Yellow fever is a tropical disease that is spread to humans by infected mosquitoes and is caused by the yellow fever virus. The disease is found in urban and rural areas of tropical zone countries in Africa and South America. Yellow fever has not been reported in Asia.
Yellow fever is a viral disease of short duration and varying severity that is transmitted primarily by mosquitoes. The infection is so named because of the yellow skin colour (jaundice) observed in people with serious illness. Symptoms of infection can be mild but often increase in severity with the sudden onset of fever, muscle pain, nausea, vomiting, headache and prostration. The disease may progress to visible haemorrhage, jaundice, kidney and liver failure. The death rate in unvaccinated people may be as high as 50 per cent.
Yellow fever virus belongs to the Flaviviridae family, other members of which cause dengue fever. The virus is introduced into the bloodstream via the saliva of the mosquito as it bites. The virus can then be transported around the body and reproduce itself in a variety of the body’s cells, usually the liver, kidneys and blood vessels. In serious cases, these cells may become damaged themselves. In addition, the cells of the immune system are affected and release large quantities of signalling substances. These substances are the cause of the normal disease symptoms, such as muscular pain and fever.
Jungle yellowfever is mainly a disease of monkeys. It is spread from infected mosquitoes to monkeys in the tropical rain forest. People get jungle yellow fever when they put themselves in the middle of this natural cycle and are bitten by mosquitoes that have been infected by monkeys. Jungle yellow fever is rare and occurs mainly in persons who work in tropical rain forests.
Urban yellow fever is a disease of humans. It is spread by mosquitoes that have been infected by other people. Aedes aegypti is the type of mosquito that usually carries yellow fever from human to human. These mosquitoes have adapted to living among humans in cities, towns, and villages. They breed in discarded tyres, flower pots, oil drums, and water storage containers close to human dwellings. Urban yellow fever is the cause of most yellow fever outbreaks and epidemics. People get yellow fever from the bite of an infected female mosquito. The mosquito injects the yellow fever virus into the bite.
Yellow fever is common in West and Central Africa and in parts of South America. Periodic epidemics in Africa lead to hundreds of thousands of cases. In total, yellow fever occurs in 33 countries and 468 million people are at risk of catching the disease.
Many yellow fever infections are mild, but the disease can cause severe, life-threatening illness. Symptoms of severe infection are high fever, chills, headache, muscle aches, vomiting, and backache. After a brief recovery period, the infection can lead to shock, bleeding, and kidney and liver failure. Liver failure causes jaundice which is revealed by the yellowing of skin and the whites of the eyes, which gives yellow fever its name. Symptoms start 3 to 6 days after being bitten by an infected mosquito. Severe yellow fever infections can be fatal.
Yellow fever is diagnosed by a blood test in the laboratory, where specific yellow fever virus antibodies are detected in the blood.
Yellow fever can be prevented by vaccination. Travellers should also take precautions against mosquito bites when in areas with yellow fever transmission. If necessary, get vaccinated for yellow fever before travel.
- Travellers should get vaccinated for yellow fever before visiting areas where yellow fever is found.
- International regulations require proof of yellow fever vaccination for travel to and from certain countries. People who get vaccinated should be given an International Certificate of Vaccination.
- Avoid mosquito bites when travelling in tropical areas. Mosquitoes that spread yellow fever usually bite during the day. Travellers should take steps to reduce contact with mosquitoes when outdoors and inside.
- Wear long-sleeved clothing and long pants. For extra protection, treat clothing with the insecticide permethrin or any other suitable insecticide.
- Use insect repellent on exposed skin. The most effective repellents contain 20% to 35% DEET (N, N-diethylmethyltoluamide).
- Spray living and sleeping areas with insecticide.
- Use a mosquito net when sleeping in a room that is not screened or air conditioned. For extra protection, treat the bed net with the insecticide permethrin.
There is no specific treatment for yellow fever. Persons with yellow fever should rest and drink plenty of fluids. There are no medicines that are effective against this virus.
Serious cases of yellow fever always need hospital treatment. As there are no medicines that combat the virus itself and the doctor can only treat the symptoms. If there is lack of fluid in the body leading to disturbances in the electrolyte balance, this can be remedied by administration of fluids by intravenous drip. In mild cases, the pain may be relieved with simple painkillers. High temperatures can be treated by cooling the patient and giving appropriate medicines to lower the temperature.
Many countries, particularly those in Asia, will refuse permission to enter to any person who has recently been in a yellow fever infected country and who does not possess a valid yellow fever vaccination certificate. Some countries will only allow unvaccinated persons to enter if they agree to be vaccinated at their border. In this situation, you may not be able to ensure the sterility of the items used to administer the vaccine.
To obtain a valid international yellow fever vaccination certificate you must be given a yellow fever vaccine that has been approved by the WHO from a vaccination provider who has been approved by a national health authority. The certificate must be in a form that has been approved by the WHO and be completed according to WHO requirements. The disease is covered by the International Quarantine Regulations, which are taken very seriously by authorities everywhere. Vaccination provides protection for 10 years.
If a traveller is unvaccinated and contracts yellow fever the consequences can be serious and may result in death.