Avian Influenza A (H5N1) “Bird Flu”

Etiology Viral disease Avian Influenza (HPAI) H5 and H7 – highly pathogenic Human case fatality estimated to be as high has 50%, but not definitely known The type A flu viruses are responsible for most human and bird disease. The strains of flu are named for the combination of H and N spikes. Certainly strains of avian flu that include H5 or H7 are highly pathogenic for both birds and people. The human case fatality rate is perhaps as high as 50%, but that is not definitely known.

Cycle of Avian Influenza viruses in animals & humans Shore birds Pandemic disease cycle Natural avian influenza cycle Mammals (primarily swine) Waterfowl Domestic birds Humans Direct bird to human transmission is also common This slide describes the transmission of avian flu viruses. They are normally passed between various species of shore birds, waterfowl like ducks and domestic birds, including chickens. However the viruses can pass from chickens to pigs to humans. The virus can also pass directly from birds, especially chickens to humans. That is what has been happening in SE Asia.

WHO Pandemic Alert Phase Plan

Map of current outbreak        FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS

Bird flu by the numbers *Source: World Health Organization Human cases since date of onset (12/26/03) 125 Human deaths 64 Suspected human-to-human transmissions 2 Number of countries affected (since Dec 04) 12 Est. international airline passengers yearly 1.6B Types of potential antivirals for bird flu Known bird flu types 15 Bird flu that can be fatal to humans 1 Best case global deaths in pandemic 2-7M Worst case potential global deaths 40-100M *Source: World Health Organization

First case of bird flu in the U.S.

Human H5N1 Incubation: 3-5 days Few URI symptoms Severe viral pneumonia picture Fever Lymphopenia Pulmonary infiltrates Hypoxia Diarrhea (50%) Time to death: 10 days (mean)

Transmission Respiratory droplets vs. aerosol Hand to hand Fomites Viral shedding starts 24 hours before clinical illness and lasts 5-7 days

Prerequisites for a pandemic Novel virus with no immunity Able to cause significant disease in humans Efficient human to human transmission Re-assort during co-infection with H3N2 Evolve in a human by spontaneous mutation

Common pandemic features Herald wave (warning): up-tick in mortality at end of prior year Increased mortality Mortality shift to younger ages Multiple waves of increased mortality for several years

Potential for influenza pandemics All influenza viruses can mutate Avian flu can cause illness in humans Little to no herd immunity to avian strains among humans If avian viruses acquire human genes Facilitate efficient person-to-person transmission H5N1 of particular concern No one can predict when a pandemic might occur Avian flu is concern to public health and medical officials around the globe. Influenza viruses are always mutating, changing form and new strains of the flu develop each year. Influenza strains can also jump from poultry and bird species to humans and cause illness. When that happens a pandemic can result because humans have not been exposed to the viral strain before. That means the avian flu strain can be extremely deadly and cause many deaths. The most worrisome scenario happens when the avian flu strain also acquires some human genes that make it easier to spread from person to person. WHO and CDC are currently monitoring the H5N1 strain to see if human-to-human transmission occurs; so far it has not been detected.

How is bird flu in humans treated? The H5N1 virus currently infecting birds in Asia that has caused human illness and death is resistant to amantadine and rimantadine Neurominidase inhibitors oseltamavir (Tamiflu) zanamavir (Relenza) inhaled, not stocked in house Resistance can develop Additional studies are needed to prove the effectiveness of these medicines.

Defenses Vaccination Prophylaxis Rapid diagnosis Treatment Infection control Respiratory etiquette Hand washing Disinfection Droplet precautions in hospitals

CDC recommendations Enhanced surveillance in the U.S. of H5N1. Travelers to countries with known outbreaks of influenza A (H5N1) should avoid: Poultry farms Contact with animals in live food markets Surfaces that appear to be contaminated with feces from poultry or other animals. CDC does not recommend any travel restrictions to affected countries at this time. For more information, visit Travelers' Health