Etiology
1.Infectious source
Patients and latently infected persons are the main sources of infection. Patients are most infectious from day 1 to 3 days after the onset of the disease. In a few patients, the virus can be isolated from the blood on the 3rd day after the fever has subsided. In addition, antibodies to dengue virus can be detected in animals such as bats, monkeys, birds and dogs, which may be the natural hosts of dengue virus and thus may be the source of infection of the disease.
2.Vector of transmission
Mosquitoes are the main vector of the disease, including Aedes aegypti and Aedes albopictus, which are the main mosquito species for dengue virus transmission.
3.Susceptibility
In the new epidemic area, all age groups are susceptible, but most of them are young adults.
Clinical manifestations
Incubation period 2 to 15 days, the average is about 6 days.
1.Dengue fever
(1)The onset of fever is mostly sudden, the body temperature reaches more than 39℃ rapidly, generally lasts 2-7 days, the fever pattern is irregular, some cases have their body temperature dropped to normal on the 3rd to 5th day, and then rise again after 1 day, showing bimodal fever or saddle type fever. In children, the onset of the disease is slower and the fever level is lower. The onset of the disease is accompanied by headache, back pain and muscle and joint pain, orbital pain, retro-ocular pain and other systemic symptoms. Gastrointestinal symptoms such as sensory allergy, nausea, vomiting, abdominal pain, poor appetite, diarrhea and constipation may be present. The face and conjunctiva are congested, and the skin of the neck and upper chest is flushed. Relatively slow pulse may be present during the febrile period.
(2) The rash appears 2 to 5 days after the onset of fever, initially on the palms, soles of the feet or trunk and abdomen, gradually extending to the neck and extremities, and in some patients on the face, and may be maculopapular rash, measles-like rash, scarlet fever-like rash, erythematous rash, slightly prickly. Brown spots, which usually subside at the same time as the body temperature.
(3) Bleeding occurs 5 to 8 days after the onset of the disease.
(4) Lymph node enlargement The lymph nodes of the whole body may be mildly enlarged with light tenderness.
(5) Other hepatomegaly may be present. Patients often feel weak after the disease and full recovery often takes several weeks. In severe dengue fever, headache, nausea, vomiting, impaired consciousness, meningoencephalitis, or in some cases, gastrointestinal hemorrhage and hemorrhagic shock appear on the 3rd to 5th day of the disease. This type often dies due to central respiratory failure and hemorrhagic shock because of the rapid development of the disease.
2.Dengue hemorrhagic fever
(1) Shock usually occurs on the 2nd to 5th day of the disease and lasts for 12 to 24 hours. Patients are irritable, have cold extremities, pale face, patterned skin, falling body temperature, fast and irregular breathing, weak pulse, progressive narrowing of pulse pressure, falling blood pressure or even undetectable, and cerebral edema and occasionally coma can occur during the course of the disease. If not rescued in time, death can occur in 4 to 10 hours.
(2) Bleeding bleeding tendency is serious, with nosebleeds, blood mass bruises on the skin, vomiting blood, blood in stool, hemoptysis, hematuria, vaginal bleeding, and even intracranial bleeding.
Examination
1.Conventional examination
(1) Peripheral blood picture of dengue fever patients has a decrease in total white blood cell count at the beginning of the disease, which is especially obvious at the rash stage; the percentage of neutrophils is also reduced, and there is an obvious nuclear left shift phenomenon, and there are abnormal lymphocytes.
(2) Urine routine may have a small amount of protein, red blood cells, white blood cells, sometimes with tubular type.
2.Virus isolation
Take the blood of early patients and inoculate it with Aedes albopictus cell line (C6/36), after isolation, the virus must be identified by specific neutralization test or hemagglutination inhibition test.
3.Serum immunological examination
ELISA is used to detect the specific IgM antibody in the patient’s serum, and a positive test can help to make a clear diagnosis of dengue fever at an early stage. If the antigen of dengue virus is detected in the patient’s serum, it can also be used as the basis for definite diagnosis.
4. Reverse transcription “RT-PCR” test
The sensitivity of RNA of dengue virus in patient’s serum is higher than that of virus isolation, which can be used for early and rapid diagnosis and serotype identification, but the technical requirements are high, and its specificity and reproducibility need to be further improved.
