- Dengue is a mosquito-borne viral infection.
- Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus.
- These mosquitoes are also vectors of chikungunya, yellow fever and Zika viruses.
- Dengue is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas.
- The virus responsible for causing dengue is called dengue virus (DENV) which belongs to the Flaviviridae family. There are four DENV serotypes, meaning that it is possible to be infected four times.
Signs and symptoms
- Dengue is a severe, flu-like illness that affects infants, young children and adults, but seldom causes death.
- Symptoms usually last for 2–7 days, after an incubation period of 4–10 days after the bite from an infected mosquito.
- There is no specific treatment for dengue fever.
- Fever reducers and pain killers can be taken to control the symptoms of muscle aches and pains, and fever.
- In 2021, India reported 110,473 dengue cases, ranking fourth among the worst-affected nations.
- In a significant development in DNA vaccination research, India’s first and only DNA vaccine candidate for dengue has shown promising results.
- In preliminary trials on mice, the candidate generated a robust immune response and improved survival rates after exposure to the disease.
- The DNA vaccine candidate has been in development since 2019 by scientists from the National Centre for Biological Sciences (NCBS), Bengaluru, in collaboration with nine institutions in India, Africa and the US.
- Developing an effective vaccine against dengue is tricky because it is caused by four closely related viruses—DEN-1, DEN-2, DEN-3 and DEN-4—called serotypes. Each one interacts differently with antibodies in human blood.
- A person infected with DEN-1 is then protected against it for life, but not against the other three serotypes. An ideal vaccine must target all serotypes.
- Further, DNA vaccines generate a weaker immune response. This means that one must take high doses or multiple boosters.
- There is another concern with dengue viruses—antibody-dependent enhancement (ADE). Typically, vaccines trigger production of antibodies that prevent the virus from binding to cells at later exposure. But with dengue, antibodies help the virus replicate and cause severe disease.
- This happens because antibodies generated after vaccination or natural infection may be of low quality and quantity and bind to the virus, resulting in a virus-antibody complex that attaches itself to immune cells. Once inside the cells, the virus makes multiple copies, increasing the viral load.
- ADE may have contributed to the partial failure of Dengvaxia, the first and only approved dengue vaccine, which contains a live attenuated (weakened) virus.
- The World Health Organization says Dengvaxia proved effective and safe in clinical trials in people with prior infection, but increased disease severity among those who got their first natural infection after the shot.
- The US Food and Drug Administration recommends Dengvaxia for children above nine years and those with prior infection. India has not approved it.
- For the DNA vaccine candidate, the research team plans to test for ADE in future trials.
What are DNA vaccines?
- DNA vaccines use engineered DNA to induce an immunologic response in the host against bacteria, parasites, viruses, and potentially cancer. DNA vaccines use small, circular DNA molecules, called plasmids, to introduce a gene from a bacterium or virus to trigger an immune response.
- They are often referred to as the third-generation vaccines. They exhibit several advantages over traditional strategies in terms of safety, stability, ease of manufacturing, etc.
- The world’s first DNA vaccine—ZyCoV-D, developed by Ahemdabad-based pharmaceutical firm Zydus Cadila—was approved in 2021 for emergency use against COVID-19. The vaccine consists of a plasmid that carries a gene that codes for the SARS-CoV-2 spike protein.
- Globally, DNA vaccines are being developed for diseases like tuberculosis and chikungunya.
Why in News?
- In Kerala, the fever cases are spiking as the monsoon intensifies in the State. Due to dengue fever, over 18 deaths have been confirmed, so far, in the State.