Focus on Infectious Diseases

Pandemic Flu: Contingency Planning Under the Threat of a Global Outbreak

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The threat of a global influenza pandemic has been sounded by the World Health Organization, and many countries, including Canada, have been busy preparing contingency plans for an outbreak that could affect millions, cause massive morbidity and mortality, and wreak havoc on industrial society. The Public Health Agency of Canada is leading the way with a dedicated team, led by Dr. Teresa Tam and Dr. Ron St John. For CSC, one of six federal departments with a specific mandate for health care delivery, this means working with federal, provincial, and local levels of government, along with internal divisions and sectors, and with unions and senior executives.

The threat of a pandemic has been heightened by the emergence of the H5N1 z-strain virus in Asia. The virus has been found in fowl (which includes chickens, ducks and geese), and pigs, and documented human infection has occurred. More importantly, documented human-to-human transmission, albeit inefficient, indicates that the possibility of genetic mutation or viral reassortment is more than just theoretical.

This volume of CSC's Focus on Infectious Diseases presents some background on the potential of a pandemic flu with a focus on the epidemiology of H5N1 to date, along with CSC's response to the threat.

Influenza Pandemics and the Potential Emergence of Avian Flu

By Jonathan Smith
Epidemiologist, CSC-NHQ Health Services, National Infectious Diseases Program

There have been three major influenza pandemics in the last century. The Spanish Flu, in 1918, has the notoriety of being one of the worst pandemics in history, taking the lives of an estimated 20-40 million people around the world. Similar pandemics, of lesser pat hogenicity and virulence occurred in 1957 ('Asian Flu"), and again in 1968 ("Hong Kong Flu"). Each was caused by a novel type of influenza A virus. ¹

Influenza is an acute viral disease of the respiratory system, characterized by fever, headache, myalgia, sore throat and runny nose. It is spread via suspension of contaminated droplets in the air, and is particularly virulent in crowded places, where there is relatively close contact among individuals, such as buses, elevators, shopping malls and prisons. Another mode of transmission is through fomites and contaminated objects such as computer keyboards, telephones, door handles and light switches. In conditions of low humidity and cold temperature, such as the Canadian winter, influenza may persist outside the body for hours ² .

The influenza virus is encapsulated by two key glycoproteins : hemagglutinin (H), and neuraminidase (N). The virulent and pathogenic potential of the particular strain is determined by the morphological sub-types of 15 H and 9 N subtypes. The particular subtypes that have caused global pandemics to date have been H1N1 (1918), H2N2 (1957), and H3N2 (1968). The natural reservoir of human influenza are fowl and pigs (see Figure 1). Influenza types that affect wild and domestic birds infect pigs, as do influenza types that infect humans; thus human and avian influenza types literally 'mix' inside the pig and new genetic variants emerge. A pandemic strain of influenza may arise by one of two processes: 1) a genetic mutation, whereby a human influenza virus spontaneously mutates and acquires pandemic potential ('shift'); or 2) a genetic reassortment of avian and human glycoprotein inside natural reservoirs ('drift') ¹.

 

 

Avian Flu (H5N1)

An avian influenza virus, H5N1, first identified in 1997 in Hong Kong and Fujian province, China, was responsible for several documented clinical cases (n=18) and a number of deaths (n=6) among humans in ten Asian countries. Human infection and mortality from avian influenza virus types are rare events ¹ . The H5N1 virus was also increasingly known to be highly pathogenic among fowl. More human infections and associated mortality were reported in February of 2004 ³ . Up until then, all the human infections were believed to have resulted from exposure to infected fowl. A massive culling operation was undertaken and by March 2004, more than 120 million birds had been destroyed in an attempt to limit the spread of the virus ⁴ . Investigations among workers involved in an earlier cull in Vietnam found a 3% prevalence of serological antibodies to H5N1; however, there were no reports of respiratory illness among this group ⁵ .

