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Making Sense of ... Yellow Fever

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Yellow fever

What is yellow fever?

Yellow fever is an acute viral illness. It is a major cause of hemorrhagic illness in many countries in Africa and South America.

Yellow fever is also known as yellow jack, black vomit and American Plague

The name refers to the jaundice seen in many patients, as hepatitis is a common feature.

Where is yellow fever usually found?

yellow fever is endemic tropical regions of Africa and South America.

Specifially, the disease occurs in significant numbers in Peru, Colombia, Bolivia, Brazil and Venezuala in South America; Cote d'Ivoire, Burkino Faso, Guinea, Cameroon, Liberia, Senegal, Mali and Ghana in Africa. Historically, the disease had a wider range, involving Central America as well as wider area of Africa, but prevetative measures have been successful in many areas.

How common is yellow fever?

In recent years, numbers of cases have been reduced to single figures in many countries where it is endemic; in 2004 (the most recent year for WHO statistics), there were 92 cases from the Ivory Coast, 61 in Peru, 30 in Combia, and much lower figures elsewhere.

How is yellow fever transmitted?

Yellow fever is caused by the flavivirus. It is passed on by the bite of the Aedes aegypti mosquito.

The cycle of infection involves the mosquito collecting the infection by biting an animal or human with the virus (the mosquito is unaffected; it merely carries the infection in its salivary glands). It will then pass on the virus to any subsequent animals or people that it bites. Once it has the virus, the mosquito remains a source of infection for the rest of its life.

The virus is widespread among monkeys that live in the jungle canopy, and occasionally, a mosquito bite passes the disease on to a person, such as a forestry worker, who can then act as a source of infection when they return to their own community.

While sylvatic (jungle) yellow fever can affect significna t numbers, the real risk is epidemics of urban yellow fever, when the the disease is carries back to town by a human reservoir of infection.

Is there a genetic / familial / hereditary factor?

No.

Can yellow fever be spread from person-to-person?

Not directly; domestic mosquitoes carry the virus from person to person.

Who is most at risk from yellow fever?

Unvaccinated travelers and workers are at risk in forest areas; any unvaccinated person is at high risk during an urban epidemic.

The level of risk will vary with season, and the level of local risk at the time. But even if there is 'epidemiological silence' at the time and place, there is still risk (someone has to be first!), and incidence is probably underreported, particularly where few recent cases have occurred.

What are the symptoms of yellow fever?

There is an incubation period of three to six days, with no symptoms at all.

This is followed by the acute phase, which usually includes fever, headache, shivers, muscle pain, nausea and vomiting, and an unusually slow pulse.

Three or four days later these symptoms will usually disappear.

Within 24 hours of the acute symptoms disappearing, around 15% of those infected with yellow fever will then develop the toxic phase.

The toxic phase includes fever, jaundice, abdominal pain, and vomiting. Bleeding can occur from the mouth, nose, eyes and / or stomach blood can then also be seen in the vomit and faeces. The kidneys can also be affected, sometimes leading to kidney failure.

Between twenty and fifty per cent of people who enter this toxic phase of yellow fever will die within ten to fourteen days.

What are the long term effects of yellow fever?

Those who recover do not generally have permanent damage, and are then immune to the disease for life.

What is the mortality rate for yellow fever?

Up to 20% of victims may die, while in epidemics where vaccination is lacking, this may exceed 50%.

This has not occurred in recent years, but historical data suggests that about half of invading armies died, and about 10% of the local population.

The individual case-mortality rate in recent years has ranged from 0 to 100%

How is yellow fever diagnosed?

The combination of a slow pulse with an elevated temperature, is often seen in yellow fever. known as 'Faget's sign' it cannot, however, be considered diagnostic. Diagnsis requires laboratory confirmation by blood tests.

Is there a treatment for yellow fever?

There is no treatment specific to the disease. Symptom support can reduce the mortality rate.

Is there a way to prevent infection?

Prevention of mosquito bites is one way of avoiding yellow fever. However, the mortality rate of the disease suggests that anyone at risk should use vaccination as a more certain protection.

What is the yellow fever vaccine?

The 17D live attenuated vaccine was developed in 1936 and has been widely since 1951.

