You don't use a bomb to kill a fly

Dr Hsu Li Yang, Infectious disease physician.

How would you describe your job to a 10-year-old.

I help to treat people who are sick from all sorts of different germs, including ones they get from eating grubby food, travelling to exotic places, touching mucky things, or staying in the hospital for too long. It is one of the most interesting jobs in the world.

Any fear that you can somehow pass these germs, some deadly, to the outside world?

Yes, and this was the case particularly during the Sars outbreak in 2003. Even now, there is sometimes a concern that I may bring the bugs home to my children. Luckily the germs that catch the public's imagination - Sars, Ebola, Mers - don't appear in Singapore very often.

Has anyone ever given you the weird eye in social situations?

Things are better now and there isn't an awkward silence at social encounters when I tell people about my job. Taxi drivers will still talk without pause, some will ask about their infections.

So what is the difference between a viral, a bacterial, parasitic and a fungal infection?

Viruses are rogue genetic material wrapped in a protein coat and are classically not "alive".

They need to hack into the machinery of living cells to reproduce.

Bacteria are single-cell germs that live everywhere. There are far more bacterial cells in a human than actual human cells. Fungi, which cause human disease, can be uni- or multicellular.

Our immune system has evolved (and continues to evolve) to deal with all these germs. Infections can and do happen when the immune system is weakened or when the protective barriers of the body are compromised.

Because viruses, bacteria, fungi and parasites are so different, the "ammo" developed to deal with them are generally specific to members of each group.

Antibiotics prescribed for bacterial infections, like penicillin or levofloxacin, don't work at all against the viruses that cause upper-respiratory tract infections.

Antifungal medications, like voriconazole or fluconazole, have no effect against bacteria, viruses or parasites.

When is an infection serious?

If the patient is very ill, his blood pressure is low and/or heart rate is very fast, or he becomes confused or unconscious.

Location matters. If the infection is in the brain or blood, then it is very likely to be serious even if the patient appears to be well.

The type of infection is often an indicator. Malaria and tuberculosis are far more serious than the common cold or dengue, for example.

The patient's immune system plays an important role.

A seemingly innocuous infection that most people survive, like flu, can be devastating in patients with severely weakened immune systems, i.e. those with advanced cancer or who have had stem cell transplantation.

Speaking of artillery and "ammo" in the war against an infectious disease, what do you use?

There are many different antimicrobial agents and the key to being an infectious diseases specialist is to use them judiciously, as these drugs have the potential to cause side effects and other unwanted outcomes.

One would not use a bomb to kill a fly. In the same light, I would not prescribe antibiotics for a viral infection.

The antifungal agent voriconazole would not be appropriate for treating toe nail fungus but it would be useful in a leukaemia patient with a severe fungal infection of the lungs.

Tell me a surprising fact about infections.

The UK government recently assembled a panel of men and women to review the problem of antimicrobial resistance (in infections), and the projection is that by 2050, this problem will account for an extra 10 million deaths every year, and cost S$100 trillion globally.

What is the grossest thing you have seen?

Here's one - it is the head of the pig tapeworm which can grow up to 6m long in our intestines. It has a row of hooks at the rostellum (fleshy protuberance) as well as a row of suckers immediately below that which enables it to securely fasten itself to our intestines.

This article was first published on April 27, 2015.
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