The possibility of human-to-human transmission of the H5N1 virus was reported in September 2004 ⁶ . A young girl, likely exposed via indirect contact with infected chickens on the farm she was living at, had an onset of fever, cough, and sore throat 3 days after the last chicken had been culled. A diagnosis of pneumonitis was made 4 days later and she died the next day. Her mother, while providing palliative care, was exposed to respiratory and oral secretions; she had an onset of fever and headache 3 days post-exposure; 10 days after exposure she was diagnosed with severe dyspnea and fever and died 13 days post-exposure ⁶ . The study authors conclude that although human-to-human transmission is the most likely explanation for their findings, genetic analysis of the virus did not find any indications that the virus had acquired binding-site capabilities for human receptors that would confer efficient transmission; rather, the secondary infections were likely due to the contact with infected fluids during the provision of clinical care ⁶ .

The Global Threat

Inmate Health Survey Planned for 2005 CSC's Research Branch, with input from Health Services Branch and the Public Health Agency of Canada, is developing an inmate survey. The last inmate survey was conducted in 1995 and covered a broad range of issues. The present survey will focus only on health issues, related to HIV, hepatitis C, and sexually transmitted infections. Jointly funded by CSC and the Public Health Agency of Canada's Hepatitis C prevention, Support, and Research Section, the objectives of the survey include: estimates on the prevalence of risk behaviours ; information on inmates' knowledge of what constitutes risk behaviour and how infection can be prevented; and information on awareness and utilization of health education programs such as the Reception Awareness Program, Peer Education and Counselling Program, Circles of Knowledge Keepers, and Choosing Health in Prisons. Data gathered from the survey will help CSC to determine what prevention and health promotion efforts are working well and identify areas that need improvement. It is expected that the survey will be conducted in late Fall 2005 and will include inmate representation from across the country, across security classifications and will include both men and women offenders. In addition, there will be specific questions regarding Aboriginal health. Completion of the survey will be voluntary.

Combined with i) high pathogenicity among fowl; ii) high pathogenicity among humans infected with the H5N1 virus; and iii) evidence of human-to-human transmission, another finding has raised concerns about a pandemic threat. Since 1997, the virus has undergone several genetic mutations, and the current predominate "z-strain" of H5N1 is resistant to amantadine and rimantidine, antivirals used against influenza; the z-strain remains susceptible to oseltamavir (Tamiflu®). The H5N1 virus was isolated from diseased pigs in 2003 ⁴ , and among ducks and other fowl with no visible signs of illness. These findings suggest that culling of infected birds, especially in rural areas among asymptomatic fowl, may become increasingly difficult.

Weir et al ⁵ have pointed out that pandemics occur when three conditions are met: i ) the emergence of a new viral subtype; ii) a high proportion of susceptible people in the community; and iii) the efficient capability of person-to-person transmissibility of the virus. A strong public health response, in keeping our communities vaccinated to increase the chances of (even) weak cross-immunity, and constant vigilance in the surveillance and research aspects of influenza and influenza-like illnesses, are essential factors in determining the final outcome of a pandemic flu outbreak, should it happen.

Lessons from previous outbreaks in Canada have demonstrated the need to be prepared for such pandemic events; the Public Health Agency of Canada (see http://www.phac-aspc.gc.ca/cpip-pclcpi/index.html for more details), along with the provinces and territories and other federal departments, has already begun the task of contingency planning for such a scenario. CSC is also in the process of contingency planning in the event of a flu pandemic. See the article, Pandemic Influenza Contingency Planning: CSC Update, on page 4 of this newsletter.

 

References

1. Monto AS; The Threat of an Avian Influenza Pandemic. N Enj J Med 352:4 Jan 27 2005 pp.323-5

2. Chin J (Ed); Control of Communicable Diseases Manual 17 th Edition. American Public Health Association, 2000

3. de Jong MD et al; Fatal Avian Influenza A (H5N1) in a child presenting with diarrhea followed by coma. NEJM 2005:352(7);686-91

4. St ö hr K; Avian influenza and pandemics: Research needs and opportunities. NEJM 2005:352(4);405-7

5. Wier E et al.;Avian influenza outbreak: update. CMAJ 2004:170(5);785-6

6. Ungchusak K et al.; Probable person-to-person transmission of Avian influenza A (H5N1). NEJM 2005:352(4);333-40

 

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