The vaccine, is very effective, offering protection from 10 days after the vaccination, for ten years. After that, further vaccination is necessary, though in some people, protection may be for longer. The incidence of Yellow fever has declined wherever high vaccination rates have been achieved, and this has lead tho regular shortages.

Vaccination is strongly recommended for all visitors to areas where the disease occurs, and in some endemic areas, there is a legal requirement for yellow fever vaccination. so obtaining a certificate of vaccination may be important.

This vaccination is not available on the UK NHS, but GP surgeries and health centers can usually advise on obtianing the vaccination at Yellow Fever Centres.

What is the protocol for yellow fever vaccination?

A single dose of the vaccine is given by deep subcutaneous injection, and provides immunity in 96-100% of travellers.

Re-vaccination is advised after ten years for persons who remain at risk of contracting the disease.

Countries may require an International Certificate of Vaccination, valid for 10 years from the tenth day after vaccination.

Other vaccines can be administered at the same time as yellow fever vaccine, but must be given at different sites and in different syringes. If they are not given on the same day, vaccinations should be separated by at least three weeks.

Vaccination centres may seek written consent, prior to vaccination.

Patient details, plus time and date, will be recorded with the batch number of the vaccine. The site of vaccination will be recorded, and an immunisation certificate issued, which is signed by the recipient and stamped by the issuing centre.

Who should get vaccinated against yellow fever?

Anyone traveling to an area where the disease is endemic currently occurring, should obtain vaccination.

If there is doubt about this, vaccination is still often a sensible precaution. Some countries have Yellow fever requirements that target travellers coming from infected areas, rather than infected countries, and local health and customs officials may have inaccurate or outdated information regarding areas of yellow fever infection and, therefore may require proof of vaccination. This can lead to local health authorities attempting to administer the vaccine using needles or syringes of unknown cleanliness. Having a valid certificate is a wiser choice.

Are there adverse reactions to the yellow fever vaccine?

There is a theoretical risk of adverse effects on pregnancy because yellow fever vaccine is a live virus. But yellow fever vaccination has been given to many pregnant women without any apparent adverse effects on the fetus. One study of women vaccinated during pregnancy showed a slightly increased risk of spontaneous abortion.

There have been a small number of fatalities reported following vaccination. This is considered to be an acceptablerisk, but undelines the importance of safe procedures and surveillance.

A history of oral intolerance to eggs or chicken protein is a contraindication for the normal procedure. These patients require testing with dilute vaccine, and may also require a desensitisation procedure.

Age less than six monthsis a contraindication, as is the presence of severe febrile illness.

The WHO recommend that the vaccine is used with caution in breast-feeding mothers. (In the UK this is a contra-indication).

Age may be a contraindication. In people aged 60 or older, the risk of adverse events is increased, so the benefits of vaccination need to be weighed against the patient's risk of exposure to yellow fever.

Severe adverse reactions have been reported. These include an extensive area of redness and swelling affecting a large area of the arm or leg, accompanied by a high fever within 48 hours of the injection.

Please note that I am NOT a doctor, and would urge you to seek advice specific to you, and not rely on this site except as a general guide.

Can yellow fever be controlled environmentally?

Much depends on the use of the vaccine, but eradication is clearly possible, though not easy. As malaria campaigns have found, dealing with disease-carying mosquitos is no picnic.

Is there legal protection for workers and others?

Workers sent to endemic or epidemic areas without vaccination may have a case aginst their employer; but they'd be wiser to refuse to go.

Bibliography and Further Information Sources

 

If this article hasn't answered your question, email me at the address below, and I'll try to get the information you seek. I regret I cannot assist with individual cases or essays and school projects, but if it's something I've missed, I'll be happy to try and help.

Article written by Andrew Heenan BA (Hons), RGN, RMN

First Published: 16 February 2008
Last updated: 25 April 2011
© Andrew Heenan 2008 et seq
 

Warning!

This site is not - and is not intended to be - a substitute for medical advice.

The information provided here is accurate, to the very best of our knowledge, but it is general facts, never, ever, specific to your circumstances.

If you need medical advice, you need a doctor.

If you need legal advice, you need a lawyer.

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