|
Avian Influenza Fact Sheet
Page last updated: 4 December 2007
1. Avian Influenza Overview
2. Epidemiology
3. Transmission
4. Vulnerable Populations
5. Incubation and Infectious Periods
6. Symptoms in Birds
7. Symptoms in Humans
8. Diagnosis
9. Medical Prevention & Treatment
10. Vaccines
11. Quarantine and Isolation
12. Concerns
13. Personal Public Health Measures
14. Links to Additional Information
1. Avian Influenza (H5N1) Overview
The current outbreaks of avian influenza began in 2003 in South East Asia and have spread across the region. Millions of chickens have been infected and died; however, transmission to humans and human mortality remain relatively low. To date, human deaths from this strain of avian influenza have been reported and confirmed in five Asia Pacific countries: Vietnam, Thailand, Cambodia, Indonesia and China.
Three influenza virus types exist: A, B, and C. Avian Influenza (‘bird flu’) is an influenza A virus and is similar in some ways to human Influenza A virus. However, genetic differences have previously kept avian influenza from infecting humans. Avian influenza is a disease that affects poultry and can be highly pathogenic (HP). There are 16 known hemagglutinin subtypes and 9 known neuraminidase subtypes and all have been identified in birds. Wild aquatic waterfowl are the natural reservoir for all known influenza A viruses. Influenza A viruses are further subtyped on the basis of the surface glycoproteins hemagglutinin and neuraminidase. Viruses are further classified into strains. Avian influenza A viruses are classified as low pathogenic or highly pathogenic on the basis of molecular and pathogenicity criteria.
H5N1 is the current avian strain of global concern, which has killed millions of poultry to date, has high pathogenicity, and is widely referred to generically as “Avian Flu” or “Bird Flu”. Some strains, like H7N7, can also be highly pathogenic, yet others like H9N2 have low pathogenicity.
A human pandemic is possible if a novel human influenza A virus subtype causes disease and is transmitted from person-to-person in a sustained manner. Such a novel human influenza A virus must have a new hemagglutin or a new hemagglutinin and a new neuraminidase. Current human influenza A virus subtypes that are circulating among people worldwide include H1N1, H1N2, and H3N2. (Refer to Figure 1) This is possible with antigenic shift or drift. For a definition and detailed explanation, refer to “A Constantly Mutating Virus: Two Consequences” at http://www.who.int/mediacentre/factsheets/avian_influenza/en/. These newly constructed strains form ‘novel’ viruses and pose potential problems since the general population has no immunity. However, this novel virus must spread efficiently from human to human before a pandemic can occur.
2. Epidemiology
For an updated number of confirmed cases, please refer here.
Currently, the Case Fatality Proportion (CFP) is just above 50%. This means that slightly more than ½ of the people known to have been infected with Avian Flu have died as a result of the disease. However, this may not be completely accurate as underreporting of milder cases may not be included. The CFR may change as more laboratory-confirmed cases occur and more data become available. A CFP of 50% is a significant finding as history of previous influenza pandemics has demonstrated lower CFPs. Surveillance for human cases of H5N1 has focused upon hospitalized cases of severe respiratory disease – pneumonia.
3. Transmission
Human influenza is transmitted by coughing or sneezing with subsequent inhalation of infectious droplets and onto the upper respiratory tract. Conjunctival mucosa is suspected to cause transmission but no good data exist to date to support it. The relative efficiencies of the different routes of transmission have not been defined. Infected birds shed the virus in their saliva, nasal secretions, and feces. Thus human acquisition has resulted from direct contact with infected poultry or contaminated surfaces. In the rare cases of non-sustained potential human-to-human transmission, close proximity and direct contact were observed. Human acquisition does not occur from ingestion of well-cooked meat. There have been no cases to date demonstrating infection through consumption of cooked poultry. Influenza A viruses are destroyed by adequate heat.
4. Vulnerable Populations
As with most influenza viruses, vulnerable populations include the very young, elderly, and immuno-compromised. However, due to the nature of transmission, poultry farmers, market workers, health professionals, and workers in other related fields with frequent or potential contact with infected birds are also at a greater risk for acquisition.
5. Incubation and Infectious Periods
The infectious period for H5N1 viruses is not known. H5N1 viral RNA has been detected at day 15 and believed that H5N1 virus is being shed much longer than human influenza A viruses.
6. Symptoms in Birds
Infection in poultry is marked by ruffled feathers, loss of appetite, cessation of egg production, and watery diarrhea. Swollen combs, wattles, and ocular edema may also occur in mature chickens. Eggs laid late along disease progression may be laid without shells. Death can occur within 24-48 hours of onset of symptoms. It may be delayed longer depending on the virus strain. Poultry mortality is near 100 percent within 2 weeks of onset of symptoms.
