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Yellow fever is a viral hemorrhagic disease caused by a flavivirus transmitted by infected Aedes or Haemagogus mosquitoes.

After a mosquito bite, the virus enters the skin and infects local immune cells. These cells carry the virus to nearby lymph nodes, where the virus multiplies and buds off.

Viral particles then enter the bloodstream—a process known as viremia—and spread to various organs, such as the liver.

In the liver, the virus infects hepatocytes, causing apoptosis.

Kupffer cells, the liver’s macrophages, release cytokines that intensify inflammation and tissue damage.

This damage disrupts bilirubin metabolism, causing it to build up in the liver and then in the blood.

Excess bilirubin leads to jaundice—the yellowing of the skin and eyes that gives the disease its name.

Yellow fever progresses in three phases: a febrile stage with fever and pain, a short remission phase, and a toxic phase with bleeding, jaundice, and organ failure.