VOL: 101, ISSUE: 01, PAGE NO: 33- Yellow fever is a viral disease that is endemic in parts of Africa and the Americas....
What is it?
- Yellow fever is a viral disease that is endemic in parts of Africa and the Americas.
- These areas also experience regular epidemics.
- The virus belongs to the flavivirus group.
- It results in a wide spectrum of disease, from mild symptoms to severe illness and death.
- Yellow fever can be easily confused with diseases such as:
- Rickettsial diseases;
- Haemorrhagic viral fevers (such as Lassa fever);
- Arboviral infections (dengue);
- Viral hepatitis;
- Poisoning (such as carbon tetrachloride).
- Laboratory tests are necessary to confirm diagnosis.
- Serology assay can detect antibodies in the blood to confirm diagnosis.
- Other more specialised tests can detect the virus itself in blood or in postmortem liver samples.
- The virus has an incubation period of 3-6 days, after which there are two disease phases.
- The acute phase is normally characterised by fever, bradycardia, muscle pain (especially backache), headache, shivers, loss of appetite, nausea and/or vomiting.
- Symptoms usually disappear after 3-4 days.
- Some patients are asymptomatic.
- Fifteen per cent of patients enter a 'toxic' phase within 24 hours of the acute phase (World Health Organization, 2001).
- The toxic phase can have a range of symptoms:
- Abdominal pain with vomiting;
- Bleeding from the mouth, nose, eyes and/or stomach, after which blood appears in vomit and faeces;
- Compromised renal function ranging from albuminuria to complete renal failure with anuria.
- Half of patients die within 10-14 days in the toxic phase; the remainder recover without significant organ damage.
- Humans and monkeys are the principal animals affected by yellow fever.
- The virus is transmitted horizontally between animals by mosquito bites.
- It is also passed vertically from mosquitoes to their offspring.
- Mosquito eggs lie dormant through dry conditions, hatching when the rainy season begins, ensuring transmission from one year to the next.
- There is no specific treatment for yellow fever, so care focuses on specific symptoms.
- Dehydration and fever can be corrected with oral rehydration salts and paracetamol.
- Superimposed bacterial infection should be treated with an appropriate antibiotic.
- Intensive care may improve the outcome for seriously ill patients, but is rarely available in poorer countries.
- Vaccination is highly effective and there have been few reports of adverse effects.
- Immunity occurs within one week in 95 per cent of people vaccinated (WHO, 2001).
- Anyone travelling to the endemic area should be vaccinated, except children under six months of age.
- Many countries require travellers to have a vaccination certificate before entering.
- The vaccine should not be given to pregnant women except during an epidemic.
- Mosquito-control programmes have successfully eradicated mosquito habitats in the past, especially in South America.
- These programmes have lapsed over the past 30 years and mosquito populations have increased.
Medline Plus: www.nlm.nih.gov/medlineplus
NHS Direct: www.nhsdirect.nhs.uk