Common Causes of Dengue & it’s Risk factors

Dengue is a viral disease that spreads through contact with mosquitoes, the most commonly known dengue causative agents. Predominantly found in tropical areas, the dengue virus-bearing mosquitoes are typically active during early dusk and dawn. You can get a dengue infection when a mosquito infected with the dengue virus bites you. This illness is not contagious, in that there is no direct person-to-person contact leading to dengue. However, mosquitoes act as a vehicle to transfer infected blood from one person to another, causing the disease to spread.

High and recurring fever is one of the prominent symptoms of dengue, albeit in its mild stage. At a severe level, the disease leads to conditions like shock, low blood pressure or even death of the infected patient. The severity depends on the dengue virus type and stage at which the illness is diagnosed or discovered. Additionally, while patients may become immune to one strain of the dengue virus, they may experience a higher risk of complications when reinfected with another strain of the virus after recovering.

Dengue is Caused by Which Mosquito?

A group of mosquito species called Aedes aegypti are primarily responsible for spreading the dengue virus. Other rare but possible species include Aedes scutellaris, Aedes albopictus, and Aedes polynesiensis. Aedes aegypti are the most prevalent dengue causative agents. They breed in tropical and sub-tropical regions in different parts of the world, including Central and South America, Southeast Asia, the Caribbean, Africa, and the Pacific Islands.

Aedes aegypti mosquitoes are small and dark. You can identify them with features like white bands on the legs and silver-white scales on the body. Such mosquitoes require warm climates and do not live at altitudes above 1000 m. You can find them in and around your house as they mainly breed in human living spaces.

Life Cycle of Dengue Mosquitoes

Dengue fever is caused by female mosquitoes, which have four life cycles. They are as follows:

• Eggs: Female mosquitoes lay their eggs above the waterline. The most preferred spaces are inside containers that hold water. These include buckets, storage jars, flower pots, tires, etc. Mosquitoes can lay up to hundred eggs at a time. Due to resilience, these eggs stick to container walls like glue and resist drying up for up to eight months. A little water is enough for female mosquitoes to lay eggs.

• Larva: The eggs hatch into larvae when the water level rises in spaces or containers holding the eggs. The larvae feed on aquatic microorganisms to survive and go through development stages, where they moult and shed skin.

• Pupa: After fully growing, a larva undergoes metamorphosis and takes on a new form called the Pupa. The Pupa is the cocoon stage for mosquitoes. During this stage, a mosquito’s life is aquatic, where it grows until it becomes an adult, breaks through the pupal skin, and exits the water.

• Adult: The last stage in the life cycle of a dengue mosquito is adulthood. In this stage, the mosquito takes on terrestrial life with the ability to fly. Female mosquitoes feed on human blood to generate eggs, while male mosquitoes rely on nectar. In the process, female mosquitoes infect humans with the dengue virus throughout their lifespan.

An Overview of Dengue

Dengue causes stem from the virus of the Flaviviridae family known as DENV. The virus is further categorised into four distinct serotypes – DENV-1, DENV-2, DENV-3, and DENV-4. You can be infected by all of the serotypes throughout your lifecycle. The serotypes behave differently and cause varied symptoms as their interaction with the human blood serum differs.

Upon entering your body, the virus attaches itself to your skin cells regardless of the serotype. After the attachment, the skin cell’s membrane folds and forms a seal around the virus. The result of this process is a pouch called an endosome. As the virus penetrates the cell within the endosome membrane, it releases a dengue nucleocapsid into the cell’s cytoplasm.

Once released, the nucleocapsid in the cytoplasm uncoats the viral genome, leading to the development of a viral RNA. The viral RNA hijacks the host cell’s machinery to replicate, and the repetition of this process spreads the virus throughout your body.

Dengue Transmission Cycle

Dengue virus spreads through a human-mosquito-to-human cycle. When mosquitoes bite an infected person, they carry the virus-borne blood. The virus develops and multiplies inside the mosquito and spreads through the mosquito’s saliva when it bites another person. The stages are explained in detail below:

• Mosquito Infection Stage: Dengue fever is caused by Aedes aegypti only after it becomes a dengue vector. To develop into the vector stage, the mosquito should feed on the blood of a person with dengue virus during the viremia period. During this phase, the infected person has high levels of the DENV serotype in the bloodstream. After the mosquito consumes the blood meal, the virus spreads within its body over eight to twelve days.

Once fully infected, the mosquito remains infected for the rest of its life cycle (three to four weeks). It can continue transmitting the dengue virus to multiple non-infected people during this time.

