Techniques for mitigating aflatoxin-producing fungi
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Transcript of Techniques for mitigating aflatoxin-producing fungi
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www.iita.org A member of CGIAR consortium
Juliet Akello
Techniques for mitigating aflatoxin-producing fungi
The Silent Killer: Aflatoxins
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www.iita.org A member of CGIAR consortium
About IITA
IITA
Aflatoxin:
What they are
Drivers
Status in sub-Saharan Africa
Interventions
Future research prospects
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www.iita.org A member of CGIAR consortium
About IITA
International research organization
founded in 1967
Develop sustainable food production
systems in tropical Africa
Most important African link in
CGIAR
198 scientists and > 2,000 staff
Operate throughout sub-Saharan
Africa
Research along entire value chain
Lusaka
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www.iita.org A member of CGIAR consortium
Highly toxic metabolite produced by
the fungus Aspergillus section Flavi
Common & widespread fungus in soil
& decaying matter
Fungus is sometimes visible, toxin is
not
Aspergillus
What is Aflatoxin?
Aflatoxin
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www.iita.org A member of CGIAR consortium
Types of aflatoxin
Aflatoxin
13 different types of aflatoxin are produced in nature
Most common: aflatoxins B1, B2, G1 & G2
Aflatoxin B1 is the most toxic.
Aflatoxin M1:
• breakdown product of Aflatoxin B1
• excreted in the urine & milk of exposed humans/
animals.
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Aflatoxin contamination: causative agent
A. flavus L- strain A. flavus S- strain A. parasiticus
+++++
- / +
Aflatoxin-producing Aspergillus spp
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Aflatoxin contamination: causative agent
Reverse
Front
A. oryzae A. sojae A. tamarii
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8
Colony & Microscopic Characteristics
Rough conidia
Smooth conidia
A. parasiticus
A. flavus
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www.iita.org A member of CGIAR consortium
Aspergillus Spp. & Aflatoxins
Ability to produce aflatoxins in A. flavus strains varies
Some strains produce a lot (toxigenic) & others little or no aflatoxins
(atoxigenic)
Species/strain B aflatoxin G aflatoxin
A. flavus ‘L-strains’ +/- -
A. flavus ‘S-strains’ + -
A. flavus ‘SBG strains’ + +
A. parasiticus + +
A. nomius + +
A. tamarii - -
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Maize
SUCEPTIBLE CROPS: MANY
Cassava
Cashew nut Groundnut
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www.iita.org A member of CGIAR consortium
Aflatoxin contamination: when does it occur?
Phase 1: Before crop maturity
a. Developing crop becomes infected
b. Linked to crop damage (pests,
stress)
Phase 2: After crop maturity
a. Aflatoxin increases with crop
maturity
b. May occur before or after
harvest
c. Seed is vulnerable till consumed
Occurs in 2 phases
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SYMPTOMS OF FUNGAL CONTAMINATION
Infected maize cobs
Maize
Clean maize
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SYMPTOMS OF FUNGAL CONTAMINATION
Clean groundnut Infected groundnut
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SYMPTOMS OF FUNGAL CONTAMINATION
Contaminated cassava
Clean cassava
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www.iita.org A member of CGIAR consortium
a) Susceptible crops b) Favorable climate
Infection before crop maturity: plant stress (high T, drought)
Aflatoxin problem in SSA: drivers
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www.iita.org A member of CGIAR consortium
Aflatoxin contamination: monitoring
Monitoring starts in the field
• diseased plant parts
• Sampling
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www.iita.org A member of CGIAR consortium
Aflatoxin contamination: monitoring
Monitoring continues in the lab
• Black light (UV light-365nm)-
for greenish gold fluorescence
• Commercial test kits
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www.iita.org A member of CGIAR consortium
Aflatoxin prevalence in foods & feeds in SSA
• Several African staple commodities affected
• High human exposure in Africa – mother to baby
• Levels and frequency of occurrence high
– >30% maize in stores with >20 ppb aflatoxin
– ~90% stores are contaminated with Afla fungi
– Up to 40% grain in households with aflatoxin
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www.iita.org A member of CGIAR consortium
Aflatoxin prevalence in foods & feeds in SSA
• Several African staple commodities affected
• High human exposure in Africa – mother to baby
• Levels and frequency of occurrence high
– >30% maize in stores with >20 ppb aflatoxin
– ~90% stores are contaminated with Afla fungi
– Up to 40% grain in households with aflatoxin
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AFLATOXIN IN ZAMBIA
