Yellow Fever
Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains particularly in the back, and headaches.
Symptoms typically improve within five days. In about 15% of people, within a day of improving the fever comes back, abdominal pain occurs, and liver damage begins causing yellow skin. If this occurs, the risk of bleeding and kidney problems is increased.
The disease is caused by the yellow fever virus and is spread by the bite of an infected female mosquito. It infects only humans, other primates, and several types of mosquitoes. In cities, it is spread primarily by Aedes aegypti, a type of mosquito found throughout the tropics and subtropics.
The virus is an RNA virus of the genus Flavivirus. The disease may be difficult to tell apart from other illnesses, especially in the early stages. To confirm a suspected case, blood sample testing with a polymerase chain reaction is required.
Yellow Fever Signs and symptoms
Most people with yellow fever do not develop symptoms, or the symptoms are very mild.Yellow fever has an incubation period of between 3 and 6 days, so it takes from 3 to 6 days for signs and symptoms to appear after a person is infected.
The disease cannot spread among humans. Only infection-carrying mosquitoes spread the disease to humans. The main symptoms of yellow fever are a high temperature, a slow pulse, albuminuria, jaundice, congestion of the face, and hemorrhage, or bleeding.
Signs and symptoms are categorized into two stages:
In the early, acute stage, the individual may experience:
- Aching muscles, particularly the back and knees
- A high fever
- Dizziness
- Headache
- Loss of appetite
- Nausea
- Shivers, or chills
- Vomiting
These symptoms usually disappear within 7 to 10 days.
These symptoms usually improve after a few days, but around 15 percent of trusted sources of people enter a second stage or toxic stage. The symptoms are more severe, and they may be life-threatening.
These include:
- Recurring fever
- Abdominal pain
- Vomiting, sometimes with blood
- Tiredness, sluggishness, lethargy
- Jaundice, which gives the skin and whites of the eyes a yellow tinge
- Kidney failure
- Liver failure
- Hemorrhage
- Delirium, seizures, and sometimes coma
- Arrhythmias, or irregular heartbeats
- Bleeding from the nose, mouth, and eyes
Between 20 percent and 50 percent trusted Source of people who develop toxic stage symptoms die within two weeks. Within 7 to 10 days, yellow fever is fatal in around half of all people who enter the toxic phase. Those who recover do not generally have any organ damage and are immune for life.
Yellow Fever Causes and risk factors
A flavivirus causes yellow fever. It is transmitted by mosquito bite, usually the Aedes aegypti mosquito. The mosquito becomes infected by biting an infected human or a monkey. An infected mosquito is a source of infection for the rest of its life.
Apart from mosquitoes, the only other known hosts of the virus are primates and humans. The flavivirus is believed to be endemic among monkeys that live in the treetops of the jungle, known as the jungle canopy, in many parts of Africa and the Americas.
If the infected mosquito passes the flavivirus on to a person who is in the jungle, that person may become a source of infection when they return to their community. They can go on to infect other people.
Anybody who travels to an area where the yellow fever virus is present is at risk of becoming infected. These areas include parts of Africa, especially sub-Saharan Africa, tropical South America, and some parts of the Caribbean.
Travelers should check if the area they are visiting requires a vaccination. A yellow fever vaccine taken 10 to 14 days before traveling provides effective protection from the disease.
Yellow Fever Diagnosis
The diagnosis will be confirmed after the doctor detects the signs and symptoms and carries out a blood test. A blood test is necessary because other diseases have similar signs and symptoms.
These include:
- Dengue fever
- Leptospirosis
- Malaria
- Poisoning
- Typhoid
- Viral hepatitis
- Some other viral hemorrhagic fevers
A blood test may reveal the virus, or it may detect antibodies that the body produces when the virus enters the body. A blood test may also reveal a drop in white blood cells, or leucopenia, another sign of infection.
The blood tests used are an enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR).
Test results may take several days.
Yellow Fever Treatment
There is no effective antiviral medication to treat yellow fever, so treatment consists of supportive care in a hospital. This includes providing fluids, oxygen, making sure blood pressure is adequate, replacing lost blood, kidney dialysis if there is kidney failure, and treating any secondary infections.
Some patients may be given plasma transfusion to replace proteins that help with clotting. The patient should be kept away from mosquitoes. If a mosquito bites the patient, they will become infected and then pass the disease on to other people. They should not use aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) because of the risk of bleeding.
In 2014, a study published in the journal PLOS Neglected Tropical Diseases reported that changes in white blood cells could signal an early sign of fatal yellow fever. This, say the scientists, could lead to better diagnosis and treatment.
Yellow Fever Prevention
In the past, yellow fever devastated communities, including those in the United States (U.S.) and Europe. In the middle of the 20th century, scientists developed a safe and effective vaccine that prevents yellow fever.