Airborne – the threat of influenza

by | February 17, 2011

Protect yourself from influenza (flu) this season. And don’t confuse this as a common cold.

BY: Dr Sitoh Yih Yiow


Every so often we get assailed by news articles of fears concerning influenza epidemics. Many of us may still recall the hype and hysteria over the recent pandemic of a new strain of H1N1 that was often referred to as swine flu. In January, we were hit with the news of a 77-year-old Singaporean man succumbing to H1N1 in Singapore General Hospital and died four days after being hospitalised for lung infection. He was the first H1N1 death reported this year.

So, just what is influenza? Are the worries over epidemics and pandemics really warranted?


The virus – a biological terrorist

The flu season in Singapore follows the winter seasons in both the northern and southern hemispheres, i.e. one around June and another around December. Influenza is caused by viral particles belonging to the “family” known as Orthomyxoviridae. Within this “family”, there are three sub-types that commonly affect human beings, namely Influenza A, Influenza B and Influenza C. The three sub-types differ in terms of the different proteins that are found within the viral particles: Haemagglutinin (the “H” of H1N1) and Neuroaminidase (the “N” of H1N1). Haemagglutinin allows the viral particle to dock with a human cell so as to facilitate insertion of the viral ribonucleic acid (RNA) strands, and the Neuroaminidase is required for replication of viral RNA before they burst out of the cell and go on to infect neighbouring cells.

Viruses differ from bacteria because, unlike bacteria, viral particles cannot reproduce themselves in a free environment. They need to invade and use a host to replicate, and often end up destroying the host cells upon replication. Viruses also demonstrate remarkable abilities to easily change their genetic makeup because of the way they use the infrastructure of host cells to replicate, and are thus able to overcome singular attempts at vaccination, hence the need for regular vaccinations to update our immune (defense) systems. For example, Influenza A (considered the most common of the three sub-types) has eight separate strands of RNA, with segments that can interchange when they invade a host cell. 

Further to this, some influenza viruses can infect both humans and animals (e.g. pigs or birds) and this multiplies the potential to undergo significant genetic shifts that can end up producing totally new strains that can potentially overwhelm any existent immunity in human beings. This is why there have been new strains causing epidemics and pandemics every 10 to 15 years, and also why there is a constant surveillance for new strains of Avian Influenza (bird flu) that can be far deadlier than Influenza A, B or C.

Influenza viruses are largely transmitted via airborne transmission and can easily be passed through aerosol droplets when an infected person coughs or sneezes. Transmission can also occur when a person touches surfaces that carry viral particles and subsequently transport them to the eyes, nose or mouth. It is thus imperative that we maintain high standards of personal hygiene and self-care to limit the risk of disease transmission in the community.


Influenza – the syndrome

Influenza infection often causes a sudden onset of a host of symptoms that can include sore throat, nasal congestion, muscle aches, headaches and fever. The infected person can feel terribly unwell and suffer loss of appetite. The fever can often range between 38ºC and 41ºC. A person usually starts to develop respiratory symptoms (cough and occasionally breathlessness) when the forementioned systemic symptoms start to subside. The cough can be persistent and last for as long as two to four weeks.

Patients infected with influenza can transmit the virus one to two days before the onset of symptoms, and remain infectious up to seven days after the onset.

It has often been asked if influenza is the same as the common cold. It is not. Common colds are caused by a different class of virus and usually cause self-limiting symptoms that are not as severe. High fevers are also uncommon in patients afflicted with the common cold. Most importantly, common colds do not usually cause the significant complications that can be associated with influenza infections.


Influenza – the killer

Influenza can be deadly because of the heightened risk of developing pneumonia and subsequent respiratory failure in susceptible individuals. By and large, older persons aged 65 and above and persons with significant chronic heart or lung ailments are most at risk. When susceptible individuals develop complications, they often demonstrate a typical pattern of a transient improvement after the initial spell of symptoms that is followed by recurrence of fever, worsening cough and breathlessness. Pneumonia occurring secondary to influenza infections can cause significant damage to the lungs of the afflicted person and result in respiratory failure, as in the case of the unfortunate Singaporean man who succumbed in late January.

Older persons with heart and lung disease may also go on to develop heart failure because of the strain imposed by the infection, and develop significant morbidity.


Our arsenal of defense

So how do we go about preventing and treating influenza?

• Vaccination – It is recommended that individuals at risk of developing complications from influenza receive annual vaccinations containing inactivated forms of the prevalent/circulating viruses that are determined by regular surveillance conducted by the World Health Organization.

Such vaccinations are easily available at most primary health clinics and polyclinics, and should cost between S$25 and S$30. Some individuals may experience a low-grade temperature or have muscle aches for two to three days after the vaccination – this is common and should not be a cause for alarm. Individuals who are allergic to egg protein must inform their doctors, as they would not be suitable candidates for the vaccination.

• Anti-viral agents – Anti-viral drugs such as Ostelmivir and Zanamivir (which are not available over-the-counter) have been used with some success in limiting the duration of symptoms in patients afflicted with influenza. These drugs act by interfering with the activity of the Neuraminidase proteins, thus disrupting the ability of the viral particles to replicate. Their use may however be associated with side effects such as confusion, dizziness, nausea and vomiting. There is also concern about the risk of the virus developing resistance.

By and large, only individuals who are at risk of developing complications, i.e. individuals who are frail or who suffer from multiple co-existent chronic diseases need to consider the use of such agents. Otherwise healthy persons will probably do well with just paracetamol and lots of rest. Antibiotics are only needed if secondary bacterial infections occur, e.g. if symptoms do not resolve after three to four days.



Different influenzas

A bird’s eye view of the different influenza viruses:

• Influenza A – Occasionally, viruses are transmitted to other species and may then cause devastating outbreaks in domestic poultry or give rise to human influenza pandemics. This includes H1N1.

• Influenza B – This virus exclusively infects humans and it mutates at a rate two to three times slower than type A, and consequently is less genetically diverse. As a result, it is less likely that pandemics of influenza B will occur.

• Influenza C – This virus infects humans, dogs and pigs, sometimes causing both severe illness and local epidemics. It is less common than the other influenza types and usually causes mild disease in children.



Dr Sitoh Yih Yiow specialises in geriatric medicine at Age-Link Specialist Clinic for Older Persons.

(PHOTO CREDIT: Sneeze woman, evah, stock.xchng)



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