What Is Yellow Fever?

Yellow fever is an acute infectious disease caused by yellow fever virus, transmitted mainly by the bite of Aedes mosquito. Clinical manifestations are high fever, headache, jaundice, proteinuria, relatively slow pulse and bleeding. The disease is endemic in the tropics and subtropics of Africa and South America, and there have been no reports of the disease in Asia. Due to the high mortality and infectiousness of yellow fever, it has been included in one of the quarantine infectious diseases regulated by the World Health Organization.

Basic Information

English name: yellowfever
Visiting department: Infectious Diseases
Common causes: Yellow fever virus

Common symptoms: Fever, jaundice, proteinuria, slow pulse, bleeding
Contagious: Have
way for spreading: Spread by Aedes mosquito bites

Causes of yellow fever

The yellow fever virus belongs to the arbovirus of the arbovirus B group. The virus has a diameter of 22 to 38 nanometers, is spherical, has an envelope, and contains a single-stranded positive-strand RNA. It is easily inactivated by heat, common disinfectants, ether, sodium deoxycholate, etc., but can be stored in blood for 1 month at 4 ° C, and can survive for several months at 0 ° C in 50% glycerol, at -70 ° Or freeze-dried conditions can remain active for several years. The initially isolated yellow fever virus Asibi strain was weakened into a 17D strain through tissue culture to prepare a live attenuated vaccine with good preventive effect.

Clinical manifestations of yellow fever

The incubation period is 3 to 6 days. Most of the infected people have mild symptoms, which can only manifest as fever, headache, mild proteinuria, etc., and they will recover after several days. Severe patients only occur in about 15% of cases. The course of the disease can be divided into 4 stages.

Infection period

Rising from high fever accompanied by chills, severe headache, and general body pain, marked weakness, loss of appetite, nausea, vomiting, diarrhea, or constipation. The patient was irritable, conjunctival congestion, flushing of the face and neck. The heart rate is parallel to the fever, and later becomes relatively bradycardia. This period lasts about 3 days, at which time the virus reaches a high titer in the blood and becomes a source of mosquito infection. May end with mild jaundice and proteinuria.

2. Remission period

The fever partially or completely subsided, and symptoms resolved, lasting from several hours to 24 hours.

3. Poisoning period

Fever and symptoms recur and are more severe. Toxemia subsided during this period, and liver, kidney, and cardiovascular function damage and bleeding symptoms appeared. Serum bilirubin was significantly increased, prothrombin time prolonged, and the degree and condition of proteinuria, oliguria, and azotemia were directly proportional. The prominent symptoms of this period are severe bleeding such as gum bleeding, nosebleeds, mucous membranes of the skin, gastrointestinal, urethral and uterine bleeding. The heart often enlarges, bradycardia slows, heart sounds weaken, and blood pressure decreases. Often accompanied by dehydration, acidosis, severe cases of delirium, coma, urinary occlusion, refractory hiccup, massive vomiting, shock and so on. This period lasts 3 to 4 days or 2 weeks. Death usually occurs on days 7-10.

4. Recovery period

Body temperature dropped to normal. Symptoms and proteinuria gradually disappear, but fatigue can persist for 1-2 weeks or more. At this stage, close monitoring of the heart is still required, and individual cases may die due to arrhythmia or heart failure. Survival cases are generally free of sequelae.

Yellow fever laboratory and other tests

1. General routine and biochemical examination

The total number of white blood cells in the peripheral blood is normal or increased, but the number of neutrophils often decreases in the early stage of the disease. Platelet count is normal or decreased. Serum bilirubin, ALT, and AST increased, and deaths were more pronounced. Prothrombin time and some thromboplastin time were prolonged in patients with jaundice. Urine protein increased, serum urea and creatinine increased.

2. Virus isolation

The virus was isolated from the brain or cell culture of mice inoculated with blood samples within 3 to 4 days of the beginning of the disease, and the virus was isolated and identified by serological methods.

3. Serology

Can be used for hemagglutination inhibition test, complement binding test or neutralization test to detect specific antibodies. Acute serum and recovery period of double serum samples more than 4 times higher can diagnose the disease. Currently, antibody capture enzyme immunoassay is used to detect yellow fever virus IgM antibody, which is positive one week after infection, which is helpful for early diagnosis, and antigen capture test can also be used to detect virus antigen in the early stage.

4. Reverse transcription / polymerase chain reaction (RT / PCR)

Detection of flavivirus RNA has strong specificity. It has been reported that viral RNA in serum is more stable than live virus and can be stored for a long time at 27 ° C, which is superior to virus isolation.

5. Other auxiliary inspections

ECG showed prolonged PR and QT intervals and ST-T abnormalities.

Yellow fever diagnosis

It is not difficult to diagnose yellow fever in typical cases, and it is not easy to diagnose sporadic, early or mild cases, and laboratory testing is needed.

Yellow fever differential diagnosis

In the diagnosis of yellow fever, attention should be paid to the identification of epidemic hemorrhagic fever, leptospirosis, dengue fever, viral hepatitis, malaria and toxic hepatitis with drugs.

Yellow fever treatment

So far there is no specific treatment.

General treatment

The treatment of yellow fever should rest in bed until complete recovery, and should live in a mosquito-free house, especially when there is viremia during the fever of the sick child should use mosquito nets. Give a liquid or semi-liquid diet. Those who frequently vomit may fast, give intravenous fluids, and pay attention to water, electrolytes and acid-base balance.

Symptomatic treatment

The treatment of yellow fever in high fever should be based on physical cooling, and aspirin fever should be disabled because it can induce or exacerbate bleeding. Frequent vomiting can be administered orally or intramuscularly. Appropriate antibiotics or antimalarial drugs are given to those with secondary bacterial infections or concurrent malaria. Myocardial damage can try adrenal cortex hormones. Severe cases should be closely observed for changes in conditions, such as shock, acute renal failure, gastrointestinal bleeding and so on.

Yellow fever prognosis

Mild patients generally recover smoothly without sequelae. The fatality rate of severe patients varies with each epidemic, and is affected by multiple factors such as race, age, and other group B arboviruses, and can reach 30% to 50%.

Yellow fever prevention

1. Manage the source of infection

As imported cases have been found in China, border quarantine should be strengthened for the prevention of yellow fever, and people from affected areas must present a valid vaccination certificate to prevent the disease from entering our country. Conduct temperature detection, medical inspections, epidemiological investigations, and medical examinations of people from yellow fever endemic areas, focusing on people with fever, jaundice and other symptoms.

2. Cut off the transmission route

Mosquito prevention and control are key measures to prevent the disease.

3. Protect vulnerable people

17D live attenuated yellow fever vaccine. A single intradermal inoculation of 0.5ml can produce effective immunity for 7-9 days and can last for more than 10 years. Children who are 9 months or older should be routinely vaccinated when they enter an epidemic area and are known or predicted to have yellow fever outbreaks. However, it should not be used in infants under 4 months, and almost all infants under 4 months experience neurological complications after vaccination.