7. Symptoms in Humans
Evidence-based reports published in the New England Journal of Medicine, by the US Centers for Disease Control and Prevention (CDC), and by the World Health Organization (WHO) indicate symptoms may be flu-like and most likely include fever, headache, cough, and shortness of breath. Additionally, diarrhea, sore throat, abdominal pain, and muscle pains have been noted in multiple cases. Nearly all cases have clinical findings of pneumonia and pulmonary infiltrates. As progression of disease ensues, more life-threatening complications occur including respiratory distress and ultimately respiratory failure.
8. Diagnosis
Diagnosis of H5N1 virus infection is by testing of acute respiratory specimens (nasal, throat swabs, tracheal aspirates) by RT-PCR using specific H5N1 primers. Generally, testing is done for influenza A, and the subtypes H1, H3, and H5. Viral culture of specimens from a patient with suspected H5N1 should only be done in enhanced biosafety level 3 conditions. More rapid forms of lab tests are being considered and researched. Requests for further CDC testing should come through state and local health departments. Contact should be made with the CDC Director's Emergency Operations Center at 770-488-7100 before sending specimens for testing. Currently, the World Health Organization (WHO) is confirming suspected cases in the Asia-Pacific region.
9. Medical Prevention & Treatment
Treatment is supportive. There is no definitive cure for avian flu; however, antivirals are currently being suggested as measures to prevent infection or temper the severity of symptoms. Additional studies are needed to prove the effectiveness of these medicines. The US Food and Drug Administration (FDA) has approved four antivirals for treatment of influenza: amantadine, rimantadine, oseltamivir (Tamiflu(TM)), and zanamivir (Relenza(TM)). However, evidence has already shown a certain amount of drug resistance to amantadine and rimantadine and two reported cases with oseltamivir to date. It is difficult to predict effectiveness of Tamiflu or Relenza until tested in larger populations on the human-to-human strain of the virus, if it were to develop. At the moment, they still serve as the best choices for treatment. Tamiflu dosing: treatment (10 days, 2 pills/day); prophylaxis or protection (1 pill/day, for duration of risk). Optimal antiviral treatment dose and duration of treatment are not known.
10.Vaccines
Currently, there is no available vaccine to protect humans against the H5N1 virus. Vaccine development is ongoing; however, it may take approximately 6 months after the onset of a pandemic strain to develop an effective vaccine. This illustrates the need for good public health measures in the absence of a proven vaccine. For more information about the H5N1 vaccine development process, visit the National Institutes of Health website.
11. Quarantine and Isolation
Quarantine is restriction of activities of exposed persons who are not ill in an attempt to prevent transmission. Isolation means separation of sick or contaminated persons to prevent transmission. It is important to note that quarantine and isolation are public health decisions, not law enforcement decisions.
12. Concerns
The concern currently is "Can H5N1 evolve and potentially become more infectious to humans and/or can the virus have the mutative capacity to evolve and jump from animal-human to sustained human-human transmission?" This is at the core of the potential pandemic concern combined with ducks and other wild waterfowls being asymptomatic reservoirs (carriers) and spreading virus on migratory routes, infecting poultry flocks worldwide.
13. Current Personal Public Health Measures to Minimize Likelihood of Infection
1. Avoid direct contact with poultry.
2. Wash hands frequently with soap and water or hand sanitizer.
3. Cover your mouth if you cough or sneeze, then wash hands with soap and water or hand sanitizer.
4. Avoid high-risk environments. CDC currently advises that travelers to countries with known outbreaks of influenza A (H5N1) avoid poultry farms, contact with animals in live food markets, and any surfaces that appear to be contaminated with animal feces.
5. Receive your annual influenza vaccine, especially if you are in a higher risk group to avoid further compromise given pre-existing vulnerability of this group; But human influenza vaccine confers no protection against H5N1.
6. If you do become sick with a febrile illness (illness with fever), record your travel and activity history for at least one week prior and avoid close or direct contact with others. You may choose to contact your medical provider for further guidance.
7. If a pandemic develops, assume limited access and availability of both vaccine and antivirals during early stages and continue sound public health measures.
8. Facemasks (surgical masks, N-95 masks, etc) can be effective. Follow CDC or WHO guidance on the wearing of masks or other personal protective devices during a potential human-to-human outbreak.
14. Links to Additional Information
Centers for Disease Control and Prevention:
http://www.cdc.gov/flu/avian/
World Health Organization:
http://www.who.int/csr/disease/avian_influenza/en/
WHO FAQs:
http://www.who.int/csr/disease/avian_influenza/
avian_faqs/en/index.html
Official US Government Site:
http://www.pandemicflu.gov/
World Organization for Animal Health:
http://www.oie.int/eng/info/en_urgences.htm
NOTE: This report has been compiled from publicly available information. Although information has been gathered from reliable sources, the currency and completeness of the information reported herein is subject to change and cannot be guaranteed. Inquiries, updates, and comments are welcome and should be directed the Medical / Public Health team at coemed@coe-dmha.org.
 Back
to top
|
