Prof. James W. Muthomi Department of Plant Science and Crop Protection
University of Nairobi
Aflatoxin Research in Kenya
Australia Awards – Africa Fellowships Short Course in Post-harvest Management of Maize, Rice and Legumes
Royal Palm Room, Southern Sun Mayfair, Parklands Rd, Parklands, Nairobi
Cases of aflatoxin poisoning reported in Kenya from 1981 to 2010
Year Number of cases Number of deaths Areas of
occurrence
1981 20 12 Machakos district 2001 - 12 Meru 2003 - 68 Eastern province
2004 317 125 Thika, Kitui,
Makueni
2005 75 32 Kitui and
Makueni
2007 84 21 Meru, Kitui,
Makueni 2008 6 2 Eastern province
2010 24 3 Kitui (Mutomo)
and Makueni
Source; Lewis et al., 2005; KEPHIS, 2008; Daily nation 2010. Home grown maize implicated in most poisoning outbreaks; 2004 was the worst outbreak ever reported in the world - aflatoxin B1 as high as 4,400 ppb
Case of aflatoxin poisoning in Kenya
Aflatoxicosis outbreak in Eastern Kenya - 2004 (CDC, KEMRI)
2004 aflatoxicosis outbreak was the largest ever described
Most maize samples had excess of 5,000µg/kg aflatoxin B1
Most of the contaminated maize was homegrown (produced
within)
Main factors associated with highly contaminated maize:
1. Onset of rains during the harvesting season
2. Storage of inadequately dry maize
3. Storage in house as opposed to storage in granaries
Practices influencing aflatoxin contamination
•Poor harvesting practices,
•Drying practices
• Mechanical damage during shelling
•Improper storage and
•Less than optimal conditions during transport and marketing
Harvesting and drying practices
•Most small scale farmers dehusk the maize during harvesting
and drop the cobs on the ground
•Some dry on polyethylene sheets or mats while others spread
it on bare ground
•These drying methods are slow and may support growth and
development of fungi
•Shelling maize - the practice of beating the maize cobs by
small scale farmers leads to damage of kernels
•Mechanical damage to maize kernels makes them much
more vulnerable to invasion by storage moulds
•Cracks and breaks in maize are caused by harvesting and
handling equipment
Shelling practices
Post harvest handling and Storage
•Insect damage
increases aflatoxin
contamination
•Insects carry spores
from plant surfaces to
the interior of the stalk or
kernels or create
infection wounds
Insect damage
Aspergillus on maize Aspergillus on ground nuts
Aspergillus flavus infection
Fusarium ear rot Fusarium red ear rot Moulded maize
Fusarium ear rot
Types of storage structures
Long term storage facilities
• Separate housing for storage
• Improved granary
• Silo
• Large pots
• Traditional crib
• Living house for storage
Short term storage facilities
• Polypropylene
• sisal bags
• Baskets
2
Storage structures
2
Traditional crib
A traditional storage structure made of
local material available in a particular
region.
Cheap to construct, good ventilation and
aeration thus reduces mouldy growths.
Disadvantage - Insecure and requires
seasonal repairs.
Cribs made exclusively of plant materials
rot fairly quickly, and most cribs have to
be replaced every two or three years.
Bamboo structures may last up to 15
years, with careful maintenance.
2
Improved granary
An improved granary - made of
wooden wall with supporting
poles or stones and roofed with
iron sheets.
Granary has good ventilation
and aeration thus discourages
growth of moulds.
2
Living house for storage
One room in the main house set
aside for maize storage.
Reason : Security
Major disadvantage: May
encourage growth of moulds and
likelihood of aflatoxin infection due
to high moisture in the house
Sisal bags
Short duration storage facilities
used widely in Kenya till the
introduction of plastic bags.
Polypropylene bags
Short duration plastic bags
widely used in Kenya.
Sizes range from 25 - 100kg
bags.
Price affordable to most
farmers.
2
BAGS
2
Metal Silo
An improved maize storage
container made of metal sheet.
Maize stored in the metal silo is
not attacked by pests and is
less infested by moulds.
Aflatoxin levels reduced by 60%
on average.
