Dr Eddy Bajrovic*
A study that claims India actually has an average of 5.75 million cases of dengue fever each year – almost 300 times the official figure – really comes as no surprise to people who work in travel medicine.
US and Indian researchers found that between 2006-2012 the annual number of cases across India averaged almost 6 million instead of the 20,474 reported by the country’s Ministry of Health. Their peer-reviewed study was published recently in the American Journal of Tropical Medicine and Hygiene.
Adding to the human misery, India’s economic burden from dengue amounts to around $1.1 billion a year in direct and indirect costs, including medical treatment, lost wages, and travel to and from clinics and hospitals, the report stated.
But, rubbery figures abound when it comes to dengue and other diseases that impact on travellers.
And, not just in India. Few countries’ figures are accurate, because despite being a ‘notifiable’ disease, there is considerable under-reporting. So, the reported figures are just the tip of the proverbial iceberg.
Why figures can’t be trusted
There are several reasons not to trust them:
- Developing countries rely on the income from tourism and potential health risks like dengue are deliberately underplayed so as not to scare prospective visitors away.
- Official figures often reflect only those people treated at government hospitals and clinics. Others seek treatment from their doctor or at private facilities.
- Many local people simply don’t receive any treatment (either because they can’t get to a facility, can’t afford treatment, or decide simply to let the disease run its course, hoping for a mild illness). Some of these people rely on dubious home-made remedies.
Even the experts can’t agree on the global burden of dengue. According to the WHO, dengue infects between 50-100 million people in more than 100 countries, resulting in around 20,000 deaths each year. However, a credible, multi-national study funded by Britain’s Wellcome Trust and published last year found that the number of annual cases worldwide is more like 390 million – four times the WHO’s top figure.
Dengue risk rising in Africa
The British study found that:
– Of the 96 million obvious infections (those resulting in significant illness), 70% occur in Asia, the favourite regional destination for Australian travellers.
– India accounts for one-third of the world’s cases.
– With 16 million infections, Africa’s burden is almost equivalent to that of Latin America – significantly larger than previously thought (mainly due to better testing and surveillance).
The Wellcome study warned that “… with globalisation and the constant march of urbanisation, there could be dramatic shifts in the distribution of the disease in the future. The virus may be introduced to areas that previously were not at risk, and those that are currently affected may experience increases in the number of infections.”
All of these studies are a reminder that dengue is one of the (if not THE) major travel health risks in the tropics. Clearly, the danger is highest in Asia, but travellers should also be wary when visiting Pacific destinations, the Caribbean, Central and South America, and Africa, too.
The number of Australian travellers infected with dengue – especially in Asia – bear this out. National figures show levels of infection have been steadily climbing, peaking at 1842 last year.
Dengue cases increasing here
To date this year Australia has seen 1281 confirmed cases, the majority in Western Australia (376) and Queensland (354). The victims include locals returning home infected with the virus and infected international travellers arriving in the 2 northern states after visiting Asia.
Ironically, a percentage of those people infected in North Queensland’s annual outbreaks also slip under the diagnostic radar. They either have a mild infection, or mistake their illness for flu or another cause and, because they don’t seek treatment, the figures published by the Queensland government are also below the true figure.
After traveller’s diarrhoea, dengue fever is the most common cause of fever in travellers returning from Asia and Central/ South America.
While it’s rare for travellers to die, recovery can be slow and subsequent infections carry the potential for dengue haemorrhagic fever, a more serious and potentially fatal version of the disease.
What you should know to dodge dengue
There is no vaccine for dengue, although several are in development and the first is due to be released next year. So, if you are travelling to the tropics, here’s what you should know about this nasty viral disease and how to avoid becoming a dengue statistic:
– It can only be spread through the bites of infected female Aedes aegypti and Aedes albopictus mosquitoes, which have distinctive white bands.
– They bite mainly during the daylight hours, especially a couple of hours after sunrise and just before sunset, the times when both species feed intensely. However, they do bite at other times.
– These aggressive mozzies are found in any urban setting (humans are their first choice for the blood the female needs to produce eggs, which can be laid in even a bottle top full of water).
– They are often found on your hotel balcony, in the grounds or shady gardens, at pool sides, and in outdoor restaurants and markets. (Upmarket hotels and resorts ‘fog’ the grounds with insecticide. This will clear most adult mosquitoes from the immediate area but it can be a little ‘hit and miss’ and the next generation is often quick to repopulate favourable habitats.)
The disease and its symptoms
There are four distinct, but closely related, serotypes of the dengue virus – DEN-1, DEN-2, DEN-3, and DEN-4. A fifth serotype was announced last year.
Recovery from one serotype provides lifelong immunity against that serotype only – cross-immunity to the other serotypes after recovery is only partial and temporary. As mentioned, subsequent infections by other serotypes increase the risk of developing severe dengue.
The symptoms of dengue include:
– Fever, headache, pain behind the eyes, joint and muscle pain, rash, nausea/vomiting, easy bruising, and mild bleeding from the nose or gums are all potential symptoms of dengue.
– Symptoms typically appear 4-7 days (range 3-14 days) after a bite from an infected mosquito. Most infections clear up on their own in 2 to 4 weeks.
– With good treatment, less than 1-in-100 dies from dengue.
Who is at risk?
The Australians at highest risk are those who live or stay for extended periods in tropical countries where dengue is common – especially during the peak transmission season/s.
However, even visitors on brief stays are at risk of infection. (Virtually all of the Australians infected overseas each year had been on short-stay holidays. Spending just one week in Bali has resulted a significant number of dengue infections.)
Preventing dengue
Reduce the number of mosquito bites and you reduce your risk of dengue. So…
– Move inside behind screened windows and doors at peak mosquito feeding times – especially around dusk.
– When outdoors, use insect repellent on all uncovered skin. Look for a repellent that contains one of the following active ingredients: DEET, Picaridin (KBR 3023), oil of Lemon Eucalyptus/PMD, or IR3535 and follow the instructions on the label as to how often it should be applied.
– Wear loose, long-sleeved shirts and long pants when outdoors – especially in the early morning and the evening before sunset.
– Get rid of any standing water around your accommodation, including pot plant bases and other containers that collect water.
– If using sunscreen, apply it BEFORE you apply insect repellent.
– If you’re likely to be consistently exposed to insect bites, soak your clothing and bed net (if your room is not screened) with permethrin. This contact insecticide repels mosquitoes and other insects, and also kills them when they come in contact with the treated material. (Permethrin shouldn’t be applied directly to your skin. Read more about permethrin and how to protect yourself against insect bites.)
Post-travel illness
Finally, if you get sick after a trip abroad, seek medical care as soon as possible – especially if you have a fever and have been in a malaria-infected area.
Most importantly, don’t forget to mention your recent travel so the full range of fever-causing diseases (including dengue) can be considered as a possible cause of your illness.
* Dr Bajrovic is the Medical Director of Travelvax Australia.
Travelling to the tropics? Get more advice on dengue, recommended vaccinations and other health-related issues for your destination from Travelvax Australia’s travel health information service on 1300 360 164 (toll free from landlines within Australia).