Dengue Fever 2011

Over several decades the global distribution and incidence of dengue fever has been dramatically increasing in the tropics. There are estimated to be more than 100 million cases of dengue fever each year with 200-500,000 cases of the more serious dengue haemorraghic fever (DHF)

Today Andy Irons, one of the world's great professional surfers, may have been killed...not by a massive wave off his Hawaiian home but by a tiny virus. What a tragedy if this is true!

Early reports suggest that he had a bout of dengue fever and he may have had it in the past. Andy Irons would have been supremely fit and healthy. In the more fortunate parts of the world we no longer expect people to die suddenly from infectious diseases. The young have not seen the epidemics of the past, no longer fear germs and may not even realize when they are in trouble. Many pro surfing events are held in the tropics and sub tropics, the regions that have seen an epidemic increase of dengue fever in the last thirty years. While urbanization decreases many "old-fashioned" infectious diseases, it plays right in to the mouthparts of Aedes, the dengue transmitting mosquito.

Reports suggest he may have been infected in Puerto Rico, a known destination which has experienced outbreaks of dengue fever over the last 40 years. Three major epidemics have been recorded since the early 90's, the most recent starting in 2007 with more than 10,000 suspected cases. Since the beginning of 2010 there has been more than 17,000 cases with 29 confirmed deaths. Dengue serotypes 1 and 4 predominate.

DENGUE FEVER

Over several decades the global distribution and incidence of dengue fever has been dramatically increasing in the tropics. There are estimated to be more than 100 million cases of dengue fever each year with 200-500,000 cases of the more serious dengue haemorraghic fever (DHF). The chance of dying from DHF is less than 5%.

Dengue fever is caused by a virus known as a FLAVIVIRUS. There are four serotypes (DEN -1,2,3,4) Its presence has been noted globally for 200 years. The virus is also known as an ARBOVIRUS because it is transmitted to humans by the bite of an insect, in this case a female mosquito of the Aedes species. The virus circulates in the blood of an infected person for about 2 to 7 days, at the time the individual experiences fever . Other mosquitoes may acquire the infection by feeding on individuals at this time.

• Humans are the only known reservoir. Infection from one serotype does not convey protection from the others.
• An infection caused by one serotype may increase the risk of DHF occurring with an infection with another serotype. Studies in SE Asia have shown that repeat infections in which DEN 2 is the infective agent have a greater possibility of producing DHF then infections with the other serotypes. DEN-3 is the next worse. The risk is less with DEN-4 or DEN-1 in that order.

The Mosquito

Aedes Aegypti mosquitoes prefer to feed on humans during the daytime. They generally live in close proximity to human dwellings in an urban area. The mosquito may be found indoors and bites frequently. One mosquito can infect many people. It remains infected for life and can also pass on the virus to the next generation. It is known as a "junkyard" breeder because it only needs a small volume of water as a breeding site eg empty cans, coconut shells, buckets, pot plant saucers or toys around the yard. The global expansion of the mosquito's habitat is in line with the global increase in population density. Squatter settlements and unplanned peripheral city areas promote breeding sites particularly when local public health measures fail to keep pace with the expansion. Global shipping trade has also spread the species to new areas and global travel enables different serotypes to be introduced into different regions through infected people. There is currently no vaccine against dengue fever and our only weapon is to control breeding sites and reducing biting. This has proved very difficult.

The illness

Dengue fever should be suspected if you have a high fever and a history of travelling in an area of risk. The temperature is usually high at 39-40C and is accompanied by severe headaches, body aches and pains behind the eyes. A rash is often present and occasionally there is nausea and vomiting. The fever lasts 5-7 days with the rash usually appearing a few days after the start of the fever. There may be 2 spikes of fevers. It must be remembered that not everyone will have symptoms. In fact for everyone who presents with symptoms there may be 4 or 5 others who are asymptomatic or only mildly unwell.

Treatment

Most individuals with Dengue Fever can be treated at home. Maintaining hydration is very important and copious fluids are recommended. There is no specific cure for dengue fever and antibiotics do not help. Paracetamol is the drug of choice to help with the joint pain and fever. Other medications such as aspirin or nurofen should be avoided as they can increase bleeding through their affect on platelets in the blood. The vast majority of people recover over 1 to 2 weeks. Post viral depression may occur. Lethargy and tiredness may continue for many months after the illness has passed. Individuals suspected to be suffering from dengue haemorrhagic fever or dengue shock should be admitted to hospital without delay and closely monitored.

TAKE HOME MESSAGES ABOUT DENGUE FEVER

1. This risk of dengue fever can be much reduced by good mosquito avoidance measures (see below)
2. Recognition of symptoms and the management of fever and hydration is very important
3. Early referral to a hospital for intensive care may be necessary in a few cases.

PREVENTION:

• Reduce exposure time by modifying activities. The dengue fever mosquito mostly bites during the day v the malaria mosquito which is most active between dusk and dawn.
• Wear light-coloured clothing. Cover arms and legs as much as possible.
• Tucking trousers into socks and not wearing sandals or thongs.
• 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

Repellents:

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.
6. If sunscreens are to be used with repellents then the sunscreen should be applied first. Wait 20 minutes before using the repellent.

Reference: Health Canada http://www.pmra-arla.gc.ca/english/consum/insectrepellents-e.html

Permethrin

Permethrin is similar to a naturally occurring chemical called pyrethrum. Pyrethrum was initially derived from the flowers of the daisy Chrysanthemum. The insecticide properties of the flower have been recognized since the 18^th century. The synthesized product has been available for over 30 years. It is colourless, odourless and biodegradeable.

Permethrin acts as a "knockdown" insecticide. It is not a repellent. It damages the central nervous system of insects which come into contact with it.
It is effective against many insects including mosquitoes, fleas, ticks, bedbugs, chiggers, scabies and flies. Permethrin-treated bednets have been found to significantly reduce malaria rates in children in Africa and the Western Pacific region.

Once opened to the air, the net should be treated every 6 months to retain its potency. Permethrin can also be used to impregnate clothes, tents and window drapes. It adheres well to fabrics like cotton and will remain effective for between 5 and 10 washes. It is not recommended for skin application.

For further information on travel health issues: "the Little Book about staying healthy when travelling", available through Globe Medical