Pandemic Potential and Singapore

Clear and present danger
Straits Times 18 Jun 08;

There has been a rising number of deadly infectious diseases - Chikungunya, dengue, Sars, bird flu, HFMD - in recent times. Scientists fear an impending pandemic
Some are exotic and many are deadly - that sums up infectious diseases making the headlines today, as cases soar worldwide.

Severe acute respiratory syndrome (Sars) and chikungunya fever were unknown to most Singaporeans until recently.

Singapore is fortunate to have been spared the ravages of avian influenza - or bird flu - but elsewhere, it has killed humans and led to mass livestock cullings.

But more than 14,500 people in Singapore have caught hand, foot and mouth disease (HFMD) since January this year.

And just last week, blood samples were taken from 311 people living in Teachers' Estate after an 86-year-old retiree and her maid were diagnosed the week before as victims of the mosquito-borne virus, chikungunya.

Luckily, the samples tested negative for the disease. The estate is still being monitored by the National Environment Agency.

However, it was reported three days later that an expatriate housewife living in Farrer Road has become the latest victim of chikungunya fever.

Meanwhile, with bird flu outbreaks still occurring elsewhere, experts fear an impending pandemic. The World Health Organisation says a flu pandemic now may cause two million to eight million deaths worldwide. Developing countries will be the hardest hit.

Going back to the last century, the then biggest pandemic - commonly referred to as the Spanish flu - occurred in 1918 and 1919: it caused an estimated 40 million to 50 million deaths worldwide.

Dr Leong Hoe Nam, consultant infectious disease physician at Singapore General Hospital, has this sobering twist to a common saying: 'There are now four things certain in life - birth, death, taxes and another epidemic.'

How do infectious diseases that strike humans pop up? Most major ones have animal origins, researchers Nathan D. Wolfe, Claire Panosian Dunavan and Jared Diamond say in a review published in May last year in international science weekly Nature.

The study by the three researchers - from the epidemiology department in the School of Public Health, University of California, Los Angeles - also highlighted the role of agriculture in the evolution of animal pathogens into human pathogens. Farming, they noted, enables a large human and animal population to be in close proximity and constant contact.

A pathogen is an agent that causes infection or disease and is usually a micro-organism or a virus.

Cross-species infection may arise again when humans colonise new environments previously untouched and come into contact with wild animals or untested surroundings. A large population concentrated in a small space, like that found in most urban areas today, then exacerbates the problem of human to human transmission.

The Nipah virus is cited as one such example in a 2004 paper by researchers Robin A Weiss and Anthony J McMichael in science journal Nature Medicine.

The virus jumped from fruit bats to pigs before infecting pig farmers and abbatoir workers when pig farms were set up near virgin tropical forests in northern Malaysia in 1998.

SGH's Dr Leong says that four factors are required to create an infectious disease epidemic - a suitable virus, a suitable host, the virus' ability to mutate in such a way as to 'jump' species, and suitable hosts around the index case.

He said: 'You need the right time and the right person to spark an epidemic.'

Most viruses are ribonucleic acid (RNA) viruses, which occur singly and do not have double strands of genetic material, unlike DNA.

This trait allows them to mutate very quickly and easily as there is no parallel strand to keep evolution in check.

Dr Chong Chia Yin, head and senior consultant at the department of paediatric medicine at KK Women's and Children's Hospital, said: 'The flu virus has a huge animal reservoir including chickens, pigs, ducks and migratory wild birds. This allows the virus to circulate and then mutate into a more virulent form.'

Globalisation, industrialisation and mass air travel have also helped spread viral diseases beyond the geographic borders of their origin.

Dr Leong said: 'The problem with these outbreaks is globalisation and the mass movement of people. You can be in the Sahara desert one day and back at work in Singapore the next.'

But it's not all doom and gloom as cross-species infection usually requires a protracted and extreme series of mutations before occurring.

Finally, preparedness is critical.

Singapore's Ministry of Health has stepped up disease surveillance programmes in hospitals, stockpiled essential supplies and drugs and drawn up a national flu pandemic preparedness plan.

