Malaria has long been the most notorious disease associated with mosquito bites. However, malaria always has a well-defined line of treatment that includes chloroquine, artemisinin, etc. Dengue, a viral disease, caused by the dengue virus-bearing mosquito (Aedes ageypti) has been an enigma for doctors and scientists as it has had no line of treatment for a long time. 

Regular dengue tests like being dengue ns1 positive means confirmation of dengue for it does not reveal the serotype. Dengue virus infects around 390 million people each year, and 36,000 cases turn fatal annually. Thus, the high incidence and fatality of the disease have made the discovery of a dengue treatment the need of the hour. But finding a cure for dengue is easier said than done. Multiple factors unique to the virus complicate the epidemiology and treatment of the disease.

Some of the reasons why a strategic means for fighting dengue has eluded us for decades are listed here

Antibody-Dependant Enhancement of Dengue Virus

An antibody is the body’s mechanism to fight an infection. The job of the antibody is to neutralise an antigen or infective particle. But dengue has not one but four serotypes. One serotype differs from the other in terms of the surface properties of the infective particle. 

So despite belonging to the same species, each of the four serotypes of dengue evokes a different immune response from the body. As a result, if you are infected with a single serotype, you develop immunological protection against only that serotype. Therefore, in the case of dengue, having an antibody against one serotype not only offers no protection against the other serotype but rather makes the pathogenicity worse (antibody-dependent enhancement).

The pre-existing antibody from one serotype forms a complex with a new serotype but does not neutralise it; instead, this complex attaches to the monocytes, promotes viral infection, and causes severe dengue symptoms (hemorrhagic fever).

Antibody-dependent enhancement is not unique to dengue; several viral infections, like AIDS, are also known to evoke a severe antibody-induced reaction.

Structural Homology of Dengue Virus To Other Flavivirus Species

Dengue, Zika Fever, and Yellow Fever are caused by viruses belonging to the genus Flavirus. Usually, an antibody recognizes and neutralizes an antibody based on its structure. Dengue virus has fifty percent structural homology with Zika virus. So this structural homology with other disease-causing viruses of the same genus makes it quite a challenge to develop an effective vaccine for dengue.

Response Of “Dengue Naive” Individuals To Dengvaxia

Dengvaxia is the only vaccine that is being used to treat dengue; however, even with dengvaxia being “dengue naive,” people are still a problem. A person is called “dengue naive” if he has not had a prior natural dengue infection. 

If such an individual gets a shot of dengvaxia, he is very likely to develop severe symptoms in the event of an actual infection. However, if a person who has had a prior infection gets vaccinated, he will have a mild response to contracting the disease. Hence, people who have never been infected naturally are not even a candidate for the dengue vaccine.

The factors cited above are some of the most potent reasons why dealing with dengue is such a challenge at the moment. Added to these is the fact that mild cases do not get reported generally, which complicates dengue research. But as science progresses in leaps and bounds, hopefully, a day will come when the world will have an effective weapon to battle the enigmatic adversary called dengue.

Conclusion

Dengue a mosquito-borne disease affects millions each year yet a trustworthy cure seems distant. The presence of four dengue serotypes increases the risk of antibody-dependant enhancement. Moreover, the structural similarities of the dengue virus with other Flavirus species and the difference in individual response to vaccines make protection against dengue a challenge.