Yellow fever

A mosquito can make you sick.

This bug carries a tiny germ. It bites people and animals. The germ causes a sickness called yellow fever.

You might feel very hot. You may have a headache. Some people feel sick to their stomach. Your skin might even turn yellow.

Most people feel better in five days. But some people get much worse. They may have pain in their belly. This can be very dangerous.

A shot can keep you safe.

This shot is called a vaccine. It helps your body fight the germ. Some lands ask for this shot when you visit.

We can also stop the bugs. Reducing the number of mosquitoes helps. This keeps people healthy and safe.

Yellow fever is a sickness caused by a virus.

A mosquito spreads the virus to humans and primates. In cities, a mosquito called Aedes aegypti is the main one. This mosquito bites people to spread the germ.

Most people feel mild symptoms. You might have a fever, chills, or a headache. You may also have muscle pains in your back. These symptoms usually go away in five days.

For some, the sickness gets much worse. This happens in about 15% of cases. The virus can damage the liver. This damage can make the skin look yellow. This is called jaundice. People may also have bleeding or kidney problems.

Doctors use blood tests to find the virus. They can use a test called PCR. This test looks for the virus in your blood.

We can stay safe with a vaccine. A vaccine is a shot that helps your body fight the virus.

Some countries require this shot for travelers. We can also try to reduce the number of mosquitoes. This helps stop the disease from spreading.

Yellow fever is a sickness caused by a tiny germ called a virus.

This virus can make people and other primates very ill. It belongs to a group of germs known as hemorrhagic fevers. These are illnesses that can cause bleeding inside the body. For many, the sickness is short and mild. Most people feel fever, chills, and headaches for a few days. They might also have muscle pains in their backs. These symptoms usually go away within five days.

The virus moves from person to person using mosquitoes. A female mosquito picks up the virus when she bites an infected person. The virus then travels to the mosquito's salivary glands. When that mosquito bites someone else, she injects the virus into their blood. In big cities, a mosquito called Aedes aegypti is the main spreader. In jungles, other mosquitoes like the Haemagogus genus help spread it. There is even a third cycle in the savannah. This cycle happens between the jungle and the cities.

Scientists have learned a lot about this virus over time. Around the year 1900, a doctor named Walter Reed showed how mosquitoes spread it. In 1927, the yellow fever virus became the first human virus to be isolated. This means scientists were able to separate it from other things. The disease has a long history in the Americas and Africa. It spread to the Americas starting in the 17th century. In the 1800s, many big cities faced scary outbreaks.

Yellow fever is very common in certain parts of the world. About 90 percent of the cases happen in Africa. In 2013, Africa had 130,000 severe cases and 78,000 deaths. Nearly one billion people live in areas where this disease is common. It is found in tropical parts of South America and Africa. However, it is not common in Asia. Since the 1980s, the number of cases has been going up. This may be because of changing climates and more people living in cities.

We have ways to stay safe from this virus. A safe and effective vaccine exists to protect people.

Some countries even require this shot if you are traveling. Doctors can also use a blood test called PCR to find the virus. This test helps them know if someone is truly sick. Another way to help is by reducing the number of mosquitoes. If there are fewer mosquitoes, the virus cannot travel as easily. This helps stop big outbreaks from starting.

Yellow fever is a viral disease caused by the yellow fever virus (YFV). This virus belongs to the genus Orthoflavivirus and the family Flaviviridae. It is an enveloped RNA virus that is roughly 40 to 50 nanometers in width. The virus is highly significant because it is the namesake for its entire family. Yellow fever is categorized as a hemorrhagic fever, which means it can cause bleeding within the body. It primarily affects humans and other primates.

The infection process begins when an infected female mosquito bites a host. The virus enters the body and replicates in the lymph nodes. From there, the virus travels to the liver to infect hepatocytes, which are liver cells. During this process, the virus attaches to cell surfaces using specific receptors. The protein E helps the virus fuse with the host cell membrane. Once inside, the viral genome is released into the cytosol. The virus then replicates its RNA within the rough endoplasmic reticulum.

There are three distinct infectious cycles for yellow fever transmission. The urban cycle involves the Aedes aegypti mosquito, which is well-adapted to city life. This mosquito can also spread diseases like Zika and dengue. The sylvatic cycle occurs in jungles or forests. In this cycle, mosquitoes like those in the Haemagogus genus infect nonhuman primates. Finally, the savannah cycle acts as an intermediate cycle between the jungle and urban areas. This third cycle is currently the most common form of transmission in Africa.

History shows how the disease has moved across the globe. Yellow fever originated in Africa and reached the Americas during the 17th century. This spread occurred during the European trafficking of enslaved Africans from sub-Saharan Africa. In the 18th and 19th centuries, the disease was considered extremely dangerous. Many major epidemics swept through cities in the United States and elsewhere. Around 1900, Dr. Walter Reed proved the virus was transmitted by mosquitoes. Later, in 1927, the yellow fever virus became the first human virus to be isolated.

The impact of the disease is reflected in significant global statistics. Nearly one billion people live in regions where yellow fever is common. Approximately 90 percent of the estimated 200,000 annual cases occur in Africa. In 2013 alone, Africa saw an estimated 130,000 severe infections and 78,000 deaths. While the overall fatality rate is about 3 to 7.5 percent, the risk is higher for severe cases. For those who develop severe disease, the mortality rate can reach 20 to 50 percent.

Symptoms of the disease can vary greatly between individuals. Most people experience a mild infection lasting three to six days. Common symptoms include fever, headache, chills, back pain, and nausea. However, about 15 percent of people enter a second, toxic phase. This phase is characterized by jaundice, which is yellowing of the skin due to liver damage. Patients may also experience abdominal pain and bleeding. This bleeding can occur in the mouth, nose, eyes, or gastrointestinal tract.

Modern medicine provides several ways to manage and prevent the disease. A safe and effective vaccine is available to protect the population. Because of this, some countries require vaccination for travelers.

Doctors use a blood test called a polymerase chain reaction (PCR) to confirm a case. This test works by amplifying the viral genome. Since there is no specific treatment to kill the virus, medical care focuses on managing symptoms. Reducing mosquito populations is another essential method for preventing large outbreaks.