The Wide Angle: Curing the Mosquito to stop Malariaby Tracy Staedter
George Dimopoulos "Some 350 to 500 million people get infected with malaria yearly, and at least 1 million die from these infections."
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Malaria is a complex disease that involves the interactions of three organisms: humans, parasites and mosquitos. If scientists can interrupt any of these interactions, they could control the disease. Research is currently being pursued to develop methods and technologies to target all of these interactions. Tracy Staedter chatted with George Dimopoulos, associate professor at the Malaria Research Institute in the Bloomberg School of Public Health at Johns Hopkins University, about what avenues scientists are pursuing. 3:00 PM me: hello 3:01 PM george.dimopoulos: Hello - me: Thanks for taking the time to chat george.dimopoulos: Sure. Let's go. me:
Ok, so as the intro graph says, "Malaria is a complex disease that
involve interactions between 3 organisms: human, parasite, and mosquito" what is the interaction? 3:06 PM george.dimopoulos:
Mosquito - Human: The female mosquito needs to feed on blood to produce
eggs, and therefore it needs to interact with humans. It uses its smell
system to find humans. Through this blood-meal the parasite can be
transmitted to humans. 3:08 PM Parasite
- Human: Once the parasite has been injected into a human by a
mosquito, it needs to complete a complex life cycle. The human immune
system will attack the parasite but the parasite has found ways to
circumvent these defenses. 3:11 PM Parasite
- Mosquito: Similarly to what happens in the human, the Plasmodium
parasite develops into an infectious sporozoite form in the
mosquito. The
mosquito's immune system attacks the parasites, but at
least some parasites survive and reach the mosquito's
salivary gland, where the parasites can be injected into a human when the mosquito feeds on blood. To control malaria we need to block at least one of these interactions. me: I see, so three different opportunities for intervention 3:12 PM How many people get sick or die from malaria? 3:13 PM george.dimopoulos: Some 350 to 500 million people are infected with malaria yearly, and at least one million die from these infections. Sadly, most of the victims are children. me: What are some of the current treatments available? Anything? 3:15 PM george.dimopoulos:
The only effective current treatment is based on anti-malaria drugs.
The bad news is that the Plasmodium parasite is good at developing
resistance to these drugs. There are many potential ways to prevent malaria, but
they require additional research, infrastructure and education. me: So is the parasite's ability to develop resistance the reason we don't have an effective vaccine? 3:17 PM george.dimopoulos:
The reason why it is difficult to develop an effective vaccine to control malaria is the Plasmodium parasite has the ability to
change its appearance in the human. This is a strategy to trick and
evade the human immune defense. me: It's a clever little devil. 3:19 PM george.dimopoulos:
Yes indeed - a very smart parasite that changes its surface coat so
that the human immune system can't recognize it. However, there is hope in
the horizon. me:
Ok. So let's talk about that hope. You told me earlier that if we can
interrupt the human/parasite or parasite/mosquito interaction, we could
stop malaria. 3:22 PM george.dimopoulos:
Let's look at a new promising vaccine for example. One vaccine that is
being developed today is based on live Plasmodium parasites that are
produced in the mosquito salivary glands. Researchers have shown that
we can develop immunity to malaria when these sporozoite form parasites
are injected into our blood stream. These parasites are isolated from
the mosquito and are irradiated so that they only can cause a partial
infection in the human liver. me: Interesting george.dimopoulos: These parasites will therefore not cause the malaria disease. me: Is that similar to how other vaccines are created? 3:24 PM george.dimopoulos: This vaccine is in some way similar to live virus vaccines in that a live, but modified, pathogen is used as the vaccine. Much research has been invested in ways to block the parasite's interaction with the mosquito; the goal is to cure the mosquito.me: Curing the mosquito. Interestinggeorge.dimopoulos: The challenge here is to develop technologies that would allow for large-scale production of this live parasite vaccine. me: Why is that difficult? 3:27 PM george.dimopoulos:
The challenge with large-scale production of a live sporozoite vaccine
is that this parasite form cannot be grown outside the
mosquito, so we would need to produce and dissect thousands, or
millions of infected mosquitoes. me: Wow. That sounds impossible. 3:30 PM george.dimopoulos:
Scientists have developed methods to scale-up this process and make it
feasible to produce large quantities of vaccine. However, a
technological breakthrough that would allow the production of these
parasites in bioreactors (or growth chambers) is needed. me: Is there anything else we can do? 3:32 PM george.dimopoulos: Let me tell you about some interesting ways by which we can cure the mosquito. me: ok 3:36 PM george.dimopoulos:
The mosquito uses its immune system to fight against the malaria
parasite when it becomes infected. My research group has discovered ways by which we
can make the mosquito's immune system stronger and more effective in
killing the parasites (paper: Resistance to Plasmodium in mosquitoes). These gene engineered mosquitoes are resistant
to the parasite. The idea here is to develop genetically engineered
malaria resistant mosquitoes and release them in nature. These
mosquitoes would have been modig=fied in a way that they would spread
their resistance genes to the existing field mosquitoes. We would
basically convert malaria transmitting mosquitoes to resistant
