1 Avian Flu update Dr Henry Cheung 11 July 2008

2 The influenza virus Orthomyxoviridae familyRNA virus with 8 chromosomes in a fatty membrane Types A, B and C Type A is further sub-typed based on 2 surface glycoproteins

3 2 surface glycoproteinsHemagglutinin (HA) Facilitate entry into host cells Binding on epithelial cell receptors and promotes membrane fusion Neuroaminidase (NA) Facilitate release of virions from infected cells

4 In human, only three known subtypes are currently circulating:In aquatic birds 16 subtypes of HA (H1 to H16) 9 subtypes of NA (N1 to N9) In human, only three known subtypes are currently circulating: H1N1 H1N2 H3N2

5 How to name an influenza virus?According to their type, the place of first isolation, the laboratory isolate number, the year of isolation and virus subtype E.g. A/Sydney/05/97 (H3N2) Influenza virus of type A, first isolated in Sydney, the fifth influenza strain isolated in that lab in 1997 and carrying H3 and N2 antigens

6 ‘Changing is the constant’Antigenic drift Immune selection of variants derived from mutations of the virus RNA, leading to a directional antigenic change over time Causing repeated epidemics Antigenic shift Genetic reassortment of segmented genome occurs when two influenza viruses infect the same cell  major antigenic change Lack of pre-existing immunity in the human population  Causing pandemics

7 Influenza Pandemics in the 20th CenturyYear Name Type Death Spanish Flu A (H1N1) 40 million Asian Flu A (H2N2) 4 million Hong Kong Flu A (H3N2) 1 million

8 Antigenic shift and Avian influenza

9 Pathogenicity of Influenza virusDepends on cleavage of the virus hemagglutinin (HA) precursor by cellular protease  virus becomes functional and infectious

10 Low pathogenic avian influenza (LPAI)have only 2 basic amino-acids at HA cleavage site only cleaved by trypsin-like enzymes which are restricted to respiratory and GI tract

11 Highly pathogenic avian influenza (HPAI)have multiple basic amino-acids (glycine & lysine) at HA cleavage site can be cleaved by most host proteases allowing systemic replication and tissue damage and resulting in high mortality First detected in diseased geese in Guangdong Province, People’s Republic of China, and designated A/Goose/ Guangdong/1/96.

12 The H5N1 bird flu incident in HK 1997The first known instance of a purely avian virus causing severe human disease and death 8 cases 6 deaths Source: appeared to be live-poultry markets The slaughter of all (1.5 million) poultry in the farms and markets of Hong Kong aborted this outbreak

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15 Demographic CharacteristicsMedian age ~18 y. o. overall case fatality 61% highest among persons y.o. lowest among persons > 50 y.o. Most patients were previously healthy 6 affected pregnant women: 4 died, 1 spontaneous abortion in the 2 survivors To date, no cases of influenza A (H5N1) illness have been identified among short-term travelers visiting countries affected by outbreaks among poultry or wild birds

16 Transmission route Avian-to-human Human-to-human Environment-to-human

17 Avian-to-human TransmissionRisk factors: Handling of sick or dead poultry during the week before the onset of illness (most commonly recognized) playing with diseased or dead poultry handling fighting cocks or ducks that appear to be well consuming raw or undercooked poultry or poultry products defeathering of dead wild swans

18 Avian-to-human TransmissionLikely inefficient in view of the relatively few cases of reported human infections despite large-scale poultry outbreaks

19 Barriers of Interspecies TransmissionAvian influenza viruses do not efficiently infect humans Conversely, human viruses do not efficiently replicate in bird Believed to be determined by multiple viral genetic determinants including the viral HA and NA genes, other internal genes such as the nucleoprotein and the PB2 genes.

20 ?Human-to-human TransmissionClusters of illness accounted for ~¼ of cases: usually 2-3 persons, largest 8 > 90% of case clusters have occurred among blood-related family members ? genetic susceptibility ? acquired infection from common-source exposures to poultry ? acquired infection from human-to-human transmission during very close, unprotected contact with a severely ill patient Respiratory secretions and all bodily fluids, including feces, should be considered potentially infectious.

21 Environment-to-human transmissionThe source of exposure is unclear in ¼ of patients Plausible transmission routes include contact with virus-contaminated fomites or with fertilizer containing poultry feces, followed by self-inoculation of the respiratory tract or inhalation of aerosolized infectious excreta

22 ? Acquisition in the GIT Suggested by Potential risky behaviour:patients presenting with diarrhoea as the only initial symptom consumption of raw duck blood as the sole exposure to poultry Presence of virus or viral RNA in faecal material or intestines had been report Potential risky behaviour: Ingestion of virus-contaminated products swimming or bathing in virus-contaminated water Eating properly cooked foods are not considered to be risk factors

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24 Cause of death Severe pneumonia  ARDS

25 CXR extensive, often bilateral infiltration, lobar collapse, focal consolidation, and air bronchograms

26 Poor prognostic lab findingsLymphopenia increased LDH

27 Investigations of Avian InfluenzaRapid antigen detection Conventional or real-time reverse transcriptase polymerase chain reaction (RT-PCR) Virus culture Serological identification of antibodies against avian influenza A(H5N1) viruses

