Yellow fever is caused by a flavivirus. It is an acute viral haemorrhagic disease. The virus is transmitted through the bite of an infected mosquito. Yellow fever is named because the virus attacks the liver and the patient’s skin and eyes become yellow, similar to how it happens in jaundice.
The disease is most prevalent in Africa and South America. It is spread through the bite of the Aedes species of mosquitoes found in Africa and the Haemagogus species in South America. The yellow fever mosquitoes typically bite during the daytime, especially around sunrise and sunset.
Symptoms of yellow fever may appear within three to six days of being infected. Initial symptoms include sudden onset of fever, chills, headache, joint and muscle pain, loss of appetite, abdominal pain, back pain, nausea and vomiting, fatigue, weakness and dehydration. Patients who do not recover during this stage and enter the toxic and more severe phase may experience internal bleeding, jaundice, shock and organ failure. Approximately 15 percent of patients reach this stage and half of them die within ten to fourteen days.
Since there is no specific treatment for yellow fever, it is in the interest of people traveling to infected regions to get vaccinated. There are countries that require proof of yellow fever vaccination to enter. The vaccine for yellow fever is a single-dose vaccine and is considered to be safe and effective for people over the age of nine months. The vaccine is generally not recommended for pregnant or breastfeeding women, children under the age of nine months, adults 60 years and older and those who have a weak immune system. The vaccine takes around ten days to become effective.
According to the WHO, there are approximately 200,000 cases of yellow fever resulting in 30,000 deaths worldwide each year. 90 percent of these cases occur in Africa. The populations at risk include forty-four endemic countries in Africa and Latin America with a total population of over 900 million.
The problem with Yellow fever is that it is difficult to diagnose and is often confused with malaria, dengue haemorrhagic fever, leptospirosis, viral hepatitis, and other haemorrhagic fevers as well as poisoning. Blood tests are used to detect yellow fever antibodies as well as other tests that require trained laboratory staff and specialized equipment.
Though restricted to Africa and South America, travellers visiting these two areas should use preventive vaccination for Yellow Fever.