Measuring the burden of aflatoxin induced human disease

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Measuring the burden of aflatoxin induced human disease

  1. 1. 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 InstituteInternational Food Policy Research Institute University of PittsburghInternational Center for the Improvement of Maize ACDI/VOCA/Kenya Maize Development Programand Wheat Kenya Agricultural Research InstituteInternational Crops Research Institute for the Semi- Institut d’Economie RuraleArid TropicsUniformed Services University of the Health Sciences 1
  2. 2.  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 2
  3. 3.  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 3
  4. 4. Hepatitis B Hepatitis C Liver cancer Cirrhosis of the liverWORLD 1.63 0.84 9.47 11.99AFRICA 1.64 0.72 8.19 3.85THE AMERICAS 0.57 0.92 4.16 12.87EUROPE 0.83 0.52 7.33 20.94SOUTH-EAST 2.21 0.82 3.50 12.57ASIAWESTERN 1.60 0.88 21.68 9.53PACIFICKENYA 0.50 0.22 2.58 2.47 4
  5. 5. Plant stress in Poor storage field conditions Fungal growth and aflatoxin accumulation in food crops Intermediate Liver Acute Aflatoxin dihydrodiol biotransformation to aflatoxicosis consumption binds to liver aflatoxin-8,9-epoxide proteins AF-8,9-Altered intestinal Modulation of epoxide binds Liver cancer integrity cytokine expression to DNA Source: Stunted Chronic hepatitis B growth in Immune Wu 2010 suppression infection children 5
  6. 6.  How many global liver cancer cases each year are caused by aflatoxin?
  7. 7.  Dose-response assessment  Exposure assessment  Slope of curve = cancer “potency”  Find, for each nation: ▪ Aflatoxin  liver cancer: 0.01 cases /  Daily consumption of maize / nuts 100,000 / yr / ng/kg bw/day  Aflatoxin levels in maize / nuts ▪ Aflatoxin + Hepatitis B virus liver cancer: 0.30 cases / 100,000 / yr / ng/kg bw/day  Hepitits B virus prevalence  Population size 7
  8. 8.  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 8
  9. 9. 13 DALYs per case  328,000-2,000,000 DALYs/yrLiu Y, Wu F. (2010). “Global Burden of Aflatoxin-Induced Hepatocellular Carcinoma:A Risk Assessment.” Environmental Health Perspectives 118:818-824. 9
  10. 10. World Region # DALYs annually attributable to aflatoxin-induced HCC Africa 147,940-778,700 North America 143-182Latin 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 10
  11. 11.  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. 11
  12. 12.  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 12
  13. 13. Aflatoxin exposure HBV AF-induced cases (ng/kg bw/day) prevalence of HCC[1]AfricaLower 5th 10 9 11,380percentileGeometric mean 42 13 26,100Upper 95th 180 20 59,900percentileKenyaLower 5th 5.2 11 82percentileGeometric mean 32.2 12.8 578Upper 95th 200 15 4080percentile 13
  14. 14.  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 14

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