By Gurumurti Natarajan
DR Tomonori Nochi and his colleagues at the University of Tokyo's
Institute of Medical Science has made an astounding breakthrough in tackling
the scourge of cholera that afflicts a vast majority of Africa, Latin
America and parts of Asia. A new rice-based vaccine has been developed to
deliver effective and inexpensive treatment against this killer disease.
Cholera is a severe intestinal disease endemic to the tropics,
manifesting as diarrhoea. The causal organism, a bacterium, Vibrio cholerae,
spreads among humans through ingestion of contaminated food or water. The
pathogen produces an enterotoxin that acts on the mucosal epithelium lining
the small intestine and is responsible for the characteristic massive
diarrhoea caused by the disease. In its most severe forms, cholera is one of
the most rapidly fatal illnesses known and can cause death in a healthy
adult within 24 hours of onset of the disease! Although antibiotics such as
tetracycline, ciprofloxacin and azithromycin can reduce the duration and
severity of cholera, drug-resistance is being reported regularly.

Traditional protection from cholera, as indeed with many other
diseases caused by microbial infections, has been bolstered through immunity
either through exposure to the disease-causing organism or through vaccines
containing live, modified or dead micro-organisms. Vaccines and their
administration though are not without their share of impediments. Right from
preparation until it is administered, with intervening steps of packaging,
storage and transportation, vaccines typically require an unbroken cold
chain which is rather hard to come by in developing third-world nations that
are struggling to have road lights and clean drinking water in their taps.
The assistance of trained para-medics is mandatory as most vaccines are
administered through a syringe and a needle. Recycling needles often
resorted to in indigent societies to save on costs open a Pandora's box of
spread of other diseases on an unsuspecting population already beset with
maladies of diseases, malnutrition and poverty. Besides, vaccines come with
a fixed shelf-life and have been known to be ineffective even under the best
of cold-chain practices.

In their research paper to be published shortly in the prestigious
Proceedings of the National Academy of Sciences, (USA), Dr Nochi's team
details their work on genetically-modifying Kitaake rice plant's genome to
include a gene from the disease-causing bacteria. The gene expresses a
subunit of the disease-causing cholera toxin B, about 30 micrograms of which
accumulated in each rice seed. Experimental mice fed on the transgenic rice
in the form of powder, absorbed the cholera toxin B antigen, which in turn
caused their immune system to release very specific antibodies that were
capable of neutralising the cholera toxin. Interestingly, the rice-based
vaccine was also resistant to digestion by gastric juices in the stomach and
remained active even after long-term storage at room temperature. The
authors conclude that "rice-based mucosal vaccines offer a highly practical
and cost-effective strategy for orally vaccinating large populations against
mucosal infections, including those that may result from an act of
bioterrorism".

This innovation augers well for the suffering masses plagued by
cholera and other endemics. Since the rice-based vaccine comes from an
edible part of the plant, it is safe, inexpensive to produce in large
quantities and can be orally administered. It is, further, a massive
improvement over most other traditional plant-based oral vaccines since rice
can easily be stored at room temperature for 18 or more months, and, once
administered, its protein body protects the vaccine from digestive enzymes
that would otherwise render it ineffective. Rice also has greater protein
content than some of the other starch-based edible vaccines currently under
experimentation for a variety of infectious diseases.

Besides, being a major food staple in most of the developing countries
that are predominantly afflicted by similar diseases, the tradition of
cultivating paddy in these societies helps. In addition to the huge savings
from obviating the cold chain which could run into several hundred millions
of dollars annually, additional issues of purifying the antigen from the
rice prior to administering it to humans is also rendered unnecessary. Other
diseases targeted for rice-based vaccines include the pesky influenza and
the much dreaded HIV.

Less than two weeks ago in an article extolling the potential benefits
of modern agricultural biotechnology in this column, I had highlighted the
numerous opportunities that this emerging facet of science was unravelling.
Genetic engineering is not a silver bullet to ameliorate all ills of modern
society but is for sure establishing itself to be one of the viable options
by scaling new vistas of science with each passing day. It therefore merits
its space under the sun without the cacophony of Luddites that seek to set
us back to a bygone era, opposing the gains of modern science for no known
reason.


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