• Human Transfer Stage: After the principal vector for dengue fever, Aedes aegypti, bites you, you develop viremia (a condition where viruses enter your bloodstream) and contract a high fever. Viremia continues to spread for up to four days, and can last for twelve days, depending on the transmission. You may not notice any symptoms on the first day of viremia, but may pick up on signs of dengue fever after five days, lasting up to a week.

Human-to-Human Transmission of Dengue Virus

Primarily dengue only transfers through a mosquito bite. But the human-to-human transmission is possible in the following cases:

• Mother to Child Transfer: One of the dengue causes is a transfer from mother to child. The foetus or the womb gets affected if the mother is infected with the dengue virus. As a result, the DENV serotype can spread from mother to baby during pregnancy. A nursing mother may also transmit the virus to the baby through breastfeeding.

• Medical Blood Infusion & Organ Transplant: If you undergo a blood infusion or organ transplant due to a medical condition, you could get infected with the dengue virus when the donor is in the viremia stage. Although a possibility, this kind of transfer is improbable as donors must undergo medical tests to identify infections before the medical procedure.

Risk Factors of Dengue

You are more likely to have dengue fever in these instances:

• You Live in Tropical Regions: People residing in tropical and sub-tropical areas are most at risk of inhibiting the dengue virus. This is because Aedes aegypti mosquitoes, the predominant dengue causative agents breed in these peri-domestic areas in large scales.

• You Have Had Dengue Fever Before: If you have recovered from dengue fever, your chances of getting infected with a different strain of DENV increase the second time.

• You Travel to Tropical Places: You can get exposed to the dengue virus when you travel to tropical places. The duration does not matter if you are in a region with a high prevalence of the virus. Hence, you must take special care and assess the risk factors before visiting.

• You Reside in Areas Close to Stagnant Water Bodies: Stagnant water is one of the leading dengue fever causes. As little as 40 ml of stagnant water can serve as the perfect breeding spot for dengue-virus-carrying mosquitoes. Hence, preventing water from stagnating inside and outside your home is a good practice to prevent the infection.

Identification of Dengue Virus

Diagnostic tests conducted to detect the presence of the DENV serotype in your blood include the following:

• Complete Blood Count: As a preliminary test, doctors check your complete blood count to identify the decrease in haemoglobin, haematocrit, red blood cell count, etc. Such diagnosis helps in understanding the possibility of dengue infection and helps in making a judgement for other diagnostic tests.

• NS1 Antigen: It takes about four to five days for antibodies to enter your blood cells. During this period, you can detect the presence of dengue infection with an NS1 antigen test. It is a faster process for early diagnosis. You should get the test done five to seven days after noticing the symptoms. Post this period, the chance of false positives and negatives increases.

• Immunoglobulin M (IgM): You must undergo an IgM test after the first three days, whether you have mild symptoms like fever or severe dengue symptoms like vomiting, nasal bleeding, belly pain, breathing difficulties, etc. It helps to recognise whether the illness is in the primary or secondary stage. The chance of finding IgM is the highest after three days of exposure and reduces as the timeline increases.

• Immunoglobulin G (IgG): IgG indicates that you have been infected by DENV before, and the illness is a repeat occurrence. When this happens, the severity increases and taking immediate action is important. As IgG levels increase at a slower rate in the blood cells, you can get the Immunoglobulin G test done after six to ten days of infection. The antibodies can also remain in your body for around 90 days of your entire lifecycle.

• Dengue RNA PCR Test: RNA PCR test is the most definitive diagnostic test to identify the DENV serotype in the early infection stage. It is best to undergo an RNA PCR test within two days of identifying the symptoms to take immediate action.

Treatment for Dengue

There is no definitive treatment available to cure dengue. Immunisation has been possible in certain parts of the country but only for people previously infected with the DENV. Research is underway on developing a dengue vaccine to fight against the disease. The only way to attain immunity against it is to identify dengue causes and take the necessary protective measures. In mild cases, you should rest as much as possible, drink fluids, and take medication to reduce dengue fever. In case of severe dengue symptoms, blood transfusion and intravenous fluid supply help control the condition if you get hospitalised on time.

Preventive Measures for Dengue

Some of the preventive measures to take to avoid getting infected with the DENV serotype are:

• Maintain cleanliness in and around your house and prevent the accumulation of stagnant water.
• Ensure doors and windows remain closed in the early morning and at night.
• Repair damaged screens or gaps/holes in windows and doors.
• Cover yourself with long-sleeved shirts and full-length pants when entering mosquito-infested areas.
• Wear mosquito repellent with a DEET concentration of 10% and use mosquito nets while sleeping.
• Avoid going outdoors without adequate protection during dusk and dawn.