Yellow fever, also known as Yellow Jack is an acute viral hemorrhagic disease caused by a RNA virus, the first human virus discovered. The yellow fever virus is transmitted by the bite of female mosquitoes (Aedes aegypti, and other species) and is found in tropical and subtropical areas in South America and Africa. Even though the main vectorAedes aegypti also occurs in Asia, in the Pacific, and in the Middle East, yellow fever does not occur in these areas; the reason for this is unknown.
Yellow fever presents in most cases with fever, chills, anorexia, nausea, muscle pain (with prominent backache) and headache, which generally subsides after several days. In some patients, a toxic phase follows, in which liver damage with jaundice (inspiring the name of the disease), can occur. Bleeding in the mouth, the eyes, and the gastrointestinal tract will cause blood vomiting, hence the Spanish name for yellow fever, vomito negro(black vomit).The toxic phase is fatal in approximately 20% of cases. Because of the increased bleeding tendency yellow fever belongs to the group of hemorrhagic fevers.
Surviving the infection provides lifelong immunity and normally there is no permanent organ damage. The World Health Organization estimates that yellow fever causes 200,000 illnesses and 30,000 deaths every year in unvaccinated populations with nearly 90% of the infections in Africa.
Yellow fever is a clinical diagnosis, which often relies on the whereabouts of the diseased person during the incubation time. Mild courses of the disease can only be confirmed virologically. Since mild courses of yellow fever can also contribute significantly to regional outbreaks, every suspected case of yellow fever (involving symptoms of fever, pain, nausea and vomiting six to ten days after leaving the affected area) has to be treated seriously.
A safe and effective vaccine against yellow fever has existed since the middle of the 20th century, and some countries require vaccinations for travelers. Since no treatment is known, vaccination programs are of great importance in affected areas, along with measures to prevent bites and reduce the population of the transmitting mosquito. Since the 1980s, the number of cases of yellow fever has been increasing, making it a re-emerging disease. This is likely due to warfare and social disruption in several African nations.
Prevention
Personal prevention of yellow fever includes vaccination as well as avoidance of mosquito bites in areas where yellow fever is endemic. Institutional measures for prevention of yellow fever include vaccination programmes and measures of controlling mosquitoes. Programmes for distribution of mosquito nets for use in homes are providing reductions in cases of both malaria and yellow fever.
Vaccination
For journeys into affected areas, vaccination is highly recommended, since mostly non-native people suffer severe cases of yellow fever. The protective effect is established 10 days after vaccination in 95 percent of the vaccinated people and lasts for at least 10 years (81% of patients retained immunity even 30 years later).
The WHO recommends routine vaccinations for people living in endemic areas between the 9th and 12th month after birth. In 2013, the World Health Organization concluded, "a single dose of vaccination is sufficient to confer life-long immunity against yellow fever disease.
Compulsory Vaccination
Some countries in Asia are theoretically in danger of yellow fever epidemics (mosquitoes with the capability to transmit yellow fever and susceptible monkeys are present), although the disease does not yet occur there. To prevent introduction of the virus, some countries demand previous vaccination of foreign visitors if they have passed through yellow fever areas.
Vaccination has to be proven in a vaccination certificate which is valid 10 days after the vaccination and lasts for 10 years. A list of the countries that require yellow fever vaccination is published by the WHO. If the vaccination cannot be conducted for some reasons, dispensation may be possible. In this case, an exemption certificate issued by a WHO approved vaccination center is required.
Besides vaccination, control of the yellow fever mosquito Aedes aegypti is of major importance, especially because the same mosquito can also transmit dengue fever andchikungunya disease. Aedes aegypti breeds preferentially in water, for example in installations by inhabitants of areas with precarious drinking water supply, or in domestic waste; especially tires, cans and plastic bottles. Especially in proximity to urban centres of developing countries, these conditions are very common and make a perfect habitat forAedes aegypti.
Treatment
For yellow fever there is no causative cure. Hospitalization is advisable and intensive care may be necessary because of rapid deterioration in some cases. A symptomatic treatment includes rehydration and pain relief with drugs like paracetamol. Aspirin should not be given because of its anticoagulant effect, which can be devastating in the case of inner bleeding that can occur with yellow fever.
In high-risk areas where vaccination coverage is low, prompt recognition and control of outbreaks through immunization is critical to prevent epidemics. The disease may be difficult to distinguish from other illnesses, especially in the early stages. To confirm any suspicions from the case history, information on the patient's journeys abroad and serology will confirm the diagnosis.
