Dengue fever is an infectious viral disease transmitted by mosquitoes in tropical and sub-tropical climates. Most people with dengue fever suffer unpleasant symptoms, such as fever, headache and vomiting, but will make a full recovery. However, repeated infections can result in a form of haemorrhagic fever.…
What is yellow fever?
Yellow fever is an infectious viral disease transmitted by mosquitoes in tropical and sub-tropical climates. It is a serious health concern, particularly in sub-Saharan African and some South American countries.
Yellow fever is caused by a virus that mainly infects monkeys. However, mosquitoes can transmit the virus from an infected monkey to a human. The virus is not able to be spread directly from person to person.
When the virus enters a person's bloodstream from a mosquito bite, it is able to spread to multiple organs in the body. It is still not clear how the virus causes the characteristic bleeding observed in the toxic stage of the illness.
Risk factors for yellow fever include:
In South America, the most prevalent season for yellow fever is the rainy season (January - May), whereas in Africa, the disease is most common between the rainy and dry seasons (July - October).
Older people have a greater chance of developing the severe form of yellow fever and dying from it.
Signs and symptoms
Many people infected with the yellow fever virus suffer few or no symptoms.
If symptoms do appear, it is usually after a period of 3-6 days. The symptoms can appear over three separate stages: early, remission and toxic.
The early stage of yellow fever appears 3-6 days after infection has occurred. Symptoms of early-stage yellow fever can include:
- Headache and back pain;
- Nausea and vomiting;
- Loss of appetite;
- Irritability, and;
After about two days with symptoms, most people fight off the infection. However, in about 15-25% of people, the illness goes into remission. This is where the symptoms subside, but the virus is not completely removed from the body. Remission can last between a few hours to a whole day, before they reappear in a more serious form, known as toxic or intoxication stage. 
At this stage, bleeding can occur from multiple internal organs, including the heart, kidneys, spleen, liver and stomach. Symptoms can include:
- High fever;
- Reddening of the eyes, face and tongue;
- Bleeding from the eyes and nose;
- Bloody stools and black or 'coffee-ground' vomit (the result of bleeding in the stomach), and;
- Brain damage, coma and delirium.
Methods for diagnosis
If a yellow fever infection is suspected, your doctor may perform specific blood tests to identify the presence of the virus or antibodies to the virus. Other blood tests may be performed to assess your liver and kidney function.
Types of treatment
There is no specific treatment for yellow fever. Antibiotics and existing antiviral medications have no effect on the virus. If you are suffering from yellow fever, treatment will focus on managing your symptoms and hydration.
Treatment measures can include:
An effective yellow fever vaccine is available and is routinely given to people living in, or travelling to, areas where the virus is commonly found. Some countries require a certificate of vaccination against yellow fever before entering them. The vaccine is given as a single injection and is thought to give decades of protection to the disease.
Bite prevention methods
A good way of reducing the chance of developing yellow fever is to avoid mosquito bites. In areas where the yellow fever virus is commonly found, you can protect yourself by taking the following measures:
- Wearing long-sleeved shirts and trousers, light-coloured clothing, and;
- Applying tropical strength repellent, containing DEET (diethyltoluamide or diethylmethylbenzamide) or picaridin, every four hours during daylight hours.
The Aedes aegypti mosquitoes, which is mainly responsible for transmitting yellow fever, are mostly active during the day. Therefore, bed nets and other night-time bite prevention strategies are less useful against yellow fever than for other mosquito-borne diseases such as malaria.
Mosquito control methods
An effective way of controlling Aedes aegypti mosquito numbers is to prevent their access to standing water in which they lay eggs. This requires governments and citizens to be aware of sources of standing water in their environment (containers, puddles, old tyres, pots, etc.) and to empty or seal them.
Activities to reduce mosquito breeding:
- Weekly removal of items that provide breeding areas (e.g. tyres, pot plant bases, palm fronds);
- Weekly flushing of stagnant water sources (e.g. dog bowls), and;
- Application of repellent surface spray to areas that may harbour mosquitoes (e.g. under beds, behind furniture, within closets).