The Serotypes (strands) of Dengue
Dengue is one of the most prominent vector-borne diseases in the world. It is caused by the transmission of a virus from the Aedes mosquito into human beings and infecting them.
This disease is very difficult to cure and like most common viral infections, a person cannot be immune to the disease even after defeating it once.
This is because of the nature of the virus. There are several strains of the dengue virus called serotypes, and those strains, too, continuously undergo mutation and changes.
Due to this, your immune system cannot possibly develop immunity against all these strains.
This is why physicians treat dengue for its symptoms and not with drugs aimed at getting rid of the virus. With the treatment of symptoms such as high fever, the doctor will usually let the virus run its course in the human body while closely monitoring the patient until their body fights off the virus.
Dengue fever, Credit: pixabay
Serotypes of Dengue
All serotypes of dengue belong to the Flaviviridae family, but differ from one another based on the antibody reactions to the surface antigens of each strain of the virus.
Every antibody consists of a “Y” shaped structure and it consists of two antigen-binding sites at the top two tips of the structure. An antigen is a foreign substance that is given off by the virus and binds to an antibody which causes and stimulates an immune response in the host.
Every serotype has different antigen proteins on itself and will only allow a specific antibody to bind with it.
There are four most common strains of the dengue virus:
Thus, this means that there are four different types of antigens for four different serotypes and they will only bind to a specific antibody. Now, we know that antibodies have “memory cells”, meaning that they can produce an immune response faster and more effectively when that particular serotype enters the body the second time. This is why immunity to dengue cannot be guaranteed as if another serotype enters the body, a different type of antibody will bind to a different type of antigen and your immune system will have no recollection of this and thus will not be able to prevent the body from getting infected.
Antigen-binding site at the two ends, Credit: Wikimedia commons
Common Genome and Structure of Each Serotype
Approximately 65% of the genome of every serotype is similar and there are only a few amounts of genetic variations that make them differ.
The Dengue virus is a single-stranded RNA that can be directly translated into proteins. Each genome encodes 10 genes and on translation, it forms a long polypeptide chain and which can be cut into ten proteins. These proteins are responsible for the structural and functional characteristics of the virus.
The structural proteins include: Capsid (C), envelope (E), and membrane (M) proteins.
The functional proteins include: NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5.
The virus as a whole is roughly spherical and its core of the virus is made of a structure that consists of the viral genome along with C proteins called nucleocapsid.
This structure is surrounded by the other structural proteins and a viral envelope that is made from the lipid bilayer of the host. The viral envelope consists of 180 copies of the M and E proteins that control the entry of the virus into all human cells.
On the other hand, functional proteins control the functional and assembly of the virus. Once the virus attaches itself to a human skin cell, the cells fold over the virus and surround it completely. This pouch-like structure is known as endosome which is capable of making its way into other cells which usually let these non-infected endosomes enter into it for nourishment.