AA
ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: May 2, 2007
[1] Fungus responsible for Africa's deadly maize identified
Date: Thu 26 Apr 2007
Source: United States Department of Agriculture, ARS News
Service [edited] <http://www.ars.usda.gov/is/pr/2007/070426.htm>
It's now clear that a poisonous strain of the fungus
_Aspergillus flavus_, known as the "S" strain, is to blame for
causing 125 food-related deaths in Kenya in 2004, according to
research by an Agricultural Research Service (ARS) plant
pathologist and his colleagues. The fungus, which produces
invisible toxins that are known to be carcinogenic, had
contaminated portions of the country's maize crop. This is the
3rd time since 1981 that the so-called "Kenyan death fungus" has
tainted the African nation's primary food staple with deadly
levels of poisons.
Peter Cotty, an ARS scientist based in the Department of Plant
Sciences at the University of Arizona in Tucson, and Claudia
Probst, of the University of Arizona, worked with Henry Njapau
of the Food and Drug Administration in College Park, MD, to
investigate which Aspergillus strain was the culprit. Cotty is
administratively part of the ARS Southern Regional Research
Center in New Orleans, LA.
The scientists' findings, reported in the current issue of
_Applied and Environmental Microbiology_, will be critical to
researchers who are trying to devise methods for preventing
future cases of fungal poisoning, or aflatoxicosis, in African
maize. Aflatoxins are natural poisons produced by certain fungi
that belong to the genus Aspergillus. Health consequences
related to consuming aflatoxin-contaminated foods include
impaired growth, cancer and death.
These toxins can contaminate an array of crops including corn,
cottonseed, peanuts and tree nuts. To ensure public safety, many
countries, including the United States, have established maximum
allowable levels for aflatoxin in farm products. Unfortunately,
these standards do little to reduce the ingestion of locally
grown, fungus-infested crops in small rural communities in
Africa.
Through a special permit, the researchers were able to obtain
samples of contaminated maize from affected Kenyan villages.
After grinding the corn, they isolated the fungi and grew them
in culture.
Surprisingly, they found the "S" strain of _A. flavus_, a potent
aflatoxin producer not previously known in Africa, to be the
most prevalent source of toxins in the maize.
[Byline: Erin Peabody]
---
Communicated by:
Dick Hamilton
Former ProMED-mail plant disease moderator
471 Foxglove Crescent
Richmond, BC
Canada, V7C 2K4
<rihamilto@shaw.ca>
******
[2] Biological control of aflatoxin contamination in maize in
Africa
Date: October 2005
Source: Proceedings, Conference on International Agricultural
Research for Development, Stuttgart-Hohenheim Oct 2005 <http://www.tropentag.de/2005/proceedings/node77.html>
Aflatoxin contamination of maize, the major cereal in African
diets, is a major risk for health and well being of African
people, primarily children. Aflatoxin-producing fungi
_Aspergillus flavus_ and _A. parasiticus_ can infect grains from
pre-harvest stages in the field through to post-harvest stages
in the stores. Based on past work by IITA [International
Institute of Tropical Agriculture] and our collaborators,
several pre- and post-harvest strategies are being tested to
reduce risk of aflatoxin contamination. One of the management
strategies being developed is biological control using the
competitive exclusion mechanism, which has been successfully
implemented on cottonseed in Arizona. Natural population of _A.
flavus_ consists of toxigenic strains that produce copious
amount of aflatoxin and atoxigenic strains that lack the
capacity to produce aflatoxin. In the competitive exclusion
mechanism, introduced atoxigenic strains out compete and exclude
toxigenic strains from colonizing grains thereby reducing
aflatoxin production in contaminated grains. We have collected
more than 4200 isolates of _A. flavus_ from different
agroecozones in Nigeria to identify atoxigenic strains. Until
now, we have identified about 50 candidate atoxigenic strains
out of 1500 strains screened so far. Tests under field
conditions have been conducted on 24 of these atoxigenic
isolates in Ibadan, Nigeria, to identify a few effective strains
that can exclude toxigenic strains. These atoxigenic strains are
being evaluated for a set of selection criteria to further
narrow down the numbers to a few for further use in biocontrol
field experiments.
One of the important selection criteria will ensure that the
candidate atoxigenic strains belong to unique vegetative
compatibility groups (for which testers have been developed)
that are unable to produce toxigenic progenies in the natural
environment. Propensity to multiply, colonize and survive are
other selection criteria to make sure that few reapplications
will be required once the atoxigenic strains are introduced in
the environment.
