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Yellow fever

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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.

Diagnosis
- Yellow fever can be easily confused with diseases such as:

- Malaria;

- Typhoid;

- Rickettsial diseases;

- Haemorrhagic viral fevers (such as Lassa fever);

- Arboviral infections (dengue);

- Leptospirosis;

- 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.

Symptoms
- 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:

- Fever;

- Jaundice;

- 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.

Transmission
- 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.

Treatment
- 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.

Prevention
- 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.

Websites
Medline Plus: www.nlm.nih.gov/medlineplus

NHS Direct: www.nhsdirect.nhs.uk

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