Dengue Fever: Causes and Risk Factors

Dengue fever is an acute infectious disease caused by the dengue virus, with its causes involving a variety of complex biological, environmental, and social factors. The virus is primarily transmitted to humans through bites from infected mosquitoes (Aedes aegypti and Aedes albopictus), and the severity of the disease is closely related to the virus strain, host immune status, and environmental conditions. Understanding these causes helps in formulating effective prevention strategies and public health measures.

The transmission chain of dengue fever involves three core links: virus-carrying mosquitoes, human infection hosts, and environmental conditions. The circulation of the virus between mosquitoes and humans depends on factors such as mosquito density, population density, and climate change. Although genetic factors are not the primary risk, individual differences in immune response to the virus may lead to varying disease severity. The following sections will delve into these key causes from different perspectives.

Genetic and Familial Factors

Although genetic factors are not a direct transmission route for dengue fever, individual genetic differences do influence disease manifestation after infection. Studies have shown that specific human leukocyte antigen (HLA) genotypes may increase the risk of severe disease, such as the association of HLA-B*13:02 subtype with hemorrhagic dengue fever. Additionally, congenital immune-related genes (such as Toll-like receptor polymorphisms) may weaken the host's initial recognition of the virus.

Family history may reflect the combined effects of genetic predisposition and environmental exposure in certain populations. For example, some Asian populations, having long been in areas endemic to mosquitoes, may have evolved certain disease resistance mechanisms, but this does not completely eliminate the risk of infection. It is worth noting that the impact of genetic factors on disease severity is usually less than that of environmental and behavioral factors, thus public health measures still focus on environmental control.

Environmental Factors

Climate conditions are a key environmental factor affecting mosquito breeding. A temperature increase of 1°C can shorten the mosquito growth cycle by 2-3 days, while relative humidity above 60% significantly increases mosquito survival rates. During urbanization, containers that hold water (such as discarded tires and rainwater tanks) become breeding grounds for mosquitoes, particularly creating "urban hotspot" effects in peri-urban areas. For instance, during the rainy season in subtropical cities, mosquito density often surges by 3-5 times, directly increasing the risk of infection.

• Global warming has expanded the geographical range suitable for mosquito distribution, leading to cases in previously non-endemic areas (such as high-altitude regions).
• Urbanization has resulted in population density and poor waste management, creating a "dual environmental pressure" for mosquito breeding.
• Climate anomalies, such as heavy rains following prolonged droughts, can create irregular water accumulation, forming temporary but high-density breeding environments.

Urban planning and infrastructure also play a crucial role. Communities lacking proper drainage systems have mosquito densities 4-7 times higher than modern urban areas. Improper management of agricultural irrigation systems can also lead to large breeding sites in rice paddies and irrigation ditches, especially evident in Asian rice-growing regions.

Lifestyle and Behavioral Factors

Human daily behavior patterns directly influence infection risk. Groups that do not use mosquito prevention measures (such as mosquito nets and repellents) have infection rates 2-3 times higher than those who regularly protect themselves. In tropical regions, when outdoor activity times overlap with peak mosquito activity (early morning and dusk), the likelihood of infection is further increased. Hygiene habits in living environments, such as not clearing water-holding containers around the home, directly elevate the chances of mosquito breeding.

Population mobility is also a key behavioral factor. International travelers can introduce the virus into non-endemic areas, which may trigger new outbreaks if suitable mosquito vectors are present. Occupational mobility (such as agricultural workers operating in jungles) may also increase exposure opportunities. Moreover, disparities in sanitation conditions caused by urban-rural economic differences often result in infection rates in low-income communities being 2-4 times higher than surrounding areas.

Other Risk Factors

The "antigenic original sin effect" of repeated infections with different virus serotypes is a key factor in severe cases. When a patient is infected a second time with a different serotype, the immune system may produce incomplete neutralizing antibodies, which can facilitate the virus's entry into macrophages, increasing the risk of hemorrhagic symptoms. This immunological mechanism explains why communities with high rates of repeated infections in certain regions have a higher proportion of severe cases.

Areas with insufficient medical resources face higher risks of complications. The lack of timely diagnosis and supportive treatment may lead to metabolic disorders or uncontrolled bleeding. Additionally, co-infections (such as concurrent outbreaks of dengue virus and Zika virus) may exacerbate symptoms, although such cases are relatively rare.

Urbanization and land-use changes are emerging risk factors. Large-scale infrastructure projects (such as road construction that disrupts existing ecosystems) may destroy habitats for natural enemies, indirectly increasing mosquito density. The urban heat island effect raises local temperatures, extending the transmission season for mosquitoes; these factors must be considered in environmental governance.

The causes of dengue fever result from the interaction of multiple factors: the genetic characteristics of the virus determine its transmission potential, environmental conditions control mosquito density, human behavior influences exposure opportunities, and differences in immune mechanisms lead to variations in disease severity. Only through integrated prevention strategies, including environmental sanitation improvements, community mosquito education, and timely monitoring systems, can we effectively reduce the global burden of this disease.

 

Frequently Asked Questions

Why is dengue fever more likely to outbreak during the rainy season or in hot regions?

The dengue vector mosquitoes (Aedes aegypti and Aedes albopictus) breed faster in high-temperature, high-humidity environments, and the water-holding containers (such as vases and discarded containers) required for egg and larval growth are more likely to accumulate water during the rainy season. Increased temperatures also enhance mosquito activity, leading to more frequent blood meals and shorter virus transmission cycles, making outbreaks more likely under specific climatic conditions.

After being infected with dengue fever, why do some people have mild symptoms while others develop severe cases?

The severity of symptoms is related to individual immunity, the type of virus strain infecting them, and whether they have previously been exposed to different serotypes. If a patient has previously been infected with one type of dengue virus, subsequent infections with other types may worsen the disease due to the "antibody-dependent enhancement effect." Older adults, those with underlying health conditions, or individuals with abnormal immune systems are also more likely to develop severe cases such as hemorrhagic shock.

Why should aspirin or other non-steroidal anti-inflammatory drugs (NSAIDs) not be used to relieve dengue fever fever?

NSAIDs may exacerbate coagulopathy caused by dengue fever, increasing the risk of internal bleeding. Currently, paracetamol is recommended for fever relief, and close monitoring for warning symptoms such as bleeding points and thrombocytopenia is advised. Patients should follow medical advice and avoid self-medication.

Is the dengue vaccine suitable for all age groups? Can it provide complete prevention?

The currently approved dengue vaccine in Taiwan (Tamarix) is only recommended for individuals aged 9-45 who have previously been infected with the dengue virus. Those who have never been infected may face an increased risk of severe disease after vaccination, thus requiring blood tests to confirm their infection history. The vaccine's efficacy is approximately 60% to 90%, and it cannot completely prevent infection, so mosquito prevention measures should still be implemented.

How can household transmission be avoided when there is a dengue fever patient at home?

During the patient's fever period, mosquito nets should be used to prevent mosquito bites, as the dengue vector mosquitoes are active during the day. Indoor mosquito control measures (such as electric mosquito repellents and mosquito traps) should be strengthened, and all water-holding containers in the home should be thoroughly eliminated. Contacts should enhance mosquito prevention measures, and if symptoms such as fever and headache occur, they should seek medical attention immediately and inform the doctor of their contact history for early diagnosis.