Yellow Fever

Definition

Yellow fever is infection caused by a virus that is spread by mosquitoes. It is prevalent in sub-Saharan Africa and tropical parts of South America. The yellow fever virus is transmitted through the bites of A.aegypti mosquitoes, which acquire the virus after feeding on an infected person. The incidence of yellow fever is highest during rainy and humid seasons.

In mild cases, yellow fever causes headache, fever, nausea and vomiting. However in more severe cases, yellow fever can become more serious and may lead to complications like bleeding, liver, heart, and kidney problems. In almost half of these severe cases, yellow fever results in death.

Symptoms

There are three phases of viral infection :

Incubation phase

The incubation period (the first 3 to 6 days after contracting yellow fever) is asymptomatic.

Acute phase

Symptoms of acute phase develop suddenly and may include:

  • Headache
  • Fever
  • Aches in muscles of back and knees
  • Chills
  • Constipation, nausea, and vomiting
  • Decreased appetite, irritability, and restlessness
  • Weakness and lightheadedness
  • Red eyes

In many patients, these symptoms usually improve within several days.

Toxic phase

In some patients the acute phase may progress into a toxic phase. Symptoms are severe and potentially life-threatening and may include:

  • Yellowing of skin and eyes (jaundice)
  • Stomach aches and vomiting
  • Hiccups
  • Bleeding from mouth, nose, and eyes
  • Decreased urination
  • Liver and kidney failure
  • Heart dysfunction (arrhythmia)
  • Brain dysfunction resulting in confusion, fits and coma

Causes

Yellow fever is caused by a virus belonging to flavivirus family. The virus is spread by A.aegypti mosquitoes. These mosquitoes live near human habitats and breed in pooled water.

The yellow fever viruses infect both humans and monkeys. Mosquitoes transmit the viruses between humans and monkeys. When mosquitoes bite a monkey or human infected with yellow fever, the viruses enters the mosquitoes’ bloodstream and resides in the salivary glands.

These infected mosquitoes can transmit the viruses to another monkey or human, where the virus may cause illness.

Treatment

The early symptoms of yellow fever are non-specific, making its diagnosis difficult. A detailed medical and travel history and testing a blood sample to reveal the presence of virus or antibodies specific to the virus help in diagnosis. There is no particular antiviral medication for yellow fever and treatment consists of supportive care.

  • Replacing and preventing blood loss
  • Providing oxygen and fluids
  • Regulating blood pressure
  • Dialysis in case of kidney failure
  • Treating infections
  • Plasma transfusions to replace blood proteins important for blood clotting
  • Maintaining isolation to avoid transmitting the virus

Prevention

Vaccine

Administration of yellow fever vaccine 2 weeks before traveling to the virus-infected areas prevents yellow fever. The vaccine may have tolerable side effects like low-grade fever, headache, fatigue, muscle pain, and tenderness at the site of injection. In rare cases, the vaccine may lead to inflammation of the brain (encephalitis) and death in infants and older adults with weak immune system.

Mosquito Protection

  • Avoiding outdoor activities during evening or night.
  • Wear full-sleeved shirt and long pants.
  • Use mosquito screens in houses.
  • Mosquito repellents like permethrin-containing mosquito repellent (on clothes, shoes, and bed netting) and DEET or picaridin-containing skin repellent may help.

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