What is the Yellow Fever Virus?

Yellow fever virus is an acute hemorrhagic disease that can be fatal. A viral infection in the Flaviviridae family, it is transmitted by female mosquitoes. Yellow fever has two main cycles: an urban cycle, and a jungle cycle that relies on monkeys as carriers. Signs of yellow fever are basically flu-like, though it can cause internal bleeding, meningitis, kidney or liver failure if left untreated.

The incubation period for yellow fever virus begins within three to six days after exposure. In mild cases of yellow fever virus, patients experience symptoms including fever, chills, headache, loss of appetite, back pain, nausea and vomiting. This is considered a mild infection and typically lasts only three or four days.

Hepatitis is a classic feature of yellow fever’s second phase. Many people with hepatitis develop jaundice, which makes their skin and the whites of their eyes turn yellow. In this toxic second phase, patients suffer severe gastrointestinal distress that results in black vomit and bleeding around the eyes and mouth. A person who survives the yellow fever virus will have life-long immunity, and there generally no permanent organ damage.

In the urban cycle, a mosquito carrying the yellow fever virus will pass it to both people and other primates via a mosquito bite. The mosquito that carries yellow fever also can transmit other diseases, including Chikungunya virus and the Dengue fever virus. The urban cycle no longer exists in South America, but it is responsible for outbreaks of yellow fever virus in Africa.

In the jungle cycle, the yellow fever virus strikes primarily non-human primates, though infected African primates are largely asymptomatic. As of 2011, the jungle cycle in South America is the only way humans infect themselves; this happens when a person goes into the jungle, is infected and carries the disease back to civilization. This jungle virus cycle is blamed for the failure to eradicate yellow fever.

In Africa, there is a third infectious yellow fever virus cycle, the savannah or intermediate cycle. The savannah cycle happens between the other two cycles. This cycle has become the most common form of yellow fever in Africa.

A clinical diagnosis of yellow fever relies on the patient’s whereabouts during the incubation time. Mild courses of yellow fever can contribute to regional outbreaks. Every patient suspected of yellow fever has to be treated seriously.

Vaccinations can help prevent the spread of the yellow fever virus. Avoidance of countries with endemic yellow fever is advised. Once vaccinated, the patient will receive a certificate that he can carry with him to confirm the vaccination. This certificate is valid after the first 10 days and is good for 10 years. People who travel to these countries should consider the vaccination, because the most severe cases are found among non-native people.