Influenza is a common infection of humans and animals.
There are three types of influenza viruses. Type A affects humans and various animals. Type B affects humans only and are the cause of seasonal epidemics. Type C affects humans and pigs, but the infections are usually mild.
There are two subtypes in type A based on two proteins on the viral surface, i.e. haemagglutinin (H) and neuraminidase (N), and these are further divided into different strains.
Type B is not classified into subtypes, but is further broken down into lineages and strains.
Type C is not classified into subtypes.
The components of the international convention for naming influenza viruses are the antigenic type, e.g. A, B, C; the host of origin, e.g. swine, equine, chicken, etc (no host of origin for human-origin viruses); geographical origin, e.g. Taiwan, etc; strain number, e.g. 5 etc; year of isolation, e.g. 1997 etc; and for type A viruses, the haemagglutinin and neuraminidase antigen description in parentheses, e.g. H1N1, H5N1, etc.
The type A virus in animals is different from that in humans. Bird flu affects domesticated and wild birds, i.e. poultry and wild birds.
It can be mild, or severe with high death rates. The former is called low pathogenic avian influenza (LPAI), and the latter, highly pathogenic avian influenza (HPAI).
The bird flu viruses have become permanent residents in the poultry population in many countries. It is rare for bird flu to affect humans. Outbreaks have led to millions of poultry infections, hundreds of human infections and many human deaths.
Human bird flu infection by HPAI A(H5N1) was first reported in Hong Kong in 1997 following an outbreak in poultry.
Since then, there have been human bird flu outbreaks in Asia, Middle East and Europe.
The LPAI A(H7N9) in humans was first reported in China in 2013. The World Health Organization announced on Feb 27 that there were reports of 460 cases and 78 deaths in humans from H7N9 from Sept 27, 2016, to Feb 27, in China, Hong Kong and Macao.
The media reported that the World Organization for Animal Health announced on March 8 that it was notified that samples taken from dead chickens in Kota Bharu tested positive for HPAI A(H5N1). The same virus sub-type was detected in Cambodia recently.
Signs and symptoms
Bird flu in humans can be mild or severe, with its incubation period, severity and outcome, dependent on the viral subtype. The features, which are no different from that of seasonal flu, include high fever, cough, red eyes, sore throat, running or stuffy nose, and difficulty breathing.
Other features include diarrhoea, vomiting, abdominal pain, bleeding from the nose and/or gums, and chest pain.
Complications may develop in some people. They include lack of oxygen, multiple organ failure, and secondary bacterial and fungal infections.
The risk factors for serious complications include pregnancy, young children, impaired immune status and senior citizens.
The death rates for A(H5N1) and A(H7N9) infections in humans is much higher than that of seasonal influenza infections.
There are also human infections by other bird flu viral subtypes.
The A(H7N7) and A(H9N2) infections are usually mild or without symptoms. However, there has been one reported death from A(H7N7) human infection in Holland.
Human infections by swine influenza viruses are usually mild, with few hospitalisations and very few reports of deaths.
There is no curative medicine for bird flu. However, some antiviral medicines, like oseltamivir, may make the illness less severe and improve survival rates.
These medicines, which may also prevent the spread of the infection to those exposed to it, are prescribed as soon as possible in suspected cases for maximal benefit.
It is also given later in the course of the infection because of the significant mortality associated with A(H5) and A(H7N9) infections.
There is no commercially available vaccine. However, some governments have a vaccine for one type of A(H5N1) infection that could be used if there is an outbreak that spreads easily from one person to another.
Spread of infection
The majority of infected humans had close contact with infected birds or with surfaces contaminated by the birds’ saliva, mucus or droppings.
Infection can also occur by breathing in droplets or dust containing the virus.
The slaughtering, defeathering and preparation of infected poultry for consumption can also increase the risk of infection.
Reports of spread of A(H5) and A(H7N9) from one person to ano-ther are rare.
There is no evidence suggesting human transmission of the bird flu viruses through properly cooked poultry or eggs. However, there have been some reports of H5N1 cases due to food prepared from raw, contaminated poultry blood.
Most human infections with swine influenza viruses were attributed to close contact with infected pigs or visits to places where pigs are exhibited. There is limited transmission of swine influenza from one person to another.
Epidemic and pandemic potential
An epidemic is an outbreak of an infection affecting many people at the same time in one or more communities.
A pandemic is an outbreak that affects a large proportion of the world. This is usually due to a novel virus and is unpredictable.
An influenza pandemic occurs when a bird or animal virus emerges with the ability to cause sustained human-to-human transmission and the human population has little or no immunity against the virus.
There have been three influenza pandemics in the last century that killed large numbers of people.
The 1918-1919 pandemic that killed more people than World War I was due to the emergence of the novel type A(H1N1) virus.
The H2N2 virus caused the Asian flu in the late 1950s, and the H3N2 Hong Kong flu occurred in the late 1960s.
The influenza virus is well known for its ability to mutate – changing in form or nature. The presence of bird flu viruses in poultry is worrisome as they commonly cause severe disease in humans and they have the potential to mutate to increase its transmission in humans.
Human-to-human transmission of bird flu is rare to date and has occurred when there has been close and prolonged contact between infected patients and caregivers. No sustained human-to-human transmission has been reported.
If the bird flu viruses adapt or acquire genes from human influenza viruses, they can cause an epidemic and/or pandemic, which would be facilitated by global travel and trade, with very little time for a public health response.
Would a bird flu pandemic occur? No one knows. However, it is a fact that the diverse bird and other animal influenza viruses have caused severe human infections and deaths. The reduction of the risk of human infection is dependent on reducing the bird flu viruses.
This means continual monitoring in animal and human populations, thorough investigation of all human infections and planning for such an emergency.
Since the A(H5) and A(H7N9) viral subtypes are persistent in some poultry populations, its control requires close co-ordination between public and animal health authorities.
More importantly, long-term governmental and societal commitment is crucial. The critical question is the country’s preparedness.
Dr Milton Lum is a past president of the Federation of Private Medical Practitioners Associations and the Malaysian Medical Association. The views expressed do not represent that of organisations that the writer is associated with. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.