Doctors and other experts are urging the public to also take individual responsibility for their health and disease prevention. Those who are ill should stay away from work, school or public areas like shopping centres.

Dr Chan Poh Chong, consultant paediatrician and head of ambulatory and adolescent paediatrics in the University Children's Medical Institute at National University Hospital, said: 'Parents, for instance, can teach hygiene practices to their children. This has proven to be the best preventive measure against not only HFMD but all other infectious diseases.'

The risks you face
Straits Times 18 Jun 08;

Chikungunya and dengue fever

Spread by: Chikungunya fever is transmitted through the bite of infected Aedes aegypti and aedes albopictus mosquitoes while dengue fever is caused by the bite of infected Aedes mosquitoes. The mozzies become infected when they feed on the blood of patients already suffering from the disease.

Peak season: Cases increase in the warmer months when mosquitoes breed more prolifically.

Symptoms: Sudden onset of fever, severe headaches, chills, nausea and joint pain although prolonged joint pain and fatigue are more commonly found in chikungunya fever.

Treatment: There is no specific drug treatment against chikungunya and dengue fever. Aspirin should, however, be avoided in cases of chikungunya fever as this may increase the risk of bleeding.

Influenza

Spread by: The three main types of this viral infection are spread through direct contact with droplets of saliva or nasal secretions or by touching contaminated objects.

Peak season: Although the disease occurs year-round here, there are two seasonal peaks, namely one from May to July and the other from November to January.

Symptoms: Headaches, chills and a cough followed rapidly by a fever, appetite loss, muscle ache and tiredness.

Treatment: Antiviral medication and influenza vaccines.

Sars (severe acute respiratory syndrome)

Spread by: The viral infection is spread by close contact with infected people and the droplets which they exhale.

Peak season: Dr Leong Hoe Nam, Singapore General Hospital's consultant infectious diseases physician, said: 'As it's a respiratory tract infection, it follows cold weather.'

Symptoms: Fever and cough but not all patients will have a runny nose and sore throat.

Treatment: Anti-bacterial and anti-viral drugs are available and vaccines are currently being developed.

Avian influenza or bird flu

Spread by: This flu viral disease is spread by contact with infected birds, which shed the H5N1 virus in their saliva, nasal secretions and faeces. Person to person transmission may occur but rarely.

Peak season: No known peak season. Dr Chong Chia Yin, head and senior consultant in KK Women's and Children's Hospital's department of paediatric medicine, said: 'Despite the destruction of an estimated 150 million birds, the H5N1 virus is considered endemic in many parts of Indonesia, Vietnam, Cambodia, Thailand, China and possibly Laos.'

Symptoms: Humans with bird flu typically report flu-like symptoms like fever, cough, sore throat, headaches and muscle aches. Symptoms can also include eye infections, pneumonia and other complications.

Treatment: Anti-viral flu medicines like Tamiflu appear to be effective in treating bird flu although Dr Chong added that some resistance is developing.

Last month, drug company GlaxoSmithKline gained approval to sell a pre-pandemic bird flu vaccine in the European Union.

HFMD (hand, foot and mouth disease)

Spread by: This childhood ailment is spread by direct contact with saliva, nasal and throat secretions, blister fluid and faeces of an infected person as well as by sharing of toothbrushes, eating utensils, food and toys.

Peak season: Dr Anita Menon from KK Women's and Children's Hospital's department of paediatric medicine, said: 'HFMD is more common in tropical climates. In temperate countries, it tends to have a seasonal variation with cases mainly occurring in summer or autumn.'

Symptoms: It usually starts with a mild fever, poor appetite, lethargy and sometimes a sore throat. One or two days after the fever starts, sores develop in the mouth and rashes, red spots or blisters may occur on palms and soles.

Treatment: Patients can only be treated for symptoms and should take adequate amounts of fluids and water.

Dr Chan Poh Chong, consultant paediatrician and head of ambulatory and adolescent paediatrics at National University Hospital's University Children's Medical Institute, said: 'Even after recovering from a strain of HFMD, a child can succumb to another episode caused by a different strain. There is no known vaccine available.'