.g., quail), improving market hygiene, andnot allowing live poultry to remain overnight. However,LBMs must be specifically assessed as they vary greatlyamong and within countries and therefore do not all havethe same risk factors.It was discussed that in many countries LBMs play animportant role in people’s cultural and economic lives, andthus appropriate and culturally sensitive ways to decreaseassociated AI risks must be sought. Specific targeted assessmentsof LBMs would allow understanding of the environmentalcontamination of different areas within LBMs andamong LBMs in different settings, communities, and countries.Having decisive political support would allow the animaland public health sectors to develop appropriatestrategies, regulatory frameworks and guidance. Measuresto decrease risks could then be integrated into national systemsto improve the general hygiene of LBMs and reducerisks for AIV and other animal and zoonotic pathogens.Contamination of environments can be heavy duringpoultry outbreaks, with virus being isolated from households,wet feces, pond water, mud under animal cages, soil(including that beneath houses on stilts), in poultry rangingplaces, and on the feathers of dead poultry. In environments,AIVs survive in water, in feces, and on surfaces.Temperature, porosity of the surface and water salinity allaffect survival time. More recent H5N1 viruses have beenshown to survive longer in chicken feces than those virusesfrom 1997, but studies suggest this is due to longer decaytimes because of higher virus titers within feces and is notan intrinsic resistance of the virus strains to inactivation.Cultural practices associated with riskSome key cultural practices may increase risk to humans.For example, traditional poultry production and peoplesharing their living areas with poultry put humans in closeand prolonged contact with infected animals and contaminatedenvironments, and cock fighting involves direct contactwith avian blood and respiratory secretions. Oftenthese practices are linked with economics (household poultryturning household waste into inexpensive protein, duckfarmers paying rice farmers to allow ducks to feed on leftover rice); practicality (food stalls and family membershelping in LBMs; eggs and poultry available in householdor village); necessity (LBM and household slaughterrequired when no available cold chain; workers staying inpoultry house to protect poultry); cultures and beliefs(entertainment and prestige of cock fighting; believing inbad luck or karma as cause of outbreaks). It was suggestedthat extensive public awareness campaigns and communicationmay improve public knowledge but not changepractices due to the considerations described above. It wasemphasized that cultural issues are complicated and taketime to change, requiring an integrated package of interventions,education, and work within the community.Poultry systems and management practices associated withriskMuch more is known about risk of spread of the virus inanimal populations than is known about human zoonoticrisk. Because exposure of humans mainly occurs directly orindirectly through infected poultry, it is important tounderstand the risk posed by different poultry populations.As well, poultry raising and marketing systems differamong countries and therefore pose different risks. In general,risk of spread among birds is increased in countriesthat have large poultry populations, and that produce avariety of avian species in all four <strong>FAO</strong>-defined poultry sectors,8 especially when much of the production is in smallscale farms or in households. The H5N1 endemic countriestend to have large domestic waterfowl and wild bird populations,although the limited available field data on the roleof wild birds in virus spread is difficult to interpret in thecontext of reservoirs and infection dynamics. The diseaseoften has seasonal occurrence, with outbreaks generallyoccurring in the winter, due to many factors including riceharvests and holiday festivals as well as weather.Risk of incursion onto a farm is determined by theamount of outside contact and whether it involves possiblyinfected or contaminated material, the local level of infection,and biosecurity measures taken. It was noted thateven in endemic countries most poultry and locations willnot be infected or contaminated (with the exception ofsome LBMs), though each flock will have its own risk profilebased on multiple factors, especially biosecurity level.Increasing human populations, food prices, and concernsabout ethical rearing could lead to more poultry raisedoutdoors, which would increase risk for exposure and virusspread.There was some discussion on the effects of naturallyacquired influenza immunity on infection dynamics inª 2010 <strong>FAO</strong>, <strong>OIE</strong> and <strong>WHO</strong>, Influenza and Other Respiratory Viruses, 4 (Suppl. 1), 1–29 11
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