Wednesday, 16 January 2008

MMIC - PBL2. Avian Flu

Avian Influenza (Bird Flu):

Pathogen involved: Avian influenza viruses (RNA viruses)



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· Typically carried by wild migratory birds in their intestines, which are immune to them. However, it is highly contagious amongst birds, and can infect domesticated birds, that usually fall severely ill.
· Several strains exist:
Denoted by “H" and “N”. “H” stands for hemagglutinin and “N” stands for neuraminidase, two proteins on the surface of the virus that allow it to enter and exit host cells.
o Sixteen different hemagglutinins and nine different neuraminidases have been identified to date.
o Typically, most avian flu is restricted to bird to bird transmission. The most deadly being H5N1 strain as it can spread from bird to human.

Indonesia has had outbreaks of H5N1 viruses, mainly from the poultry breeding farms. Typically, H5N1 transmission is from bird to humans. However in 2006, there was a case of human to human transmission of H5N1 versus between a group of small families, but the spread appears to have died off. H5N1 can last indefinitely at a temperature dozens of degrees below freezing.

Pathogenesis:
Spread to humans via contact, potentially airborne (incubation period is longer, less adapted to droplet transmission):
· Directly from birds or from avian virus-contaminated environments to people (consumption of poultry products, direct contact with live poultry – bodily fluids such as blood, salvia etc and contaminated food sources).
· Through an intermediate host, such as a pig.
Typically develops 1 to 5 days following exposure.

Signs and symptoms:

Common:
- Cough
- High fever (typically > 38°C)
- Headaches
- myalgia (muscle ache/pain)
- malaise (general discomfort)
- Sore throat
- Shortness of breath
- Diarrhoea
- A relatively mild eye infection (conjunctivitis), sometimes the only indication of the disease.

Severe signs and symptoms:
- Viral pneumonia
- Acute respiratory distress (the most common cause of bird flu-related deaths)
- Seizures

Necessary precautions:
· Avoid contact with live birds, and all forms of poultry:
- Chickens, ducks, turkeys and geese and their feces, feathers and pens if at all possible.
· Avoid poultry products in Indonesia, as cases of H5N1 have been reported there.
· All foods from poultry, including eggs should be cooked thoroughly. Egg yolks should not be runny or liquid. Influenza viruses are destroyed by heat, hence cooking temperature for poultry meat should be 74oC (165 F).
· Avoid cross contamination of other foods by use of separate kitchen utensils and surfaces exposed to raw poultry.
· Wash hands with soap and water after any poultry contact.
· Avoid live food markets.

Treatment:
A) Antivirals:
Suppress virus, keep it from replicating and infecting within the host. Must be taken soon (often within 48 hours following infection).
· Neuraminidase inhibitor:
Mode of action consists of blocking the function of the viral neuraminidase protein, preventing the virus from reproducing.
1. Relenza
2. Tamiflu

B) Vaccination:
Vaccines expose an individual to a weakened/dead virus to stimulate antibody production against it, so that immune system can fight off infections should it arise.
· There are at least 15 different strains of avian flu and they are constantly mutating, hence vaccination may not prove to be effective for long.
1. Live vaccines (attenuated, weakened):
- Requires less antigen (active ingredient) than killed vaccine.
- Live vaccine may contain too few copies of the weakened virus to trigger an immediate immune response.
- However, once inside the host, the virus can replicate to render it detectable by the immune system and trigger an immune response.
- Does not require injection – oral consumption will do.
2. Killed virus (inactivated):
- Must be injected – only route to administer them that will bring them into contact with the immune system.
Requires larger dosage than live vaccines due to its lack of ability to multiply within host.
3. Recombinant vaccine:
- Genetically engineered vector (usually a low virulence virus) to express H5N1 protein antigen on surface, to stimulate immune response (production of antibodies).

References:
sciencedaily.com > releases > 2007 > 08/070828154944.htm
cidrap.umn.edu > cidrap > content > influenza > avianflu > news > dec3005halvorson.html
evolution > berkeley.edu > evolibrary > news > 51115_birdflu
http://www.cbc.ca/> news > background > avianflu > protection.html

Cheers,

Debra, TG02

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