Yellow Fever Yellow Fever, a continuing burden across Africa and South America, has been making a dramatic comeback since the 1980s, particularly in rapidly expanding cities where population growth has not been matched by adequate mosquito control.
With an estimated 200,000 cases reported every year, it's likely the real figure is higher. Whilst not receiving the same high profile as malaria, with its series of global action days, the facts are that 30,000 known deaths result each year from this vaccine-preventable disease.
As well as ensuring employee safety, responsible organisations with staff involved in widespread travel need to ensure travellers are informed, immunised and do not, as a consequence, inadvertently spread this pervasive disease.
Yellow Fever fact fileThere are two types of Yellow Fever Jungle Yellow Fever also known as Sylvatic Yellow Fever occurs in tropical rainforests where monkeys, infected by sylvatic mosquitoes, pass the virus onto other mosquitoes that feed on them; these mosquitoes, in turn bite and infect humans entering the forest. This produces sporadic cases, the majority of which are often young men working in the forest e.g. logging.
Urban Yellow Fever, the major cause of infection in humans, results in large explosive epidemics when travellers from rural areas introduce the virus into areas with high human population density. Domestic mosquitoes carry the virus from person to person. These outbreaks tend to spread outwards from one source to cover a wide area.
Both are viral illnesses, caused by the Yellow Fever Virus which belongs to the flavivirus group. It is spread by mosquitoes, most notably by the bite of the female Aedis Aegypti mosquito, which has unfortunately adapted well to living in villages, towns and cities, breeding in water storage containers, flower pots and discarded tyres found in residential areas. This particular mosquito is also found in Australia and many countries in Asia, areas which are currently uninfected, but could be at risk if visited by people carrying the disease.
The Yellow Fever Virus is an arbovirus and as such, has two characteristic phases, the first causing high fever as the virus invades the host cells, and then after a brief respite of a few days, the second when the body's immune system kicks in. It's this second phase that is most dangerous, as the antibodies generated can cause damage to the blood cells leading to bleeding as well as kidney and liver failure.
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Signs and symptoms
Many Yellow Fever symptoms are mild and can go unrecognised. Early signs of a more severe infection include high fever, headaches, chills, vomiting and characteristic muscle pain, often with permanent backache. The high fever is paradoxically often associated with a slow pulse. Symptoms tend to kick in within 3 to 6 days of an infection and after 3 to 4 days, most patients will improve and the symptoms disappear.
More severe are the second round of symptoms and around 15% of patients will advance into this toxic stage, usually within 24 hours. Noticeable warning signs are bleeding from the nose, mouth, eyes or stomach, as the antibodies attack the blood cells. Blood may also appear in vomit or faeces. Kidney function deteriorates, indicated by abnormal protein levels in the urine to complete kidney failure and no urine at all. The patient's skin and whites of the eyes turn the characteristic jaundice yellow, caused by liver failure. Around 50% of patients who enter the toxic phase die, usually within 10-14 days.
Preventative measures
With no cure for Yellow Fever, anyone likely to enter a Yellow Fever Zone must have a yellow fever vaccination and will, at any rate, be required to present a Yellow Fever Certificate to prove it.
Vaccination
Safe and effective, the single Yellow Fever vaccination provides immunity within one week for 95% of people who receive it and continues to give effective protection for ten years. Yellow Fever Vaccinations should only be given at registered Vaccination Centres that are able to provide the necessary certification. To date more than 300 million doses have been given and side effects are extremely rare, although recently there have been a few serious adverse outcomes reported in Brazil, Australia and the US - a second reason for ensuring these vaccinations are not given in remote environments, but close to main stream medical support.
'Yellow Cards' proving vaccinations are also required for travellers to non Yellow Fever areas including Australia and Asia, to prevent trans-continental spread of the disease. Travellers need to plan ahead to ensure their arrangements are not curtailed by a local shortage of the Yellow Fever vaccination.
Anyone visiting or working in an area where the vaccine cover in the population is low should be particularly alert to Yellow Fever symptoms. Prompt recognition of symptoms is essential to prevent a rapid outbreak.
Avoiding mosquito bites
As with all mosquito-spread diseases, visitors to tropical areas should avoid mosquito bites. The Aedis Aegypti mosquito, a major culprit in spreading Yellow Fever, usually bites during the day so usual precautions, such as wearing long-sleeved clothing and trousers apply round the clock, not just dusk till dawn. Extra protection can be achieved by spraying clothes with the insecticide, Permethrin. Exposed skin should be treated with an effective repellent containing 20-35% DEET (N.N-diethylmethyltoluamide) which can also be sprayed in living and sleeping areas. Always use a bednet if there is no window screening or air-conditioning.
Treatment
There is no specific treatment or cure for Yellow Fever. In the early stages, dehydration and fever can be corrected with rehydration salts and Paracetamol.
It is possible to identify the presence of Yellow Fever antibodies with a blood test. During the toxic stage, intensive supportive care may improve the outcome for seriously ill patients, but unfortunately this is rarely available when and where you need it, in poor, developing countries.
Anyone who contracts Yellow Fever and then recovers will do so completely and gain full immunity to the virus. |
