Yellow Fever

Introduction
Yellow Fever is a mosquito-borne acute viral hemorrhagic fever. It is caused by mosquito Aedes aegypti and some other species also which transmit the virus into the human body. The virus responsible for the disease belongs to the group of flavivirus family. This disease is named as 'yellow fever' because it mainly affects the liver and causes jaundice.
Yellow fever was the most deadly disease in United States and African countries. In late 70's, the yellow fever out broke first time in Philadelphia which killed many people. It was believed that the disease was first originated in Africa and then transferred to USA via trading system.

Classification of Yellow Fever - Yellow fever is classified into two
1) Jungle Yellow Fever - It is spread by jungle mosquitoes. It mainly affect the monkeys. When the mosquito bites the infected monkey, virus enters into the mosquito and hence it spreads to humans too when same mosquito bites the humans.

2) Urban Yellow Fever - It is spread by the mosquito Aedes aegypti. When this mosquito bites the infected humans or monkeys the virus also enters into the mosquito which in turn go on biting human and thus the viral infection spreads. But urban yellow fever is very rare in USA.

Transmission of virus
Yellow fever virus is transmitted and spread by mosquitoes. It carries the virus from monkey to humans or from one person to other person.
Yellow fever is not contagious disease because it is not passed from person to person or any close contact.

Clinical signs and symptoms
The symptoms appear after 3-6 days of infection. The symptoms are seen in 2 phases
1) Acute phase - The initial and immediate symptoms seen are high grade fever with chills, headache, nausea, vomiting and loss of appetite.
Usually patients recover from this phase in 3- 5 days. It is difficult to make a diagnosis of yellow fever at this stage because the symptoms matches with the malaria, dengue, etc.

2) Toxic phase - In some patients even after the recovery in first week the symptoms appear again but this time patient goes into toxic phase where the disease becomes very sever and life-threatening. The symptoms are -

• Jaundice - Yellow discoloration of skin and eyes.
• Recurrent fever with chills.
• Bleeding from mouth, nose and eyes.
• Abdominal pain and vomiting sometimes blood in vomit present.
• Liver and kidney failure.
• Heart dysfunction - irregular heartbeats
• Respiratory failure due to sepsis .
• Brain disorder - seizures, delirium and coma.

Diagnosis of Yellow fever
Yellow fever cam be mistaken for other infectious disease like dengue fever, hepatitis, viral encephalitis, etc.
1) Complete blood count (CBC) - It is the common and necessary test to get an idea of the type of disease. Finding like decrease in WBC count and decrease in platelet count commonly seen.

2) If the patient has respiratory problems then chest x-rays helps to detect the level of disease and to what extend lung is affected.

3) CT Scan Brain - It helps to detect if there is any hemorrhage in the brain and also to understand the prognosis of the disease.

3) Specific yellow fever test - Serological test like ELISA helps to know the exact diagnosis of disease. IgM Elisa test should be done during the rise of fever and 3-6 days of the appearance of the symptoms so that the diagnosis is correct.

4) Liver function test - As yellow fever mainly affect the liver, it is necessary to understand the level of jaundice and other functions of liver.

Medication for yellow fever
There is no specific treatment for yellow fever. The treatment is given based on the symptoms and organ affection. The critical patients need to be hospitalized in the intensive care unit so that all emergency care for bleeding, jaundice and multi - organ failure can be taken properly.
No anti-viral drugs are effective against yellow fever.

Sometimes due to excess blood loss the platelets are reduced and need to be replaced by plasma or platelet transfusion.

Prevention of yellow fever
A) Vaccination
There is an effective vaccine against yellow fever virus which was introduced in the year 2000. Vaccine is the only most effective way to prevent the virus especially if someone is travelling to the high risk areas like South America and African countries. Vaccination for yellow fever is mandatory for the travelers especially to or from high risk areas.

B) Protection from Mosquitoes
Mosquitoes are the main source of virus transmission. So it is necessary to either control the number of mosquitoes or take the proper protection from mosquito bites.

1) Mosquitoes breed in the evening and night and at damp , marshy places. So avoid going to such places frequently.
2) Use skin repellent cream to protect from mosquito bites.
3) Use full covered or full sleeved clothes to avoid bites.
4) Close the windows especially at night so that mosquitoes don't enter inside the house.
5) Keep the house and surrounding clean and avoid any kind of contamination.
6) Use mosquito nets and mosquito coils for the kids.