How is it contracted?
Several different species of mosquitoes transmit the virus between humans and also animals, mainly monkeys. The classification of the disease depends on where it is contracted. Jungle yellow fever is mainly transmitted among monkeys by mosquitoes and people can become infected when they spend time in the jungle. Urban yellow fever is spread to urban areas by mosquitoes, that have bitten monkeys or people infected with yellow fever, particularly where populated areas are in close proximity to jungle. Intermediate yellow fever occurs only in Africa in humid savannah regions where mosquitoes infect both monkeys and people, causing localised outbreaks.
Signs and symptoms
Once contracted, the virus incubates in the body for 3 to 6 days, followed by infection that can occur in one or two phases. The initial acute phase usually causes fever, muscle pain with prominent backache, headache, shivers, loss of appetite, and nausea or vomiting. Most patients improve, and their symptoms disappear after 3 to 4 days . However, 15% of patients enter a second more toxic phase within 24 hours of a remission period . This takes the form of an acute haemorrhagic fever, in which there may be bleeding from the mouth, eyes, ears, and stomach, pronounced jaundice (from which the disease gets its name), and kidney damage. The patient develops shock and there is deterioration of major organ function, which can lead to death.
Around half of patients, in the toxic phase i.e. with severe disease, die within 10 to 14 days . This gives an overall mortality rate of about 7.5% although this is higher in infants and people over 50 years where disease severity is increased. Those who do not die tend to recover with no long-term problems and will have lifelong immunity.
There is no specific treatment for yellow fever, only supportive care to treat dehydration, respiratory failure and fever.
Recommendations for travellers
The disease remains a very rare cause of illness in travellers and can be prevented effectively through vaccination and avoiding mosquito bites. Vaccination is recommended for all travellers visiting areas where there is a risk of yellow fever transmission, and travellers should be aware that certain countries have yellow fever certificate requirements. Yellow fever vaccination can only be administered at designated yellow fever centres.
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Yellow Fever vaccination. Here’s the point...
Although rare, there have been six recorded deaths from yellow fever in non-vaccinated European and American travellers between 1996 and 2010. In 2002, an American died of the disease after returning from a fishing trip on the Amazon near Manaus, Brazil. There have been no confirmed cases in the UK since 1930, when a laboratory worker contracted the disease while working with the virus at the Hospital for Tropical Diseases in London.