Talking Dengue

I have been researching Dengue Fever from a scientific aspect and writing down some current research and news. I thought it would be interesting to discuss the topic with a fellow student to see what they know about Dengue Fever. I hope you will find it interesting...

Press the link below and enjoy! 

Genetically Modified Mosquitos Released

In Jacobina, Brazil a new campaign has began to tackle Dengue Fever head on. Millions of modifies newly hatched Aedes aegypti mosquitoes have been released to disrupt the breeding cycle. These engineered mosquitoes are ultimately created to wipe out their own species which would hopefully stop the spread of Dengue Fever.
 

 http://www.all-about-india.com/mosquitoes-in-india.html

 How are the mosquitoes modified? 

The newly hatched mosquitoes are genetically modified with a lethal gene designed to be detrimental to the Aedes aegypti population. In the laboratory  the mosquitoes are kept alive by tetracycline. The females are disposed of and the males are released to mate with wild females. In essence their offspring will inherit the lethal gene and will die before being reproductively developed (no tetracycline to keep them alive).  

Controversy 

Scientists say this is the only way of protecting people from the disease. However, genetically modifying the blood-sucking Dengue vector and then setting them free raises concerns.  Critics say more laboratory studies are crucial before releasing the mosquitoes as we can not be certain of the potential impact the modified vectors will have on human health and the environment. They don't think enough is known about the modified mosquitoes which could potentially be dangerous.    



 Our best chance of beating Dengue Fever 

A small number of these genetically modified mosquitoes were released in Malaysia in 2010 but nothing in comparison to the field tests now underway in Jacobina, Brazil. Despite the possible complications of releasing genetically modified Aedes aegypti this strategy is thought to be our best chance of fighting the spread of Dengue Fever.    


http://www.pri.org/stories/2014-04-10/these-genetically-modified-mosquitos-have-been-launched-mission-end-dengue-fever

 http://www.globalpost.com/dispatch/news/health/140407/brazil-genetically-modified-mosquitoes-dengue

Dengue, Football and Brazil

The football world cup is on its way to Brazil this summer, but, will the fans be getting more than what they bargained for? 


Dengue transmission will be at its highest during the world cup in June.  Brazil was reported to have over a million cases of Dengue Fever last year. The infectious disease is slowly becoming a global burden and this summer is thought to provide the highest number of cases yet. The increase in infection rates indicate how difficult it is to control the Dengue vector. Management strategies in Brazil including the use of chemical control does not seem to be having the desired effect on the Dengue vector. Bellow is a graph to illustrate the severity of the disease;   

 

 

http://www.oxitec.com/health/dengue-information-centre/brazil-dengue-case-study/

The tropical seasonal climate of Brazil provides the optimum conditions for Aedes aegypti to breed. Brazil has a population of 192.9 million, a large portion of the population live in conurbations including Rio de Janeiro and Salvador. As mosquitoes thrive in areas that are densely populated with stagnant water these cities provide the optimum conditions for Aedes aegypti to thrive.


How is Brazil preparing for the world cup?

Currently there are 6 dengue fever vaccines candidates at various stages of clinical trials but non are commercially available. Educating travelers of the precautions that should be undertaken is currently the best option.  
   

"Fifa, the Brazilian authorities and the World Cup sponsors must use their influence and experience to communicate the risk." says Prof Simon Hay, of Oxford University. 

With travelers expected to arrive in the Dengue endemic country in two months time, are these efforts a little too late? 


  
 http://www.oxitec.com/health/dengue-information-centre/brazil-dengue-case-study/

 http://europepmc.org/abstract/MED/21292885/reload=0;jsessionid=SzaJQN96cQdZAzTFODv8.20

 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1253857/  

 http://www.bbc.co.uk/news/health-25118849

Mosquito and Virus Interaction

Scientist have discovered Dengue Fever to only occur as a result of specific interaction between mosquito and virus strains 

 

        http://en.wikipedia.org/wiki/File:Aedes_aegypti.jpg

           

     When the right strain of mosquito meets the right strain of Dengue a genetic interaction occurs between them and Dengue infection occurs. Researchers discovered that mosquitoes can be susceptible to a certain strain of the Dengue virus, and at the same time they can be resistant to another.  

      
     Although scientist suggest there are genetic interactions occurring between the mosquito and the virus, they have never been mapped onto the chromosome of the mosquito. Therefore understanding exactly where the genes are interacting is unknown. 

     What's next? 

      

      Scientists hope to determine the genetic factors in Aedes aegypti that lead to Dengue Fever by creating finer mapping of the mosquitoes chromosomes. They believe this research is crucial and it may be a the foundation for other studies to completely stop the mosquitoes from transmitting the virus.

