Yellow fever

Introduction to yellow fever Yellow fever (alellowfever) is an acute infectious disease caused by yellow fever virus, which is mainly transmitted by Aedes mosquitoes. Severe patients have fever, jaundice and proteinuria, and the disease is endemic in tropical and subtropical regions of Africa and South America. There is no report of this disease in Asia. basic knowledge The proportion of illness: 0.001% Susceptible people: no specific population Mode of transmission: insect vector transmission Complications: shock pneumonia disseminated intravascular coagulation

Cause of yellow fever

(1) Causes of the disease

Yellow fever virus is an arbovirus group B. The virus is about 22~38nm in diameter. It is spherical, enveloped, contains single-stranded positive-strand RNA, easy to be heated, commonly used disinfectant, ether, deoxycholic acid. Sodium and other inactivated, but can be stored in blood for 4 months at 4 ° C, can survive for several months in 0% glycerol at 0 ° C, and can remain viable for several years at -70 ° C or freeze-dried conditions.

The initially isolated yellow fever virus Asibi strain was weakened into 17D strain by tissue culture to prepare a live attenuated vaccine with good prevention effect.

(two) pathogenesis

After the virus invades the human body, it quickly enters the local lymph nodes and continues to multiply in it. After 3 to 4 days, it enters the blood circulation to form viremia. Then, the virus invades the liver, spleen, kidney, heart, bone marrow, lymph, etc. It disappears from the blood, but the lymph nodes, spleen, and bone marrow still exist.

The pathological damage of yellow fever is caused by the accumulation of viruses in different organs and tissues, and the main damaged organs are liver, kidney, heart, and other tissues and organs may have different degrees of degeneration.

Liver lesions are mainly in the lobules, hepatocytes turbid and swollen, the nucleus becomes large, showing multiple microscopic vacuolar fat changes, coagulative necrosis and eosinophilic degeneration, mild or lack of inflammation, no obvious tissue hyperplasia, severe liver Lesions can lead to deep jaundice, hemorrhage and hypoglycemia, etc., renal lesions vary in severity, from tubular epithelial edema to tubular necrosis, special staining shows glomerular basement membrane thickening, balloon gap and proximal renal tubule There are protein substances inside, the distal renal tubules are transparent and pigmented tube type, renal dysfunction and uremia are caused by blood volume reduction, renal tubular necrosis, etc., myocardium has extensive degeneration and fat infiltration, and severe cases may have stoves. Bleeding, lesions often involving the sinus node and His bundle, clinical symptoms such as slow heart rate, arrhythmia, heart failure, occasional edema and small hemorrhage in the brain, histological changes in cell degeneration, fat infiltration, necrosis There is no obvious inflammatory cell infiltration, and the lesions are scattered.

Yellow fever prevention

1. Patients with infectious infections should be treated on the spot, protected from mosquitoes, and quarantined by borders. Travelers from infected areas must have valid vaccination certificates.

2. Cut off the route of transmission The scale of the epidemic depends on the conditions suitable for increasing the density of vector mosquitoes. Anti-mosquito and anti-mosquito are one of the important measures.

3. Protection of susceptible persons Vaccination is an effective measure to prevent outbreaks and protect susceptible people. The long-term use history proves that yellow fever attenuated live vaccine 17D is an effective vaccine, and the dose is 0.5-1.0ml subcutaneously. Yes, immunity can be produced 7 to 9 days after inoculation, and it should be used for more than 10 years. Egg allergy should be used with caution. Since the application in 1945, the total dose has reached 2 billion people. Only 18 cases of encephalitis and vaccine have been found to be short-lived. The association of 15 children aged 4 months or less suggests that this live attenuated vaccine is neurotropic, especially for the immature nervous system. Some national regulations Children under 6 months should not be vaccinated. Recent studies have shown that yellow fever vaccine combined with hepatitis B vaccine, polio vaccine, and typhoid Vi polysaccharide vaccine will not reduce their immune effects, and the side effects have not increased.

Yellow fever complications Complications, shock pneumonia, disseminated intravascular coagulation

Important complications include shock, intestinal bleeding, heart damage, multiple organ dysfunction, and DIC, bacterial pneumonia, and mumps.

Yellow fever symptoms Common symptoms Irritability, fatigue, nausea, high fever, loss of appetite, bodyache, bleeding, chills, myalgia, diarrhea

[clinical manifestations]

The incubation period is 3 to 6 days. Most of the affected people have mild symptoms. They can only show fever, headache, mild proteinuria, etc., and they will recover in a few days. The severe patients only occur in about 15% of the cases. 4 issues.

1. Infection period, high fever accompanied by chills, severe headache and systemic pain, obvious fatigue, loss of appetite, nausea, vomiting, diarrhea or constipation, etc., patients with irritability, conjunctival congestion, facial, neck flushing, heart rate and fever parallel, after Turned to relative heartbeat, this period lasts about 3 days. At this time, the virus reaches a high titer in the blood and becomes a source of mosquito infection. At the end of the period, there may be mild jaundice and proteinuria.

2. During the remission period, the fever partially or completely subsided, and the symptoms were relieved, lasting for several hours to 24 hours.

