Yellow fever

Yellow fever is a disease caused by a virus and spread through the bite of infected mosquitoes. Most people with yellow fever feel very sick for a few days, with fever, chills, headaches, nausea, and muscle pains. In some cases, the sickness returns after a short improvement, and the person may suffer from liver damage, which turns the skin yellow, and may have problems with bleeding and the kidneys.

The disease is common in parts of Africa and South America, where nearly a billion people live in areas where it can be found. It is rare in Asia. Yellow fever became a big problem in many cities, especially in the past, and it still causes many severe illnesses and deaths today, especially in Africa.

There is a safe vaccine that protects people from yellow fever, and many countries require travelers to get this vaccine. Stopping the disease also involves keeping the number of mosquitoes low and making sure many people are vaccinated. While there is no special treatment for the virus itself, doctors can help manage the symptoms.

The disease started in Africa and was carried to the Americas in the 17th century by enslaved people. Since then, it has caused many serious outbreaks in many parts of the world. In 1927, scientists were the first to isolate the yellow fever virus, a major step in understanding and fighting the disease.

Signs and symptoms

Yellow fever starts after a few days of feeling unwell. Most people only have mild symptoms like fever, headache, chills, back pain, feeling tired, not wanting to eat, muscle aches, nausea, and vomiting. In these cases, the illness goes away in about three to six days.

In about 15% of cases, the illness becomes more serious. Fever comes back, and the skin may turn yellow because of problems with the liver. Some people may feel pain in their stomach, and there can be bleeding from places like the mouth, nose, eyes, or inside the body, which can cause vomit that looks black. Other issues like problems with the kidneys, hiccups, and confusion may also happen.

Cause

Yellow fever is caused by the Yellow fever virus. This virus is very small and can spread through the bites of certain mosquitoes. It was discovered a long time ago by a doctor named Walter Reed.

The virus spreads when a mosquito bites an infected person or animal and then bites another person. This is how the disease moves from one person to another. There are different ways the disease can spread, including in cities and in forests, depending on the type of mosquito involved.

Pathogenesis

After a mosquito bites someone with yellow fever, the virus grows in special parts of the body called lymph nodes. It then moves to the liver and affects cells there, causing damage. This can lead to serious problems in the body, including shock and when many parts of the body stop working well.

Diagnosis

Yellow fever is usually identified by looking at a person's symptoms and knowing where they have traveled. When someone shows signs like fever, pain, nausea, and vomiting a few days after visiting an area with yellow fever, doctors take it seriously.

There are special tests that can help confirm if someone has yellow fever. These tests look for parts of the virus or the body’s response to it. However, some tests may need to wait until a certain time after the illness starts. Doctors also need to make sure the illness isn’t caused by something else, like malaria or other similar diseases.

Prevention

To stay safe from yellow fever, it is important to get a vaccination and avoid mosquito bites in areas where the disease is common. This includes using insect repellent when outdoors, such as those containing DEET, picaridin, ethyl butylacetylaminopropionate (IR3535), or oil of lemon eucalyptus on exposed skin. Wearing long sleeves, pants, and socks can also help. Mosquitoes can bite through thin clothing, so spraying clothes with repellent containing permethrin or another EPA-registered repellent gives extra protection. The peak biting times for many mosquitoes are from dusk to dawn, but some that spread yellow fever bite during the day. Staying in screened or air-conditioned rooms helps reduce the risk.

Vaccination

Vaccination is the best way to prevent yellow fever, especially for travelers to areas where the disease is found. The vaccine starts working about 10 days after being given and offers protection for at least 10 years. The World Health Organization (WHO) recommends that people living in areas where yellow fever is common get the vaccine between 9 months and 1 year old. Some side effects like mild fever or soreness at the injection site can happen, but serious reactions are very rare.

Vector control

Stopping mosquitoes that carry yellow fever is very important because they can also spread other diseases like dengue fever and chikungunya disease. Mosquitoes that spread yellow fever like to breed in standing water, such as in old tires, cans, or plastic bottles. To reduce these mosquitoes, people can remove standing water and use special substances called larvicides or add small fish and copepods that eat the mosquito larvae. One successful method used in Vietnam involves copepods from the genus Mesocyclops. Another way to reduce adult mosquitoes is using special traps called lethal ovitraps and treating mosquito nets with insecticides. These methods help protect people from mosquito-borne diseases.

Treatment

There is no cure for yellow fever, just like with some other infections caused by similar viruses. If someone gets yellow fever, they should go to the hospital. Sometimes, they might need special care because their condition can get worse quickly.

Doctors can help with symptoms. They give fluids to keep the person hydrated and use certain medicines to help with pain. One medicine they use is called paracetamol. They usually don’t give another medicine called aspirin because it can cause problems with bleeding in the stomach.

Epidemiology

Yellow fever is common in tropical and subtropical areas of South America and Africa. About 600 million people live in areas where this disease is found. The World Health Organization estimates that there are about 200,000 cases of yellow fever worldwide each year. In some cases, the illness becomes severe, and sadly, some people can pass away.

Yellow fever mostly occurs in Africa, where about 90% of infections happen. In 2016, a large outbreak started in Angola and spread to nearby countries. This was stopped by a big effort to vaccinate many people. In March and April 2016, some cases were reported in China, marking the first time the disease appeared in Asia in recorded history.

In South America, there are two types of the yellow fever virus. These types likely came from West Africa and were first brought to Brazil a long time ago. In late 2016, a big outbreak began in Minas Gerais, a state in Brazil. This outbreak spread among wild monkeys and moved toward the coast. Health officials started a vaccination campaign to protect people.

Although the main mosquito that spreads yellow fever is also found in parts of Asia, the Pacific, and Australia, the disease had never been reported there until some cases were brought from the 2016 Angola and DR Congo yellow fever outbreak by jet travel. Scientists have a few ideas about why yellow fever hasn’t appeared there before, but none fully explain it yet.

History

Main article: History of yellow fever

Yellow fever likely started in Africa, spreading from animals to humans. It moved from Africa to the Americas with the trade of enslaved people. Early outbreaks happened in places like Barbados and the Yucatán Peninsula.

Many places faced serious problems with yellow fever, especially in warm areas. Outbreaks affected soldiers, cities, and whole countries. For example, during a big conflict, a French army lost many soldiers to yellow fever, which changed plans for North America.

Scientists later learned that mosquitoes spread the disease. This discovery helped control yellow fever in places like Cuba and Panama. Vaccines were developed in the 1930s, which helped reduce the disease further.

Today, yellow fever is rare in cities because of vaccines and mosquito control. However, in some areas, especially in Africa, the disease still appears because of challenges in vaccination programs and changes in the environment.

Research

Scientists have studied yellow fever in animals to find ways to treat it. In one study with hamsters, giving a medicine called ribavirin early on helped reduce damage to important body parts and improved health outcomes. This medicine works in a way that might be similar to how it helps with another virus called hepatitis C.

Researchers have also looked at how to stop yellow fever from spreading. Some countries have even looked at the disease for other purposes, which is why it is important to keep research safe and careful.