Yellow Fever

Yellow fever is a mosquito-borne viral illness commonly seen in tropical and subtropical areas of South America and Africa. The yellow in the name refers to jaundice, which is one of the key symptoms of yellow fever seen in certain patients. Many people do not experience symptoms, but the most common symptoms that occur are fever, muscle pain with prominent backache, headache, loss of appetite, and nausea or vomiting.

Causes #

The yellow fever virus is an arbovirus of the flavivirus genus and is transmitted by mosquitoes, belonging to the Aedes and Haemogogus species. Different mosquito species live in different habitat some lives in the wild, some are domestic and some in both habitat.

There are 3 types of transmission cycles:

Sylvatic (or jungle) yellow fever #

In tropical rainforests, monkeys, which are the primary reservoir of yellow fever, are bitten by wild mosquitoes of the Aedes and Haemogogus species, they pass the virus on to other monkeys. The humans traveling in the forest are bitten by infected mosquitoes and later develop yellow fever.

Intermediate yellow fever #

During this type of transmission, semi-domestic mosquitoes (those that breed both in the wild and around households) infect both monkeys and people. Increased contact between people and infected mosquitoes leads to increased transmission. This is the most common type of outbreak in Africa.

Urban yellow fever #

Large epidemics occur when infected people introduce the virus into heavily populated areas with a high density of Aedes aegypti mosquitoes and where most people have little or no immunity, due to lack of vaccination or prior exposure to yellow fever.

Symptoms Of Yellow Fever #

The first symptoms of yellow fever usually develop 3 to 6 days after being infected. They include:

• Muscle pain and backache

• Feeling sick or vomiting

• Fatigue (feeling tired)

• General body aches

• Nausea

• Severe headache

• Eyes being sensitive to light

Most people with the initial symptoms improve within one week. For some people after recovery, weakness and fatigue (feeling tired) might last for several months. Yellow fever can be deadly among those who develop severe disease

Up to 1 in 4 people might develop a more severe form of the disease with symptoms such as:

• Yellowing of the skin and eyes (jaundice)

• Organ failure

• Bleeding from the mouth, nose, eyes, or ears

• High fever

• Shock

Risk Factors For Yellow Fever #

Being unvaccinated #

Unvaccinated young children are prone to yellow fever and its complications including death. Unvaccinated pregnant women and nonimmune people can become infected.

International traveling #

Traveling to countries where yellow fever is common and less controlled puts you at a higher risk of developing the disease.

Countries experiencing a yellow fever outbreak #

Countries experiencing or recovering from a natural disaster. Damage to health infrastructures interrupts routine immunization and greatly increases the risk of infection.

Diagnosis #

History and physical examination #

• The diagnosis requires a thorough travel history and record of immunization.

• The doctor may evaluate the present symptoms such as headache, malaise, jaundice, and myalgias with severe back pain. The incubation period of the virus is usually 3-7 days, with most individuals having a mild flu-like illness.

• In severe 15% of cases, symptoms include chills, low back pain, headache, and fever.

• During the physical examination, the doctor may check the Faget sign or pulse fever dissociation, facial flushing, and conjunctival injection. During the most toxic phase, patients develop jaundice, dark urine, and vomiting.

• Bleeding may occur from mucous membranes and in the gastrointestinal tract.

Lab tests #

• Laboratory confirmation is important after the physical evaluation is done by the doctor.

• Antigen detection: Rapid detection methods include the detection of yellow fever antigen using a monoclonal enzyme immunoassay in serum specimens.It is accomplished by testing serum to detect virus-specific IgM and neutralizing antibodies.

• Polymerase chain reaction: This improved technique not only ensures the specific detection of a wide range of yellow fever virus genotypes but also may increase the sensitivity of detection.

• Enzyme-linked immunosorbent assay (ELISA): This is a common test that is able to detect different types of antibodies produced at different stages of the infection. This test uses the binding of antibodies to antigens to identify and measure certain substances.

Other tests #

• Lumbar puncture: In case of altered mentation, a lumbar puncture is performed. A lumbar puncture is sometimes called a cerebrospinal tap a medical procedure that can involve collecting a sample of cerebrospinal fluid (CSF).

• Computed tomography (CT) scan: A CT scan uses computers and rotating X-ray machines to create cross-sectional images of the body. In case the brain is involved in yellow fever, a CT scan is performed.

• Liver function tests (LFT): If the liver is involved, the coagulation profile may be abnormal.

• Chest X-ray: A chest x-ray is done in patients with respiratory distress because of pulmonary edema.

• Electrocardiograph (ECG): This test is performed in case of prolonged QT and PR intervals. Arrhythmias are common when the myocardium is affected.

• Complete blood count (CBC): The blood test may also show a reduction in the number of infection-fighting white blood cells (leucopenia). This can occur because the yellow fever virus affects bone marrow (the spongy material at the center of some bones that produces blood cells).

Treatment #

• Rest, drink fluids, and use pain relievers and medication to reduce fever and relieve aching.

• Avoid certain medications, such as aspirin or other nonsteroidal anti-inflammatory drugs, like ibuprofen or naproxen which may increase the risk of bleeding.

• People with severe symptoms of yellow fever infection should be hospitalized for close observation and supportive care.

• People with yellow fever should be protected from further mosquito exposure (for example, they should stay indoors or under a mosquito net) during the first few days of illness, so they do not contribute to the disease transmission cycle.

• Paracetamol and ibuprofen can be taken for controlling fever and the pain caused by the virus, for children liquid paracetamol can be used.

• If a person is having a high temperature increase the intake of fluids to eliminate the risk of dehydration.