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
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
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