AFRO-NETS> A Bug's Death

[Dr Rana Jawad Asghar <jawad@alumni.washington.edu>]

A Bug's Death
-------------
 
By Olivia Judson
New York Times, 25 September 2003
 
LONDON - Should we send the malaria mosquito the way of the dodo?
 
So far, genetic modification has been a tool of creation. We've 
made crops that grow faster or that are resistant to pests, we've 
made animals that produce useful hormones in their milk, we've 
even - presto! - made white rabbits that glow green under black 
light. But now another, more radical use for genetic modification 
is in the offing: the engineering of extinction.
 
The basic idea is simple. Specicide - the deliberate extinction 
of an entire species - could be engineered by exploiting the bi-
ology of selfish genetic elements. These are segments of genetic 
material found in the genomes of all organisms; they contribute 
nothing to the well-being of their hosts, but simply proliferate 
themselves. And proliferation is something they excel at. A fea-
ture of all selfish genetic elements is that they cheat at Men-
del's rules of inheritance and so have better odds for getting 
into eggs and sperm than regular genes do. As a result, a selfish 
genetic element can spread through a population extremely fast - 
far faster than a regular gene - even if it is harmful to its 
host.
 
That is why these elements are attractive to genetic engineers: 
attach a useful gene to a selfish genetic element, release indi-
viduals modified to carry the element and, within about a dozen 
generations, that gene should be present in every individual in a 
population. Or, to engineer extinction, devise an extinction gene 
- a selfish genetic element that has a strongly detrimental ef-
fect. The element could, for example, be designed to put itself 
into the middle of an essential gene and thereby render it use-
less, creating what geneticists call a "knockout." If the knock-
out is recessive (with one copy of it you're alive and well, but 
with two you're dead), it could spread through, and then extin-
guish, a species in fewer than 20 generations.
 
Whether this can work in practice remains to be seen. Designing 
an extinction gene won't be easy. A suite of technical problems 
remains to be solved. But the idea is moving from theory to ex-
periment; suitable selfish genetic elements are starting to be 
engineered to attack the genes of laboratory fruit flies, the 
guinea pigs of the insect world. And although field trials remain 
far in the future, it is not too soon to ask ourselves whether we 
should even think about using such a potentially powerful tech-
nology to wipe out a creature.
 
Given how hard we try to prevent the demise of one species or an-
other - from the African elephant to the northern hairy-nosed 
wombat - it may seem perverse to entertain the notion of causing 
an extinction on purpose. Yet there's a handful of species we've 
tried (and failed) to destroy - at great expense, both to the en-
vironment and to our wallets. Chief among these, and the most ob-
vious candidate for specicide, is the Anopheles mosquito, the 
mosquito that spreads malaria.
 
Each year, malaria kills at least one million people and causes 
more than 300 million cases of acute illness. For children world-
wide, it's one of the leading causes of death. The economic bur-
den is significant, too: malaria costs Africa more than $12 bil-
lion in lost growth every year. In the United States, hundreds of 
millions of dollars are spent every year on mosquito control. 
What's more, a malaria vaccine is still out of reach; the para-
site's resistance to drugs is a growing problem, as is the mos-
quito's resistance to insecticide. The proposed extinction tech-
nology could eradicate the malaria mosquito, and malaria with it, 
within 10 years of the time mosquitoes modified to carry an ex-
tinction gene are released into the wild. Tempting stuff.
 
Or tempting fate? As with any new technology, the benefits of us-
ing it must be measured against possible risks. Here, the risks 
are two: ecological collapse and genetic escape.
 
Genetic escape is the idea that the extinction gene might somehow 
get into a species other than the target and inadvertently wipe 
it out as well. In principle, this could happen in either of two 
ways. Anopheles mosquitoes might not be fussy about whom they 
mate with; if they engage in sex with mosquitoes of other spe-
cies, the gene could spread into those species and eliminate 
them, too. Most animals avoid sex with members of different spe-
cies, so a priori, the likelihood of hybridization seems small; 
all the same, this is something that should be investigated ex-
perimentally before the technology is put in place.
 
Alternatively, the extinction gene itself might prove unstable, 
and jump into a different species entirely. Though such jumping 
is not unknown for wild selfish-genetic elements, it is rare, and 
the chance of this being a problem seems remote. (The risk to us 
from this technology is negligible. Even supposing an extinction 
gene appeared in humans - by accident or by malice - it would 
take thousands of years for extinction to be effected. During 
this time, it is inconceivable the gene's spread would go unno-
ticed; once noticed, it could easily be stopped.)
 
What about the ecological impact of removing Anopheles mosqui-
toes? Hard to predict. But several facts are worth bearing in 
mind. First, our current methods of mosquito control are crude 
and kill more than just mosquitoes. An extinction gene at least 
has the benefit of being precise and clean. Second, there's noth-
ing sinister about extinction; species go extinct all the time. 
The disappearance of a few species, while a pity, does not bring 
a whole ecosystem crashing down: we're not left with a wasteland 
every time a species vanishes. Removing one species sometimes 
causes shifts in the populations of other species - but different 
need not mean worse.
 
Moreover, the earth is home to more than 2,500 species of mos-
quito. Even if we were to eradicate the approximately 30 species 
that are regular carriers of malaria, and for good measure, the 
Aedes mosquitoes that spread dengue and yellow fever, we'd hardly 
be creating a mosquito-free world. It is hard to argue that a 
targeted, genetic attempt to remove an insect that is clearly 
harmful to us is worse than the haphazard, expensive, destructive 
and largely unsuccessful approach we're using now.
 
Nevertheless, friends of the mosquito will say that eradicating 
the mosquito is akin to shooting the messenger. Why not, they 
will surely ask, commit specicide on the malaria parasite in-
stead? Alas, this is probably impossible to do by extinction 
gene: the parasite is prone to self-fertilizing, a habit that 
would prevent the gene's spread. Besides, to get the genetically 
modified parasite into the wild, you'd have to infect people with 
it, which would clearly be unethical. The obvious mosquito-saving 
alternative - modifying the creature so that it cannot spread the 
disease - is probably also unfeasible. This is technically harder 
than the extinction approach and there are, in any case, theo-
retical reasons to suppose the effort would fail.
 
Ideally, malaria would be defeated in other ways. Uganda has re-
cently reported a 50 percent drop in death rates as a result of 
handing out free malaria medicines; if the program can be emu-
lated and the trend sustained, perhaps by the time the technology 
is ready, it will no longer be needed. But if, by then, the 
situation is not much improved, we should consider the ultimate 
swatting.
 
--
Olivia Judson, an evolutionary biologist at Imperial College in 
London, is author of "Dr. Tatiana's Sex Advice to All Creation: 
The Definitive Guide to the Evolutionary Biology of Sex."
 
 --
Dr Rana Jawad Asghar
Program Manager Child Survival, Mozambique
Provincial Coordinator Sofala Province, Mozambique
Health Alliance International, Seattle, WA, USA
http://depts.washington.edu/haiuw/
Coordinator South Asian Public Health Forum
mailto:jawad@alumni.washington.edu 
http://www.DrJawad.com

--
To send a message to AFRO-NETS, write to: afro-nets@healthnet.org
To subscribe or unsubscribe, write to: majordomo@healthnet.org
in the body of the message type: subscribe afro-nets OR unsubscribe afro-nets
To contact a person, send a message to: afro-nets-help@healthnet.org
Information and archives: http://www.afronets.org