Aflatoxin Research in Kenya - Department of Plant...

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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

Storage structures

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.

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.

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

Price affordable to most

farmers.

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

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

Fusarium head blight on wheat

Fusarium head blight

Identification of mycotoxigenic fungi

Mycotoxin management in food value chain: the case of

aflatoxin in Kenyan maize

Maximum Mycotoxin Regulatory Limits (ppb) Commodity / use Mycotoxin FDA EU Codex Kenya

Milk and milk products Aflatoxin M1

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

Cereals and cereal products (feed)

Deoxynivalenol

Maize by-products (feed) -

12,000

Unprocessed maize(food) Zearalenone - 200 - -

Maize products (food) Zearalenone - 200 - -

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

Percentage isolation frequency of Aspergillus spp from whole maize grain

Mureithi et al

CFU/g of Aspergillus species in soil and posho mill dust samples from lower eastern region of Kenya

Mureithi et al

Percentage isolation frequency of Aspergillus spp from whole maize grain

Mureithi et al

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

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

Mycoflora and mycotoxins associated with ear rot of maize in Central Kenya (Oduor, Mutitu, Narla and Gathumbi)

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

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

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

Storage materials Mureithi et al

Farmers Traders

District

Polythen

Synthetic

Polythene

Synthetic

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

Aflatoxin and fumonisin in samples from Makueni and Nandi

Sample type Aflatoxin

(% positive)

Fumonisin

(% positive)

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

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

Aflatoxin Research in Kenya - Department of Plant...

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