ARBOVIRUS – YELLOW FEVER

Arbovirus - Yellow Fever

Definition:

• Yellow fever is a viral disease caused by the yellow fever virus (YFV),
• An arthropod-borne flavivirus transmitted by the bite of an infected Aedes mosquito
• Characterized by fever, chills, loss of appetite, muscle and back pain, headache, and sometimes jaundice and hemorrhagic symptoms.

Causes:

• The yellow fever virus is primarily transmitted through the bite of an infected Aedes mosquito
• Mainly Aedes aegypti and Aedes albopictus species mosquitoes
• Can also be transmitted through organ transplantation and laboratory exposure.

Types:

• There are two main types of yellow fever: a. Classical or severe form (50-70% of cases): high fever, jaundice, and hemorrhagic symptoms b. Mild or non-severe form (30-40% of cases): mild fever, headache, and muscle pain
• Rarely, yellow fever can progress to a hemorrhagic or toxic form, which is characterized by severe bleeding and organ failure.

Pathogenesis:

• The virus enters the human body through the bite of an infected mosquito
• Replicates in the lymph nodes, then spreads to the liver, spleen, and other organs
• Causes damage to the liver and kidneys
• Leads to jaundice, hemorrhagic symptoms, and organ failure in severe cases.

Morphology:

• The yellow fever virus is a single-stranded RNA virus
• Belongs to the flavivirus family
• Has a lipid envelope and a nucleocapsid core
• Can be visualized using electron microscopy.

Clinical Features:

• Phase 1 (incubation period): a. High fever b. Chills c. Loss of appetite d. Muscle and back pain e. Headache
• Phase 2 (febrile period): a. Jaundice b. Hemorrhagic symptoms (e.g., bleeding gums, nosebleeds) c. Organ failure (e.g., liver, kidney)
• Phase 3 (recovery period): a. Resolution of fever and symptoms b. Return of appetite and energy.

Complications:

• Organ failure (liver, kidney)
• Hemorrhagic symptoms (bleeding, bruising)
• Seizures
• Coma
• Death.

Diagnosis:

• Clinical diagnosis based on symptoms and history
• Laboratory tests: a. Blood tests for antibodies against the virus b. Polymerase chain reaction (PCR) to detect viral RNA.
• Confirmation by laboratory tests.

Management:

• Supportive care: a. Rest b. Fluid replacement c. Pain management d. Antipyretics
• Specific treatment: a. Vaccination (pre-exposure or post-exposure) b. Immunoglobulin (in severe cases).

Memory Trick:

• "Yellow fever comes in three phases:
  1. Incubation period (high fever)
  2. Febrile period (jaundice and hemorrhage)
  3. Recovery period (resolution of symptoms)"