Controlling Dengue Fever

Dengue Fever (also known as Dengue Haemorrhagic Fever or Bone Break Fever) is a tropical disease vectored by the mosquito Aedes aegypti.  The initial infection isn’t super deadly; however, unlike most diseases, a second infection by a different serotype of the virus increases the severity of infection.  The deadliest aspect of this illness, is that it has no cures or vaccines, although scientists are making progress on developing them.

Just recently, scientists discovered a human antibody that defends against dengue type 2.  The antibody prevents the virus from injecting its genes into the host cell, effectively putting a stop to the viral replication.  Although this is an antibody for only one of the four serotypes of dengue, it’s a promising step.  If similar antibodies can be found for the other three serotypes, they could be combined to provide a treatment for the disease, and prevent the increased risk of severe illness that results from subsequent infections. [1]

Promising as that is, it doesn’t help treat or prevent dengue fever now, and dengue certainly isn’t waiting for science to catch up with a treatment.  The current methods of controlling dengue are more along the lines of controlling the population of its vector.  There are two different directions this is being taken.  One, the more “traditional method, is to manage the environment to decrease the available breeding grounds for the mosquito.  The second, which is currently still in trials, is using genetically modified male mosquitoes that can’t produce viable offspring to decrease the population.

Aedes aegypti breed in still pools of water, and there are plenty of those in human settlements.  Normally, mosquito larvae are preyed upon by several aquatic species, which keeps their populations controlled.  However, in urban environments, there are many places where still water can accumulate that the mosquitoes can lay their larvae in and experience no predation.  Generalized spraying and cleanups have had very little effect on the management of the mosquito population, so surveys have been done that identified “key containers” that have the highest mosquito productivity.  Using community outreach, information about what these “key containers” are is being spread around and communities are being encouraged to remove these containers, and use coverings for those that can’t be removed (like water storage containers).  This directed management has produced improved results. [2]

Another method that is being applied in a similar vein, is the introduction of predatory copepods to human formed still water in order to eliminate the larvae before they can reach their adult form.  This is being implemented on a community level in Vietnam, and the incidence rate of dengue within these communities has dropped to no reported cases, compared to the hundred or more in communities where this isn’t being implemented. [2]

The second, more experimental, method being applied is the use of genetically modified male mosquitoes.  The biotech company Oxitec has designed a genetically modified Aedes aegypti male that contains a lethal allele that will kill the mosquito if it’s not given the proper antibiotics.  These mosquitoes are then released into the wild by the millions and compete with wild males for mates.  The females that mate with these males have offspring that die as larvae, reducing the population of adults in the wild.  Sounds great, yeah?  Well, one of the complications of this is that it requires new lethal males to be introduced each year to keep populations low, which could prove costly to do on a large scale (since it took 6 million mosquitoes being released in one suburban area to achieve the desired effect).  However, it also means that there aren’t genetically modified insects persisting in a population for long periods of time.  So it’s a bit of a double edged sword, but it has been effective in the areas they’ve tested it. [3]
These management techniques and the developing cure offer hope and relief for the hundreds of countries and millions of people affected by dengue fever.

Sources [1] [2] [3]

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