What is Yellow Fever?
Yellow fever is an illness caused by a virus that is commonly transmitted through mosquito bites. It is mainly found in tropical and subtropical regions in South America and Africa. The mosquitos that carry this virus are primarily from the Aedes and Haemagogus species. The symptoms can vary significantly, from a mild fever which lasts for a short time to serious complications such as severe bleeding and liver disease. The name “yellow fever” comes from “jaundice”, a condition that causes skin and eyes to turn yellow and can affect some patients with severe disease.
Yellow fever is usually diagnosed based on a person’s travel history to areas where the disease is common, their exposure to infected mosquitoes, their vaccination history, their symptoms, and lab tests. Most people who get yellow fever experience symptoms similar to many other common viral infections, and these symptoms usually go away on their own. However, severe cases of yellow fever can be deadly, with up to half of these patients dying from the disease.
Unlike many other viruses carried by mosquitoes, humans infected with yellow fever can also infect mosquitoes when the virus is in their blood, which helps spread the virus. While there isn’t a specific antiviral treatment for yellow fever, there is an effective vaccine available for people traveling to areas where the disease is common. The best way to avoid getting yellow fever is to prevent mosquito bites and get vaccinated if you’re visiting an area where the disease is commonly found.
What Causes Yellow Fever?
The virus that causes Yellow Fever belongs to the same family as the viruses that cause West Nile, St. Louis, and Japanese encephalitis; they all share a material called RNA. This virus is mainly spread by mosquitoes that breed in tree-holes, like the Aedes aegypti and Haemagogous species, especially during the rainy season.
The Yellow Fever virus spreads in three different ways – through the jungle, intermediate, and urban cycles. In the jungle cycle, the virus passes between monkeys and mosquitoes. Humans can get infected if they are bitten by a mosquito carrying the virus while they are in the jungle.
The intermediate cycle usually happens in the African savannah, near jungle borders. Here, humans who live or work in these areas can get infected by mosquitoes that have bitten infected monkeys or other infected humans.
The urban cycle occurs when a human, who got infected in either the jungle or intermediate cycle, travels to an urban area. The virus in their blood can infect local mosquitoes, which then can spread the virus to other humans in these urban areas.
However, it’s important to note that Yellow Fever doesn’t spread directly from person to person, or from monkey to human, without a mosquito involved in the process.
Risk Factors and Frequency for Yellow Fever
Thanks to vaccines, global yellow fever epidemics have downgraded, but the disease is making a comeback in many regions of Africa and South America. Yellow fever does not discriminate, it affects people of all races and ages. The highest death rates are seen in babies and the elderly, as their immune systems are often weaker. In the United States, yellow fever is extremely rare. Most of the cases diagnosed are in travelers who have not been vaccinated and have visited sub-Saharan Africa or South America. While most infected people have symptoms that go away on their own, others could develop severe disease.
- Thanks to vaccinations, worldwide yellow fever epidemics have decreased.
- However, yellow fever has reemerged in many parts of Africa and South America.
- It can affect people of all races and ages.
- The highest death rates from yellow fever are seen in infants and the elderly, whose immune systems might be weaker.
- In the United States, yellow fever is very rare.
- The majority of diagnosed cases involve unvaccinated travelers who have been to sub-Saharan Africa or South America.
- While most people have symptoms that go away on their own, some people could develop severe disease.
Signs and Symptoms of Yellow Fever
To diagnose this condition, doctors need a detailed travel history and a record of the patient’s vaccinations. Some people may experience symptoms like headaches, general discomfort, yellowing skin or eyes (jaundice), and muscle aches, often coupled with intense back pain.
After being exposed to the cause of the disease, it usually takes 3-7 days for symptoms to appear. Most people experience mild flu-like symptoms. However, about 15% of cases can be severe, with chills, low back pain, headaches, and fever.
Patients often get a short break in symptoms that might last one to two days. But then the symptoms return along with severe body poisoning. At this stage, it’s common to see liver or kidney disease, which is life-threatening.
Doctors may notice certain signs during a physical examination. These include the Faget sign or pulse fever dissociation, flushing of the face, and redness in the whites of the eyes. In the most severe phase, patients may start to show signs of jaundice, have dark urine, and vomit. Bleeding can occur from places like the nose and mouth, and in the digestive tract. Some of these symptoms are similar to malaria, leptospirosis, viral hepatitis, other severe fever illnesses, dengue, and other infections caused by the flavivirus.
Testing for Yellow Fever
The detection of yellow fever can be done using several quick methods. These include identifying the yellow fever antigen (a specific part of the yellow fever virus that our immune system can recognize) using a type of test called a monoclonal enzyme immunoassay, which is performed on your blood serum. Another method is by locating the specific genetic material of the yellow fever virus using a test known as polymerase chain reaction (PCR) assay.
The ELISA, which is a test that checks for specific antibodies in your blood that your immune system produces in response to yellow fever, can also be used. Similarly, the titers of antibodies (the amount of antibodies in your blood) can be measured using serology.
Additional tests depend on what body part is affected. If it seems like your mental state has changed, a lumbar puncture (which involves taking a sample of fluid from your spine for testing) and a CT scan (a special X-ray test that can produce detailed pictures of the inside of the body) are carried out.
