Why can some mosquitoes spread Zika?

[Jeff Rosenbury]

Some mosquitoes (ex. aedes aegypti) spread zika virus and some don't. My question is, what are the key differences between the species?

My motivation: I recently read an article about spreading genetically modified sterile mosquitoes to try to impact the populations of zika spreading mosquitoes. This seems like a short sighted solution since it opposes survival of the fittest and populations will soon become immune to this sort of thing.

A better solution is often finding another species which out competes the undesirable species. (Still rather short sighted, BTW.) The most obvious choice would be to genetically modify the mosquitoes to not carry zika. (It's not as if zika is essential to the mosquitoes life cycle.) Dropping this GM strain with the sterile strain might make the zeka immune strain a competitive advantage and embed it as a competitor to the unmodified strain.

If I understand my disease models properly, even a small drop in transmission rates can halt an epidemic.

However this does depend on being able to easily genetically modify the mosquitoes. The big concern would be making them non-viable in the wild. I don't know if that is possible. Hence the question.

There are obvious problems with smashing the natural order like this (these interventions always seem to have blowback), but as long as were doing it anyway with the sterile strain, why not do it right? Anyway, that's a policy discussion for another thread.

 

[jim mcnamara]

Zika is a Flavivirus. So is West Nile virus. Both are spread by several species in the genus Aedes. Aedes is dirnal, and active only during the day. Zika was first identified in Uganda, where Aedes comes from. There no citation on the actual origin, but as a guess: coevolution of Flavirvirus species and Aedes species.

So in whatever region the mosquito vector species occurs, Zika will eventually become endemic. In a sense we brought the problem on ourselves. Because mosquitoes and in fact lots of insect disease vectors occur on imported and exported goods like lumber, fruit, seeds, and so on. Humans have been moving almost everything that bugs can hitch a ride on around for centuries. So Aedes is all over the New World. All it takes is one person with an active Flavirvirus infection to come over from (example: ) Uganda to Brazil, and zingo! Zika has fresh territory.

Some species of monkeys can harbor the disease, therefore, a trade in pet those species of monkeys can spread it as well.

This goes into a detailed history of Zika, from obscure infections in animals in 1947 to a problem today.
http://theconversation.com/explaine...-from-and-why-is-it-a-problem-in-brazil-53425

 

[Jeff Rosenbury]

So in whatever region the mosquito vector species occurs, Zika will eventually become endemic. In a sense we brought the problem on ourselves. Because mosquitoes and in fact lots of insect disease vectors occur on imported and exported goods like lumber, fruit, seeds, and so on. Humans have been moving almost everything that bugs can hitch a ride on around for centuries. So Aedes is all over the New World. All it takes is one person with an active Flavirvirus infection to come over from (example: ) Uganda to Brazil, and zingo! Zika has fresh territory.

Thank you for the information.

Zika is a somewhat mild virus. But I doubt it's the last one we will see, so fixing this can be used as a testbed for more lethal virus strains.

Would you know why other mosquitoes can't spread Zika? Does the Zika reproduce in the Aedes, or does it simply carry the virus from one host to another?

I was thinking of a genetic trigger that caused death when the mosquitoes became infected. Another possibility would be to boost the mosquito immune response (assuming there is one). But these presume the mosquitoes can be easily modified to recognize the virus.

Aedes might be a vector because:

1. It largely targets Zika host species. (A less selective mosquito would rarely bite potential carriers twice.)
   
2. It injects saliva into its prey.
3. It preys on multiple hosts.

In which case any mosquito sharing these characteristics would be a carrier. This would make the solution I'm thinking about much more problematic. Any disruption in feeding pattern would shift the ecological niche of Aedes enough so the new strain would not directly compete with the problem strain.

But if an immune response already exists in Aedes (because of coevolution), it could be triggered artificially. This would only slightly affect Aedes lifecycle, leaving the new strain to directly compete with the problem strain. That plus a little external nudge might be enough to displace the problem strain.

Hmm... Maybe we could do something about the bites itching while we're at it...

 

[Ygggdrasil]

I recently read an article about spreading genetically modified sterile mosquitoes to try to impact the populations of zika spreading mosquitoes. This seems like a short sighted solution since it opposes survival of the fittest and populations will soon become immune to this sort of thing.

Even though the sterile mosquitoes will not persist in the environment (allowing for populations to rebound later), it can still be a very effective means of reducing the population to levels that they can be managed or eradicated using other techniques. See the case of the screw worm fly.

A better solution is often finding another species which out competes the undesirable species. (Still rather short sighted, BTW.) The most obvious choice would be to genetically modify the mosquitoes to not carry zika. (It's not as if zika is essential to the mosquitoes life cycle.) Dropping this GM strain with the sterile strain might make the zeka immune strain a competitive advantage and embed it as a competitor to the unmodified strain.

You're definitely on the right track with your thinking. Work like this is being done for malaria, for which much more is known about the mosquito-pathogen interactions. I'm not sure enough is known about the virus to be able to engineer Zika-resistant mosquitoes.

Scientists have also developed "gene drive" technologies that allow genetically-modified traits—even those that decrease the fitness of the organism—to be spread throughout the population. These gene drives employ a molecular biology trick that allows for "super-Mendelian" inheritance: basically, any organism that inherits one copy of the genetic modification will be guaranteed to pass that copy along to its offspring. In the past few months, papers demonstrating gene drives to spread malaria resistance among mosquitoes or to spread genes for female sterility have been published.

Here's are a few good articles discussing the different techniques being developed for mosquito eradication:
http://www.nature.com/news/gene-drive-mosquitoes-engineered-to-fight-malaria-1.18858
http://www.slate.com/articles/healt...are_a_global_scourge_and_must_be_stopped.html

 

[NascentOxygen]

Releasing genetically engineered male mosquitoes into the wild: When they breed with females, they pass a self-destruct gene to their offspring that causes them to die before they reach adulthood. Oxitec, the British company that produces that mosquito, claims in tests that it cut wild Aedes populations by as much as 90%.

 

[Jeff Rosenbury]

Releasing genetically engineered male mosquitoes into the wild: When they breed with females, they pass a self-destruct gene to their offspring that causes them to die before they reach adulthood. Oxitec, the British company that produces that mosquito, claims in tests that it cut wild Aedes populations by as much as 90%.

It is very difficult to kill a species by killing its members. To our regret, we've learned habitat destruction and targeted biological attacks (ex: Mice eating eggs) are much more effective. Habitat destruction would be costly since Aedes Aegypti has taken to storm sewers and the like. Targeted biologicals are an option, but usually there's lots of blowback caused by deliberately introducing exotic species. (Hopefully we will find a specific pathogen or something, but that's a dice roll.)