New Anti-Malarial Aims at "Vaccinating" Mosquitos, Not People

[SteveGrenard]

WASHINGTON -- Scientists have tested in mice an experimental vaccine for malaria that does not provide immunity but aims to stamp it out in whole regions by eradicating the disease-causing parasite from mosquitoes that spread it.
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http://www.boston.com/news/globe/health_science/articles/2006/12/25/vaccine_could_stop_malaria_transmission/

People would be used as the means by which biting mosquitos get "vaccinated" - a sort of variation on the man bites dog theme:



The vaccine, developed by scientists at the US National Institutes of Health, is not designed to make the recipient less susceptible to malaria.The hope instead is that when a mosquito bites a victim, because of changes in the person's immune system brought about by the vaccine, the parasite would be eliminated from the digestive tract of the blood-feasting mosquito, researchers said. The idea would be to make mosquitoes in a given area free of the parasite.





Malaria is caused by a parasite that is carried by mosquites. Get bit, you can get the parasite and develop the disease. A new approach being investigated targets the parasite that the mosquitoes carry, by vaccinating a host so that when a mosquito bites them, the mosquitoes get infected with the vaccine which kills the host in the mosquito. This approach targets the pool of parasites in the local mosquito population and is radically different from trying to either eliminate the mosquitoes or cure the person of the infection. In essence, you would be biting the mosquitoes right back.

http://technocrat.net/d/2006/12/22/12523

[Amapola]

It says they've tried it in human volunteers. Why not develop it to be used in livestock? That way a flock of goats or sheep etc. could protect a whole village.......

[SteveGrenard]

It says they've tried it in human volunteers. Why not develop it to be used in livestock? That way a flock of goats or sheep etc. could protect a whole village.......

That sounds like a plan!

[Kaylee]

Gives a whole new spin to herd immunity! :D

[SteveGrenard]

Seriously, if you want to, send along the idea to the NIH Director who has been quoted in the news regarding this program:

Dr Elias A Zerhouni
NIH ID: xxxxxxxxxx
Preferred Name: Dr Elias Zerhouni
E-Mail: ez26y@nih.gov
PH alias: ez26y
Location: Building 1 - Shannon Bldg, Room 126
1 Center Dr
Bethesda, MD
Mail Stop: 0148
Phone: 301-496-2433
Fax: 301-402-2700
IC: OD (Office of the Director)

Here is a preprint abstract and full text w/authors of the original research:

http://www.pnas.org/cgi/content/full/103/48/18243?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=malaria&searchid=1&FIRSTINDEX=0&sortspec=date&resourcetype=HWCIT

[Amapola]

Thanks, Steve, I will do that. Although it seems so dead obvious to me, I feel certain it has occured to the guy and maybe there is some reason they can't. But if that is the case, I would like to know what the reason is.

[Soapy Sam]

I wonder when Greenpeace will object?

Imagine the tropics without malaria (or sleeping sickness), The whole place would be slashed, burned and planted with soya and McBurger Ranches inside a month. Ecodisaster in the making.

Of course, that may look pretty good to someone dying of malaria.

[Goshawk]

It says they've tried it in human volunteers. Why not develop it to be used in livestock? That way a flock of goats or sheep etc. could protect a whole village.......

Because... (http://www.cdc.gov/malaria/biology/mosquito/index.htm)
One important behavioral factor is the degree to which an Anopheles species prefers to feed on humans (anthropophily) or animals such as cattle (zoophily). Anthrophilic Anopheles are more likely to transmit the malaria parasites from one person to another. Most Anopheles mosquitoes are not exclusively anthropophilic or zoophilic. However, the primary malaria vectors in Africa, An. gambiae and An. funestus, are strongly anthropophilic...
Inoculating the village's goats wouldn't help if their local anopheles mosquitos preferred people for dinner.

Also, not everyone who lives in a malaria zone lives in a village that keeps local livestock. Malaria is endemic worldwide in the tropics. (http://0-www.cdc.gov.mill1.sjlibrary.org/malaria/distribution_epi/distribution.htm) But not that many of those billions of people who live in tropical Africa, India, South America, or Southeast Asia live in villages with livestock.

[Amapola]

Thanks Goshawk. I have written to the guy and it will be interesting to see what he says - if he responds at all as he well might not do.

I looked at the distribution map and I was wondering how you came to the conclusion that these people don't have livestock around? I suppose there might be some cities with no livestock, but it seems to me most areas would have livestock if only to provide food for the people that live there. Did you have specific information about this? If so thanks.