28 Rapid antigen detectionBy immunofluorescence (IF) or enzyme immunoassay (EIA) methods directed at conserved viral antigens (e.g. virus nucleoprotein, matrix protein) detect all subtypes of influenza A viruses will not differentiate human virus subtypes from avian influenza require 1000 times higher levels of virus than viral cultures to be positive

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30 RT-PCR Short turn around time (4 to 6 hrs)detects viral RNA in respiratory specimens, rectal swabs, CSF, and blood Can be performed under bio-safety level 2 conditions Frequent updating of primers and probes are needed due to the genetic variability of H5N1 viruses

31 Diagnostic yields (depend on viral load): tracheal aspirates > throat swabs > nasal swabsPrevious antiviral treatment may reduce the diagnostic yield

32 Viral culture Turn around time: 2–10 days Advantage:viruses are available for further characterization also detect other clinically important respiratory viruses Usually performed only in specially qualified and equipped laboratories because of the biosafety concern

33 In HK Typing and subtyping of all influenza isolates are performed at the Public Health Laboratory Services Branch (PHLSB) of DH Antigenically atypical isolates would be forwarded to the WHO Collaborating Centres for further analysis

34 Serological identification of antibodies against avian H5N1 virusesImportant for diagnostic confirmation and epidemiological studies Positive criteria: >=4 times elevations in paired sera (acute and convalescent) single titers of >=1:80 in convalescent-phase samples Disadvantage: not useful for rapid diagnosis require biosafety level 3 facilities standard panels of reagents for H5N1 and other novel strains are not widely available results vary widely among the laboratories

35 Anti-viral tx: Neuraminidase inhibitorsOseltamivir (Tamiflu) Treatment of choice Early treatment is recommended

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37 Oseltamivir Standard dose in adults: 75 mg BD for 5 daysDose reduction in renal impairment Resistant H5N1 had been isolated in Vienam and Egypt Consider higher dose and increased duration (150 mg BD for 10 days) if progressive disease despite early administration of standard dose, especially if there is pneumonic disease at presentation

38 Anti-viral tx: Neuraminidase inhibitorsZanamivir inhaled has not been studied in human influenza A (H5N1) disease

39 Anti-viral tx: M2 protein inhibitorsE.g. Amantadine and rimantadine High resistant rate: Clade 1 viruses and most clade 2 viruses from Indonesia are fully resistant Clade 2 viruses from the lineages in other parts of Eurasia and Africa are usually susceptible Insufficient evidence to evaluate its benefit WHO recommendation: might administer amantadine as a first-line treatment if NI not available and especially if the virus is known or likely to be susceptible

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41 Corticosteroids Not effective Increased mortality in northern Vietnam59% among 29 recipients vs 24% among 38 persons who did not receive corticosteroids (P = 0.004) Prolonged or high-dose corticosteroid therapy can result in serious adverse events, including opportunistic infections such as CNS toxoplasmosis (Soeroso S: unpublished data)

42 Prevention Virus readily inactivated by a variety of chemical agents and physical conditions, including soaps, detergents, alcohols, and chlorination WHO guidelines for various risk groups poultry workers Travelers health care workers

43 Chemoprophylaxis (WHO statement)No clinical trial has evaluated oseltamivir / Zanamivir for chemoprophylaxis of H5N1 infection. Oseltamivir / Zanamivir might effectively provide an important reduction in H5N1 virus transmission. This view is based on extrapolation from studies performed in populations with seasonal influenza. Decisions to initiate should generally be guided by the risk stratification Continuing for 7–10 days after the last known exposure WHO has a stockpile of oseltamivir for targeted antiviral chemoprophylaxis in the event of an outbreak, in order to extinguish or delay pandemic spread of the virus.

44 Chemoprophylaxis High risk exposure groups are currently defined as:Household or close family contacts of a strongly suspected or confirmed H5N1 patient, because of potential exposure to a common environmental or poultry source as well as exposure to the index case Moderate risk exposure groups are currently defined as: Personnel involved in handling sick animals or decontaminating affected environments (including animal disposal) if personal protective equipment may not have been used properly. Individuals with unprotected and very close direct exposure to sick or dead animals infected with the H5N1 virus or to particular birds that have been directly implicated in human cases. Health care personnel in close contact with strongly suspected or confirmed H5N1 patients, for example during intubation or performing tracheal suctioning, or delivering nebulised drugs, or handling inadequately screened/sealed body fluid without any or with insufficient personal protective equipment. This group also includes laboratory personnel who might have an unprotected exposure to virus containing samples Low risk exposure groups are currently defined as: Health care workers not in close contact (distance greater than 1 metre) with a strongly suspected or confirmed H5N1 patient and having no direct contact with infectious material from that patient.

45 Vaccination No effective vaccine a/v More research is needed

46 Take home message For H5N1 infection Prevention is better than curePresentation is non-specific High clinical suspicion if presence of TOCC hx Early isolation Rapid diagnosis by RT-PCR Early initiation of Oseltamivir

47 References Abdel-Ghafar et al. Update on Avian Influenza A (H5N1) Virus Infection in Humans. N Engl J Med 2008;358: Gambotto et al. Human infection with highly pathogenic H5N1 influenza virus. Lancet 2007; 371: 1464–75 Peiris et al. Avian Influenza Virus (H5N1): a Threat to Human Health. Clinical Microbiology Reviews, Apr. 2007, p. 243–267