0
20
40
60
80
100
2011/2012 2013/2014
To
xig
en
ic s
tra
ins (
%)
Atoxigenic
Toxigenic
Aflatoxin producing fungus (Aspergillus) in Zambian soils
fungus colonizing groundnut root zones in soils
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www.iita.org A member of CGIAR consortium
Year Maize Groundnut Reference
1979 - 5 Kannaiyan et al. 1979
1998 900-929 6200-8600 Njapau et al. 1998
2009 0.7-108.4 - Kankolongo et al. 2009
2010 10 - Mukanga et al. 2010
2012/2013 0-255 0-5350 IITA-unpublished
Aflatoxin levels (ppb) detected in maize & groundnut samples from different
parts of Zambia
Surveillance studies
Aflatoxin levels depended on: locality, crop, processing method &
presence of microbial contaminants
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FACTORS PROMOTING CONTAMINATION
a) Late planting and harvest
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FACTORS PROMOTING CONTAMINATION
b) Poor drying techniques
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FACTORS PROMOTING CONTAMINATION
c) Poor storage and informal marketing systems
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d) Lack of awareness & inadequate regulatory systems
Aflatoxin problem in SSA: drivers
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FACTORS PROMOTING CONTAMINATION
d) Favorable climate (High temperatures and drought/
dry periods) and insect pests
35°N
35°S
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HARMFUL EFFECTS OF AFLATOXIN
Taiwan
1967
Uganda
1970
Western India
1974
Kenya
1982
2002
2004
2005
2006
2007
2008
Malaysia
1988
35°N
35°S
Causes death: history of Acute Outbreaks
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HARMFUL EFFECTS OF AFLATOXIN
Causes poisoning and death: Acute toxicity in humans are rare, but deaths have been reported
40 deaths in 1974 (India); 13 deaths in 1990 in Malaysia
14 deaths in 2001 (Kenya); > 200 deaths in 2010 (Kenya)
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HARMFUL EFFECTS OF AFLATOXIN
• Enhances stunting and underweight in children
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HARMFUL EFFECTS OF AFLATOXIN
• Causes liver rot, enlarged liver, and liver cancer
• Enhances susceptibility to illnesses
• Suppresses the immune system
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HARMFUL EFFECTS OF AFLATOXIN
Up to 3.4 increment in Feed conversion ratio
Livestock and poultry losses
losses in feed efficiency
Recurrent infection due to losses in feed efficiency
Bird mortality
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HARMFUL EFFECTS OF AFLATOXIN
40% reduction in live weight
500 ppb AF diet AF-free diet
Livestock and poultry losses
reduced growth rate
AF-free diet
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HARMFUL EFFECTS OF AFLATOXIN
Livestock and poultry losses
decreased milk & egg yield
embryo toxicity (reduced
reproductivity)
death (cattle, turkey, swine..)
Carry over: high levels
Meat, eggs, Gizzards, Diary products, Kidneys & cheese
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HARMFUL EFFECTS OF AFLATOXIN
Aflatoxin, a threat to trade! Serious Trade Barrier (Market exclusion)
~2.3 M bags untradeable Many SSA unable to sell
<4 <10 <20 <10
EU WFP US COMESA
Acceptable Limits (ppb)
>20
unsafe
CODEX Alimetarius Commission
Regulatory standard: 20 ppb
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REDUCING AFLATOXIN CONTAMINATION
1. Awareness, advocacy & training
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Early harvest, proper drying and storage
REDUCING AFLATOXIN CONTAMINATION
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REDUCING AFLATOXIN CONTAMINATION
Maintain crop hygiene at all levels: sorting/ physical
separation, and destruction of contaminated grains
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REDUCING AFLATOXIN CONTAMINATION
Use of mechanical groundnut sheller instead of wetting
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BIOLOGICAL CONTROL OF AFLATOXIN
AflaSafe biopesticide
Mixture of 4 atoxigenic
strains of A. flavus of local
origin
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BIOLOGICAL CONTROL OF AFLATOXIN
At application: Maize
Broadcast aflasafe by hand 2 to 3 weeks before flowering by
broadcasting at a rate of 10 kg/ha
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BIOLOGICAL CONTROL OF AFLATOXIN
At application: Groundnut
Apply aflasafe between 30 to 40 days after planting by side
dressing along the rows on the soil surface (rate of 10 kg/ha).
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www.iita.org A member of CGIAR consortium
Aflatoxin mitigation: what can be done?
Detection systems
Management options
Afla-ELISATM, AcuScan flow readers
Africa-wide surveillance fungal populations, climate change, predictive modeling
Plant breeding resistant maize/ groundnut lines
AflasafeTM
Mycotoxin assessment
research pathway example of research
Technology adoption
Capacity building
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