[SteveGrenard]

Clearly individual area, mosquito and malaria parasite species have to be determined for Amapola's theory to produce results: the ecosystem approach mentioned below. Here is an abstract of one such study which indicates that the local malaria vector feeds extensively on cattle (bolded) while accompanying a fairly high prevalence rate (23.5%) of infection in children of malignant malaria, P. falciparum.

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Mutero CM et al:
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International Water Management Institute (IWMI), Private Bag X813, 0127 Silverton, Pretoria, South Africa. c.mutero@cgiar.org


An ecosystem approach was applied to study the links between malaria and agriculture in Mwea Division, Kenya. The study was organized into five phases. Phase I had two components including a stakeholder workshop conducted with community representatives and other key stakeholders, and the collation of data on common diseases from outpatient service records at the local hospital. Phase I aimed at an a priori needs-assessment in order to focus the research agenda. Workshop participants directly contributed to the selection of two villages with rice irrigation and two non-irrigated villages for detailed health studies. In Phase II, various Participatory Rural Appraisal (PRA) tools were used to gather more detailed qualitative information from the study villages. The qualitative results indicated that Mwea residents considered malaria and lack of clean drinking water to be their most important health problems, and this was corroborated by local hospital records. Phase III consisted of a comprehensive household survey developed with inputs from Phases I and II. Phase IV involved a comparative evaluation of entomological and parasitological aspects of malaria in the villages with and without rice irrigation.

The malaria parasitological survey found an average Plasmodium falciparum parasite rate of 23.5% among children up to 9 years of age. Results of the entomological evaluation showed a 30-300-fold increase in the number of the local malaria vector, Anopheles arabiensis, in villages with rice irrigation compared to those without irrigation yet malaria prevalence was significantly lower in these villages (0-9% versus 17-54%). The most likely explanation of this 'paddies paradox' in Mwea appeared to be the tendency for A. arabiensis in irrigated villages to feed overwhelmingly on cattle. The results suggested that zooprophylaxis was potentially a practical option for long-term malaria control in the rice irrigated areas, in spite of the large number of A. arabiensis. Phase V consisted of end-of-project workshops for the dissemination of research results and participatory decision-making regarding follow-up actions. Owing to the utilization of a transdisciplinary and participatory approach to research, it was possible to identify opportunities for maintaining zooprophylaxis for malaria in Mwea, through the integration of agroecosystem practices aimed at sustaining livestock systems within a broader strategy for rural development.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=14732239&query_hl=3&itool=pubmed_docsum

[Goshawk]

I was wondering how you came to the conclusion that these people don't have livestock around? I suppose there might be some cities with no livestock, but it seems to me most areas would have livestock if only to provide food for the people that live there. Did you have specific information about this? If so thanks.
Well, take India. If the Wiki statistics (http://en.wikipedia.org/wiki/Demographics_of_India) are accurate (and I don't see any particular reason why they shouldn't be accurate enough for the purposes of this discussion), there are 1.1 billion people in India, 70% of whom live in 550,000 villages. This means that 30% of them, or 330,000,000 people, do not live in villages, i.e. they live in urban areas which don't have livestock. That's a pretty big group of people to escape the hypothetical protective umbrella of having their livestock immunized against malaria instead of themselves.

And 770,000,000 divided by 550,000 villages works out to an average of 1400 people per village, which isn't really what you visualize when you're talking about a [quote unquote] "village" with its small flocks and herds that live cheek-by-jowl with their owners, close enough to share parasites. A "village" of 1400 people takes up enough space that it's really a "small town", and the flocks and herds just can't be physically close enough to all the people in town in order to theoretically protect them by attracting the mosquitos to them instead of to the people.

And I found a statistic here (http://www.neoncarrot.co.uk/h_aboutindia/india_statistics_1.html) that says there are--ballpark figure--200 million cows in India. That works out to .18 of a cow per person, again not what I would consider comprehensive coverage, not like where you have a "village" of, say, a couple hundred people, and each family of, say, 4 to 10 people has its own herd of goats and/or cows, thus making a higher ratio of animals to people.

The estimated 40,000 cows in Delhi (http://www.pbs.org/wnet/nature/holycow/hinduism.html) are spread out among 13 million people, which, again, seems like the wrong proportion of livestock to people in order for the herd of cows to be able to protect anyone against malaria.

It wasn't a bad idea, but I think it becomes clear why the NIH guys didn't come up with it themselves--it's because not that many people in the world live in close proximity to herds of livestock, and because there are many different species of anopheles mosquitos, and because some of them tend to prefer people anyway.