      Possible areas for Dengue Fever management include interrupting the transmission of Dengue in the mosquito and interrupting the cycle of the disease in the human host. Scientists hope the information gained from further research into these areas may provide possible drug targets to control the disease. Researchers believe that it may be necessary to genetically modify Dengue resistant mosquitoes. Oppositions claim this theory may be dangerous. The jury is still out whether genetically modified Aedes aegypti is our strongest defense against Dengue Fever.




     http://www.dw.de/thai-french-genetic-investigation-of-dengue-fever-reveals-a-fussy-little-disease/a-17162657

     Halstead, S. B. (2008). Dengue virus-mosquito interactions. Annu. Rev. Entomol., 53, 273-291.

 

     Rosen, L., Roseboom, L. E., Gubler, D. J., Lien, J. C., & Chaniotis, B. N. (1985). Comparative susceptibility of mosquito species and strains to oral and parenteral infection with dengue and Japanese encephalitis viruses. The American journal of tropical medicine and hygiene, 34(3), 603.

Mosquitoes Evolving Resistance Against Dengue

As previously stated in my first post, there are currently no vaccines commercially available for Dengue Fever. So what is in the pipeline? 

Earlier this year a study was carried out on investigated the effects of the microsporoidan parasite Vavraia culicis on the female Aedes. aegypti mosquito. A series of experiments were created involving the female mosquito and its microsporoidian parasite to show how intra-specific competition and parasitism shape life history traits. Many of these life-history changes are thought to be down to reallocation or decrease in the host's resources either caused by the host to minimize the effects of infection or caused by the parasite to maximize its growth rate. Parasitic infection is often associated with changes in host life-history traits, such as host development.

http://onlinelibrary.wiley.com/doi/10.1111/eva.12144/full

Results showed Vavraia. culicis caused changes in the behaviour of the female Aedes. aegypti this is seen in the graphs above.Infected female mosquitoes were found to be less likely to take a blood meal in the first few days after Vavraia. culicis infection (shown in graph A). Females that did feed took smaller volumes of blood than uninfected females (Shown in graph B). Infected females were noted to produce 20% fewer eggs than uninfected female mosquitoes (Shown in graph C). It was also suggested the female mosquitoes could alter their life-history traits to bring forward their schedule of reproduction and The survival rates of the adult mosquitoes were reduced if infected with Vavraia. culicis.

Could this information be the breakthrough we have been looking for? Is this a possible future management strategy?

Sy, V. E., Agnew, P., Sidobre, C., & Michalakis, Y. (2014). Reduced survival and reproductive success generates selection pressure for the dengue mosquito Aedes aegypti to evolve resistance against infection by the microsporidian parasite Vavraia culicis. Evolutionary Applications.

Mosquitoes and Climate Change

       

      Evidence suggest average global temperatures will increase between approximately 1.5°C and 6°C by the end of this century. This rise in temperature may be beneficial for the spread of some infectious diseases. Global incidence of Dengue has increased in recent decades with climate change being a suspected cause. Dengue Fever is typically seen in the tropic and sub tropic climates. Changes in weather such as milder winter and warmer summers could lead to ecological changes in Dengue.     

  

   Female Aedes Spotted in Germany!

      

      Due to milder winters and moist air, mosquitoes are capable of surviving and  thriving in Germany. During a period of 8 weeks in 2011 two adult females of the Aedes genus were collected for the first time in June and August. Previously, only immature stages of the genus had been collected in Germany.   

      The table below shows the amount of mosquitoes that were trapped over the 8 week period;         

 

 

 http://www.eurosurveillance.org/images/dynamic/EE/V17N04/Werner_Tab.jpg

      

      Currently the mosquitoes survive for a limited time and die during the cold winter. However, due to global warming, it it thought the climate in Germany will on average become warmer and the winters shorter and the count of exotic mosquitoes will continue to increase. 

      Mosquitoes typically travel with a companion such as viruses. The further from their native tropic climates the mosquitoes can migrate, the further the virus can also. Thus the spread of infectious diseases such as dengue will spread further around the wold.  

    

       Werner, D., Kronefeld, M., Schaffner, F., & Kampen, H. (2012). Two invasive mosquito species, Aedes Albopictus and Aedes japonicus japonicus, trapped in south-west Germany, July to August 2011. Euro Surveill, 17 (4).

 

 

 

 

Prevalence of Dengue Fever

Cases of Dengue Fever have increased dramatically in the last 50 years. The graph below illustrates the rapid change in reported Dengue Fever cases; 

http://www.who.int/csr/disease/dengue/impact/en/

Now in 2014 who exactly is effected by the infectious disease? 

- Half of the population is now at risk of contracting dengue
- Dengue is endemic in more than 100 countries in Africa, the Americas, the  
  Eastern Mediterranean, South-east Asia and the Western Pacific
- Up to 100 million cases of Dengue Fever are reported per year
- Dengue is predominantly found in areas of overcrowding and major urban
   centers
- Leading cause of serious illness and death among children in some Asian and
   Latin American countries.