mosquitoes in the field. This would stop the transmission of the malaria parasite between humans. me: So genetically engineering mosquitoes to be resistance to the parasite, that would mean that you wouldn't have to deal with the other challenge of growing parasites to produce a vaccine, right? 3:40 PM george.dimopoulos:
No these are two separate approaches. The vaccine is to block the
parasite in the himan, and the GM mosquito is to block the parassite in
the mosquito. Two separate stories. me:
Okay, I understand. I guess I was thinking that if you could GM the
insects, you wouldn't need the vaccine, but it sounds like that's not
the case. 3:43 PM george.dimopoulos:
Well, we still need multiple approaches to target malaria: vaccines,
drugs, Plasmodium resistant mosquitoes, insecticides, mosquito repellants, etc. It is very
unlikely that the disease would be eradicated through one single
approach, so we need to attack malaria from multiple angles with
multiple weapons. me: Makes sense. So what else were you going to tell me about? 3:44 PM george.dimopoulos: Another way to stop transmission of malaria is by blocking the interaction between the mosquito and the human. 3:49 PM The
mosquito uses its smell system to find humans to feed on, and scientists are trying to understand how this smell system (or olfactory
system) works. Human sweat contains some 350 different aromatic
compounds that are odors, and the mosquito is attracted to some of them. If
we knew which of these compounds are the best attractants for the
mosquito we could use them to build mosquito traps. We would attract
the mosquito into a device that would kill them. The difficulty here
lies in the complexity of the smell system. The mosquito is
attracted to a specific combination of these smell compounds, and we
need to figure out the right compositions and concentration to make this method effective. me: Hmmm 3:50 PM Even if that would work, it seems like it wouldn't work across the board like you'd still have lots of mosquitoes out there carrying the parasite 3:51 PM george.dimopoulos: This approach would contribute, together with the other control methods and technologies, towards the eradication of malaria. me: I see. Of course No one solution. Like any problem, I suppose george.dimopoulos: Let me tell you about one of the most effective ways to control malaria now me: ok, bring it on 3:54 PM george.dimopoulos:
Malaria is a disease of poverty, and it is almost exclusively found in
the poor parts of the world. The inadequate health and housing
infrastructure and the lack of education are the main reasons why
malaria has persisted in sub-Saharan Africa. There was malaria in North
America and most parts of Europe some 100 to 200 years ago, but because of economic
and social development it was eradicated. 3:56 PM The socioeconomic development of malaria-endemic countries will provide the potential to eliminate this and other the other diseases that plague those parts of the world. me: What is it about the poor the perpetuate the disease? 4:00 PM george.dimopoulos:
The mosquitoes that transmit malaria need breeding sites to propagate
and in poorer regions there is plenty of standing water where they can
breed. Malaria is mostly transmitted indoors and the indadequate quality of housing does not hinder mosquitoes to enter. People who are exposed to malaria in these regions often do not
have the knowledge to prevent and treat it appropriately. These people
cannot afford buying the expensive drugs, insecticides and bed nets. me: I see. Is anyone trying to tackle the cost issue? 4:05 PM george.dimopoulos:
This is the responsibility of everyone, but particularly the wealthy and rich nations, corporations, organizations and even individuals. It's well-invested money. Let me tell you about another interesting approach to target and kill mosquitoes. Researchers have discovered microbes (a type of fungus) that can infect and kill the mosquito upon contact. The idea is that people in malaria-endemic villages can grow these microbes and impregnate fabric (towels) with them and simply hang them up in their houses. When a mosquito will sit on this towel it will be exposed to the microbe that will infect and kill the mosquito within a few days. This is an affordable bio-control method that does not require technologically advanced products, but it still requires education and training on how to use it. me: That is very interesting who developed this? do you know? 4:07 PM george.dimopoulos:
An international group of scientists, including Matt Thomas from the Imperial College, London published this study in
Science magazine some years ago and I know they have been testing it in
Africa. My group has also shown that the mosquito's natural bacteria flora that resides in the gut can stimulate a mosquito's immune response against the malaria parasite (this study will be published in PLoS Pathogens on Friday, May 8). We are now trying to identify bacteria species from field mosquitoes that could make them completely resistant to Plasmodium. me: It seems like there are a range of solutions out there from high to low tech george.dimopoulos:
Yes, I recently read that the Bill & Melinda Gates Foundation is
supporting research that aims at the development of a high-tech laser-based
system to kill mosquitoes. me: Yes, I saw that. We ran a news story about that on Discovery News. george.dimopoulos:
It uses technology from the Star Wars anti-missile program. A sensor
detects the mosquito's wing beat sounds and a computer targets a laser
beam on it. me: that's VERY high tech and very good aim I know I've taken up a lot of your time, is there anything you'd like to add? 4:11 PMgeorge.dimopoulos: I think we have addressed some major approaches. me: Well thanks so much for your time george.dimopoulos: ok, great me: This has been truly enlightening for me and I'm sure for our readers, too. george.dimopoulos: You're welcome, and thanks for highlighting such an important issue on the Discovery Channel. 4:13 PM me: Have a nice day george.dimopoulos: Have a nice day! |
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