Yellow fever: overview and more

Yellow fever is caused by a flavivirus that is transmitted by mosquitoes in Africa and South America, especially in dense forests or jungle areas .

A flu-like illness can cause symptoms such as fever, chills, and body aches about three to six days after infection, and usually no treatment is needed.

However, in about 10-15% of those infected, the disease can become severe, leading to fever, jaundice, and other problems. Yellow fever can be fatal .

History, influence and scope

Over the years, yellow fever has been better controlled than before, mainly because there is a vaccine that protects against it. However, the WHO estimates that between 84,000 and 170,000 people contract yellow fever each year. Many cases are believed to go unrecognized, so the full extent of the disease's impact is unclear.

Yellow fever is present in geographic regions where the virus and mosquitoes can survive. This largely depends on the climate and the presence of the jungle.

In most South American countries, the virus does not cause urban outbreaks. It is found only in very specific regions, usually in remote jungles or forest areas, where the virus spreads between animals.

There it is concentrated in the Amazon, mainly in Brazil, reaching Peru, Ecuador, Bolivia, Colombia, Venezuela and Argentina. Risk countries also include Panama, Trinidad and Tobago, French Guiana, Guyana, Paraguay, and Suriname.

But it is estimated that about 90% of yellow fever cases occur in Africa, where the majority of deaths from this infection occur. It is found in West and Central Africa, as well as parts of East Africa.

African countries at risk for yellow fever include: Angola; Benin; Burkina Faso; Burundi; Cameroon; Central African Republic; Chad; Republic of Congo; Ivory Coast; Democratic Republic of Congo; Equatorial Guinea; Ethiopia; Gabon; Gambia; Ghana; Guinea; Guinea-Bissau; Kenya; Liberia; Mali; Mauritania; Niger; Nigeria; Rwanda; Senegal; Sierra Leone; Sudan; South Sudan; Togo and Uganda.

In 2016, there was an outbreak in the Angolan capital, where more than 100 people were confirmed to have died from the infection. The virus has spread to the capital and most of the country's provinces. Although not considered endemic in Asia, travelers and workers have returned to China from Angola with the virus.

The virus used to spread much more geographically than it is now. It first came to the United States in the late 17th century. It is believed to have been brought in as a result of human trafficking between Africa and America, when mosquitoes and the virus were transported together with people living in endemic areas. It came to Boston, New York, and Philadelphia and remained in southern cities until the late 19th century. The virus also spread through trade to European ports, as far as Cardiff and Dublin, although countries like Greece were most at risk.

Symptoms of yellow fever.

For most people, yellow fever causes mild or unrecognized illness. Usually three to six days elapse between exposure to the virus through a mosquito bite and illness. If you have a mild illness and are never seriously ill, you are expected to make a full recovery. However, in some people, yellow fever causes fever, chills, pain, bleeding, yellowing of the eyes and skin, nausea, vomiting, confusion, shock, organ failure, and even death .

In people who experience symptoms of yellow fever , there are three stages of the disease:

Early infection occurs three to six days after infection. You may experience fever, muscle aches, nausea, vomiting, dizziness, and fatigue .

Remission occurs in a few hours, up to a day. Fever, if present, subsides and symptoms improve. This can last between 24 and 48 hours. Most people will recover at this point. About 15% of people infected with this virus develop more severe forms .

Serious Illness – Serious illness causes fever, nausea, and vomiting. With severe infections, new symptoms and signs appear :

  • Jaundice: Many people with serious illnesses have yellowing of the skin (including the palms of the hands and the soles of the feet), the whites of the eyes, and the skin under the tongue. This symptom has given its name to yellow fever.
  • Some people bruise or bleed easily in different parts of the body. In particular, you may notice bleeding from your nose, other mucous membranes, or an intravenous injection site, or you may see blood in your vomit.
  • The white blood cell count may be low, which means that there are fewer immune cells during the infection.
  • Blood tests can show that the liver is damaged, which can be determined by increased liver enzymes in the blood. This can happen before jaundice develops.
  • If the infection improves, liver enzymes are expected to rise until the second week of illness and then begin to decline to normal levels.
  • Those who recover develop antibodies that fight the virus as it disappears. For those who are very sick, the virus lasts longer in the blood.
  • A serious illness can lead to symptoms of confusion and ultimately organ failure.

Between 20% and 50% of people with serious illnesses can die .

Causes

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Yellow fever is caused by Flavivirus , a single-stranded RNA virus transmitted by the Aedes aegypti mosquito.

This mosquito, which also causes the Zika virus and dengue, is actually called the yellow fever mosquito.

