The Dangers Of Dengue: How Is The Dengue Virus Able To Trick The Body's Immune System?

What happens when the dengue virus enters the body? What kind of immunity cells does it encounter? What does the body's preparedness look like? Read on to find out.

Dengue virus and the threat to health: It is important to protect yourself and your health from mosquito-borne illnesses that are prevalent during this time of the year. Dengue, for instance, can take a deadly turn, unless it is diagnosed and treated in a timely manner. The dengue virus (DENV) is the cause of dengue fever. It is a single positive-stranded RNA virus, says Dr Sandeep Patil, chief intensivist and physician at Fortis Hospital, Kalyan. He adds that dengue has four different serotypes: DENV-1, DENV-2, DENV-3, and DENV-4). Interestingly, infection with one serotype can provide lifelong immunity to that specific serotype, but only temporary immunity for other serotypes.

"When someone is infected with a different serotype after a previous infection, the antibodies from the first infection can bind to the new serotype, but they do not neutralise it properly. Instead, they help the virus enter immune cells, allowing it to replicate more rapidly and causing a more severe infection -- this is known as antibody-dependent enhancement (ADE) in the medical parlance," Dr Patil explains.

A Higher Risk Of Severe Dengue

The doctor warns that an enhanced viral replication can lead to a higher risk of severe dengue, including dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS). They can be life-threatening.

He goes on to explain that the ADE mechanism involves the virus 'attaching' to the cell's surface via the 'pre-existing antibodies', then being 'engulfed' into the cell. "Inside the cell, the virus replicates and releases more virus particles, leading to a more widespread and severe infection. While secondary infections are more dangerous, studies suggest the risk is more pronounced when the second infection occurs within a few years of the first," he warns.

How Does The Body Defend Itself?

What happens when a pathogen like the dengue virus invades the body? How does the body defend itself? The doctor says that the human body's main defence against any invading pathogen is the immune system, which is made up of two parts. "The first part -- called the innate immune system -- provides the body with immediate and general protection from any invading pathogen. The innate immune response rapidly recognises and responds to pathogens, but it does not provide a person with long-term immunity against an invading pathogen.

"The second part -- the adaptive immune system -- produces cells that specifically and efficiently target the pathogen and infected cells. The cells produced by the adaptive immune system include antibody-secreting B cells and cytotoxic T cells. The antibodies (called immunoglobulin, or Ig) secreted by the B cells specifically recognise and bind to foreign molecules. The cytotoxic T cells kill cells infected with pathogens. The adaptive immune system takes longer to respond to an invading pathogen, but it provides long-term immunity."

Aedes Aegypti And Dengue

What happens when the mosquito Aedes Aegypti infects someone with the dengue virus? According to Dr Patil, when an infected mosquito feeds on a person, it injects the dengue virus into the bloodstream. The virus infects nearby skin cells called keratinocytes, the most common cell type in the skin. The dengue virus also infects and replicates inside a specialised immune cell located in the skin -- a type of dendritic cell called a langerhans cell, which helps detect invading pathogens and display molecules from the pathogens (antigens) on their surface.

"The langerhans cells then travel to the lymph nodes -- small organs located throughout the body connected by vessels that form a network called the lymphatic system -- and alert the immune system to trigger the immune response. The lymph nodes are stations in the body for immune cells that help fight against infections," the expert explains.

Recovery From A Dengue Infection

While it is true that the dengue virus manages to trick the immune system to infect cells and spread throughout the body, the immune system has additional defences to fight it. The infected cells, for instance, produce and release small proteins called 'interferons' that are part of a large group of proteins called 'cytokines', the health expert states, adding that interferons have the ability to interfere with viral replication and they activate both the innate and adaptive immune system defences. "They help the immune system recognise dengue-infected cells and help protect uninfected cells from infection. As the immune system fights the dengue infection, the person experiences a fever."

Virus Versus The Body's Immunity

The doctor explains that as the adaptive immune response starts fighting the dengue infection, B cells produce antibodies called IgM and IgG that are released in the blood and lymph fluid, where they are tasked to specifically recognise and neutralise the dengue viral particles.

"In another adaptive immune response, cytotoxic T cells -- or killer T cells -- recognise and kill the cells that are infected with the dengue virus. The innate immune response activates the complement system, a response that helps the antibodies and white blood cells remove the virus. Together, the innate and adaptive immune responses neutralise the dengue infection, and under proper care, the patient recovers from dengue fever," he concludes.