Yellow fever symptoms

Yellow fever is a viral infection in the tropical areas of South America and Africa. The symptoms of Yellow fever might take 3-6 days to appear after the infected mosquito bite. The most common initial symptoms of yellow fever virus are similar to those of other viral hemorrhagic infections (arenavirus, hantavirus, or dengue): fever, dizziness, profound fatigue, headache, pain in the back and lower extremities, nausea, vomiting, and muscle pain. The initial symptoms usually last for 2-4 days.

The initial symptoms are followed by a remission lasting about 24-48 hours. Symptoms improve for most people during this period, and they recover fully. However, 12% of infected people will enter the more toxic second stage of the disease. In this stage, people experience fever, nausea and vomiting, abdominal pain, and skin jaundice. This phase is characterized by the dysfunction of multiple organs, including the liver, kidneys, and heart. Multi-organ failure is common.

Half of the people who enter this toxic second stage die within 10-14 days, while the rest fully recover without significant organ damage.

Treatment is symptomatic and aimed at reducing symptoms and making the patient comfortable. Vaccination plays a vital preventative role against yellow fever disease. The vaccine is safe and effective (99 % of vaccinated people develop immunity) after 30 days of vaccination. A single dose provides life-long immunity.

Key facts about yellow fever

Incubation period

The incubation period (time between infection and first symptoms) for yellow fever is 3–6 days.

Symptoms

No symptoms

About 55% of infected people have no symptoms.

Mild symptoms

About 33% of infected people will have mild symptoms such as fever, muscle pain, nausea, and vomiting.

Severe symptoms

In 12% of cases, people have severe, life-threatening symptoms such as abdominal pain, yellowing of the skin, vomiting of blood, bleeding from the eyes, nose, and mouth, brain damage, and coma. Up to 50% of these patients will die from yellow fever–related complications.

Duration of symptoms

• Mild symptoms last three to four days. However, in more than 12% of cases, people begin to experience severe symptoms a day after their mild symptoms are gone.
• About 30%–50% of people with severe symptoms will die from disease-related conditions within 7 to 10 days.

Diagnosis

Diagnosing yellow fever disease clinically (based on symptoms and physical examination) is very difficult since it can be confused with other conditions such as malaria, hepatitis A, leptospirosis, dengue fever, and even food poisoning.

Urine and blood PCR (polymerase chain reaction test) can establish the diagnosis of yellow fever in the initial stage. ELISA or PRNT tests that look for antibodies are the tests of choice for the later stage.

Transmission

Yellow fever virus is transmitted by daytime biting mosquitos (Aedes species in Africa, Haemagogus species in South America). Both humans and nonhuman primates (monkeys) can be hosts in the transmission cycle.

In Africa, yellow fever virus transmission is most common during the rainy season when mosquitoes breed in the abundant savannah vegetation. Mosquitoes also breed in the containers used to store potable water.

In South America, mosquitos breed in jungle tree holes that contain rainwater. So, the person entering the forest is at the highest risk.

Treatment

The treatment of yellow fever consists of supportive care; no specific antiviral therapy is available. Modern intensive care may help with the management of severe cases.

Travelers hospitalized after returning to the United States or Europe have had fatal outcomes despite intensive care, demonstrating the inevitable course of severe yellow fever.

The outcome is determined during the second week after onset, at which point the patient either dies or rapidly recovers.

Approximately 20 to 50 percent of patients who have severe cases of yellow fever who are severely ill do not survive.