Yellow fever Virus

Yellow fever could cause epidemics. Sporadic cases are not uncommon in endemic areas.

It is considered to be endemic in Africa and South America.

There is only one serotype.

There are  5 genotypes.

Transmission

In urban type, the transmission is person to person whereas in Jungle cycle (Sylvatic), the transmission is from  monkey.

The vector involved in these transmissions is a mosquito (A aegypti)

 

Incubation period is between 3 to 6 days.

Case fatality rate is over 50 %.

Clinical presentations

Asymptomatic and mild infection is common.

Hepatitis is the main characteristic signs as the name implies (jaundice with fever).

The illness has biphasic phases

1. Just after infections

Abrupt onset of fever, nausea, vomiting, headache, back pain, bradycardia (Faget’s sign), and conjunctival injections.

 

2. Remission

Most patients will recover however in some patients the clinical symptoms disappear for brief period ( usually for 24 hours).

 

3. Intoxication- 15-25 % progress to intoxication stage

Develop high grade fever, vomiting, epigastric pain, and jaundice.

 

Complications

Bleeding that would lead to hypovolumic shock and renal failure.

DIC.

Delirium, stupor, coma followed by death within 7 to 10 days.

 

 

Investigations

CBC

Bleeding time- prolonged clotting time and prothrombin time and reduced fibrinogen level

LFT- increase in transaminase level, increase in bilirubin level

RFT- increase in creatinin and urea

Glucose level- hypoglycaemia

ECG- abnormal finding

Urine analysis- albuminuria, increase in specific gravity

 

Tests

Specimens- clotted blood

EIA- IgM and IgG

 

Treatments

 

There is no specific treatment.

Yellow fever specific immunoglobulin or  g-interferon may have beneficial effect if they are given at the early stage of the illness.

Hypovolumic shock does not responds to fluid replacement therapy.

The use of corticosteroid has not been evaluated.

Prevention

 

Vaccination is effective.

Vector control- protective clothing (long sleeves and long trousers) and insect repellents.

 

 

  

 

Text Box:  Yellow fever vaccine   17 D,  Live attenuated vaccination.   The vaccine Single subcutaneous injection is adequate to stimulate the immune system. Protective level of antibody will be detected in 90 % of recipient within 10 days and 99 % within 30 days. Immunity can be considered life long however booster dose is normally recommended after 10 years.   Indications ü      Travel to endemic countries ü      Travelling from endemic countries to endemic countries ü      During outbreak   Adverse effects The vaccine can generally be considered to be safe. Local- pain Systemic side effects Hypersensitive reaction especially for people allergic to eggs Encephalitis- rarely seen in children Hepatitis- it is very rare complications.   Contraindication 1. Pregnant women- may be given in epidemics if the benefit is considered to be high. May cause congenital infection but not congenital abnormality. 2. Egg intolerance- skin testing should be carried out before the vaccine is given for patients who have history of allergy to eggs. 3. Immunocompromised patients- HIV/IDS patients can receive vaccination if their CD4 count is greater than 200/ml. 4. Infants less than 4 months- may be given for infant between 4-9 months if there is epidemic.   Immunoglobulin It can be used in immunocompromised patients.