Environmental safety of most promising atoxigenics would be also
evaluated. Research to develop atoxigenic strains is resource
intensive and will further require downstream development
activities. Nevertheless, biological control holds promise of
offering a long-term solution for reducing aflatoxin
contamination in maize.
[Byline: Bandyopadhyay, et al.]
Links:
Full paper is available at:
<http://www.tropentag.de/2005/abstracts/full/398.pdf>
<http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5334a4.htm>
<http://www.ehponline.org/members/2005/7998/7998.html>
Maps of Kenya are at:
<http://www.un.org/Depts/Cartographic/map/profile/kenya.pdf>
<click
HERE>
--
Communicated by:
Dick Hamilton
Former ProMED-mail plant disease moderator
471 Foxglove Crescent
Richmond, BC
Canada, V7C 2K4
<rihamilto@shaw.ca>
[The major aflatoxins of concern are designated B1, B2, G1, and
G2. These toxins are usually found together in various foods and
feeds in various proportions; however, aflatoxin B1 is usually
predominant and is the most toxic. Aflatoxin M is a major
metabolic product of aflatoxin B1 in animals and is usually
excreted in the milk and urine of dairy cattle and other
mammalian species that have consumed aflatoxin-contaminated food
or feed.
The toxicity can be influenced by environmental factors,
exposure level, and duration of exposure, age, health, and
nutritional status of diet. Aflatoxin B1 is a very potent
carcinogen in many species, including nonhuman primates, birds,
fish, and rodents. In each species, the liver is the primary
target organ of acute injury. Metabolism plays a major role in
determining the toxicity of aflatoxin B1.
Animal species respond differently in their susceptibility to
the chronic and acute toxicity of aflatoxins. Trout are often
regarded as the most sensitive. Clinical signs in animals, other
than aquatic animals, range from lethargy, anorexia, jaundice,
and death. Removal of the affected foodstuffs usually results in
a return to normal as aflatoxin is excreted fairly rapidly from
the body. Of course, the length of time to normalcy depends upon
the severity of the affect, the dose ingested and the length of
time the ingestion continued. Although aflatoxin has been
designated as a carcinogenic compound, cancer from aflatoxin is
not seen in domestic animals because the
life span is too short.
Portions of this comment were extracted from <
http://www.cfsan.fda.gov/~mow/chap41.html >- Mod.TG]
[Thank you also to Prof A. Dodds who alerted us to the same
finding.
_Aspergillus_ spp. are cosmopolitan, ubiquitous pathogens of
plants, animals and humans of great economic importance. _A.
flavus_ is mainly a saprophyte degrading dead tissue of any
origin, and it is therefore important in nutrient recycling.
However, it can also be pathogenic on some plant species
affecting for example injured seeds of maize. Spores can be
dispersed in soil, by air or carried by insects.
A picture of _A. flavus_ infection on maize kernels is at:
<http://www.ipm.iastate.edu/ipm/icm/files/images/aspercorn.jpg>
Pictures of fungal structures are at:
<http://www.cbs.knaw.nl/ICPA/ASPFLA2.JPG>
Links:
The original article for title 1 is Probst et al. 2007, Applied
and Environmental Microbiology 73, 2762-2764.
Prof Dodd's source of a similar article:
<click
HERE>
Information on _Aspergillus_ spp. is at:
<http://www.doctorfungus.org/thefungi/Aspergillus_spp.htm>
Information on _A. flavus_ is at:
<http://www.aspergillusflavus.org/aflavus/index.html>
<http://www.doctorfungus.org/thefungi/Aspergillus_flavus.htm>
- Mod.DHA]
[see also in the
archive:
2006
----
Aflatoxin poisoning, fatal - Kenya 20060505.1306
2005
----
Aflatoxin poisoning, fatal - Kenya 20050514.1324
2004
----
Aflatoxin poisoning - Kenya (Makueni) (06) 20040903.2460
Aflatoxin poisoning - Kenya (Makuei) (04) 20040607.1532
Aflatoxin poisoning - Kenya (Makueni): susp. 20040514.1306
2003
----
Food poisoning, children - China (Hunan, Hubei) 20031114.2822
2000
----
Mycotoxins: a review 20001130.2089
Aflatoxin-producing fungi, resistant crop plants 20000918.1602] |
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