5.Other
In dengue hemorrhagic fever cases, blood concentration, prolonged bleeding and clotting time, elevated serum glutamic transaminase, prolonged prothrombin time, electrolyte imbalance, reduced blood albumin, metabolic acidosis, etc. may also occur. Various coagulation factors are mildly reduced, fibrinogen is decreased, and fibrinogen degradation products are mildly to moderately increased.
Diagnosis
A comprehensive analysis based on etiology, clinical manifestations and laboratory tests can all lead to a clear diagnosis.
Differential diagnosis
1.Influenza
Symptoms of upper respiratory tract infection such as nasal congestion, runny nose, sore throat and cough are more obvious, and rash is rare.
2.Measles
Cough, runny nose, lacrimation, congestion and photophobia of the conjunctiva of the eyes, as well as sore throat, and general malaise are common. On the second to third day of the disease, more than 90% of patients have Cochlear’s spots in the mouth. The rash is a maculopapular rash that first appears on the hairline behind the ears, then gradually spreads to the forehead, face and neck, and from top to bottom to the chest, abdomen, back and extremities.
3. Scarlet fever
Acute pharyngitis is more pronounced and is characterized by sore throat, painful swallowing, localized congestion and purulent discharge, and swollen and painful submandibular and cervical lymph nodes. The rash starts 24 hours after the onset of fever and begins behind the ear, on the neck and upper chest, then spreads rapidly throughout the body. The rash is a diffuse, congested, pinpoint-sized papule that recedes under pressure and is accompanied by an itchy sensation. The face is congested, but the congestion around the mouth and nose is not obvious, forming a perioral pale circle.
4.Epidemic hemorrhagic fever
Also known as renal syndrome hemorrhagic fever, patients mainly present with fever, toxic symptoms, congestion, hemorrhage, shock, oliguria, and hypervolemic syndrome. IgG and IgM antibodies against epidemic hemorrhagic fever virus can be detected in the serum.
5.Leptospirosis
History of epidemic water contact before the disease. The gastrocnemius muscle pressure pain is more obvious on physical examination. Anti-Leptospira IgG and IgM antibodies can be detected in the serum.
6.Chiggers
Characteristic crusts or ulcers can be found near the enlarged and painful lymph nodes. Serum Aspergillus agglutination test (exo-Fei reaction) examination, OXK agglutination antibody potency of 1:160 or above has diagnostic significance. Blood was inoculated into the peritoneal cavity of mice, and Rickettsia tsutsugamushi could be isolated after 7 to 10 days of feeding.
7.Typhoid fever
The potency of “O” antibody can be more than 1:80 and “H” antibody can be more than 1:160 in the fatta reaction (S. typhi serum agglutination reaction). Blood and bone marrow cultures may show the growth of S. typhi.
Treatment
At present, there is no exact and effective pathogenic treatment for this disease, mainly taking supportive and symptomatic treatment measures.
1.Lower body temperature
Patients with high fever should first use physical cooling, such as ice, alcohol swabbing bath, cautious use of pain-reducing antipyretic drugs. For patients with high fever and severe toxemia, small doses of adrenocorticotropic hormone, such as oral prednisone, can be applied for a short time.
2. Rehydration
For those who sweat a lot and have diarrhea, make oral rehydration first and pay attention to water, electrolytes and acid-base balance. If necessary, intravenous rehydration should be used to correct dehydration, hypokalemia and metabolic acidosis, but one should always be alert to the possibility of inducing cerebral edema, intracranial hypertension and brain herniation.
3.Lower intracranial pressure
In cases of severe headache and intracranial hypertension, a rapid intravenous drip of 20% mannitol injection should be applied promptly. At the same time, intravenous dexamethasone can help reduce cerebral edema and intracranial pressure. Patients with central respiratory depression should be treated with artificial ventilator in time.
Prognosis
Dengue fever is an infectious disease with a self-limiting tendency, and the duration of illness is about 10 days in patients without complications. The prognosis of the disease is usually good. Most of the deaths are in severe cases.
Prevention
1. Specific laboratory tests should be performed as soon as possible to identify lighter patients. Strengthen the national health quarantine.
2, cut off the transmission route. Anti-mosquito and mosquito control are the fundamental measures to prevent this disease. Improve the sanitary environment, eliminate the breeding place of Aedes aegypti, clean up the stagnant water. Spraying mosquito killer to eliminate adult mosquitoes.
3.Improve the population’s resistance to disease, pay attention to diet and balanced nutrition, work and rest, appropriate exercise, enhance physical fitness.
4, the vaccine is still in the development and testing stage.