Major disadvantage - High cost
and the limited storage capacity
2
Matrix Scoring for three grain storage structures
Metal bin Improved crib Traditional crib
Durability of structure ***** ***** **
Ease of handling ***** ***** ****
Peace of mind ***** *** ***
Low construction costs * *** *****
Does not attract pests ***** **** **
Total Score: 27 21 21
Infected wheat field
Infected wheat ears Infected spikelets
12
Fusarium head blight on wheat
2
Fusarium head blight
13
Identification of mycotoxigenic fungi
24
Mycotoxin management in food value chain: the case of
aflatoxin in Kenyan maize
25
Maximum Mycotoxin Regulatory Limits (ppb) Commodity / use Mycotoxin FDA EU Codex Kenya
Milk and milk products Aflatoxin M1
0.5
0.05
0.5
Maize (food) Aflatoxin B1 20 2 15 5
Maize (food) Total aflatoxins 20 4 - 10
Maize (food) Fumonisins 4000 2000 - Maize products (food) Fumonisins 2000 1000 - -
Cereals and cereal products (feed)
Fumonisins 5000 – 100,000 60,000 - -
Maize (Feed) Aflatoxins 100 - 300 20 -- - Raw cereal grains (food) Ochratoxin A - 3 – 5 - -
Unprocessed maize(food) Deoxynivalenol
- 1750
- -
Cereal flour (food) Deoxynivalenol
1000
750
- -
Cereals and cereal products (feed)
Deoxynivalenol
-
8000
- -
Maize by-products (feed) -
12,000
- -
Unprocessed maize(food) Zearalenone - 200 - -
Maize products (food) Zearalenone - 200 - -
6
Research areas in mycotoxins
1. Pre-harvest technologies – crop residue management, breeding for resistance, drought tolerance, pest and disease management
2. Postharvest handling & storage – storage structure, insect pest & mould management
3. Animals – chicken, livestock products, feeds
4. Monitoring – surveys, collaboration in national programmes, analysis, mould identification & detection
5. Food processing
Effect of different harvest intervals on incidence of ear rot fungi, fumonisin B1 and aflatoxin B1 (Alakonya, Monda, Ajanga and Owino)
Investigated 4 maize varieties grown in Western Kenya in 2001 and 2003
Mycotoxins and fungi determined at 4, 8 and 12 weeks after physiological
maturity (WAPM)
FB1 detected in both clean and rotten maize samples
FB1 increased with increased delay in harvesting (21.8 – 1,178µg/kg)
FB1 in rotten maize ranged from 38.5 - >5,000µg/kg
Highest aflatoxin level was 16.8µg/kg in rotten maize
Dominant fungus was Fusarium verticillioides (80% incidence). Aspergillus Flavus
incidence was up to 44%
Mureithi et al
Mycotoxin management in food value chain: the case of
aflatoxin in Kenyan maize
Percentage isolation frequency of Aspergillus spp from whole maize grain
Mureithi et al
Mycotoxin management in food value chain: the case of
aflatoxin in Kenyan maize
CFU/g of Aspergillus species in soil and posho mill dust samples from lower eastern region of Kenya
Mureithi et al
Mycotoxin management in food value chain: the case of
aflatoxin in Kenyan maize
Percentage isolation frequency of Aspergillus spp from whole maize grain
Mureithi et al
Mycotoxin management in food value chain: the case of
aflatoxin in Kenyan maize
Percentage isolation frequency of Aspergillus spp in muthokoi from traders in eastern Kenya
Mureithi et al
Percentage isolation frequency of Aspergillus spp in maize flour from eastern Kenya
Mycotoxin management in food value chain: the case of
aflatoxin in Kenyan maize
Muthomi, J. W. Fungi & mycotoxins in food grains 33
Fungi and mycotoxins in freshly harvested wheat (Muthomi, Ndung’u, Mutitu and Gathumbi)
Wheat grain sampled at harvest during 2004 in Nakuru and Nyandarua
Districts
Mycotoxins DON, zearalenone, T-2 toxin and aflatoxin B1 detected
No. samples % incidence Range (µg/kg) Mean (µg/kg)
DON 82 68 105 – 303 101
ZEA 82 57 1.2 – 95.8 5.5
T-2 toxin 80 76 20 – 66 26
Aflatoxin B1 50 45 2 - 7 2
