Yellow fever is a viral disease of typically short duration. The disease is caused by the yellow fever virus and is spread by the bite of an infected female mosquito. It infects humans, other primates and several species of mosquitoes. In cities, it is spread primarily by Aedes aegypti, a type of mosquito found throughout the tropics and subtropics. Aedes aegypti also transmits the viruses that cause dengue fever, West Nile fever, chikungunya, eastern equine encephalitis and Zika virus.
In areas where yellow fever is common and vaccination is uncommon, early diagnosis of cases and immunisation of large parts of the population is important to prevent outbreaks. Death occurs in up to half of those who get severe disease.
Avoid mosquito bites
When you go outdoors, use oil of lemon eucalyptus on exposed skin. Wear proper clothing to avoid mosquito bites. When weather permits, wear long-sleeves, long pants and socks when outdoors. Mosquitoes may bite through thin clothing, so spraying clothes with repellent containing Permethrin gives extra protection. Mosquito repellents containing Permethrin are not approved for application directly to skin. Be aware of peak mosquito hours. The peak biting time for many mosquito species is dusk to dawn. However, Aedes aegypti feeds during the daytime.
Get vaccinated if recommended
Yellow fever vaccine is recommended for persons aged ≥ 9 months who are travelling to or living in areas at risk for yellow fever virus transmission in South America and Africa. Mosquitoes acquire the virus by feeding on infected primates (monkeys), and then can transmit the virus to other primates (human or non-human). People infected with yellow fever virus are infectious to mosquitoes (referred to as being ‘viraemic’) shortly before the onset of fever and up to 5 days after onset.
Symptoms
The majority of persons infected with yellow fever virus have no illness or only mild illness. In persons who develop symptoms, the incubation period is typically 3–6 days. The initial symptoms include sudden onset of fever, chills, severe headache, back pain, general body ache, nausea, vomiting, fatigue and weakness. Most persons improve after the initial presentation. Roughly 15% of cases progress to develop a more severe form of the disease. The severe form is characterised by high fever, jaundice, bleeding and eventually shock and failure of multiple organs.
Treatment
No specific treatments have been found to benefit patients with yellow fever. Whenever possible, yellow fever patients should be hospitalised for supportive care and close observation. Treatment is symptomatic. Rest, fluids, and use of pain relievers and medication to reduce fever may relieve symptoms of aching and fever. Yellow fever patients should be protected from further mosquito exposure (staying indoors and/or under a mosquito net) for up to 5 days after the onset of fever.
Outcome
The majority of infected persons will be asymptomatic or have mild disease with complete recovery. In persons who become symptomatic but recover, weakness and fatigue may last several months. Those who recover from yellow fever generally have lasting immunity against subsequent infection.
The writer is a physician, public health specialist & a gerontologist.
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