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International Food Policy Research Institute International Center for the Improvement of Maize
and Wheat International Crops Research Institute for the Semi-Arid Tropics Uniformed Services University of the Health Sciences
University of Pittsburgh ACDI/VOCA/Kenya Maize Development Program Kenya Agricultural Research Institute Institut d’Economie Rurale
Felicia Wu and Yan Liu
Department of Environmental & Occupational Health Graduate School of Public Health
University of Pittsburgh
And
Clare Narrod, Marites Tiongco, Rosemary Scott International Food Policy Research Institute
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Aflatoxin: background & health effects Influence diagram linking aflatoxin to sequelae Burden of disease caused by aflatoxin
Global liver cancer cases
Expected liver cancer cases in Kenya Results using Kenya Integrated Household Budget Survey (KIHBS, 2005-2006) data
to Limitations and future directions
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Produced by Aspergillus flavus, A. parasiticus Maize, peanuts, almonds, pistachios, hazelnuts Exposure highest in warm regions when these foods
are dietary staples Poor nations
(Postulated) Human health effects Liver cancer (fatal in 1-3 months)
▪ Synergizes with chronic hepatitis B virus (HBV) infection: >> higher risk than either exposure alone
Childhood stunting Acute aflatoxicosis Cirrhosis Immune suppression A. flavus invasive aspergillosis
Hepatitis B Hepatitis C Liver cancer Cirrhosis of the liver
WORLD 1.63 0.84 9.47 11.99
AFRICA 1.64 0.72 8.19 3.85
THE AMERICAS 0.57 0.92 4.16 12.87
EUROPE 0.83 0.52 7.33 20.94
SOUTH-EAST ASIA
2.21 0.82 3.50 12.57
WESTERN PACIFIC
1.60 0.88 21.68 9.53
KENYA 0.50 0.22 2.58 2.47
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Aflatoxin
consumption
Stunted
growth in
children
Immune
suppression
Acute
aflatoxicosis
Liver cancer Modulation of
cytokine expression
AF-8,9-
epoxide binds
to DNA
Chronic hepatitis B
infection
Liver
biotransformation to
aflatoxin-8,9-epoxide
Altered intestinal
integrity
Poor storage
conditions
Fungal growth and
aflatoxin accumulation
in food crops
Intermediate
dihydrodiol
binds to liver
proteins
Plant stress in
field
Source: Wu 2010
How many global liver cancer cases each year are caused by aflatoxin?
Dose-response assessment
Slope of curve = cancer “potency” ▪ Aflatoxin liver cancer: 0.01 cases /
100,000 / yr / ng/kg bw/day
▪ Aflatoxin + Hepatitis B virus liver cancer: 0.30 cases / 100,000 / yr / ng/kg bw/day
Exposure assessment
Find, for each nation: Daily consumption of maize / nuts
Aflatoxin levels in maize / nuts
Hepitits B virus prevalence
Population size
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Global population cancer risk = Σ(all nations) ([PopulationHBV+ /100,000 * PotencyHBV+ * Average aflatoxin intake] + [PopulationHBV- /100,000 * PotencyHBV- * Average aflatoxin intake])
PotencyHBV+ = 0.30 cases per 100,000/yr per ng/kg bw/day PotencyHBV- = 0.01 cases per 100,000/yr per ng/kg bw/day
Data Sources: • Hepitits B virus prevalence: WHO, multiple peer-reviewed
papers • Aflatoxin exposure & food consumption: WHO GEMS
database, multiple peer-reviewed papers
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13 DALYs per case 328,000-2,000,000 DALYs/yr
Liu Y, Wu F. (2010). “Global Burden of Aflatoxin-Induced Hepatocellular Carcinoma: A Risk Assessment.” Environmental Health Perspectives 118:818-824.
World Region # DALYs annually attributable to aflatoxin-induced HCC
Africa 147,940-778,700
North America 143-182
Latin America (inc. Central America) 8,749-65,520
Eastern Mediterranean 10,231-219,960
Southeast Asia 41,600-583,700
Western Pacific 117,260-360,230
Europe 2093-7,228
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Estimated daily maize and peanut consumption (KIHBS 2005): ▪ Maize: 357 g/day/person
▪ Peanuts: 44 g/day/person Hepatitis B Virus prevalence: 11-15% Lifetime average daily dose (LADD) of aflatoxin in Kenyan adults
5.2 to 200 ng/kg bw/day Estimated aflatoxin-induced Liver cases/yr: 82- 4,080 Estimated DALYs associated with aflatoxin-induced Liver
Cancer: 1066-53,040 per year
Note: These exposures do not take into account occasional excursions to very high aflatoxin levels (e.g., 2004, 2010), as acute toxicoses are not associated with subsequent HCC.
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Estimated daily maize consumption in urban vs rural areas:
Maize: urban areas 352 g/day/person, rural 624 g/d/ person
Currently no way to estimate aflatoxin exposure in urban vs. rural populations
What we do know: rural maize consumption 1.77 times higher than urban maize consumption
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Aflatoxin exposure (ng/kg bw/day)
HBV prevalence
AF-induced cases of HCC[1]
Africa
Lower 5th percentile
10 9 11,380
Geometric mean 42 13 26,100
Upper 95th percentile
180 20 59,900
Kenya
Lower 5th percentile
5.2 11 82
Geometric mean 32.2 12.8 578
Upper 95th percentile
200 15 4080
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Globally - 25,200-155,000 aflatoxin-induced liver cancer cases each year Translates to 328,000 to 2,000,000 DALYs per year
Most DALYs are suffered in 3 world regions: Africa, Southeast
Asia, and Western Pacific (China) Kenya 82- 4,080 aflatoxin-induced HCC cases/yr:
Translates to 1066-53,040 DALYs associated with aflatoxin-induced HCC
But secondary data of different quality – poor quality data leads to high variance
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