Yellow Fever

Yellow Fever

Article
Diseases & Conditions
Infectious Diseases
Contributed byMaulik P. Purohit MD MPHOct 25, 2020

What are the other Names for this Condition? (Also known as/Synonyms)

  • Jungle Yellow Fever
  • Sylvatic Yellow Fever
  • Urban Yellow Fever

What is Yellow Fever? (Definition/Background Information)

  • Yellow Fever is a viral illness that is transmitted by a mosquito. It is common in certain regions of Africa and South America
  • The infection can affect both, the residents in the endemic areas, and travelers visiting these areas
  • Generally, the symptoms of Yellow Fever are mild and a majority of the individuals recover, without any serious medical issues. However, if the infection is severe, then mortality rates can reach up to 50%

Who gets Yellow Fever? (Age and Sex Distribution)

  • A Yellow Fever infection affects both males and females with equal predisposition
  • It is generally seen to infect individuals, between the age ranges of 20-40 years. However, younger and old individuals, are also prone to be infected by the Yellow Fever virus
  • Travelers visiting endemic areas

What are the Risk Factors for Yellow Fever? (Predisposing Factors)

  • Living in or visiting tropical areas, where Yellow Fever is endemic. Traveling to endemic area increases the risk. The main endemic areas include Sub-Saharan Africa and the tropical regions of South America
  • Yellow Fever usually infects individuals between the ages 20-40 years. When older individuals are infected, they are more likely to get a fatal form of the disease

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Yellow Fever? (Etiology)

  • A virus that is transmitted by a mosquito, called Aedesaegypti, causes Yellow Fever. These mosquitoes are found near human dwellings and are known to breed, even in clean water sources
  • Mosquitoes can also transmit the fever to humans, after carrying the virus from an infected monkey. Once, the virus reaches the mosquito from an infected monkey (or a human), it is stored in their salivary glands. An infected mosquito can subsequently transmit the virus, when it either bites a human, or a monkey
  • After bitten by a mosquito, the virus travels through the blood stream resulting in the viral illness/infection
  • The virus can be transmitted from an infected individual, to someone who is not infected

What are the Signs and Symptoms of Yellow Fever?

During the incubation period, which can last between 3-6 days, there are no signs or symptoms exhibited by an infected individual. After this incubation period, an acute phase of the illness begins.

Signs and symptoms an individual may experience during the acute phase of Yellow Fever include:

  • Body aches, headaches
  • High fevers
  • Gastrointestinal symptoms, such as nausea, vomiting
  • Decreased appetite
  • Spells of dizziness
  • Congested eye, which result in red eyes

The signs and symptoms may get better and completely disappear, after the acute phase. After getting better from the acute phase, the disease can progress to its toxic phase. Yellow Fever does not progress from acute phase to toxic phase in all individuals; a majority of the individuals fully recover from the acute phase.

Signs and symptoms in the toxic phase include:

  • Abdominal pain
  • Nausea and vomiting; occasionally, vomiting of blood
  • Yellowish discoloration of skin and mucous membrane resulting from jaundice (hence the name Yellow Fever)
  • Decreased urine output resulting from kidney failure (renal failure)
  • Bleeding from various parts of the body including the mouth, eyes, and nose
  • Abnormal rhythms of the heart due to cardiac infection (myocarditis)
  • Confusion, dizziness, convulsions, due to brain infection (encephalitis)

The toxic phase of the infection is usually deadly in 50% of the cases.

How is Yellow Fever Diagnosed?

A good clinical history, which includes any travel history, is vital towards early detection and diagnosis of Yellow Fever. The initial symptoms of the patient can resemble that of common flu, and the diagnosis may be missed, early in the course of the infection.

Available tests to diagnose Yellow Fever include:

  • Enzyme-linked immunosorbent assay (ELISA), performed on blood
  • Polymerase chain reaction (PCR) tests; PCR is a molecular blood test. However, it may take up to 72 hours to get the molecular testing results

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Yellow Fever?

Generally, Yellow Fever infection is mild and results in a complete recovery, without any complications. However, the mortality rate is 50%, once the infection enters the toxic phase.