Your blood might also be tested. If the bloodwork shows a decrease in white blood cells (known as leukopenia) along with raised levels of an enzyme called transaminase, it can be a sign of yellow fever. Additionally, having a low count of a type of white blood cells called neutrophils (a condition known as neutropenia) is common during the first week of infection.
If the liver is affected, then the coagulation profile (which examines how well your blood clots) could be abnormal. Other signs of serious yellow fever are a raised creatinine level (which indicates how well your kidneys are working), low blood sugar (hypoglycemia), and metabolic acidosis (a condition that happens when your body produces too much acid).
Specific yellow fever testing can mostly be done at the Centre for Disease Control (CDC), but the results will be sent to the state health department. Moreover, when blood samples are sent directly to the CDC, it’s important to inform the health department.
If you experience difficulties in breathing because of fluid build-up in the lungs (pulmonary edema), a chest X-ray will be performed. An ECG (a test that checks the electrical activity of your heart) can detect a delay in the electrical signals that regulate your heartbeat (prolonged QT and PR intervals). Irregular heartbeats, or arrhythmias, can frequently occur if yellow fever infection affects the heart muscle (myocardium).
Treatment Options for Yellow Fever
Yellow fever is an infection that needs to be reported if contracted. If you get infected, symptoms, such as fever, headache, nausea, and muscle pain, usually show up after 3 to 6 days. Unfortunately, there’s no specific treatment for yellow fever, but severe cases need intensive care to help the body fight off the disease. This usually includes a lot of fluid and essential care.
People with severe cases might be placed in an intensive care unit (ICU) and closely watched for potentially serious complications. These complications might include issues like uncontrolled bleeding, problems with the kidneys and liver, and a condition called disseminated intravascular coagulation (DIC), where clots and bleedings can happen throughout the body.
While yellow fever isn’t spread from person to person, infected individuals should be kept apart from others until doctors confirm the diagnosis. You should take precautions when taking care of people infected with yellow fever. Also, it’s important that infected patients avoid contact with mosquitoes because if a mosquito bites an infected person, it can carry the virus and spread it to others.
The best way to deal with yellow fever is to prevent it in the first place. The first piece of advice is to avoid getting bitten by mosquitoes. You might be thinking that you’d have to stay indoors all the time, but that’s not the case. Just make sure you’re well-protected when you’re outside. Wear clothing that covers your skin like long sleeves, long pants, socks, and close-toed shoes. Spraying anti-mosquito sprays or other repellents that contain ingredients like DEET or oil of lemon eucalyptus on your skin and clothing can also help reduce the risk of bites. You should also avoid standing water sources, which are common breeding grounds for mosquitoes.
Furthermore, there’s a very safe and effective vaccine available for yellow fever. It can provide protection for a lifetime and it works for nearly 100% of people who get it 30 days after receiving it. If you have certain health conditions you should talk to your doctor before getting the vaccine or if you plan to travel to an area where yellow fever is commonly found.
What else can Yellow Fever be?
When a doctor is trying to figure out if a patient has yellow fever, they consider a wide range of other conditions that share similar symptoms. This is why knowing the patient’s travel history can be very important. The diseases they often consider include:
- Viral hemorrhagic fevers
- Viral hepatitis
- Malaria
- Lassa fever
- Ebola virus
- Typhoid fever
- Dengue fever
- Disseminated Intravascular Coagulation (a condition affecting the blood)
- Louse-borne relapsing fever
- West Nile virus encephalitis
- Japanese encephalitis
- Herpes simplex encephalitis
- Eastern and Western equine encephalitis
- Venezuelan Equine encephalitis
- Enterovirus meningitis
- Mycoplasma meningitis
- Cytomegalovirus infection in immunocompromised host
- Tuberculous meningitis
- Nipah virus infection
- Rocky Mountain spotted fever
- Fungal meningitis
- Leptospirosis
- Neurocysticercosis
- Amebic meningoencephalitis
What to expect with Yellow Fever
Most people who contract yellow fever don’t show severe symptoms and recover quite well. Approximately 15% of those showing symptoms may develop a more serious form of the disease. Despite the severity, most patients will recover, though it may take several weeks or even months for them to bounce back completely. In most instances, any liver or kidney dysfunction that occurred during the disease will also get better. However, severe cases of yellow fever can be fatal, with a mortality rate ranging from 30% to 50%.
Protection against yellow fever is supremely important for anyone travelling to areas where the disease is prevalent, and the live attenuated vaccine is recommended for suitable candidates. Unfortunately, if someone gets infected and they haven’t been vaccinated, the disease can progress rapidly and possibly be fatal within two weeks during the toxic phase of the infection. Travellers without a vaccination are more likely to contract the disease compared to native residents who have developed immunity. Even though it’s rare, there have been some reports of people developing neurological and viscerotropic (affecting the internal organs) diseases after receiving the vaccine.
Possible Complications When Diagnosed with Yellow Fever
- Failure of multiple organs
- Severe lung condition (ARDS)
- Bloodstream infection (Sepsis)
- Difficulty in breathing due to lung failure
- Inflammation of the heart (Myocarditis)
- Brain inflammation (Encephalitis)
- Severe bleeding (Hemorrhage)
- Blood clotting disorder (DIC)
