Yellow fever is a mosquito-borne virus that most people contract in subtropical and tropical environments throughout South America and Africa. Though rare, it is a serious illness that, in the worst stages, can result in severe organ damage and death.
If you plan to travel to an area in which yellow fever is a risk, or if you or a loved one has already contracted the virus, it may help to learn everything you can about the disease. In this guide, you will find everything you need to know about transmission, incubation periods, symptoms, treatment, prevention and more.
Yellow fever is considered an arbovirus and belongs to the same genus as West Nile, Japanese encephalitis and St. Louis encephalitis viruses. It is primarily transmitted to humans via the bits of the Haemagogus or Aedes mosquitoes. These mosquitoes become carriers of the virus after feeding on infected primates and transfer the virus after feeding on another primate. “Primate,” for the purposes of this discussion, refer to human and non-human creatures.
Though humans cannot transmit the virus to other humans directly, they are infectious to other mosquitoes. The remain infectious from shortly before the onset of the fever to up to five days after.
Health organizations have identified three transmission cycles of yellow fever: jungle (sylvatic), intermediate (savannah) and urban.
Not everyone who contracts yellow fever develops symptoms. Those who do, however, begin to show signs at between three to six days of transmission. When symptoms do occur, they are typically flu-like and include the following:
For most people, symptoms resolve within one week. However, they may experience weakness and fatigue for months following their initial recovery.
In approximately 85% of cases that result in symptoms, patients make a full recovery. However, the remaining 15% enter the second, more toxic stage of yellow fever. In this stage, individuals may experience a brief period of “recovery.” That period is short lived, lasting anywhere from a couple of days to a few hours. Following this period, individuals develop a more intense fever. Shortly after the fever returns, organ damage begins to occur. The first organs affected are typically the liver and kidneys. Once the organs start sustaining damage, patients may develop intense abdominal pain, vomiting, dark urine and jaundice (yellowing of the skin). Patients may bleed from their nose, eyes, mouth or stomach.
The mortality rate for the second stage of yellow fever is high, with between 30% to 60% of patients dying within seven to 10 days of entering stage two. Those who do survive the second stage live their lives with considerable organ damage.
Because, it its initial stage, yellow fever resembles several other illnesses, it is difficult to diagnosis. Even in its more sever stage, yellow fever resembles other mosquito-borne illness, such as malaria, viral hepatitis, leptospirosis and other haemorrhagic fevers.
Though testing does exist, it does not guarantee a diagnosis. A polymerase chain reaction (PCR) test may be able to detect the virus in the blood or urine and in the early stages, but not always. If a person develops the second stage of the virus, doctors may use a ELISA or PRNT test to identify antibodies.
Unfortunately, there is currently no cure for yellow fever. However, the best outcomes occur when individuals seek early care and treatment from hospitals, and when they and healthcare teams treat for kidney and liver failure, dehydration and fever early on. Antibiotics may be able to control associated infections, though not the yellow fever itself.
There are two main means of preventing yellow fever: through a vaccine and through mosquito repellent measures.
The yellow fever vaccine is the number one way to prevent yellow fever. The yellow fever vaccine is not a part of the typical vaccine schedule for most countries. However, it is recommended to people who travel to parts of the world where yellow fever is prevalent, such as South America and Africa.
The yellow fever vaccine is safe and affordable, and just a single shot provides life-long protection. Unlike the flu or other common vaccines, there is no need to get a booster. The vaccine has been around for nearly 100 years, a fact that demonstrates both its effectiveness and safe nature.
Health organizations take three approaches to vaccinating against yellow fever: routine infant immunization in high-risk areas, mass vaccination and vaccination for travellers to high-risk areas.
In high-risk areas, health organizations aim for at least an 80% vaccination rate. They strive to accomplish their goals by making infant immunization routine and by enlisting mass vaccination campaigns. The higher vaccination rates are, the lower the risk of transmission becomes.
Individuals outside of high-risk areas should receive a yellow fever vaccine before travelling to one. Receiving a vaccine not only protects oneself against yellow fever but also, prevents the risk of transmitting the disease outside of high-risk borders.
Understandably, many people are concerned with the possible side effects of the yellow fever vaccine. Though side effects can and have occurred, they are rare. The rates for severe “adverse events following immunization” (AEFI) are low, at about 0.21 per 10,000 vaccines delivered within high-risk areas. For vaccines delivered outside of high-risk areas, the rates for AEFI are between 0.09 and 0.4 per 10,000.
When AEFI of yellow fever do occur, the side effects are severe and typically entail an attack on the nervous system, liver and kidneys. The risk of AEFI climbs with age, with people over 60 more susceptible to adverse events than younger individuals. Individuals with severely compromised immune systems—such as persons living with HIV/AIDS—also have a risk of developing an AEFI to the yellow fever vaccine. For these individuals, doctors should carefully weigh and discuss with patients the risks and potential benefits before delivering the vaccine.
Certain groups of people either cannot or should not receive the yellow fever vaccine. Those are as follows:
Save for individuals with certifiable medical grounds for not receiving the vaccine, countries do have the right to require travellers to provide a certificate of vaccination upon entering the country. The purpose of such a request is to contain the spread of yellow fever and other infectious diseases.
Outside of getting the vaccine, there are other measures you can take to protect yourself and others against yellow fever. Those are as follows:
When you can prevent mosquito bites, you can prevent the spread of yellow fever.
Individuals are not naturally immune to yellow fever. You can only become immune to yellow fever in one of two ways. The first is by vaccinating yourself. The second is by contracting yellow fever and surviving it. If you had yellow fever once, you cannot contract it again.
To date, there are currently 13 countries throughout South America and 34 countries throughout Africa that are either endemic for, or have regions that are endemic for, yellow fever. In these countries, the incident rate is around 84,000 to 170,000 severe cases per year, with the death rate being between 29,000 and 60,000 deaths. Travellers to these endemic regions have a heightened risk of contracting the virus.
In earlier centuries, yellow fever did make its way to Europe and North America, causing large and deadly outbreaks. Since then, countries have cracked down, requiring travellers either to show proof of vaccination or quarantine upon return home.
Yellow fever has the potential to be a serious and deadly disease, which is why travellers to and residents of high-risk areas should take every precaution to prevent infection. If you do happen to receive a mosquito bite in a high-risk area, monitor yourself for signs of infection and seek medical attention immediately upon developing symptoms.