Most people who are infected with the yellow fever virus do not develop symptoms of the yellow fever disease. And if they do, the symptoms are usually mild. A small number of those who are infected develop serious symptoms of yellow fever disease and about half of those who develop serious symptoms of the disease die within 7 to 10 days.
- The symptoms of yellow fever usually occur in different phases (initial phase and toxic phase). The initial phase occurs three to six days after an individual has been infected with the yellow fever virus. Yellow fever incubation period is about 3 to 6 days; so, during this period, the infected person will not have any symptoms.
- The symptoms of yellow fever are similar to those of some other diseases (like malaria, influenza and typhoid fever), especially in its initial phase.
The symptoms that are commonly seen in the initial phase of the disease are:
- Back ache
- Joint ache
- Sensitivity to light
- Loss of appetite
- Nausea and vomiting
- Fever and chills
- Muscle pain
- After three to four days, these symptoms disappear in many cases – this initial phase of yellow fever ends after about three to four days. Most people make a complete recovery after the initial phase.
- But within about 24 to 48 hours (1–2 days) of recovering from the initial symptoms, there are a few people (about 15% of those who are infected) who enter a more serious phase of the yellow fever disease. This phase is called the toxic phase; and it is life-threatening. In this phase, many organs of the body are affected – especially the kidneys and liver.
Signs and symptoms seen in the toxic phase of yellow fever are:
- High fever
- Abdominal pain
- Jaundice (yellow discolouration of the skin and whites of the eyes)
- Reduced urination
- Decreased heart rate
- Dark urine
- Bleeding from the eyes, nose, and mouth
- Bleeding in the stomach – internal bleeding
Failure of multiple organ systems leads to death. Usually, half of those who enter this serious phase (toxic phase of yellow fever) die within 7-10 days.
Yellow fever-infected individuals are infectious – that is, they are able to transmit the yellow fever virus – a short while before the fever starts and about three to five days after the symptoms of the disease start.