  • Death usually occurs within 15 days from the start of symptoms during the toxic phase.  It is important to note that very few individuals progress to this toxic phase
  • Complete recovery is possible without complications, even in individuals, who progress into the severe toxic phase of Yellow Fever
  • 50% of the individuals, who recover from toxic phase, have a slow recovery process. Such individuals may get better slowly over a period of time, which may take up to several months
  • During recovery from the toxic phase, individuals may develop pneumonia and infections, of other body organs. For this reason, close follow-up with regular healthcare check-up, is necessary

How is Yellow Fever Treated?

  • Currently, there are no specific treatment measures for Yellow Fever, including the availability of anti-viral medication
  • The treatment generally consists of supportive and symptomatic care, which includes appropriate fluids infusions, maintaining blood pressure, oxygen therapy, and dialysis for kidney failure
  • If a hemorrhage occurs, there could be a significant blood loss. In such cases, plasma and packed red cells transfusions may be necessary
  • Excessive bleeding can result in loss of clotting factors, which increases the bleeding. In such situations, administration of clotting factors can improve the abnormal bleeding, seen due to the viral disease

How can Yellow Fever be Prevented?

Preventive measures for Yellow Fever include:

Yellow Fever vaccine: 

  • A safe and highly effective vaccine is available that can prevent Yellow Fever. A single dose of vaccine normally provides 10 years of immunization protection
  • This vaccination is usually administered 10-14 days, before traveling to the endemic areas. Travel to endemic areas usually requires a medical certificate of immunization (to visit such countries)
  • The vaccination can also be administered to resident's living/staying in such areas

In a majority of individuals, the Yellow Fever vaccine causes no side effects. However, a minority of them may suffer from mild flu-like symptoms, which include mild fevers, body aches and headaches, getting tired easily, fatigue, and increased pain at the vaccine inoculation site.

Rarely, serious side effects may occur, after the vaccination. Most of these cases are in individuals, who are either very young or very old. Hence, the safest recommended age for Yellow Fever vaccine is between 9 months to 60 years old.

Mosquito bite protection:

Protection against mosquito bites is an important component of prevention. This can be achieved using mosquito repellents or wearing long-sleeved clothes.  Mosquito nets and mesh-like screens on house windows/doors/ventilators will result in reduced mosquito bites.

An exposure to mosquitoes can be decreased by:

  • Decreasing outdoor activity
  • Using suitable clothing to cover your body, which can decrease exposure to mosquitoes
  • Using mosquito nets while sleeping.

There are a variety of mosquito repellents that can be utilized to decrease mosquito bites. Broadly, these are categorized as non-skin repellents and skin repellents.

Non-skin repellents:

  • These are permethrin-containing compounds that are applied to clothing, bed nettings, bed sheets, and other suitable objects (like shoes, camping gear)
  • It is very important to note that permethrin-containing repellents should not be directly applied to the skin

Skin-repellents:

  • These are compounds that may be directly applied to the skin, and usually contain DEET and picaridin
  • The chemical compound DEET contains ingredients that are not recommended for children or infants, under 2 months old
  • The Center for Disease Control and Prevention (CDC) also recommends the use of oil of lemon eucalyptus, which is a natural product. However, this oil is not recommended for children, who are less than 3 years of age

What is the Prognosis of Yellow Fever? (Outcomes/Resolutions)

  • In a high percentage of individuals with the acute Yellow Fever, the infection is mild and a complete recovery expected
  • If the condition progresses to its toxic phase, then around 50% of these infections may become severe. Severe infections can result in death, if proper and timely treatment is not administered
  • However, a complete recovery is possible without complications, even in individuals who progress to the severe toxic phase of Yellow Fever
  • During the recovery from the toxic phase, individuals may develop pneumonia and other organ infections. For this reason, close monitor of the condition with regular healthcare checkups are essential

Additional and Relevant Useful Information for Yellow Fever:

Besides Yellow Fever, the Aedesaegypti mosquito can also cause several diseases, like dengue, chikunguniya, and other viral infections.

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Maulik P. Purohit MD MPH picture
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Maulik P. Purohit MD MPH

Assistant Medical Director, Medical Editorial Board, DoveMed Team

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