Beware the bite: Macaques, mozzies, and malaria

Travellers used to have just two concerns if they encountered Asia’s ubiquitous macaque monkeys.

The first was having the light-fingered mammals pinch food or some other irresistible item from their hand, pocket or bag.
The second was angering one (usually by running out of food!) and getting bitten. Besides being painful, a bite from a monkey could potentially pass on a serious infection, such as the herpes B virus or the deadly rabies virus.
However, it’s what’s biting the macaques that is also raising concern.
If a female Anopheles mosquito takes a blood meal from a macaque and later bites a person there’s a growing risk it could pass on the parasite Plasmodium knowlesi, that causes the fifth and most recently identified form of malaria in humans. (The others include the most dangerous, P. falciparum, as well as P. vivax, P. ovale, and P. malariae.)
P. knowlesi is known as ‘monkey malaria’ because, until relatively recently, it was thought to circulate only among the macaque monkeys.

Why monkey malaria is causing concern

Why should Asia-bound Aussies be concerned about macaques, mozzies, and malaria?
- Monkey malaria can be severe. Increasingly, the knowlesi strain is the cause of malaria deaths.
- It’s on the move. Monkey malaria is no longer confined to Malaysian Borneo, where it’s thought to have originated. It’s now widespread throughout Southeast Asia.
- Testing for the parasite is problematic. Some rapid test kits have proven unreliable in identifying P. knowlesi, while differentiating it from other malaria parasites under a microscope is difficult – especially when the parasite ‘load’ in the infected person’s bloodstream is low. All of which can delay treatment. 
In Malaysian Borneo, the strain was responsible for more than two thirds (68%) of the human cases contracted there in 2013. In some areas of the island, P. knowlesi is causing all locally acquired malaria cases, having effectively taken over from other strains.

Fears of human-to-human infection

It’s clear that monkey-to-human transmission by mosquitoes has been occurring for some time.
But, experts now believe it is inevitable that human-to-human transmission will also occur – if it’s not already – as the number of human cases continues to rise.
Deforestation is one of the factors driving monkey malaria in the human population: more humans are living close to wild macaque populations harbouring monkey malaria than ever before.
The fact that towns are taking the place of the trees on forest fringes is a likely explanation for the growing number of local human cases, experts believe.
More infections are also being reported among international travellers: Cases have also been reported in Vietnam, Cambodia, and the Philippines. (It should be noted that travellers visiting Bali – which has its share of macaques – are not at risk of malaria, although the disease exists on most other Indonesian islands.)
Most recently, two German travellers were infected while visiting forested areas in southern Thailand, including Ranong Province, Khao Sok, and Kra Buri National Parks, where macaques are plentiful. Both required hospital treatment: one for a fairly mild illness, while the other developed acute kidney failure and battled pneumonia before recovering.

Get expert advice on malaria

Experts warn the growth of eco-tourism may increase the risk of monkey malaria, even in areas where prevalence is currently low.
But, malaria isn’t only a risk ‘off the beaten track’. It also occurs in towns and cities: even travellers staying in upmarket accommodation occasionally get malaria.
If you are heading to any tropical region with malaria, you need to know if it’s a risk there and, if so, should you consider taking prevention medication?
The best way to find out if malaria will be a significant risk is NOT to ask your travel agent. Instead, ask a doctor – preferably one experienced in travel medicine – who can access the latest information and maps on malaria.
Your doctor can also recommend the medication that’s best for you and your destination, and take you through the other measures to help you avoid infection.
Allow yourself enough time (6 weeks is ideal) and you can even trial one of the malaria prevention medications suitable for the destination to ensure that it’s right for you.

Lots of reasons to avoid mozzie bites

Besides taking medication, it’s also important to minimise mosquito bites. Not just to prevent malaria: dengue and Chikungunya are a more significant risk for travellers in many tropical and sub-tropical destinations because they’re spread by the urban-breeding, daytime-feeding Aedes species.
Adopt some or all of these bite avoidance measures:
- Apply an insect repellent containing an effective ingredient such as DEET (30-50% formulations for adults, or 10-20% formulations for young children and infants as young as 2 months of age), Picaridin, IR3535, or preparations containing extract of lemon eucalyptus oil as necessary when outdoors.
- Wear long, loose-fitting, light-coloured clothing after dark, when malaria mozzies are active. Treating your clothing with the contact insecticide permethrin creates a deadly barrier to mozzies and other bugs that can bite through light material.
- Sleep under a treated bed net, especially if you are staying in a tent or in budget accommodation without screened doors and windows, or air-conditioning. You can buy a treated net or purchase a DIY kit and use it to treat a net and clothing to give yourself a strong barrier against biting insects.

Read more about malaria and avoiding biting insects.

Did you know you can get no-obligation, country-specific advice on malaria and other the potential health risks of your next overseas destination by calling Travelvax Australia’s travel health advisory service on 1300 360 164 (toll free to landlines)?