This infectious disease is related to mosquito bites! What are the symptoms? How to treat it?

Author: Zou Yang, Chief Physician, Beijing Friendship Hospital, Capital Medical University

Reviewer: Wang Linghang, Chief Physician, Beijing Ditan Hospital, Capital Medical University

Dengue fever is a viral infectious disease caused by dengue virus infection. There are four types of dengue virus in serology, namely type I, type II, type III, and type IV.

Dengue fever is a global disease that is very widespread. According to the latest statistics from the World Health Organization, 2.5 billion people are at risk of dengue fever infection each year, and 3.2 million people can be diagnosed with dengue fever each year, so dengue fever is now receiving more and more attention.

Dengue virus is distributed globally, mainly in tropical and subtropical regions, such as Southeast Asia, the Pacific Islands, Africa, etc., including Guangdong and Yunnan in my country, where there have been group outbreaks. In recent years, dengue fever has spread from my country's southeastern coast to the northern region.

In 2023, the global dengue fever epidemic was severe, and outbreaks occurred in many provinces of my country, including Yunnan. It was the largest epidemic since 2019.

1. How is dengue fever transmitted?

Dengue fever is a mosquito-borne infectious disease that is mainly transmitted by mosquitoes, with the main vectors being Aedes albopictus and Aedes aegypti.

Figure 1 Original copyright image, no permission to reprint

These two types of mosquitoes carry the dengue virus for life. The dengue virus becomes contagious after 7-10 days of development in the mosquito's body and is transmitted to other people through bites. If the scope gradually expands, it will cause local infectious and epidemic cases.

Dengue virus has seasonal fluctuations, which are related to the increase and decrease of mosquitoes. In my country, the seasonal fluctuation of mosquito vectors is from March to November, and the most important period is from July to September. For subtropical regions, the seasonality may not be particularly obvious, but as long as there is obvious activity of Aedes albopictus and Aedes aegypti, dengue fever is likely to occur.

2. What are the symptoms of dengue fever?

After being infected with the dengue virus, the disease will not occur immediately. There is an incubation period, which is usually 1-14 days, mostly concentrated in 5-7 days. Some people will become ill within 1 day. There are no symptoms during the incubation period. Most people do not become ill after being infected with the dengue virus.

The World Health Organization divides dengue fever into two major categories: common dengue fever and severe dengue fever. The entire course of dengue fever is divided into fever stage, peak stage and recovery stage.

The first thing that occurs during the fever phase is a sudden acute high fever, which can reach 40, 41, or 42 degrees Celsius, and is accompanied by very typical "bone-crushing fever," which is pain in large joints throughout the body. Fever and bone-crushing fever are very typical clinical manifestations of dengue fever. If you travel to Southeast Asia and develop a fever after one day, you should consider the possibility of dengue fever.

The fever period can last for 3-5 days. Generally, some rashes will appear after 3-5 days. Once the rash appears, it is actually the virus that has been released and the body temperature will gradually drop.

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If there is no rash after 5-7 days of fever, but respiratory, circulatory, and brain symptoms appear, it may have entered the extreme stage, which is severe dengue fever. Once severe dengue fever occurs, it may be life-threatening within 24-48 hours.

If very good symptomatic treatment and supportive treatment are given at the peak stage, the patient's condition will improve after 2-3 days and will enter the recovery period, so the total course of dengue fever is generally about 10 days.

3. How to treat dengue fever?

For common dengue fever, the main treatment is symptomatic and supportive treatment. Rest is the most important, and oral rehydration support treatment is given. Because there is no specific antiviral drug, some common antiviral drugs can be used, such as Isatis root, antiviral capsules, etc. If fever occurs, antipyretic treatment can be given, and physical cooling can be adopted, such as alcohol bath, warm water bath, and antipyretic drugs can choose acetaminophen. Use acetylsalicylic acid (aspirin) and ibuprofen with caution. These drugs can cause gastric bleeding or worsen gastric ulcers. Other symptomatic treatments, such as liver protection, etc.

Severe dengue fever mainly relies on supportive treatment based on the extent of organ damage. For example, for high fever, an ice blanket can be used to reduce the temperature, and antipyretics can be given intravenously. For damaged liver function, liver-protecting drugs should be used. For arrhythmias and respiratory problems, symptomatic supportive treatment should be given. Patients in shock should be given fluid resuscitation in a timely manner. For massive internal bleeding, bleeding should be stopped and blood transfusions should be given.

In addition, dengue patients need to be isolated and quarantined to prevent mosquitoes, and the transmission route must be cut off. Because the patient is in the viremia stage from 1 day before the onset of the disease to 5 days after the onset of the disease, the blood contains viruses, and mosquito isolation should be carried out during this period. After 5 days of onset, the viremia will enter the reduction stage by itself, and there will be no so many viruses in the blood, so the isolation time cannot be less than 5 days.

Common dengue fever is a self-limiting disease within 10 days, and the prognosis is very good. Taking the dengue fever outbreak in Guangdong in 2014 as an example, our country has conducted a lot of clinical research, and the elderly, infants and pregnant women; those with underlying diseases such as diabetes, hypertension, coronary heart disease, peptic ulcer, asthma, chronic kidney disease, and those with immunodeficiency are at high risk of severe dengue fever.

Generally speaking, dengue fever is a benign, self-limiting viral infectious disease with a relatively good prognosis.

4. Will antibodies be produced after being infected with dengue virus?

Antibodies will be produced after infection with dengue virus. Generally, IgM antibodies will be produced around 10 days after infection, which is an indicator for early prediction of dengue fever. IgG antibodies will be produced around a month later. IgG antibodies are protective antibodies. If they can last, they will have a certain degree of protection against reinfection with the same type of virus.

For example, if the current infection is with type 1 virus, and the next infection is also with type 1 virus, if there are antibodies in the body, there will be protection. If the current infection is with type 1 virus, and the next infection is with type 2 virus, there will be an antibody-dependent infection enhancement effect, and the risk of developing severe disease is relatively high.