3. During the poisoning period, fever and symptoms reappear and are more serious. In this period, the toxemia subsides, liver, kidney, cardiovascular function damage and bleeding symptoms appear, serum bilirubin is significantly increased, prothrombin time is prolonged, proteinuria The degree of oliguria and azotemia is directly proportional to the condition. The prominent symptoms in this period are severe bleeding such as gum bleeding, nose bleeding, skin mucosal ecchymoses, gastrointestinal tract, urethra and uterine bleeding, etc. Slow pace, weak heart sounds, lower blood pressure, often accompanied by dehydration, acidosis, severe convulsions, coma, urinary closure, intractable hiccups, massive hematemesis, shock, etc., this period lasts 3 to 4 days or 2 weeks, often Death occurred on the 7th to 10th days.

4. During the recovery period, the body temperature drops to normal, the symptoms and proteinuria gradually disappear, but the fatigue can last for 1-2 weeks or more. In this period, the heart condition should be closely observed. Individual cases may die due to arrhythmia or heart failure. Survival cases generally have no sequelae.

diagnosis

Yellow fever can be classified into extremely light, light, heavy and malignant depending on the severity of the disease.

Extremely light and light is difficult to diagnose by clinical alone. Because of its fever, headache, and myalgia, it only lasts for 1 to 2 days and is difficult to distinguish from influenza and dengue fever. It can only be confirmed by pathogen or serological tests. The number of two types of cases is high and easy to ignore. It is an important source of epidemiology. Mild and latent infections often rely on serum immunological tests including monoclonal antibodies, ELISA and other techniques to draw conclusions. PCR can also be used. The virus RNA of the blood sample is detected, and if necessary, the blood of the suckling mouse is inoculated in the brain to isolate the virus. If the patient has not had the same virus infection in the past, the blood coagulation inhibition test, the neutralization test, the supplemental test, etc. may be positive. In order to make a diagnosis, if there is still no specific antibody in the second serum, the possibility of yellow fever can be excluded.

Severe and malignant yellow fever, clinically can be divided into three phases, the whole course of disease is about 10 days, the diagnosis of severe cases is generally no difficulty, epidemiological data and some special clinical symptoms such as facial hyperemia, obviously relatively slow pulse, a large number Black vomit, a large amount of proteinuria, and jaundice have important reference values.

Yellow fever check

(1) In the early routine and biochemical examination, the number of neutrophils decreased, the platelet count was normal or slightly decreased, serum bilirubin, ALT, AST, etc. were elevated, and the urinary protein was increased to 3 to 5 g in 4 to 5 days. L, fecal occult blood is often positive, cerebrospinal fluid pressure is often increased, the number of cells is normal, ECG can show ST-T wave abnormalities, PR and QT interval changes, etc., clotting time, prothrombin time and partial thromboplastin time prolonged in jaundice Case.

(2) Virus isolation The blood of patients within 4 days of the disease can be injected into the brain of the suckling rat or passaged Vero cells, and the virus can be isolated and identified by serum immunology.

(3) Serum immunology test Take the acute phase and recovery period 2 to 4 weeks after the onset of serum for IgM anti-accept ELISA (IgM ontibodycapture ELISA), hemagglutination inhibition test, complement binding test or neutralization test, IgM antibody, blood coagulation Inhibitory antibodies and intermediate antibodies appear within 5 to 7 days after onset, CF antibodies appear within 7 to 14 days after the onset of disease, and the antibody titer of the serum during the recovery period is increased by more than 4 times, which can be diagnosed as a disease due to the presence of IgM and CF antibodies. The time is relatively short, and when the titer is elevated, it suggests a recent infection, such as a specific IgG antibody in the serum and no dynamic change in the titer, suggesting that the patient has been infected with the disease in the past.

The use of ELISA to detect viral antigens in the early stage of the disease helps early diagnosis. This method is specific and sensitive, and can be obtained within a few hours. It can be used in general laboratories.

(IV) Detection of viral nucleic acid The reverse transcription (RT)-PCR method is used to detect flavivirus RNA, which has strong specificity and high sensitivity. It has been reported at home and abroad, providing a reliable method for early diagnosis and rapid diagnosis of this disease. The inspection requires certain techniques and conditions, and it is difficult for general laboratories to promote.

(5) Liver puncture examination is not suitable for patients with liver puncture, which can lead to serious consequences such as bleeding. In the case of death, a small piece of liver tissue can be taken for pathological examination by visceral puncture knife, mouse inoculation and enzyme immunoassay (using monoclonal antibodies or Human polyclonal IgM antibody).

(6) Electrocardiogram shows prolongation of PR and QT interval and abnormal ST-T wave.

Diagnosis of yellow fever

The disease must be associated with dengue fever, epidemic hemorrhagic fever, leptospirosis, falciparum malaria, relapsing fever, viral hepatitis, drug-induced or toxic jaundice, and rickettsial disease, typhoid fever, and various other hemorrhagic fevers (Lassa Heat, African hemorrhagic fever, Bolivian hemorrhagic fever, Argentic hemorrhagic fever, etc.).

Malaria may be combined with this disease. Therefore, even if the blood or bone marrow smear detects the malaria parasite, the disease cannot be excluded. The early spread of yellow fever, early or mild cases, neglect or missed diagnosis can often lead to the disease. The outbreak is popular.

The material in this site is intended to be of general informational use and is not intended to constitute medical advice, probable diagnosis, or recommended treatments.