The yellow fever virus can also be transmitted by other mosquitoes: Aedes africanus in Africa or the Haemagogus and Sabethes mosquitoes in South America .

Mosquitoes transmit the virus by feeding on the blood of an infected person or another primate, such as a monkey, and then bite another person or another primate. A mosquito can become infected with the virus if it consumes infected blood just before a person or animal develops a fever and within five days afterward.

Transfer cycles

The virus has three distinct transmission cycles: jungle (forest), intermediate (savanna), and urban. The effects of the infection itself are the same whether or not it is transmitted in any of these cycles.

When yellow fever spreads in the jungle, it spreads without people. Instead, it is transmitted from non-human primates (such as monkeys), from non-human primates through mosquitoes. If people visit jungle areas (for example, for mining, hunting, or tourism), they can also be bitten by a mosquito and become ill.

In the intermediate cycle (also called the savanna cycle), yellow fever is regularly spread between monkeys and humans via mosquitoes in areas on the edge of the jungle. It can be transmitted from monkey to person, monkey to monkey, person to person, or person to monkey.

In the urban cycle, yellow fever spreads mainly between people through mosquitoes that live in urban areas. This usually begins when someone who has been infected with the virus returns from the jungle area. This can lead to sudden and large outbreaks in densely populated urban areas.

Diagnostics

The diagnosis of yellow fever is based on the medical history of a mosquito bite in an endemic region, as well as the history of symptoms. There are several tests that can confirm or confirm the diagnosis of yellow fever .

  • Antibody test: This test is the best established diagnostic test for yellow fever. It searches your blood for immune proteins against yellow fever, indicating that you are fighting or effectively fighting the infection. However, it can take several days for your body to produce enough antibodies to be detected. You may need to wait up to two weeks for results.
  • Virus PCR test: PCR tests can detect the genetic material of the virus in your blood. A positive PCR test indicates the presence of a virus in your body, so it is considered a stronger indicator of an ongoing infection than an antibody test. Important limitation: viral RNA is detectable early after infection, but not easy to detect after several days of infection. This means that you can get a negative PCR result even if you have an infection.
  • Urinalysis – A relatively new test can detect viral CRP in urine, making diagnosis more practical. However, this test, while promising, has yet to gain widespread acceptance.

Watch out

There is no specific antiviral treatment for yellow fever, but the disease can become quite serious and complications associated with it may require medical attention.

This could include:

  • Prevention of bleeding: Due to the risk of bleeding, medications that cause bleeding, such as aspirin, ibuprofen, and naproxen, should be avoided.
  • Hydration: It may be necessary to maintain hydration during illness with oral or intravenous fluids, especially if you experience vomiting or low blood pressure.
  • Fever control: Yellow fever is usually associated with subfebrile fever. But if your temperature rises more than expected, you may need medicine to lower it.
  • Pain: If you experience muscle pain or general discomfort, oral or injectable pain relievers may be controlled.
  • Blood pressure support: For those in shock that occurs when blood pressure is extremely low, blood pressure can be raised with medications that constrict blood vessels, often called pressors.
  • Treatment of organ failure: When yellow fever causes organ failure, these organs must be maintained until the infection clears. For example, a ventilator may be necessary to facilitate breathing; Dialysis may be required for the kidneys to work.

Prevention

Since yellow fever has been around for some time, the transmission of the virus is well known. Here are some effective ways to prevent infection :

  • Vaccination : Vaccination is recommended for some people. If you live in an endemic area, you may already be immune to infection and must follow the official vaccination guidelines for yourself and your children. If you travel to an area where yellow fever is endemic, you will probably need to get vaccinated. Travel vaccinations are generally not widely available and you may need to make an appointment at your local travel clinic. It's also best to plan ahead, as vaccinations need to be done at least 10 days before the trip.
  • Mosquito Precautions: If you are in an endemic area, you can protect yourself and your children from mosquitoes. While mosquito bites cannot always be completely avoided, you can wear multiple layers of clothing, especially when traveling through the jungle and woods, and use an insect repellent spray. Sleeping under safety nets is also recommended, even if you are indoors.
  • Protect others: In general, since the virus can be transmitted from person to person through mosquitoes, it is a good idea to stay under mosquito nets to prevent the spread of the virus if you know you have been infected.

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If you travel to an area where yellow fever is endemic, you should take the recommended precautions; This will significantly reduce the risk of infection.

Also, be sure to check general symptoms to seek medical attention if you become infected. Although most people with yellow fever recover well, the chances of recovery are much greater if you get professional help before complications develop.

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