Mycotoxin incidence and concentration in wheat: Nakuru and Nyandarua districts,2004
Main fungi: Fusarium, Epicoccum, Alternaria, aspergillus
Main Fusarium spp: F. poae, F. graminearum, F. equiseti, F. chlamydosporum
Muthomi, J. W. Fungi & mycotoxins in food grains 34
Mycoflora and mycotoxins associated with ear rot of maize in Central Kenya
(Oduor, Mutitu, Narla and Gathumbi)
Fusarium verticillioides (moniliforme) most predominant (59% of total fusaria)
Other Fusarium spp.: F. graminearum, F. proliferatum, F. poae, F. oxysporum
Aspergillus was low (5%)
Incidence (%)
Stored Ear rot
Mycotoxin levels in ear rot
maize (µg/kg)
Fumonisin B1 100 100 147 – 82,000
DON 50 100 950 – 28,000
Aflatoxin B1 21 8 124 - 399
Mean level of mycotoxins in the ear rot groups
Ear rot group Mean level (ppb)
FB1 DON AFB1
Stalk borer 37,998 2,530 22.8
General rotting 28,637 2,568 1.3
Pink rot 34,409 9,245 29.4
Yellow rot 20,746 3,350 0
mean 30,448 4,423 13.4
2
Mycoflora and mycotoxins associated with ear rot of maize in Central Kenya (Oduor, Mutitu, Narla and Gathumbi)
2
Grain drying practices Mureithi et al
Form of drying Drying place
District Shelled grains In cobs Bare ground Mats
Eastern region
Makueni 0.0 100.0 50.0 50.0
Kitui 5.0 95.0 80.0 20.0
Machakos 5.0 95.0 65.0 35.0
Mean 3.3 96.7 65.0 35.0
North Rift region
Trans Nzoia 50.0 50.0 10.0 90.0
Uasin Gishu 57.1 42.9 9.6 90.4
Mean 53.6 46.5 9.8 90.2
Percentage of farmers who dried maize in different forms in Easter and North
Rift regions
2
Transportation practices Mureithi et al
District Vehicles Carts Bicycles People Donkeys back
Eastern region
Makueni 95 0 10 15 25
Kitui 90 10 20 5 15
Machakos 94.7 5.3 5.3 0 0
Mean 93.2 5.1 11.8 5.0 33.3
North Rift region
Trans Nzoia 45 20 90 15 100
Uasin Gishu 50 10 80 0 95
Mean 47.5 15.0 85.0 7.5 97.5
Percentage of traders who transported maize by different means
2
Storage structures Mureithi et al
District House Cribs
Traditional
granary Improved stores
Eastern region
Makueni 25.0 50.0 5.0 20.0
Kitui 60.0 15.0 0.0 25.0
Machakos 45.0 5.0 0.0 50.0
Mean 43.3 23.3 1.7 31.7
North Rift region
Trans Nzoia 20.0 0 10.0 70.0
Uasin Gishu 23.8 0 0 76.2
Mean 21.9 0 5 73.1
Percentage of farmers who used different storage structures
2
Storage materials Mureithi et al
Farmers Traders
District
Polythen
e bag
Sisal
bag
Synthetic
Bags
Polythene
Bags
Sisal
bag
Synthetic
bag
Eastern region
Makueni 0.0 35.0 90.0 5.0 15.0 90.0
Kitui 0.0 15.0 95.0 0.0 10.0 85.0
Machakos 20.0 35.0 84.2 0.0 26.3 45.0
Mean 6.7 20.0 89.7 1.7 15.4 73.3
North Rift region
Trans Nzoia 0.0 15.0 95.0 5.0 15.0 90.0
Uasin Gishu 0.0 23.8 100.0 0.0 25.0 76.2
Mean 0.0 19.4 97.5 2.5 20.0 80.6
Percentage of traders and farmers using different storage materials
9
Aflatoxin and fumonisin in samples from Makueni and Nandi
Sample type Aflatoxin
(% positive)
Fumonisin
(% positive)
NANDI
Maize (Market and homegrown (n= 305) 66 82
Cow Milk (n= 246) 93
Breast Milk (n= 67) 59
Sorghum and millets (n=105) 77 90
Children < 5 Urine (n= 362) 80
Feed samples (n= 207) 56 92.8
MAKUENI
Maize (Market and homegrown (n= 378) 72 92
Cow Milk (n= 233) 93
Breast Milk ( n=98) 86
Sorghum and Millets (n=215) 56 97
Children < 5 Urine (n= 377) 80
Feed Samples (n= 2) 100 100
Kangethe et al
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AREAS FOR ATTENTION
1. Mycotoxin legislative limits for all harzadous mycotoxins
2. Mycotoxin monitoring especially at local level – majority of population feed of potentially contaminated foods
3. Simple, cheap and user friendly mytoxins detection kits that can used by publich health officers and traders in rural areas
4. Enhancing mycotoxin reference laboratories
5. Training of personell and continuous public awareness creation on mycotoxins
THANK YOU
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