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Ross River Virus Disease (RRVD)

by Dr Bob Kass - February 19, 2017

South Eastern Australia is currently experiencing a large increase in the number of cases of Ross River virus disease.  The Murrumbidgee Health district has reported more than 150 cases in January, up from 118 in December. According to the Department of Health in Victoria, this is the worst outbreak in the last decade, with more than 1000 cases since January 1.

Travellers to SE Asia and the Pacific are constantly warned about the dangers of mosquito-borne disease.  Despite this, many people still have their holidays curtailed early or are diagnosed shortly after return.  Over the last few years there have been many outbreaks of Dengue, Chikungunya and more recently Zika.  RRVD does occur in overseas travellers.  The largest ever outbreak occurred in 1979 across the Pacific with more than 500,000 cases in Fiji alone.  It is believed the outbreak was introduced into the region by an infected Australian traveller. (This outbreak is presumed to be largely human to human transmission via a local mosquito vector for lack of vertebrate reservoir).

In counselling individuals on mosquito-borne disease in the tropics much emphasis is placed on the high risk periods towards the middle and end of the dry season, just before the wet and the biting habits of particular mosquitoes.  This current outbreak of mosquito-borne disease comes as no surprise to Travel Medicine service providers. The mosquito and the disease may be different but the underlying environmental aspects are just the same. SE Australia experienced unusually late rains, just as conditions were warming up. This large amount of water has now receded into small quantities of water, ideal for mosquito breeding sites!  These ideal conditions have occurred in the past and will do so in the future.

The responsible mosquitoes are most active between Spring and late Autumn.  They are generally late afternoon biting but can be around most of the day. Their range is 5-10 km.

THE DISEASE

Native animals such as wallabies and kangaroos are considered to be the reservoir for the disease. Mosquitos transmit the disease from animals to humans.   The incubation period is usually between 1 and 2 weeks but ranges from a few days to 3 weeks.

The majority of infected individuals have little or no symptoms.  Between 25 and 45% will report joint pain and swelling, muscle pain and rash.  Apart from the initial joint pains, the most debilitating feature of RRVD can be overwhelming tiredness and low mood level. This can last from a few weeks to many months. The reason for this individual variation is not well understood.  The disease appears to be worse in adults.

PREVENTION:

  • Reduce exposure by modifying outdoor activities. The Ross River mosquito mostly bites late afternoon.

  • Wear light-coloured clothing. Cover arms and legs as much as possible.

  • Tuck trousers into socks and avoid open footwear like sandals or thongs.

  • Consider Permethrin impregnation of clothing

  • Avoid highly-scented perfumes or toiletries.

  • Use personal repellents on exposed skin (see table).

  • Use insecticide aerosols, mosquito coils or other agents in the immediate environment

  • Take extra care if you are a “mosquito magnet”  – you will receive many more bites than others

[Related: 8 Steps to Avoiding Insect Bites on Holiday]

 

REPELLENTS:

DEET

The repellent of choice should contain DEET (N,N-diethyl-meta-toluamide). The higher the concentration the longer it protects. There seems, however, to be no added benefit beyond 50% concentration. DEET is toxic when ingested and may cause skin irritation in some people. DEET has been used over a long period of time and by many millions of people with few reported serious side effects. Despite this, a few precautions should be undertaken.

1. Apply DEET lightly to exposed areas only

2. Where possible, wash off on returning indoors

3. Do not apply to open cuts or sores

4. Do not use aerosol applications to the face directly. Apply to the hands and then rub on the face avoiding eyes and mouth

5. Do not allow young children (under 10 years) to apply it to themselves. Special weaker formulations are available for children. If they have never used it before, it is wise to test a patch on the arm for a few days before applying all over.

 

CONCENTRATION OF DEET

PROTECTION TIME (approx)

30%

6-8 hrs

15%

5 hrs

10%

3 hrs

5%

2 hrs

 

Well known DEET containing brands in Australia are Repel, Bushmans, Rid, Aerogard Tropical.

Our Travel Medicine experts recommend:  Repel Rollon  |  Repel Stick  |  Repel Spray  |  Repel Junior

Picaridin

PICARIDIN (KBR3023) or 1 methyl propyl 2-(2hydroxyethyl)-1piperidine carboxylate, is a newer chemical insect repellent. At 20% concentration it is as effective as 20-30% DEET for 4-6 hours. It doesn't feel sticky or damage plastics. Brands available in Australia are "Repel" (20%), "Protect" (19%), "Off Skintastic" (9.5%),Off Tropical Strength (16%) and Aerogard Odourless (9.5%).

There is evidence that anopheles species of mosquitoes are becoming increasingly tolerant to both DEET and Picaridin IRs.

Our Travel Medicine experts recommend: Repel "New Era" Rollon  |  Repel "New Era" Spray  |  Protect Spray

Citronella

Citronella oil was discovered in 1901. While it works, it only does so for 20 to 30 minutes.

Products containing extracts form Australian native plants have been shown to provide very little protection, with the exception of oil of lemon eucalyptus (p-methane 3,8- diol or PMD). When trialed, it is equivalent to a weaker DEET, protecting for about 2 hours.

Combination sunscreen/IR products

There is some evidence that the sunscreen may increase DEET absorption, especially if reapplied. The IR may also make the sunscreen less effective.  It is probably best to be specific as to why you are using the chemical on your skin. If you require both, apply the sunscreen first.

ENVIRONMENTAL MEASURES

(Not to be forgotten)

The mosquito readily finds habitats for its larvae in water storage containers and domestic rubbish. Residents in Ross River Disease prone areas are strongly recommended to:

1. Empty all pot plant trays of water or add sand to them

2. Screen all water tanks with fine mesh

3. Keep ponds and other water features stocked with appropriate Australian native fish

4. Clean up yards and dispose of all containers which may collect water

5. Empty wading pools at the end of the day

6. Make sure all bird baths and pet drinking water containers are regularly filled with fresh water

7. Make sure all gutters are free of debris allowing water to run freely. Avoid pooling of water at all times

8. Remove vegetation from the edges of dams

Image Credit: ABC News


Author

Dr Bob Kass

Dr Bob Kass is Medical Director of Globe Medical. He holds specialist qualifications in paediatrics and public health medicine and is one of Australia's pioneers in the discipline of Travel Medicine. 

Full professional biography | Book an Appointment with Dr Kass