Yellow fever virus

Definitions & Key takeaways

Yellow fever virus is a single-stranded RNA virus from the flaviviridae family. It is typically found in parts of Africa and South America and is primarily transmitted by the Aedes aegypti mosquito. While many people who contract the virus may not show any symptoms, some individuals may experience more severe symptoms involving the liver and kidneys, such as jaundice, upper abdominal pain, vomiting that looks like coffee grounds, and decreased or no urine output. To prevent yellow fever, a live attenuated yellow fever vaccine is available, and treatment generally consists of supportive measures.

Watch video only
Yellow fever virus causes a disease called yellow fever name. So because severe forms of the disease result in jaundice which is a yellowish pigmentation of the skin and mucous membranes.
Yellow fever virus belongs to the flavoviride family of viruses which also includes dengue fever virus and zika virus. Interestingly, the flavoviride family is actually named after the yellow fever virus.
Flavus being latin for yellow. The virus is endemic to regions of Africa and South America.
Yellow fever virus is an enveloped virus with an icosahedral capsid, which is a spherical protein shell made up of 20 equilateral triangular faces inside the capsid.
There's a single stranded positive sense, ribonucleic acid or RNA. This means that their RNA is actually MRNA, which can directly be translated by the host cell ribosomes into new copies of the viral proteins which get assembled into new viruses.
Yellow fever virus doesn't just affect humans but also other primates like monkeys and apes. And it's also considered an arbovirus because it's transmitted via certain arthropod vectors or carriers specifically mosquitoes and the haemagogus and aedes genera.
Haemagogus, mosquitoes transmit the virus among monkeys in the jungle and that's called the somatic cycle if an unsuspecting person on a track, chances upon one of these mosquitoes in the jungle, then they get infected too and end up spreading the virus to other people.
Aedes mosquitoes, most commonly called Aedes aegypti transmit the virus in urban areas and that's called the urban cycle.
All right. So when a mosquito bites you, it releases the yellow fever virus in between your skin cells.
The virus especially targets dendritic cells which are specialized immune cells that normally eat up or phagocytose antigens in the skin and transfer them to immune cells in the lymph nodes.
The virus then latches onto specific receptors on the dendritic cell membrane which allows the virus to be endocytosed or engulfed into cells.
During endocytosis, the icosahedral capsid breaks open, allowing the viral RNA to gain access to the host cell cytoplasm.
In the cytoplasm, the viral RNA hijacks the host cell ribosomes which start making viral proteins that are later assembled into new viruses.
The newly made viruses leave the cell intact by exocytosis which is like reverse endocytosis. Now from the skin infected dendritic cells travel through the lymphatic vessels to the lymph nodes where the virus escapes into the bloodstream from there.
The infection spreads to various organs like the liver, kidneys, stomach or the heart. The liver is usually the first target.
So yellow fever is associated with hepatitis or inflammation of the liver. The liver cells shrivel up and die and they're seen as councilman bodies on histology.
If the virus spreads to the kidneys, it causes renal tubular damage, resulting in renal failure in the stomach. The virus can erode the gastric mucosa causing hemorrhage.
If blood stays in the stomach for some time, the red blood cells are broken down by gastric acid giving it a dark coffee ground like color.
Finally, if the virus infects the heart, it can damage myocardial fibers which can result in arrhythmias and myocardial infarction.
Most yellow fever virus infections are asymptomatic. But when there are symptoms, they usually show up after an incubation period of about 3 to 5 days.
Initial symptoms are caused by the virus spreading through the bloodstream and include fever with chills, fatigue, severe headache, back pain, nausea and vomiting.
In most people, these symptoms usually start to improve within 3 to 4 days and eventually disappear. Sometimes symptoms improve for a brief period of a few hours to a day called the remission period.
Before becoming worse. After the remission period, symptoms are caused by the infection spreading to other organs.
So there may be a high fever jaundice, upper abdominal pain, blood in the stool or urine, bloody or coffee ground vomit and decreased or absent urine output diagnosis of yellow fever is based on clinical symptoms and a recent history of travel to endemic areas.
A definitive diagnosis can be made with a reverse transcriptase polymerase chain reaction or RT PCR where a blood sample is tested for viral RNA other tests include isolation of virus and growing it in a cell culture, using blood plasma and serological tests to look for antibodies against viral particles.
Treatment is mostly supportive and involves providing adequate rest and oral rehydration or IV fluids to prevent dehydration.
Medications like acetaminophen can be given to help reduce pain and fever care should be taken to avoid certain nonsteroidal antiinflammatory drugs or nsaids like aspirin and ibuprofen, which may increase risk of bleeding.
Finally, yellow fever can be prevented with the help of a live attenuated yellow fever vaccine. It's recommended as a single subcutaneous shot for people nine months or older who travel to endemic regions.
Some people might need a booster shot such as those with an underlying HIV infection or people who work directly with the yellow fever virus.
In a laboratory setting, it's contraindicated in individuals who have a severe allergy to vaccine ingredients like eggs gelatin or chicken protein.
And since it's a live vaccine, it's contraindicated in immunodeficient individuals. It can be used if needed in pregnant females with caution at the discretion of the health care provider.
All right. As a quick recap yellow fever virus is a single stranded RNA virus from the flavo vridi family.
It is endemic to parts of Africa and South America and is most commonly transmitted by the Aedes aegypti mosquito. It causes asymptomatic infection in most people.
Sometimes it can progress to involve the liver and kidneys causing jaundice upper abdomen. Pain, coffee, ground vomit and decreased or absent urine output.
Yellow fever can be prevented with the help of a live attenuated yellow fever vaccine. And the treatment mostly involves supportive care.